The acid meta vol can ic rocks of the Orlica-Œnie nik Dome (Sudetes): their origin and tectono-metamorphic evolution

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1 Ge olo gia Sudetica, 2006, 38: The acid meta vol can ic rocks of the Orlica-Œnie nik Dome (Sudetes): their origin and tectono-metamorphic evolution Men tor Murtezi In sti tute of Geo log i cal Sci ences of the Pol ish Acad emy of Sci ences, Podwale 75, Wroc³aw, Po land, mmurtezi@poczta.fm Key words: sacid meta vol can ic rocks, geo chem is try, petro gen esis, P-T-d path, Stronie For ma tion, Orlica-Œnie nik Dome. Ab stract The Orlica-Œnie nik Dome (OSD) be longs to the mo saic of geo log i cal units form ing the Sudetic part (NE mar gin of the Bo he mian Mas sif) of the Variscan belt. Acid meta vol can ic rocks re ferred to as leptites ap pear in the OSD as in ter ca la - tions in the mica schists of the Stronie For ma tion the supracrustal cover of the gneiss core of the unit. Two types of acid meta-volcanogenic rocks have been dis tin guished: mas sive leptites (ML) and bi o tite-bear ing leptites (BBL); to gether they are referred the leptite se ries. The ML orig i nate from acid vol ca nic rocks that could have con tained only small amounts of sed i men tary ma te rial. The BBL are meta mor phosed tuffites with a vari able share of sed i men tary ma te rial. All the ana lysed leptites from the en tire OSD area re veal sim i lar geo chem i cal char ac ter is tics. The high con cen tra tion of strongly in com pat i ble el e ments such as REE, as well as the en rich ment in large-ion-lithophile el e ments in di cates the con ti nen tal crust af fin i ties of the leptites protolith. On the other hand, as cer tained the high Th/Ta ra tios, neg a tive Nb and Ta anom a lies, and low Ti, Zr and Hf con tent can be in ter preted as in di ca tors of magmatism con nected with a suprasubduction en vi ron ment. Such am big u ous char ac ter is tics may in di cate that an ensialic rift en vi ron ment, con sid - ered as the place of or i gin for the mag matic rocks dated at c. 500 Ma and oc cur ring in the OSD, de vel oped due to ex ten - sion be hind a collisional zone of Lower Palaeozoic age. An extensional en vi ron ment cre ated dur ing this event could be the lo ca tion for the pos tu lated early de for ma tion and meta mor phism of the Stronie For ma tion. The Œnie nik metagran ites would have been emplaced into such, al ready de formed, supracrustal cover. The sig na ture of an ac tive mar gin found in these con ti nen tal crust rocks that were stretched and melted due to the in creased heat trans fer re sulted from an ear lier (Neoproterozoic?) tectono-ther mal ep i sode. The re con structed path of the tectono-meta mor phic evo lu tion of the leptites en tirely re sults from a Variscan collisional ep i sode oc cur ring in the bor der land of the West and the East Sudetes. The se quence of the de for ma tions es - tab lished for the stud ied rocks is in ter preted as an ef fect of the con tin u ous con ver gence of crustal units in an E W di rec - tion. Struc tural and phase-equi lib ria lines of ev i dence show that the tectono-meta mor phic evo lu tion of the Stronie For - ma tion was that of early burial (D1) to a depth not ex ceed ing up per am phi bo lite fa cies con di tions, and sub se quent up lift con nected with subvertical short en ing and flat ten ing strain (D2). As a re sult of the con tin u ous con ver gence, thrust ing took place along the edges of the col lid ing units. The fi nal ad ap ta tion of the col lid ing crustal slices led to zonal lat eral oblique dis place ments (D3). This lat ter event is treated as the cause for dis tur bance of the isograd and iso therm pat tern ob served within the rocks of the Stronie For ma tion. It is also re spon si ble for zonal shear ing, gen er ally tak ing place in a N S di rec tion. Dur ing the col li sion that oc curred along the east ern mar gin of the OSD, the rocks of the Stronie For ma - tion reached the high est P-T con di tions of meta mor phism at c. 9 kbar and 650 C. The pre sented data shows a con sid er - able de crease in the peak-meta mor phic con di tions from the east to the west of the OSD. Manu script re ceived 15 No vem ber 2005, ac cepted 5 Au gust 2006 INTRODUCTION The Orlica-Œnie nik Dome (OSD) forms the east ern - most unit of the West Sudetes; it is sep a rated from the Silesian do main (Variscan East Sudetes) by the east erly verg ing Nýznerov overthrust (Skacel, 1981; Don et al., 2003) (Fig. 1). It is bor dered by two NW-trending fault zones: the Sudetic Mar ginal Fault to the north-east and the Bušin Fault to the south-west. These fault zones are par al - lel to the Odra and the Elbe lin ea ments, which sep a rate the West Sudetes from the other seg ments of the Variscides. The OSD is di vided into two parts: the L¹dek-Œnie nik meta mor phic unit (LSMU) to the east, and the Bystrzyca and Orlica Mts. to the west. These two parts are sep a rated by the N S trending, Late Cre ta ceous Nysa Graben (Don & Don, 1960). The name OSD is used in this work as a

2 2 M. MURTEZI Fig. 1. A geo log i cal sketch map of the Sudetes and their fore land. OFZ Odra Fault Zone, SMF Sudetic Mar ginal Fault, ISF Intra-Sudetic Fault, EFZ Elbe Fault Zone, NT Nýznerov Thrust. com monly ac cepted in the Sudetic re gional geo log i cal di vi - sion scheme since pub li ca tion of Don et al. (1990). The core of the OSD con sists of partly migmatised gneiss es with lo cal oc cur rences of HP granu lites and eclogites. This core is over lain by a se ries of mica schists, paragneisses, mar bles, acid volcanics and am phi bo lites, metamorphosed under upper amphibolite facies condi - tions. The Early Palaeozoic gran ites (Borkowska et al., 1990; Kröner et al., 1994; Turniak et al., 2000) in truded the pri mary se quence of vol cano-sed i men tary rocks re ferred to as the Stronie For ma tion. The gran ites were sub jected to polyphase deformation and metamorphism leading to the de vel op ment of the two main gneiss va ri et ies of the OSD, tra di tion ally re ferred to as the Œnie nik and Giera³tów gneiss es (Fischer, 1936). The rocks in cluded in the Giera³tów gneiss suite are usu ally fine-grained, streaky and some times migmatitic, whereas the term Œnie nik gneiss es is used to de scribe coarse-grained, mylonitically lay ered augen orthogneisses. The strong tex tural dif fer ence be - tween the two types of gneiss in di cates their or i gin from apparently unrelated intrusive rock series. On the other hand, their sim i lar geo chem i cal char ac ter is tics (Kryza & Pin, 1997; Turniak et al., 2000; Kröner et al., 2001; Lange et al., 2003) im ply their com mon or i gin as de riv a tives of a sin - gle ig ne ous suite. This con curs with the hy poth e sis about the gen e sis of the OSD gran ites in the en vi ron ment of the ini tial rift de vel oped on the Cadomian con ti nen tal crust (Kryza & Pin, 1997). The gen e sis of the OSD gran ites in the same geotectonic set ting does not ex clude the pos si bil - ity of the oc cur rence of a few melt ing and migmatisation events in volv ing ma te rial with the same geo chem i cal char - ac ter is tics, lead ing to the de vel op ment of dif fer ent types of gneiss (Grzeœkowiak, 2004). The age of the protolith for - ma tion for both types of gneiss and for the acid meta vol - can ic rocks of the Stronie For ma tion in di cate their Lower Palaeozoic af fin i ties. Be cause the hith erto un der taken geo chem i cal in ves ti - ga tions of the OSD gneiss es and acid meta vol can ic rocks (Wojciechowska et al., 2000, 2001; Turniak et al., 2000) did not per mit a def i nite de ci sion to be made on the geotectonic en vi ron ment of for ma tion of their protoliths, the geo chem i cal anal y ses of the leptites from the en tire OSD pre sented herein were de signed to en able their de tailed comparison and consideration about their possible diversi - fication. The results of these investigations allowed a re-evaluation of the existing, contrasting and often contro - versial models on the origin and mutual relationships of the OSD-form ing rocks, re veal ing traces of a Cambro- Orovician tectono-ther mal event (Pin & Marini, 1993; Floyd et al., 1996; Kryza & Pin, 1997). An other goal of this study is to char ac ter ise the tectono-metamorphic evolution of the Stronie Formation

3 ACID META VOL CAN IC ROCKS 3 of the OSD on the ba sis of the struc tural and pet ro log i cal in ves ti ga tions ap plied to the acid meta vol can ic rocks and ac com pa ny ing mica schists. The be low pre sented data can be used for test ing of the con trast ing mod els of geodynamic evo lu tion of the bor der land be tween the West and the East Sudetes. PREVIOUS STUDIES Acid meta vol can ic rocks, the so-called leptites a term used in this work ac cord ing to def i ni tion given by Ryka & Maliszewska (1991), ap pear in the OSD as in ter ca la tions in the mica schists of the Stronie For ma tion. Large oc cur - rences of these rocks are well known from the L¹dek- Œnie nik Meta mor phic Unit in the east ern part of the OSD. Wojciechowska (1972), work ing on out crops of the rocks in the vi cin ity of Romanowo vil lage, was the first to de scribe them as acid metavolcanites. She con sid ered them meta mor phosed rhyolites, rhyolithic tuffs or tuffites. The chem i cal clas si fi ca tion of leptites was pro posed by Koz³owska-Koch (1973), who treated those rocks as blastomylonites ge net i cally con nected with the en tire com plex of schists and gneiss es in the L¹dek-Œnie nik Meta mor phic Unit. Smulikowski (1979) held a sim i lar view, in clud ing the leptites in the blastomylonitic se ries of the Z³oty Stok-Skrzynka Tec tonic Zone (in this work the zone is reffered to as the Z³oty Stok-Skrzynka Shear Zone ). Older char ac teri sa tions and dis crim i na tions of leptites were car ried out us ing petrographic meth ods and chem i cal anal y ses of their main el e ments. This al lowed only for their rough classification. Subsequent geochemi - cal anal y ses of the leptites from the Z³oty Stok-Skrzynka Tec tonic Zone (Wojciechowska et al., 2001), tak ing into ac - count trace el e ments and REE, con firmed as sump tions about their rhyolithic, volcanogenic char ac ter. Ac cord ing to Wojciechowska et al. (2001), the mica schists ad ja cent to the leptites have a sim i lar or i gin. The for mer would have been char ac ter ized by a higher con tent of pelitic ma te rial in their protolith. Although there is some geochemical recognition of leptites, the geotectonic en vi ron ment of their protolith for ma tion is still un de fined. On the discriminative di a - grams based on the pro por tions of their trace el e ments and REE, leptites oc cupy the field for the within-plate en vi ron - ment and the field of vol ca nic arcs (Wojciechowska et al., 2001). The au thors of that pa per also had a hy poth e sis about the post-collisional char ac ter of the leptites from the NE part of the L¹dek-Œnie nik Meta mor phic Unit. The so-called Haniak gneiss es show sim i lar char ac ter is tics to the leptites from the Z³oty Stok-Skrzynka Tec tonic Zone; the Haniak protolith, ac cord ing to Wojciechowska et al. (2000), shows a geo chem i cal con nec tion with the protoliths of the Œnie nik and Giera³tów gneiss es from the OSD. The dif fer ence be tween the protoliths of the Haniak gneiss es and the other OSD gneiss es would have to be due to the pres ence of sed i men tary ma te rial rich in mafic com - po nents in the case of the for mer. Wojciechowska et al. (2001) as sume that the leptites from the L¹dek-Œnie nik Meta mor phic Unit are ge net i cally con nected with the gneiss es or that they achieved a sim i lar geo chem i cal char ac - ter during their subsequent tectono-metamorphic evolu - tion. The for ma tion of the OSD gneiss protoliths is con - nected with Cambro-Or do vi cian mag matic ac tiv ity at an ac tive con ti nen tal mar gin (Ol i ver et al., 1993; Kröner et al., 1994; Kröner et al., 2001) or with an ensialic ini tial rift en vi - ron ment (Kryza & Pin, 1997). The tim ing of the dis tinct stages of the polyphase struc tural evo lu tion of the OSD rocks is still un cer tain. At least 3 main deformational events are re cog nis able (Don in Don et al., 1990), but some work ers de scribe up to 7 stages of de for ma tion (e.g. Dumicz in Don et al., 1990). The prob - lem of the in flu ence of the pre-variscan meta mor phism and de for ma tion on the evo lu tion of the OSD re mains un - solved. More over, the mech a nism of the geodynamic evo - lu tion of the re gion is still de bat able. The ex is tence of sev - eral mod els for this part of the Variscan belt, each plac ing the OSD in a dif fer ent re gional unit (i.e. Matte et al., 1990; Cymerman et al., 1997; Franke & elaÿniewicz, 2000; Schulmann & Gayer, 2000, Aleksandrowski & Mazur, 2002) in di cates the need for a de tailed in ves ti ga tion of the tectono-metamorphic processes controlling the geodynamic evo lu tion of the area. The rocks of the Early Palaeozoic Stronie For ma tion seem to be the most ap pro - pri ate for that pur pose, be cause of their min er al og i cal com - position and distinct structural record. SAMPLING AND ANALYTICAL TECHNIQUES This pa per pres ents the re sults of macro- and microstructural anal y ses car ried out on 88 sam ples of acid meta vol can ic rocks from 70 dif fer ent lo cal i ties within the en tire OSD area. More than 200 pol ished thin sec tions were ana lysed in terms of their pe trog ra phy and mi crostruc tural re cord. The first stage of the study in volved the field pros pect ing of the leptite out crops and geo met ric and ki ne matic anal y ses of the ob served mesostructures. In this pa per, the term leptite is used for mas sive, quartzo-feldspathic rocks, whereas meta-volcanogenic rocks with higher amounts of phyllosilicates (mainly bi o tite and chlorite) are re ferred to as bi o tite-bear ing leptites (a fuller de scrip tion and dis crim i nat ing cri te ria are pre sented in the pe trog ra - phy sec tion). In ad di tion to the struc tural and pet ro log i cal data com ing from the two types of leptite, the ac com pa ny - ing mica schists were also stud ied en abling a better cor re la - tion (due to their more suit able chem i cal com po si tion) be - tween the struc tural and pet ro log i cal re cords. The field

4 4 M. MURTEZI Fig. 2. A sim pli fied geo log i cal map of the Orlica-Œnie nik Dome and the ad ja cent units based on the 1:100,000 Geological map of Lower Silesia with the ad ja cent Czech and Ger man Ter ri to ries (with out the Qua ter nary de pos its) com piled by L. Sawicki, Pol ish Geo log i cal In sti - tute, work was con ducted in three stages, cor re spond ing to the three ar eas dis tin guished in the used re gional di vi sion of the OSD (Fig. 2): the Z³oty Stok-Skrzynka Shear Zone (ZSSSZ); the Krowiarki Mts.; the Orlickie and Bystrzyckie Mts. On the ba sis of those in ves ti ga tions, the se quence of deformation and the succession of the metamorphic assem - blages was es tab lished for the rocks from each of the dis tin - guished re gions. Over 1000 microprobe anal y ses were per formed on min er als from se lected sam ples of the leptites and mica schists, with spe cial fo cus on the gar net zonation. Rep re - sen ta tive anal y ses are given in ta bles 1 5. Ab bre vi a tions of min eral names used in this work are af ter Kretz (1983). All the microprobe anal y sis re sults are avail able at the De part - ment of Ge ol ogy of the Sudetes of the In sti tute of Geo log i - cal Sci ences of the Pol ish Acad emy of Sci ences. Phase com - positions were obtained using an EDS spectrometer with the ThermoNORAN an a lyt i cal sys tem at the Lab o ra to - ries of the In sti tute of the Geo log i cal Sci ences of the Pol ish Acad emy of Sci ences, War saw, Po land (op er at ing con di - tions: 15 kv ac cel er a tion volt age, 0.5 na beam cur rent). For the two sam ples of mica schists cho sen for the P-T pseudosection calculations, whole rock bulk compositions were measured using atomic absorption spectroscopy anal - ysis at the Laboratories of the Institute of the Geological Sci ences of the Pol ish Acad emy of Sci ences, War saw, Po - land. Pseudosection cal cu la tions for the two se lected mica schists: Sk19 from the ZSSSZ and K/a from the Krowiarki Mts. (sam ple lo ca tion shown in Fig. 2) were per formed with the THERMOCALC pro gram (Powell and Hol land, 1988) ver sion 3.1, us ing the in ter nally con sis tent dataset of Hol land & Powell (1998). The pre sented pseudosections were cal cu lated in the model chem i cal sys tem KFMASH which, in spite of its sim pli fi ca tion, cor re sponds well with the min eral as sem blages ob served in the stud ied rocks. Quan ti ta tive P-T es ti ma tions were also per formed us ing conventional thermobarometric calculations. This data, in con junc tion with the con straints from the pseudosections, was used to re con struct the de tailed P-T paths for the stud - ied rocks. 28 rep re sen ta tive sam ples of both the mas sive leptites and the bi o tite-bear ing leptites com ing from the en tire OSD area were se lected for the geo chem i cal anal y sis of the trace el e ments (in clud ing REE). The in stru men tal chem i - cal anal y sis was per formed in the Ac ti va tion Lab o ra to ries Ltd. in Can ada us ing the ICP-MS method. The re sults of the geo chem i cal anal y ses are avail able in the De part ment of Ge ol ogy of the Sudetes of the In sti tute of Geo log i cal Sci - ences of the Pol ish Acad emy of Sci ences.

5 ACID META VOL CAN IC ROCKS 5 PETROGRAPHY AND MINERAL CHEMISTRY The term leptite was tra di tion ally as signed to meta - morphosed, fine-grained, sedimentary or volcanic rocks with lam i nar or gran u lar struc ture. At pres ent, leptite is used for fel sic rocks with a vol cano-sed i men tary protolith com posed mainly of quartz, al kali feld spar and white micas. In this study, the phyllosilicate con tent was cho sen as a cri te rion for dif fer en ti at ing be tween the mas sive leptites (ML) and the as so ci ated bi o tite-bear ing leptites (BBL). Quartzo-feldspathic rocks with a phyllosilicate con - tent higher than 10% are here re ferred to as BBL. The two dis tin guished types of leptites co ex ist on the en tire area of the OSD. In many places, a grad ual tran si tion be tween more and less bt-rich spec i mens can be seen, in di cat ing very close ge netic re la tion ships be tween the rock types. LEPTITES The leptites oc cur as strongly elon gated lensoidal in - ter ca la tions within mica schists of the Stronie For ma tion. The big gest oc cur rence of the leptites is in the ZSSSZ, where their out crops can be found across a ca. 3-km long area, the width of which lo cally ex ceeds 100 m. In the rest of the OSD area, the leptites form lenses not ex ceed ing a few tens of me ters in length. The leptites are fine-grained, pale rocks with a lepidoblastic tex ture ex pressed by al ter - nat ing quartz and quartzo-feldspathic laminae. The pla nar struc ture of the leptites is emphasised by a plane-par al lel ar - range ment of mus co vite, chlorite and some times bi o tite plates. Lo cally, due to the oc cur rence of al kali-feld spar, quartz and al bite porphyroblasts, the leptites tex ture be - comes grano-lepidoblastic. In places where the rocks were ex posed to a very strong shear ing un der HT con di tions, the leptites were turned into blastomylonites. Quartz is the main min eral com po nent of the leptites, con sti tut ing up to 80% of their vol ume (Tab. 6). The other two main min er als of the leptites are mus co vite and feld - spars, and small amounts of bi o tite and chlorite can be pres ent. Quartz Quartz forms a fine mo saic in the quartz and quartzofeldspathic laminae. In the monomineral laminae, the quartz crys tals are on av er age 0.2 mm in di am e ter, and in the polymineral laminae, they are usu ally half of this size. All the ob served crys tals have ir reg u lar curved edges and dis play undulose ex tinc tion. The for ma tion of this pat tern can be at trib uted to such pro cesses of dy namic recrystallization as grain bound ary mi gra tion and subgrain ro ta - tion. In some spec i mens, there are quartz porphyroblasts reach ing 2 mm in di am e ter (Fig. 3a), of ten form ing ag gre - gates with the K-feld spars. In such ag gre gates, the min eral su tures along the grain bound aries con sisted of a dy nam i - cally recrystallized fine-grained quartz mo saic (Fig. 3b). New, stat i cally recrystallized grains were some times formed as a re sult of the grain bound ary area re duc tion (Fig. 3c). K-feldspar K-feld spar ccurs in the form of cor roded xenomorphs up to 3 mm in di am e ter (Fig. 3b). Some grains show Carlsbad twin ing. Very rarely, crys tals with rem nants of the pri mary idiomorphic shape can be found (Fig. 3d). K-feld spar also oc curs in polymineral lay ers (with quartz and micas) in the form of small crys tals not ex ceed ing 0.25 mm. The orthoclase share is ca. 90%. The ana lysed grains do not show signs of chem i cal zonation. Plagioclase Most of the ana lysed plagioclases have an albitic com - po si tion (Tab. 1). The Ca con tent rises slightly to wards their rims, usu ally not ex ceed ing ca. 10%. Elon gated porphyrocrysts, with their lon ger axes up to 3 mm, of ten dis play Carlsbad twin ing and some times also mul ti ple al - bite twin ing (Fig. 3e). The ir reg u lar ar range ment and peaked shape of the al bite twins in di cates their meta mor - phic gen e sis. Pericline twinning is very rare and barely vis i - ble. The small grains of plagioclase (ca mm) oc cur ring in the rock ma trix have the same chem i cal com po si tion as the porphyrocrysts. White micas In the leptites, it is pos si ble to dis tin guish 3 gen er a tions of white micas on the ba sis of their struc tural po si tion. The old est white mica crys tals from the leptites of the L¹dek-Œnie nik meta mor phic unit oc cur in the form of in - clu sions in plagioclase. Those in clu sions have ca. 7 Si at oms p.f.u. (Tab. 2) and are ar ranged in sur faces rep re sent ing rem nants of an old meta mor phic fo li a tion. Their equiv a - lents from the Orlickie and Bystrzyckie Mts. have a lower Si con tent, not ex ceed ing 6.5 Si at oms p.f.u. The sec ond gen er a tions of the white micas, char ac ter ised by a lower Si con tent (in gen eral ca at oms p.f.u. for the leptites from the en tire OSD), emphasise the main meta mor phic fo li a tion of the leptites. For some crys tals of the sec ond gen er a tion, it was pos si ble to es tab lish that the Si con tent in creases to wards their rims. Plates of min er als be long ing to these two gen er a tions are usu ally smaller than 0.25 mm long. The white micas of the third gen er a tion oc cur in pres sure shad ows be hind feld spar and quartzo-feldspathic blasts. Their Si con tent is lower than 6.25 at oms p.f.u. Biotite Only a small amount of bi o tite oc curs in the ML (see Tab. 6). Biotites oc cur ring as small plates (up to 0.25 mm long) with no chem i cal zon ing have on av er age an X Mg of ca Most of the ana lysed biotites dis play signs of chloritization (Tab. 3). Chlorite Apart from the post-bi o tite chlorites char ac ter ised by the ad di tions of Ti and K, the leptites also con tain chlorites that are Ti-free and very low in K (Tab. 4); to gether with the low-si mus co vites and epidotes, they are grouped in pres sure shad ows.

6 6 M. MURTEZI Rep re sen ta tive microprobe anal y ses of plagioclases from the rocks of the leptite series. Anal y ses from the BBL are shown against a grey back ground Ta ble 1 Mineral/ Spot lo ca - tion Sample/ Anal y sis Pl/core Pl/rim Pl/core Pl/rim Pl/core Pl/rim Pl/core Pl/rim Pl/core Pl/rim Pl/core Pl/core Sk29/ Pl 4.3 Sk29/ Pl 4.2 Sk23/ Pl 1.1 Sk23/ Pl 1.2 Sk23/ Pl 8.1 Sk23/ Pl 8.2 SiO TiO Al2O FeO* CaO Na2O K2O Total Recalculated to 8 O Si Ti Al Fe Ca Na K Total Ab An * To tal iron as FeO Ro3b-a Pl 2.1 Ro3b-a Pl 2.2 Sk20 Pl 3.1 Sk20 Pl 3.4 Z9 Pl 1.1 Sk6a Pl 1.1 Epidote group Subidiomorphic or xenomorphic crys tals of the epidote group mainly oc cur in the pres sure shad ows and in the ex ten sions of feld spar porphyroblast tails (Fig. 3a). In terms of their chem i cal com po si tion, they be long to the clinozoisite-epidote se ries, with Fe/(Fe+Mg) = ca (Tab. 5). The most epidote-rich leptites oc cur in the LSMU. Ac ces sory min er als Apart from those listed above, such min er als as ti tan - ite, rutile, zir con and tour ma line also oc cur in the leptites. The con tent of each of those ac ces sory min er als never ex - ceeds 1% vol. The higher ac ces sory min eral con tent is char - ac ter is tic for the leptites from the LSMU and in par tic u lar from the ZSSSZ. BI O TITE-BEAR ING LEPTITES These are more mica-rich than the ML, and thus have a better de vel oped shistosity. Due to that, the BBL have much better re corded struc tures of the con sec u tive stages of de for ma tion than the ML. The main fea ture of the BBL is the penetrative metamorphic foliation, expressed by the plane-par al lel ar range ment of micas form ing thin (up to 0.25 mm) laminae, be tween which, there are much thicker bands of quartz and feld spars. The plagioclase share in those quartzo-feldspathic laminae is con sid er ably larger than in its equiv a lents from the ML. More over, apart from the min er als that also oc cur in the ML, the BBL some times con tain small amounts of staurolite and gar net. Ta ble 6 presents the approximate modal proportion of minerals in the leptites and BBL com ing from dif fer ent ar eas of the OSD. Considering their mineral composition, in some cases the BBL could be taken for mica schists. How ever, field ob - ser va tions based on spa tial re la tions be tween the two types of leptites and sur round ing mica schists clearly in di cates close ge netic con nec tions be tween the BBL and the mas - sive quartzo-feldspathic leptites. The con tacts be tween the ML and the BBL are blurred and grad ual (Fig. 3f), whereas the con tacts be tween the two leptite types and the mica schists are sharp, emphasising their strong lithological con - trast. The chemical compositions of the minerals common for the ML and the BBL are very sim i lar. Two char ac ter is - tic fea tures of the BBL are the oc cur rence of oligoclase plagioclase and a slightly higher Mg/Fe ra tio in mus co - vites. The min eral com po si tion of the BBL can some times be en riched with small amounts of gar net. Subidiomorphic gar net grains (up to 0.3 mm in di am e ter), re veal an in crease of Fe and Mg con tent from core to rim. Small subidiomorphic staurolite crys tals were found in one of the ana lysed BBL sam ples.

7 ACID META VOL CAN IC ROCKS 7 Rep re sen ta tive microprobe anal y ses of white micas from the rocks of the leptite series. Anal y ses from the BBL are shown against a grey back ground Ta ble 2 Mineral/ Spot lo ca - tion Sample/ Anal y sis Ms/ core Sk29/ M3.1 Ms/ core Sk29/ M7.1 Ms/ incl. in Pl Sk23/ M4.1 Ms/ core Sk23/ M5.1 Ms/ core Sk23/ M9 Ms/ core Ro3b/ M1.1 SiO TiO Al2O FeO* MnO MgO CaO Na2O K2O Total Recalculated to 22 O Si Al(IV) Al(VI) Ti Fe Mn Mg Ca Na K Total XMg = Mg/(Fe+ Mg) * To tal iron as FeO Ms/ rim Ro3b/ M Ms/ core Z1/ M1 Ms/ core Wp1/ M1.2 Ms/ core Z9/ M1 Ms/ core Sk11/ M1.1 Ms/ core Sk20/ M1 PETROGRAPHY AND MINERALOGY OF THE MICA SCHISTS USED FOR PSEUDOSECTION CALCULATIONS The char ac ter is tic fea ture of the two cho sen mica schist samples is their mineralogical composition, indica - tive of their or i gin from a vol cano-sed i men tary se quence. They are of ten Al-, Fe- and Mg-poor, and Si- and K-rich. The most pelitic va ri et ies were cho sen for the thermobaromet ric and phase di a gram cal cu la tions. The ma jor el e ment com po si tion of the two rocks cho sen for the phase-di a - gram in ves ti ga tion are given in ta ble 7. Pa ram e ter A (see the bot tom of ta ble 7) re flects the de - gree to which alu minium was used up by the micas, plagioclase and ferro mag nesi an min er als (Vance & Mahar, 1998). A is pos i tive for both of the sam ples, but the A value for K/a is al most twice that for Sk19. This can ex - plain the ab sence of chloritoid in Sk19, where more alu - minium was used up by non-afm phases. Sam ple K/a is also more Fe-, Mg- and Mn-rich than Sk19. Gar net Gar net is a very rare min eral in the rocks of the ZSSSZ, but is more com mon in the mica schists of the Krowiarki Mts. Sk19 con tains small gar nets (up to 1.2 mm across). The gar nets from K/a are big ger, reach ing 4 mm in di am e ter. All the ana lysed grains ex hibit zonation in their ma jor el e ment chem is try. The gar nets from the two ar eas show sim i lar i ties in their tex tural char ac ter is tics. Those from the ZSSSZ have a straight in clu sion pat tern (quartz, il men ite, rutile, chlorite and some times staurolite and bi o - tite) in their cores and curved in clu sion trails of quartz and il men ite in their rims. The gar nets from K/a have curved in clu sion trails of quartz, il men ite, and chlorite through - out the en tire grains, and in some of their cores, they con - tain chloritoid and chlorite ar ranged in straight relictic fo li - ation planes. The chem is try of the gar nets is given in ta bles 8 and 9 and rep re sented in the zon ing pro files in fig ure 4. The zonation of the gar nets from the two sam ples strongly dif - fers, as is par tic u larly well il lus trated in the Fe/(Fe+Mg)

8 8 M. MURTEZI Fig. 3. (a) Quartz porphyroblasts, with zoisite crys tal lised in their pres sure shad ows, sur rounded by mus co vite and chloritized bi o tite (from a mas sive leptite from the ZSSSZ). (b) A dy nam i cally recrystallized fine-grained quartz mo saic fill ing a su ture in cor roded xenomorphs of K-feld spar (from a mas sive leptite from the ZSSSZ). (c) Pris matic subgrains de vel oped due to a grain bound ary area re - duc tion vis i ble in stat i cally recrystallized quartz (from a mas sive leptite from the ZSSSZ). (d) A subidiomorphic K-feld spar crys tal sur - rounded by a fine quartz mo saic (from a mas sive leptite from the vi cin ity of Romanowo in the Krowiarki Mts). (e) Plagioclase with sin - gle Carlsbad and mul ti ple al bite twinning (from a mas sive leptite from the ZSSSZ). (f) The con tact be tween the ML and BBL show ing a grad ual tran si tion be tween the two types of rock; out crop of leptites with vis i ble su per po si tion of an open F4 fold on a F2 tight fold (from the vi cin ity of Romanowo in the Krowiarki Mts). (g) Relic grains of staurolite sur rounded by synkinematic an da lu site (from the mica schists out crop ping near the Javornik granitoids in the ZSSSZ). (h) Small, ran domly ori ented crys tals of kyan ite oc cur ring in paragenesis with staurolite (from the mica schists from the vi cin ity of Konradów in the Krowiarki Mts).

9 ACID META VOL CAN IC ROCKS 9 Rep re sen ta tive microprobe anal y ses of biotites from the rocks of the leptite series. Anal y ses from the BBL are shown against a grey back ground Ta ble 3 Mineral/ Spot lo ca - tion Sample/ Anal y sis Bt/core Bt/core Bt/core Bt/core Bt/core Bt/rim Bt/core Bt/core Bt/core Bt/rim Bt/core Bt/rim Sk29/ Bt1 Sk23/ Bt1 Sk23/ Bt2 Sk4/ Bt1 Ro3b/ Bt1.1 Ro3b/ Bt1.2 SiO TiO Al2O FeO* MnO MgO CaO na Na2O na K2O Total Recalculated to 22 O Si Al(IV) Al(VI) Ti Fe Mn Mg Ca na Na na K Total XMg = Mg/(Fe+ Mg) *To tal iron as FeO; na not ana lysed Z1/ Bt1 Z9/ Bt1 Wp1/ Bt1.1 Wp1/ Bt1.3 Sk20/ Bt5.1 Sk20/ Bt5.2 Fig. 4. Pro files of the chem i cal zonation of rep re sen ta tive gar net porphyroblasts from the Z³oty Stok-Skrzynka Shear Zone (a) and the Krowiarki Mts (b).

10 10 M. MURTEZI Rep re sen ta tive microprobe anal y ses of chlorites from the rocks of the leptite series. Anal y ses from the BBL are shown against a grey back ground Ta ble 4 Mineral/ Spot location Sample/ Anal y sis Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Chl/core Z1/ Ch2 Z1/ Ch3 Sk29a/ Ch2 Sk29a/ Ch3 Sk16a/ Ch4 SiO TiO Al2O FeO* MnO MgO CaO Na2O K2O Total Recalculated to 28 O Sk16b/ Ch1.1 Si Al Ti Fe Mn Mg Ca Na K Total XMg = Mg/ (Fe+Mg) *To tal iron as FeO Wp1a/ Ch4 Wp1a/ Ch6 Wp1a/ Ch7 Sk11a/ Ch Sk11a/ Ch2 pro files. In the case of the gar nets from K/a, those pro files re veal a grad ual, rel a tively uni form Fe/(Fe+Mg) de crease to wards the rim, whereas a typ i cal fea ture of the gar nets from Sk19 is the step-like pro file of this ra tio. This, to - gether with the change in the ori en ta tion of the in clu sions, in di cates that the growth of the gar nets from the rocks of the ZSSSZ was two-staged, ac com pa nied by a change in the chemical environment and/or P-T conditions. A further dif fer ence be tween the gar nets from Sk19 and K/a is il lus - trated by the Ca zonation. Ca de creases monotonically to - wards the rim for Sk19 and is rather sta ble for K/a. The Fe and Mg zonation trends are quite sim i lar for the gar nets from the two sam ples the pyrope and almandine com po - nents slightly in crease from core to rim. The Mn con tent, typ i cally for meta mor phic gar nets, de creases to wards the rim in both cases. Short re ver sals of the zonation trends are ob served in the outer 100 µm; these can be due to re-equil i - bra tion with the ma trix min er als sub se quent to gar net growth. Feldspars Both of the sam ples have two gen er a tions of plagioclases, as cer tained on the ba sis of the chem i cal anal y sis and microstructural po si tion of the crys tals: an older one with nor mal zonation from max. 22% An in the cores to 5% An in the rims, and a youn ger one rep re sented by albites with slightly in verse zonation from 5% in the cores to 8% in the rims. The plagioclases of the older gen er a tion, pres ent in the form of porphyroclasts reach ing up to 2 mm in di am e - ter, some times con tain in clu sions of phengite with an av er - age Si con tent of about 3.3. The crys tals of the youn ger gen er a tion are usu ally free of in clu sions, or con tain phengites with an Si con tent of about 3.1. The orthoclase con - tent in all the ana lysed plagioclase grains from the two gen - er a tions never ex ceeds 2%. Ta bles 8 and 9 gives the com po - si tion of a rep re sen ta tive plagioclase from the two gen er a - tions. Potassic feld spars com monly oc cur in the schists from both ar eas; they ex hibit a large share of volcanogenic ma te - rial in their protolith. The feld spars con tain mi nor al bite com po nents, reach ing a max i mum of ca. 5%. In leptitic af - fin i ties, subidiomorphic porphyroclasts of K-feld spars with lon ger axes reach ing up to 6 mm can some times con - sti tute about 15% of the modal com po si tion of these rocks. Micas Mus co vite is a com mon com po nent of all the sam ples from both units. There are only small dif fer ences in the range of its com po si tion within the two stud ied ar eas. The rocks of the ZSSSZ con tain two pop u la tions of white micas char ac ter ised by dif fer ent Si con tents. The mus co - vites of the first pop u la tion oc cur as small in clu sions in

11 ACID META VOL CAN IC ROCKS 11 Ta ble 5 Representative microprobe analyses of the epidote-group min er als from the rocks of the leptite series. Anal y ses from the BBL are shown against a grey back ground Mineral/ Spot lo ca - tion Sample/ Anal y sis Ep/core Ep/rim Ep/core Ep/core Ep/rim Ro3da/ Ep1.1 Ro3da/ Ep1.2 Wp1a/ Ep1 Gn8b/ Ep1.1 Gn8b/ Ep1.2 SiO Al2O Fe2O3* MnO CaO Y2O La2O Ce2O ThO UO Total Recalculated to 25O Si Al Fe Mn Ca Y La Ce Th U Total Ca/(Ca+Y +La+ Ce+Th+ U) *To tal iron as FeO plagioclases and K-feld spars, and have Si con tents reach ing Larger crys tals are very rare in this pop u la tion. They have a clear zonation: from core to rim, the Si con tent de - creases from up to 3.45 to 3.15, while their X Na = Na/ (Na+K) in creases slightly, from 0.05 to Those crys - tals cut the last fo li a tion plane at a mod er ate an gle. The sec - ond population of muscovites consists of crystals lying par - al lel to the fo li a tion planes. The core and rim com po si tion of those crys tals is al most iden ti cal, with only a slight de - crease in Si con tent from core (3.12) to rim (3.08). Sim i - larly, two pop u la tions of mus co vites were iden ti fied in the rocks of the Krowiarki Mts. In this case, the av er age Si con - tent is slightly lower for each of the pop u la tions. Bi o tite, al though pres ent in all the stud ied rocks, is less com mon than mus co vite. In gen eral, all the ana lysed bi o - tite crys tals have a sim i lar com po si tion, with an X Mg of ca. 0.4 and an Al IV of per 22 ox y gen at oms. Ta ble 6 The approximate modal proportions of minerals forming the mas sive leptites (white back ground) and the BBL (grey back ground) in dif fer ent ar eas of the OSD. ZSSSZ Z³oty Stok-Skrzynka Shear Zone ML (Sk23) ZSSSZ BBL (Sk27) Area Krowiarki Mts. ML (Ro5a) BBL (Ro3a) Bystrzyckie Mts. ML (Gn1) BBL (Gn8b) Orlickie Mts. ML (Z1) BBL (Z9+ Z5) % Qtz Pl Kfs Ms Bt Chl Ep AlSi 1 (sill and) 1 (and) Ttn Ap 1 1 Rt Ilm Zm MnZ 1 Tur St 1 Grt 2 2 Ta ble 7 XRF-de rived bulk com po si tions (given as weight per cent ox ides) of the two mica schists cho sen for pseudosection cal cu la tions. ZSSSZ Z³oty Stok-Skrzynka Shear Zone Sk 19 (ZSSSZ) Ko10a (Krowiarki Mts.) SiO Al2O FeO MgO MnO K2O Na2O CaO XFe A' X Fe = FeO/(FeO+MgO) 2 Pa ram e ter as used by Mahar et al., (1997), cal cu lated from mole per cent ox ides: A = (Al 2 O 3-3K 2 O-CaO-Na 2 O)/(Al 2 O 3-3K 2 O-CaO-Na 2 O+FeO+MgO)

12 12 M. MURTEZI Rep re sen ta tive microprobe anal y ses of min er als from mica schist Sk19 (ZSSSZ) Ta ble 8 Mineral/ Spot location Gt core Gt rim Bt inclus. in Gt Bt S2 fo li a tion Ms inclus. in Gt Ms S2 fo li a tion Plcore Plrim St Anal y sis Gt8.1 Gt8.2 Bt12 Bt14 M2a M7 Pl1.3 Pl1.1 St1 SiO TiO na na 0.75 Al2O FeO* nd MnO na na 0.59 MgO na na 2.02 CaO Na2O nd nd K2O Total Recalculated to: 12 O 12 O 22 O 22 O 22 O 22 O 8 O 8 O 46 O Si Al to tal Al(IV) Al(VI) Ti Fe Mn na na Mg na na Ca Na K Total XFe= Fe/(Fe+Mg) XMg = Mg/(Fe+Mg) *To tal iron as FeO; nd not de ter mined; na not ana lysed; Gt gar net; Bt bi o tite; Ms mus co vite; Pl plagioclase; St staurolite Staurolite In the metamorphosed volcano-sedimentary rocks of the ZSSSZ, staurolite is pres ent in a very small amount, oc - cur ring as small relic grains sur rounded by an da lu site (Fig. 3g). The staurolites from the Krowiarki Mts. are larger and idiomorphic, and con tain in clu sions of mus co vites with an Si con tent of ca In both cases, the staurolite crys tals are unzoned, with a similar chemical composition showing an Fe/(Fe+Mg) ra tio of ca Chloritoid Chloritoid can be found ex clu sively in the form of in - clu sions in some gar net grains from the Krowiarki Mts. It is pre served in the gar net cores as tiny nee dles de fin ing the in ter nal fo li a tion. All the chloritoid nee dles have a sim i lar chem i cal com po si tion with an Fe/(Fe+Mg) ra tio of ca. 0.87, ir re spec tive of the dis tance from the cen tre of the em - bodying garnet grain. Fe-Ti ox ides In the sam ples from the two units, Fe and Ti ox ides are rep re sented by il men ite and rutile as in clu sions in gar net. Rutile is only sta ble in the cores of the stud ied gar nets, whereas il men ite was sta ble dur ing the growth of the en tire gar net. In ad di tion, il men ite is com mon in the ma trix of all the sam ples, while rutile is found only oc ca sion ally. Al 2 SiO 5 poly morphs All three Al 2 SiO 5 poly morphs were found in the study area, some times oc cur ring in pairs: sillimanite with an da lu - site or kyan ite with sillimanite. The first com bi na tion is char ac ter is tic for the rocks of the ZSSSZ, where the over - print of the high-temperature metamorphism connected with the ad ja cent Javornik granitoid in tru sion is clearly vis i ble. Synmetamorphic and synkinematic blasts of an da - lu site usu ally grew at the ex pense of staurolite (Fig. 3g), and only relicts of the then al ready metastable fibrolitic sillimanite can be found. Rocks with two types of co-ex ist - ing Al 2 SiO 5 min er als were also found in the Krowiarki Mts. where, apart from fibrolitic sillimanite (ori ented par - al lel to the S2 fo li a tion), small, ran domly ori ented crys tals of kyan ite can some times be found (Fig. 3h). How ever, the most com mon sit u a tion ob served in the stud ied rocks is

13 ACID META VOL CAN IC ROCKS 13 Rep re sen ta tive microprobe anal y ses of min er als from mica schist K10/a (Krowiarki Mts.) Ta ble 9 Mineral/Spot location Gt core Gtrim Bt S2 fo li a tion Ms inclus. in Gt Ms S2 fo li a tion Chl Cld Plcore St Anal y sis Gt1.11 Gt1.20 Bt10 M1 M7 Chl2 Cld3 Pl4 St2 SiO TiO Al2O FeO* MnO na 0.13 MgO na 1.91 CaO nd Na2O nd nd K2O Total Recalculated to: 12 O 12 O 22 O 22 O 22 O 28 O 12 O 8 O 46 O Si Al to tal Al(IV) Al(VI) Ti Fe Mn na Mg na Ca nd Na nd nd K Total XFe= Fe/(Fe+Mg) XMg = Mg/(Fe+Mg) *To tal iron as FeO; nd not de ter mined; na not ana lysed; Gt gar net; Bt bi o tite; Ms mus co vite; Chl chlorite; Cld chloritoid; Pl plagioclase; St staurolite. the oc cur rence of only one of the Al 2 SiO 5 min er als, and such sam ples were cho sen for P-T pseudosection cal cu la - tions (sam ple Sk 19 con tains only an da lu site, and sam ple K/a sillimanite). Chlorite Chlorite is pres ent in the rocks from both ar eas as in - clu sions in the gar nets and in the com mon ma trix min eral. The chlorite in clu sions in the gar nets are al most po tas - sium-free, show ing a high Fe/(Fe+Mg) ra tio of up to The ap par ent chem is try of those in clu sions could have been in flu enced by the anal y sis of the sur round ing gar nets, which are very small. The X Fe value for the chlorites from the ma trix ranges from 0.55 to 0.70, whereas larger val ues seem to char ac ter ise the youn gest grains. GEOCHEMISTRY OF THE LEPTITES De ter mi na tion of the geo chem i cal char ac ter is tics of the leptites was car ried out based on anal y ses of the 28 rep - re sen ta tive rock sam ples com ing from the en tire OSD area. 17 sam ples were from the ML and 11 sam ples from the BBL. The ma jor and trace el e ment com po si tions of the ana lysed sam ples are shown in ta ble 10. The ana lysed sam - ples came from the 2 parts of the OSD: the LSMU and the Bystrzyckie and Orlickie Mts. In ad di tion, two sam ples were col lected to the east of the Giera³tów gneiss thrust into the Bialskie Mts.; these rep re sent the acid metavolcanic rocks of the Staré Mìsto Zone. As the stud ied rocks from all of the re gions were sub - jected to the polyphase tectono-meta mor phic changes, it is possible that the primary chemical compositions of the ana lysed sam ples were changed by the se lec tive mo bi li sa - tion of their chem i cal com po nents. There fore, the re sults given here are for the most suit able (i.e. the least sus cep ti - ble to mo bi li sa tion) el e ments, such as REE and Zr, Ti, Nb, Ta and Th.

14 14 M. MURTEZI GEN ERAL GEO CHEM I CAL CHAR AC TER IS TICS OF THE LEPTITES Leptites from the W and the E part of the OSD, and those from the Staré Mìsto Belt have very sim i lar ma jor el - e ment com po si tions. All the ana lysed sam ples of the ML have a high SiO 2 con tent rang ing from 76 to 81% wt. The SiO 2 con tent of the BBL is slightly lower, be tween 71 and79 % wt. Apart from that, the ML have higher Mg and Fe con tents than the BBL. All the ana lysed rocks have peraluminous, subalkaline char ac ter is tics (Fig. 5). The Ca con tent is usu ally be low 0.5% in the mas sive va ri ety and around 1% in the BBL. K 2 O/Na 2 O changes widely (from 0.3 up to 21%) av er ag ing at ca. 3%. TRACE EL E MENT GEO CHEM IS TRY On the Winchester & Floyd (1977) di a gram based on Nb/Y and Zr/TiO 2 ra tios, the pro jec tion points of the ML are con cen trated at the bound ary be tween the rhy o lite and rhyodacite/dacite fields (Fig. 6). The BBL pro jec tion points re veal a stron ger dis per sion and most of them oc - cupy the rhyodacite/dacite field. One sam ple draws spe cial at ten tion, plot ting within the trachyte field. This sam ple co mes from a mas sive rock out crop on the slopes of Mt. Wapnisko in the Krowiarki Mts. re gion. More over, meta - vol can ic rocks from Mt. Wapnisko re veal high Na and K contents. The REE vari a tion pat terns When nor mal ised to chondritic val ues (An ders & Grevesse, 1989), the REE pat terns for all the ana lysed sam - ples of the ML show sim i lar char ac ter is tics (Fig. 7a). The LREE pro files are slightly sloped, while at the HREE side of the di a gram, the pro file lines run flat. The leptites are only slightly more en riched in the LREE than in the HREE. All the ana lysed sam ples dis play a strong neg a tive Eu anom aly. The low est val ues of the Eu/Eu* (ca. 0.03) are typ i cal for sam ples from the ZSSSZ and the Staré Mìsto Belt, whereas the high est (ca. 0.35) char ac ter ise those from the west ern part of the OSD. More over, sam ples from the Orlickie and Bystrzyckie Mts. show a pos i tive Ce anom - aly. The Ce/Ce* ra tio reaches a value of 1.40 for sam ples from the vi cin ity of Gniewoszów in the Bystrzyckie Mts., and are slightly lower (1.30) for those from the east ern slopes of the Orlickie Mts. near Zieleniec. The Eu anom a lies, es pe cially for fel sic melts, are feld - spar-con trolled, as the di va lent Eu is a com pat i ble el e ment in plagioclase and potassium feldspar. Additionally, the value of the Eu anom aly is in flu enced by the magma ox i da - tion state, de fined by ox y gen fugacity. With a low fo value, the par ti tion co ef fi cient be tween the feld spar crys - tals and cre ated melt is high. The as cer tained Eu anom aly points to a feld spar frac tion ation event, pos si bly con nected with a par tial melt ing of the source rocks. The pos i tive Ce anom aly is an ef fect of the ac cu mu la tion of the Ce 4+ cre - ated due to the ox i da tion of Ce 3+ previously dissolved in marine water. Under oxidation conditions, Ce is less solu - ble in wa ter and in ef fect ac cu mu lates in sed i ments Fig. 5. The chem i cal clas si fi ca tion of granitoidic rocks ac cord - ing to a di a gram based on the con tent of Al 2 O 3, CaO, K 2 O and Na 2 O (af ter Maniar & Piccoli, 1989) show ing the peraluminous char ac ter is tics of the leptites. ZSSSZ Z³oty Stok-Skrzynka Shear Zone. Fig. 6. The chem i cal clas si fi ca tion of vol ca nic rocks us ing Nb/Y and Zr/TiO 2 ra tios (af ter Winchester & Floyd, 1977). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. (Takahashi et al., 2000). The pos i tive Ce anom aly can be in - ter preted as an in di ca tor of par tic i pa tion of shal low wa ter ma rine sed i ments in the leptites protolith. It is also pos si - ble that the as cer tained Ce anom aly is due to ac ces sory min er als pres ent in the leptites; how ever, there is no dif fer - ence in amount of ac ces sory min er als oc cur ring in the sam - ples with a Ce anom aly and those with out. The lack of a clearly vis i ble de ple tion of the leptites in the HREE rel a tive to the LREE in di cates the ab sence of such min er als as gar net and hornblende in the magma source. In fel sic melts, the par ti tion co ef fi cients of the LREE and HREE are in tro duced by the pres ence of such ac ces sory min er als as zir con, ti tan ite, ap a tite, al la nite and monazite. In fer ring from the in flu ence of the frac tion ation of those min er als on the ob served REE pat terns is very dif - fi cult due to the pos si bil ity that their pri mary ra tios were

15 ACID META VOL CAN IC ROCKS 15 Fig. 7. Chondrite-nor mal ised (val ues af ter An ders & Grevesse, 1989) REE vari a tion pat terns for the mas sive leptites (a) and the BBL (b). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. disturbed by the admixture of a sedimentary component in the leptites protolith. This dis tur bance is clearly vis i ble in the di a gram of the REE vari a tion for the BBL (Fig. 7b). They are char ac ter ised by a con sid er ably lower Eu anom - aly. Most of them re veal clearly vis i ble en rich ment in the LREE rel a tive to the HREE. The pro file lines rep re sent ing the BBL are more scat tered than those of the ML. A com - par i son of the REE vari a tion pat terns of the two dis tin - guished types of OSD leptites in di cates that the rocks of the leptite se ries orig i nate from a di verse vol cano-sed i men - tary se quence com pris ing mas sive sur face flows and/or subvolcanic bod ies as well as tuffs and tuffites of acid vol ca - nic rocks. Taking into account the chemical composition of the leptites, it is rea son able to re late their REE con tent to the REE con cen tra tions of con ti nen tal crust. The REE dis tri - bu tion vis i ble in the di a gram con structed with the use of Rudnick & Foun tain s (1995) data on the REE con cen tra - tions in the mid dle con ti nen tal crust (Fig. 8), re veals sim i - lar trends to those nor mal ised us ing chondritic val ues. There is a large dif fer ence vis i ble in the rel a tive con cen tra - tion of the REE. The crust-nor mal ised REE con tents are close to one. The mas sive leptites re veal a strong neg a tive Eu anom aly and sig nif i cant en rich ment in the HREE in comparison to the LREE. Extrapolating Eu N from Sm N and Gd N, it be comes ap par ent that the in creas ing trend in the REE con cen tra tion starts from Sm, which to gether with Eu, Gd, Tb, Dy and Ho forms the some times dis tin - guished mid dle REE (MREE) group. The com mon oc cur - rence of ti tan ite and ap a tite in the leptites ex plains their rel - a tively high MREE con tent, be cause these min er als par ti - tion the MREE rel a tive to the LREE and HREE. Zir con, as a com monly oc cur ring ac ces sory min eral in the leptites, is re spon si ble for their en rich ment in the HREE rel a tive to the LREE. Nor mal ized multi-el e ment di a grams Ex tended multi-el e ment di a grams (so-called spi der plots) are based mainly on in com pat i ble trace el e ments. The con cen tra tion of these el e ments is strongly de pend ent on the de gree of par tial melt ing. On this ba sis, it is pos si ble to in ves ti gate the con di tions un der which the pri mary magma was gen er ated. Un der fa vour able cir cum stances, pro cesses such as crys tal frac tion ation, mix ing of mag mas, assimilation/contamination and liquid immiscibility can be re cog nised (Rollinson, 1993). In the case of the geochemical anal y sis of these leptites, due to their polymetamorphic char ac ter, one needs to be care ful when de duc ing the processes acting during formation of their parental Fig. 8. The REE vari a tion pat terns for the mas sive leptites (in - clud ing the Mt. Wapnisko metatrachyte). The mea sured el e ment con cen tra tions were nor mal ised to the val ues char ac ter is tic for the mid dle con ti nen tal crust (af ter Rudnick & Foun tain, 1995). ZSSSZ Z³oty Stok-Skrzynka Shear Zone.

16 16 M. MURTEZI Fig. 9. Chondrite-nor mal ised (val ues af ter Thomp son, 1982) multi-el e ment pat terns for the mas sive leptites (a) and the BBL (b). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. magma. Nev er the less, spi der plots based on prop erly cho - sen cal i bra tions can be very help ful in the rec og ni tion of the geotectonic en vi ron ment of the leptites protolith for - ma tion. The com po si tion of the leptites pre sented here is re lated to the ocean-ridge granitoid (ORG) com po si tion and the chondrite com po si tion listed by Thomp son (1982). Ac cord ing to the spi der plots pre sented in this study, the leptite com po si tions show the chondritic val ues listed by Thomp son (1982), and the ocean-ridge granitoid (ORG) val ues ac cord ing to Pearce et al. (1984). When nor mal ised to chondritic val ues (Fig. 9a), the trace el e ment con cen tra tions in all of the ML re veal sim i lar trends with a char ac ter is tic in crease in the in com pat i ble trace el e ment con cen tra tions. All the ana lysed sam ples show a strong neg a tive Ti anom aly (Ti/Ti* = ). Most of the sam ples (be sides one from the ZSSSZ and two from Bystrzyckie Mts.) also show a strong neg a tive Sr anom aly (Sr/Sr* = c. 0.04). A neg a tive Nb anom aly (Nb/Nb* = c. 0.33) char ac ter ises all the sam ples but two from the vi cin ity of Zieleniec in the Orlica Mts. Those sam ples (Z4 and Z7) are rel a tively K 2 O and Rb poor, and in ef fect show a pos i tive Th anom aly. A rel a tively low Ba con cen tra tion is typ i cal for all the ana lysed sam ples. In terms of the trace el e ment char ac ter is tics, the BBL are sim i - lar to ML, but their pro file lines show a stron ger dis per sion (Fig. 9b). Sam ple Wp1 from the Wapnisko Mts. con trasts strongly to the rest of the ana lysed leptite sam ples. The most char ac ter is tic fea ture of this sam ple is rel a tively high con cen tra tion of Nb and Th. On the ORG-nor mal ised di a grams, the con cen tra tion of trace el e ments in creases with the in crease of their in - com pat i bil ity (Fig. 10a, b). The amounts of such im mo bile in com pat i ble trace el e ments as Yb, Y or Sm are close to the nor mal is ing val ues. Apart from the im mo bile el e ments, the in com pat i bil ity of which in creases from right to left, ORG-nor mal ised di a grams also con tain mo bile el e ments: Ba, Rb and K. The de gree of their in com pat i bil ity in creases from left to right., With the ex cep tion of sam ples Z4 and Z7, the mas sive leptites are strongly en riched in those mo - bile trace el e ments. A very char ac ter is tic fea ture of all of the leptites is a neg a tive Ta and Nb anom aly. Most of the leptites also show a neg a tive Ba anom aly. De ple tion in Hf and Zr is typ i cal for the sam ples from the ZSSSZ and the Staré Mìsto Belt. The trends vis i ble on the ORG-nor mal - ised di a gram for the BBL are much like those of the ML. Sam ple Wp1 again stands out, hav ing con sid er ably higher con cen tra tions of all of the en vis aged im mo bile trace el e - ments. Their con cen tra tion in creases evenly with the in - crease of their in com pat i bil ity. The mo bile trace el e ment con cen tra tions also in crease ac cord ing to their in com pat i - bil ity, with the ex cep tion of the an oma lously low con cen - tra tion of Ba. The neg a tive Ti and Sr anom a lies as cer tained for the ana lysed sam ples can be in ter preted as an ef fect of a frac - tional crystallisation pro cess, be cause those el e ments are incorporated in minerals developing in the early stages of magma evo lu tion. More over, Sr can be frac tion ated in dif - fer ent stages of magma evo lu tion be ing cu mu lated in feld - spars. The rel a tively low Ti and Sr con cen tra tions can in di - cate that the leptites protolith de vel oped as the ad vanced prod uct of fel sic magma evo lu tion, as the early mem bers of a mag matic suit orig i nat ing from such magma would have an in creased con tent of these el e ments. The ob served neg a - tive Ba anom aly, typ i cal of most of the ML, can be ex - plained by the ac cu mu la tion of this el e ment in the feld - spars due to a crys tal frac tion ation pro cess. The de gree of frac tion ation of the al kali feld spars is in versely pro por - tional to the wa ter pres sure and to the depth of the magma (Bonin, 1990). The dis tinct neg a tive Eu and Ba anom a lies as cer tained in the leptites in di cates a high ef fi ciency of frac tion ation of the al kali feld spars dur ing the evo lu tion of the pa ren tal

17 ACID META VOL CAN IC ROCKS 17 Fig. 10. Ocean-ridge gran ite-nor mal ised (val ues af ter Pearce et al., 1984) multi-el e ment pat terns for the mas sive leptites (a) and the BBL (b). ZSSSZ Z³oty Stok-Skrzynka Shear Zone magma. The low con cen tra tions of K, Rb and Ba in sam - ples Z4 and Z7 and their low Sr con tent in di cates an early re moval of those el e ments from the evolv ing melt due to the crys tal li za tion of the al kali feld spars. The par tic u larly strong in flu ence of this pro cess on the chem i cal com po si - tion of sam ples Z4 and Z7 is also re flected in their very low Mg con tent a typ i cal fea ture of an ad vanced frac tion - ation. The high Th/Ta ra tios ob served on the ORG-nor mal - ised di a grams, the neg a tive Nb and Ta anom a lies, and the low Ti con tent of all the stud ied leptites can be in ter preted as an in di ca tor of magmatism con nected with a suprasubduction en vi ron ment. The high Rb con tent in com bi na - tion with the neg a tive Ta and Nb anom aly is a typ i cal fea - ture of orogenic rhyolites. The strong en rich ment in LILE in di cates a sig nif i cant share of con ti nen tal crust ma te rial in the leptites protolith. Such fea tures as the neg a tive Nb anom aly and the high Th/Nb ra tio are also typ i cal for mag mas de rived from con ti nen tal crust, some times in ter - preted as an in di ca tor con nect ing a magma source with a con ti nen tal arc en vi ron ment (e.g. Whalen et al., 1998, Zellmer et al., 2000). The high Th/Nb ra tio as cer tained for the ML could be con sid ered a re sult of an ad mix ture of a pelitic ma te rial into their protolith; how ever, the lack of in crease in this ra tio in the BBL stands against such an in - ter pre ta tion. The ORG-nor mal ised pat tern of the trace-el - e ment con cen tra tions in the leptites has much in com mon with those typ i cal for rocks cre ated at ac tive con ti nen tal mar gins. Sim i lar trends have been as cer tained for syncollisional peraluminous granitoids from the Hi ma la yas (Inger & Har ris, 1993) and for neo-pro tero zoic mus co - vite-bi o tite orthogneisses from Su dan (Kuster & Liegeois, 2001). The neg a tive Ta and Nb anom a lies and the low Zr and Hf con tent viv idly dis tin guish the OSD leptites from vol ca nic rocks cre ated in an in ter con ti nen tal pas sive rift. Sam ple Wp1 from the Krowiarki Mts, clas si fied as metatrachyte, shows a lack of the neg a tive Ta and Nb anom a lies typ i cal for rocks of this type (Fig. 10b). This sam ple also has a con sid er ably higher Zr con tent than the rest of the ana lysed sam ples, and the low est Al 2 O 3 /(CaO+ K 2 O+Na 2 O) ra tio. The protolith of this sam ple could have de vel oped from the same mag matic source as the rest of the OSD leptites, but could rep re sent an ear lier stage of magma dif fer en ti a tion. The trace el e ment con tent in Wp1 matches the con cen tra tions char ac ter is tic for intracontinental rift tra chytes; how ever, trachyte-rhy o lite as so ci a - tions are also known to oc cur at ac tive con ti nen tal mar - gins. Geotectonic set ting dis crim i na tion di a grams The pri mary com po si tion of rocks such as the OSD leptites can be mod i fied by a meta mor phic ex change of el e - ments, in particular by hydrothermal activity. Even a small dis tur bance of the pri mary ra tios of indicatory el e - ments can be very mis lead ing. De spite the fact that di a - grams cho sen for the de ter mi na tion of the geotectonic en - vi ron ment of the leptites protolith for ma tion are based on im mo bile trace el e ments, the re sults be low should be treated with cau tion. On the Nb vs. Y di a gram (Pearce et al., 1984), most of the ana lysed sam ples plot in the field shared by the vol ca - nic-arc gran ites and syn-collisional gran ites, but still close to the field bor ders junc tion (Fig. 11a). The metatrachyte Wp1 ex clu sively oc cu pies the field of within-plate gran ites. On the di a gram based on Rb vs. Y+Nb (Pearce et al., 1984), the geotectonic clas si fi ca tion of the leptites is even less clear (Fig. 11b). Ac cord ing to the clas si fi ca tion based on the Rb, Hf and Ta ra tios pro posed by Har ris et al. (1986), the leptites pro jec tion points are widely dis persed. On the Rb/10 Hf

18 18 M. MURTEZI Fig. 11. The Nb-Y (a) and Rb-(Y+Nb) (b) tec tonic en vi ron ment dis crim i na tion di a grams (af ter Pearce et al., 1984). VAG vol ca - nic-arc gran ites; syn-colg syn-collisional gran ites; WPG within-plate gran ites; ORG ocean-ridge gran ites. ZSSSZ Z³oty Stok-Skrzynka Shear Zone Ta x 3 di a gram (Fig. 12a), most of the sam ples oc cupy the area at trib uted to gran ites from a collisional tec tonic set - ting, but theprojection points spread along the line that de - lim its the field of within-plate gran ites. Sim i larly the Rb/30 Hf Ta x 3 di a gram pro vides no un am big u ous data on the geotectonic set ting of the leptites protolith (Fig. 12b). On both di a grams, sam ples Wp1, and Z4 and Z7 plot in the field of within-plate gran ites. Con trary to the above-de scribed di a grams, the Ta/Yb vs. Th/Yb based clas si fi ca tion of Pearce et al. (1983), adapted by Gorton & Schandl (2000) for fel sic vol ca nic rocks, univocally char ac ter ises the stud ied leptites as rocks cre ated in an ac tive con ti nen tal mar gin en vi ron ment (Fig. 13). Sam ple Wp1 stands out, plot ting in the within-plate field. The dif fer ence be tween the rhyolithic leptites and sam ple Wp1 with its trachitic af fin i ties also has its re flec - tion on di a grams for the geo chem i cal clas si fi ca tion of the granitoids. On the Whalen et al. (1987) di a gram, most of the leptites plot in the field of I and S gran ites (Fig. 14a). Sam ple Wp1 shows the big gest shift to wards the field of Fig. 12. The Rb/10-Hf-Ta x 3 (a) and Rb/30-Hf-Ta x 3 (b) tec - tonic en vi ron ment dis crim i na tion di a grams (af ter Har ris, 1986). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. A-type gran ites. On the ba sis of the Nb-Ce-Y di a gram (Eby, 1992), which dis tin guishes A-type gran ites de rived by dif fer en ti a tion of man tle melts (type A1) and those typ i - cal for within-plate (non-arc) en vi ron ments (type A2), sam - ple Wp1 is char ac ter ised as the A1 type (Fig. 14b). Rocks of this type, hav ing con ti nen tal crust af fin i ties, are dif fer en ti - ates of mag mas de rived from sources hav ing sim i lar char ac - ter is tics to those of the oce anic is land bas alts. On the ba sis of the above-pre sented data, rec og ni tion of the geotectonic en vi ron ment of the leptites protolith formation is ambiguous. An active margin affinity for the leptites is mainly dic tated by their neg a tive Ta and Nb anom a lies. Those anom a lies could have de vel oped in re - sponse to the crystallization of titanite and/or ilmenite dur ing the evo lu tion of the fel sic magma be cause Ta and Nb have a high min eral/melt par ti tion co ef fi cient for

19 ACID META VOL CAN IC ROCKS 19 Fig. 13. The Ta/Yb-Th/Yb tec tonic en vi ron ment dis crim i na - tion di a gram (af ter Pearce et al., 1983, re-cal i brated by Gorton & Schandl, 2000). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. Fig. 15. The in flu ence of Ti-rich min eral frac tion ation on the Ta and Nb con cen tra tions in the ex am ined leptites, based on the ra tios: Nb-TiO 2 (a), Ta-TiO 2 (b) and Th/Nb-TiO 2 (c). Fig. 14. The Ga/Al-Zr dis crim i na tion of A-type ver sus other gran ite types (af ter Whalen et al., 1987) (a), and the Nb-Ce-Y dis - crim i na tion plot for man tle A-type (A1) and crustal A-type (A2) gran ites (b) (af ter Eby, 1992). ZSSSZ Z³oty Stok-Skrzynka Shear Zone. high-ti min er als (Green & Pearson, 1987). To ex am ine if this is the case for leptites, plots of Ta vs TiO 2, Nb vs TiO 2 and Th/Nb vs TiO 2 were con structed show ing for the stud ied sam ples an in verse re la tion ship be tween the TiO 2 and Nb and the TiO 2 and Ta con tents (Fig. 15a, b). More - over, there is no in verse re la tion ship be tween the Th/Nb ra tio and TiO 2 con tent a fea ture that would in di cate a strong frac tion ation of Ti-rich min er als (Fig. 15c). As HFSE el e ments, Ta, Nb and Ti are treated as par tic u larly re sis tant to chem i cal al ter ation (e.g. Floyd & Winchester, 1978, Hansen, 2002), and thus the con cen tra tions of those el e ments mea sured to day should cor re spond to their orig i - nal share in the rock. How ever, in the case of the stud ied rocks, there is a pos si bil ity that the pri mary ra tios of those el e ments could have been dis turbed by the ad di tion of sed i - men tary ma te rial. DIS CUS SION ON THE GEN E SIS OF THE LEPTITES The above-pre sented data dem on strates that the dif fer - ence be tween the ML and BBL re sults from the de gree of contamination of the primary volcanic material by sedi - men tary ad mix tures. Nev er the less, the protoliths of the ML and BBL can be grouped into one rock suite the leptite se ries. The ML orig i nate from acid vol ca nic rocks that could have con tained only small amounts of sed i men - tary ma te rial. These rocks could have had the form of mas -

20 20 M. MURTEZI Chem i cal data for the rocks of the leptite se ries from the OSD Ta ble 10 Sam ple B5 B7 Gn1 Gn13 Gn1a Gn2 Gn9 Ko2 Ko4 Ko5 Ro2 Ro4 Ro5 Sk15 Sk16 Lo cal ity Bielice/ LSMU Rock type Bielice/ LSMU Gniewoszów/Bszów/Bszów/Bszów/BM Gniewo- Gniewo- Gniewo- Gniewoszów/BM Konradów/ LSMU Konradów/ LSMU Konradów/ LSMU Romanowo/ LSMU Romanowo/ LSMU Romanowo/ LSMU ML ML ML ML BBL BBL ML BBL ML ML ML ML BBL ML ML Ma jor ox ides (wt%) SiO TiO Al2O Fe2O MnO MgO CaO Na2O K2O P2O LOI To tal Trace el e ments (ppm) Cr Ni Co Sc V Cu Pb Zn Bi Sn W As Sb K Rb Cs Ba Sr Tl Ga Ta Nb Hf Zr Ti Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Be Chem i cal group: BBL bi o tite-bear ing leptite; MT Mt. Wapnisko metatrachyte; ML mas sive leptites. Lo cal ity: BM Bystrzyckie Mts.; KM Krowiarki Mts.; ZSSSZ Z³oty Stok-Skrzynka Shear Zone; OM Orlickie Mts; LSMU L¹dek-Snie nik Meta mor phic Unit. ZSSSZ ZSSSZ

21 ACID META VOL CAN IC ROCKS 21 Chem i cal data for the rocks of the leptite se ries from the OSD Ta ble 10 continued Sam ple Sk20 Sk23 Sk27 Sk29 Sk30 Sk38 Sk4a Sk6 Wp1 Wp3 Z3 Z4 Z7 Lo cal ity ZSSSZ ZSSSZ ZSSSS ZSSSZ ZSSSZ ZSSSZ ZSSSZ ZSSSZ Rogó ka/ LSMU Rogó ka/ LSMU Zieleniec/ OM Zieleniec/ OM Zieleniec/ OM Rock type BBL ML BBL ML ML ML BBL BBL MT BBL BBL ML ML Ma jor ox ides (wt%) SiO TiO Al2O Fe2O MnO MgO CaO Na2O K2O P2O LOI To tal Trace el e ments (ppm) Cr Ni Co Sc V Cu Pb Zn Bi Sn W As Sb K Rb Cs Ba Sr Tl Ga Ta Nb Hf Zr Ti Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Be Chem i cal group: BBL bi o tite-bear ing leptite; MT Mt. Wapnisko metatrachyte; ML mas sive leptites. Lo cal ity: BM Bystrzyckie Mts.; KM Krowiarki Mts.; ZSSSZ Z³oty Stok-Skrzynka Shear Zone; OM Orlickie Mts; LSMU L¹dek-Snie nik Meta mor phic Unit.

22 22 M. MURTEZI sive lava flows, but it is also pos si ble that they rep re sent parts of a pyroclastic se quence. The lower SiO 2 and higher Mg and Fe con tents of the BBL in di cate that they are meta - mor phosed tuffites with a dif fer ent share of sed i men tary ma te rial, which ex plains their di ver si fied trace el e ment content. The characteristic high concentration of strongly in - com pat i ble el e ments such as REE, and the good cor re la - tion with the geo chem i cal fea tures of con ti nen tal crust in - di cate that the rocks of the leptite se ries rep re sent a highly dif fer en ti ated prod uct of magmatism con nected with the melt ing of con ti nen tal crust. The as cer tained neg a tive Eu, Ti and Sr anom a lies in di cate that frac tional crys tal li za tion played an im por tant role in the dif fer en ti a tion of the leptites pa ren tal magma. In ves ti ga tion into crys tal frac - tion ation is dif fi cult due to the polymetamorphic char ac ter of the stud ied rocks. The ob served en rich ment in in com - patible elements most probably results from a partial melt - ing pro cess. The low TiO 2, Cr, V and Ni con tent can be ex - plained as the ef fect of a com mu ta tion of those el e ments in min er als left as a restite af ter the par tial melt ing of the source rocks. The lack of gar net in the magma source, as - cer tained on the ba sis of the rel a tively high HREE con tent, in di cates the dom i nant role of crustal ma te rial. The pres - ence of gar net or other mafic min er als, such as hornblende, in the source of the leptites pa ren tal magma would lead to a sig nif i cant en rich ment of the leptites in LREE rel a tive to the HREE. The lack of such a fea ture in the OSD leptites sup ports the the sis on the purely con ti nen tal char ac ter of their protolith, de void of in flu ence of a gar net-rich subducted oce anic slab. On the other hand, the anal y sis of the ORG-nor mal ised pat terns of trace el e ments in di cates ac tive con ti nen tal mar gin af fin i ties for the leptites. Such a char ac ter is tic is sup ported by their high Th/Ta ra tio and low Nb, Ta and Ti con tents fea tures con sid ered typ i cal for rocks de rived from a con ti nen tal vol ca nic arc (e.g. Whalen et al., 1998; Zellmer et al., 2000). Also, geotectonic discriminant di a grams, de spite some dis crep an cies, fa vour active continental margins as the formation environment of the leptites protolith. Most prob a bly, the protolith of the Wp1 metatrachyte co mes from the same mag matic suite as the rest of the stud - ied rocks, but rep re sents an ear lier stage of dif fer en ti a tion. It can not be ex cluded that the Stronie For ma tion con tains rocks coming from different geotectonic environments. It is worth emphasising that the two ex am ined sam ples from the Staré Mìsto Belt do not show any sig nif i cant geo - chem i cal dif fer ences to the OSD leptites. This re sult con - curs with the view of Skácel (1989) and Don (2001), who classed the var ie gated schists of Hranièna to the Stronie For ma tion and set the bound ary of the Staré Mìsto Belt fur ther to the east. THE TECTONO-METAMORPHIC EVOLUTION This chap ter com prises re sults of the struc tural and pet ro log i cal in ves ti ga tions ap plied to the acid meta vol can ic rocks and ac com pa ny ing mica schists. In or der to pro vide an unambiguous background for the later interpretation, the col lected struc tural data is first pre sented in a de scrip - tive way. The fol low ing two sec tions of this chap ter con - tain dis cus sion on the pre sented struc tural data and fi nally dis tinc tion of the suc ces sive stages of de for ma tion. On the basis of petrological investigations and geothermobarometrical cal cu la tions the dis tin guished stages of de for ma tion have been finally correlated with changing P-T conditions. THE STRUC TURAL RE CORD OF THE LEPTITES AND THE AD JA CENT MICA SCHISTS Field stud ies re vealed vari a tions in struc tural re cord of the stud ied rocks over the OSD area. There fore, the struc - tural char ac ter is tic pre sented be low is di vided into three parts cor re spond ing to the three ma jor ar eas of leptite oc - cur rence in the OSD: Krowiarki Mts., West ern part of the OSD sub di vided into Zieleniec area (Orlickie Mts.) and Gniewoszów area (Bystrzyckie Mts.), The ZSSSZ. The orientation and spatial relations typical for mesostructures in the three re gions dis tin guished within the OSD is il lus trated in fig ure 16. Block di a gram vis i ble in fig ure 17 pres ents suc ces sion of mesostructures typ i cal for rocks from the ZSSSZ. The gen er al ised ori en ta tion of dominant metamorphic foliation and the most conspicuous lin ear struc tures re cog nised in out crops of the leptites in the W side of the OSD is pre sented in fig ure 18. Same data for the E part of the OSD is com prised in fig ure 19. Comprehensive representation of spatial relations typical for mesostructures com ing from leptites and mica schists outcropping in the respective regions distinguished within the OSD is il lus trated in fig ure 20. Krowiarki Mts. The superposition of several deformational structures has been as cer tained in the leptites of this re gion. The old - est deformational struc tures of the Krowiarki Mt. leptites are intrafolial, iso cli nal folds. These rarely vis i ble folds have strongly elon gated, at ten u at ing limbs and thick ened hinges. Their am pli tude does not ex ceed sev eral centi - metres. The limbs of these intrafolial folds are par al lel to the penetrative foliation, dipping in this region at moderate an gles (20 40 ) to wards the NW and SE. These pen e - tra tive fo li a tion planes are de vel oped par al lel to the flat-ly - ing ax ial planes of the asym met ric tight to iso cli nal folds plung ing at low an gles to the NE and SW. Those bi-vergent folds, com monly ob served within the rocks of the Stronie Formation, are often overturned to recumbent. Superposi - tion of the two old est re cog nis able in the leptites and sur - round ing mica schists gen er a tions of folds is ex em pli fied in

23 ACID META VOL CAN IC ROCKS 23 Fig. 16. Superposition of the mesostructures char ac ter is tic for the rocks of the leptite series from the Krowiarki Mts., Bystrzyckie Mts. and Orlickie Mts. The ori en ta tion of the struc - tures cor re sponds to that mea sured in the rocks of the leptite series out crop ping in the vi cin ity of Gniewoszów in the Bystrzyckie Mts. L2int in ter sec tion lineation; L3m min eral stretch ing lineation; L5 lineation due to late wrin kling. figure 21a. On a stereographic projection, the orientation of the axes of these sec ond-gen er a tion folds re veal two max i mums, at 330/40 and 40/30 (Fig. 20). Due to strong flat ten ing, the newly de vel oped ax ial pla nar fo li a tion is al - most par al lel to the lon ger limbs of these folds. The new fo - li a tion planes are well dis tin guish able in the BBL, in which de for ma tion of this stage lead to the recrystallization of plate minerals; the newly developed foliation is emphasised by the al ter na tion of bi o tite-rich lay ers with quartzfeld spar ones. In the BBL and mica schists of this re gion, an in ter sec tion lineation was de vel oped par al lel to the asym - met ric fold axes. In the ML, the sur faces of the new fo li a - tion developed by transposition of the older foliation, which in the fold s limbs be came par al lel to their ax ial planes (Fig. 21a, b). The in ter sec tion of the great cir cles representing the planes of the penetrative foliation (Fig. 20), de fines the axis of the later-de vel oped open folds; this is a very char ac ter is tic fea ture for rocks from the Krowiarki Mts. The stretch ing lineation dip ping at low an gles to the W and E, marked by elon gated quartzo-feldspathic ag gre gates, is ap prox i mately per pen dic u lar to the asym - met ric fold axes. As the vergence of the asym met ric folds changes widely (from NE or NW to SE and SW), it is im - pos si ble to de ter mine the re gional sense of lat eral move - ment ac com pa ny ing the for ma tion of these folds. Gen er - ally, it can be stated that this move ment must have oc - curred in an E W di rec tion, as in di cated by the range of Fig. 17 A sche matic rep re sen ta tion of the suc ces sion of mesostruc tures vis i ble in the rocks of the leptite series from the Z³oty Stok-Skrzynka Shear Zone. L3m min eral stretch ing lineation; L4cren crenulation lineation. changes in the vergence of the asym met ric folds. The elon - ga tion of the quartzo-feldspathic ag gre gates cor re sponds with this di rec tion. The later de vel oped lin ear struc ture con nected with the shear ing of the rock masses in the Krowiarki Mts. in an N S di rec tion is far better vis i ble. This stretch ing lineation over laps the above-de scribed N S trending in ter sec tion lineation. Asym met ric porphyroblasts of K-feld spars and plagioclases indicating non-coaxial deformation with a top-to-the-n sense of shear are ar ranged par al lel to the N S trending stretch ing lineation. Porphyroblasts with elon - gated, recrystallized, fine-grained tails usu ally have a -type geometry, but -blasts are also pres ent. Recrystallized bi o tite (of ten chloritized), mus co vite and chlorite are grouped in the pres sure shad ows be hind those porphyroblasts. The shear ing de for ma tion led to the for ma tion of the S-C fab ric (Fig. 21c). The S-sur faces, par al lel to the ax ial sur faces of the pre vi ously de vel oped asym met ric folds, are emphasi- sed by a flat ar range ment of micas, whereas the grain shape fab ric of quartz and feld spars de fines the C-sur - faces. Dis place ments on this stage oc curred along ear lier surfaces of discontinuity constituted by the axial planar foli a tion of the asym met ric folds. Such shear sense in di ca tors as asym met ric porphyroblasts and S-C struc tures in di cate that the de vel op ment of the N S trending stretch ing lineation was con nected in this area with top-to-the-n move ments. All the above-de scribed struc tures are folded by open folds with axes plung ing at an an gle of to wards the NNW or SSE. In the leptites, there is no sign of recrystallization lead ing to the for ma tion of new fo li a tion planes par - al lel to the steep ax ial planes of these folds.

24 24 M. MURTEZI Fig. 18. A sche matic tec tonic map of the west ern part of the OSD show ing the gen er al ised ori en ta tion of the dom i nant meta - morphic foliation and the most conspicuous linear structures re - cog nised in the out crops of the leptites and sur round ing mica schists. The youn gest tec tonic struc tures vis i ble in the rocks of the Krowiarki Mts. re gion are open to chev ron folds, and wrin kles ori ented par al lel to their NE SW trending axes. West ern part of the OSD (Bystrzyckie and Orlickie Mts.) The old est struc ture vis i ble in the leptites from the west ern part of the OSD is a folded meta mor phic fo li a tion. This old est re cog nis able sur face mim ics the pri mary bed - ding and, as the in leptites of the Krowiarki Mts., can be traced in the hinges of the asym met ric folds (Fig. 21d). On the limbs of these folds, this fo li a tion be comes par al lel to the newly de vel oped ax ial pla nar fo li a tion. Microstructural anal y sis showed that the folded fo li a tion is ex pressed by the al ter na tion of thin (up to 0.1 mm wide) micaceous lay ers and thicker quartzo-feldspathic ones. The lon ger axes of the micas, quartz and feld spars lie in the plane of the asym met ric fold ax ial sur faces. It needs to be emphasised that asym met ric folds do not oc cur in all the rocks of the leptite se ries. The se lec tive oc - cur rence of these folds re sults from dif fer ences in the rhe ol - ogy of the rocks of the Stronie For ma tion as well as the dif - fer ent sus cep ti bil ity of these rocks to recrystallization pro - cesses. The mas sive leptites, as highly com pe tent rocks with a poor min eral com po si tion, have a clear re cord of Fig. 19. A sche matic tec tonic map of the north ern part of the L¹dek-Œnie nik Meta mor phic Unit (the E part of the OSD) show ing the gen er al ised ori en ta tion of the dom i nant meta mor - phic fo li a tion and the most con spic u ous lin ear struc tures re cog - nised in the out crops of the leptites and sur round ing mica schists. Dou ble asterixes in di cate the lo ca tion of sam ples used for pseudosec tion cal cu la tions. KZSG K³odzko-Z³oty Stok granitoids, JG Javornik granitoids. fold struc tures, the hinges of which are emphasised by the pre served pri mary strat i fi ca tion. The sur round ing mica schists are less com pe tent rocks, pre dis posed by their min - eral com po si tion to pro cesses of recrystallization, and thus do not show as clear ev i dence of fold ing as the leptites. In those rocks, the com bi na tion of stress and tem per a ture led to meta mor phic recrystallization giv ing rise to new fo li a - tion planes. Ac cord ing to elaÿniewicz (1976, 1978) the for ma tion of asym met ric folds started from ac tive buck - ling leading to progressive flattening, and continued by shear ing act ing par al lel to the ax ial sur faces. Lineation re sult ing from the in ter sec tion of the folded lay ers and newly formed ax ial pla nar fo li a tion is well vis i - ble in the ML out crop ping in the vi cin ity of Zieleniec in the Orlickie Mts. In rocks from this lo cal ity, it is pos si ble to find hinges of asym met ric folds, where the two gen er a - tions of planes can be eas ily re cog nised. This in ter sec tion lineation usu ally runs par al lel to the fold axes (Fig. 21d),

25 ACID META VOL CAN IC ROCKS 25 Fig. 20. A com pre hen sive rep re sen ta tion of the spa tial re la tion ships typ i cal for the mesostructures in the leptites and mica schists out - crop ping in the re spec tive re gions dis tin guished within the OSD. ZSSSZ Z³oty Stok-Skrzynka Shear Zone. mod er ately plung ing to wards the NNE. In the vi cin ity of Gniewoszów (Bystrzyckie Mts.), the ori en ta tion of the in - ter sec tion lineation and the asym met ric fold axes ro tate about 45 along the great cir cle with a pole at 265/30. Af ter the de vel op ment of asym met ric folds, the rocks in this area were sub jected to rel a tively strong shear ing; a weaker im - print of this shear ing can also be seen in rocks near Zieleniec. This shear ing oc curred in a NNE SSW di rec tion and could have caused the ro ta tion of the pre vi ously de vel oped struc tures. The struc tural re cord of this shear ing con sti - tutes a min eral stretch ing lineation, shal lowly dip ping to - wards the NE and SW. Over the area of Bystrzyckie Mts., this lineation, like the ro tated axes of the asym met ric folds and in ter sec tion lineation, is par al lel to the di rec tion of tec - tonic trans port. The asym met ric blasts of quartz and feld - spars that de vel oped dur ing this stage in di cate non-co ax ial shear ing de for ma tion with a change able sense of shear top-to-the-nne and -SSW. Lo cally, be sides asym met ric porphyroblasts, the ex treme elon ga tion of quartz and feld - spars de vel oped into a rodding struc ture. All the above-de scribed struc tures change their ori en - ta tion in the limbs of the later-de vel oped open folds plung - ing at low an gles to wards the NW. Folds of this type are less com mon in the west ern part of the OSD than their equiv a lents in the east of the unit. More over, they oc cur more of ten near Gniewoszów than in the sur round ings of Zieleniec. The ax ial sur faces of these open folds are not marked by min eral recrystallization. The su per im posed brit tle and semi-brit tle de for ma - tion led to the de vel op ment of kink bands and chev ron folds that ad di tion ally dis turb the ori en ta tion of the pen e - trative metamorphic foliation. In the studied rocks from the Zieleniec area, the axes of an gu lar folds ac com pa nied by wrin kles plunge at about 30 to wards the WSW and ENE, whereas in the vi cin ity of Gniewoszów, these struc - tures plunge at a slightly shal lower an gle to wards the S and N. The di ver gence in ori en ta tion of these struc tures re sults from the slightly different orientation of the foliation planes in her ited from the ear lier stages of de for ma tion and re flects dif fer ences in the lo cal stress field. Z³oty Stok-Skrzynka Shear Zone The struc tural re cord of the leptites from this zone strongly dif fers from that de scribed above. While the leptites from the rest of the OSD area have a rel a tively flatly ori ented fo li a tion in ex treme cases, its slope reaches c. 60 the most con spic u ous fea ture of the rocks from the ZSSSZ is a very steeply (lo cally al most ver ti cally) ori ented penetrative metamorphic foliation. In this zone, the folia - tion planes run me ridi on ally, dip ping in most cases to -

26 26 M. MURTEZI Fig. 21. The se quence of deformational struc tures oc cur ring in the rocks of the leptite se ries and sur round ing mica schists. (a) Superpo - si tion of the two old est re cog nis able gen er a tions of folds vis i ble in the leptites from the Krowiarki Mts. The pen e tra tive S2 ax ial pla nar fo li a tion is al most par al lel to the lon ger limbs of the sec ond-gen er a tion folds and also to the older S1 sur faces. (b) The hinge of an iso cli - nal F2 fold emphasised by the con trast in com pe tence be tween the quartzo-feldspathic and micaceous layer (from the leptite se ries, Krowiarki Mts). (c) The S-C fab ric de vel oped dur ing top-to-the-n thrust ing vis i ble in the BBL from the Krowiarki Mts. (d) An asym - met ric F2 fold in a leptite from the vi cin ity of Zieleniec in Orlickie Mts. The old est re cog nis able sur face vis i ble in the hinges of these folds mim ics the pri mary bed ding, whereas on the limbs, it be comes par al lel to the newly de vel oped ax ial pla nar fo li a tion. (e) The asym - met ric F2 fold from the rocks of the leptite se ries from the Z³oty Stok-Skrzynka Shear Zone (ZSSSZ) out crop ping in do mains char ac ter - ised by a lower in ten sity of shear strain. The west ern limb of the Bzowiec fold, NE of Skrzynka vil lage. (f) An asym met ri cal F3 fold from the leptites of the ZSSSZ in di cat ing a sinistral sense of shear tak ing place along the re ac ti vated S2 fo li a tion planes. (g) A mica schist from the Krowiarki Mts. A synkinematic gar net blast de vel oped dur ing the E W ori ented D2 shear ing. Its asym me try in di cates a dextral sense of shear. (h) An intertectonic gar net from the mica schists of the ZSSSZ; the straight in clu sion pat tern pre served in the core defines the S1 foliation.

27 ACID META VOL CAN IC ROCKS 27 wards the WNW. Lo cally, mainly in the north ern part of the zone, the fo li a tion planes dip to wards the ESE. In the south-west ern part of the zone, the fo li a tion planes dip at shal lower an gles to wards the NW, grad u ally turn ing west. How ever, in the rocks of the leptite series out crop ping in the ZSSSZ struc tures de vel oped in a strike-slip re gime dom i nate, and it is pos si ble to dis tin guish a set of older struc tures, cre ated prior to the shear zone. The rel ics of an older fo li a tion are pre served in rocks outcropping in domains characterised by a lower intensity of the shear strain. This old pla nar struc ture is folded by asym met ric folds (Fig. 21e) with the same ge om e try as their equiv a lents from rocks stud ied in the Krowiarki Mts. and in the west of the OSD. The axes of these type folds vis i ble in leptites of the ZSSSZ plunge at an gles of to wards the NE and SW. An in ter sec tion lineation is vis i - ble in the hinge parts of these folds, where the newly de vel - oped ax ial pla nar fo li a tion cuts folded laminae. The in ter - sec tion lineation can be also traced on the shorter limbs of the asym met ric folds, while the lon ger limbs, where the folded and the ax ial pla nar sur faces be comes par al lel, are free of this lineation. A min eral stretch ing lineation de vel oped par al lel to the asym met ric fold axes is vis i ble in all the leptites of the ZSSSZ area. This lineation, ex pressed by the elon ga tion of quartzo-feldspathic ag gre gates and asym met ric K-feld spar and plagioclase porphyroblasts, shal lowly dips to wards the NNE and SSW. Microstructural anal y sis re vealed that commonly observed - and -shaped porphyroblasts in di - cate the same sense of shear in the en tire ZSSSZ. This and other indicators (e.g. composite foliation and asymmetric boudinage) re veal that the shear ing of rocks in the en tire ZSSSZ oc curred in a sinistral strike-slip re gime. An S-C fab ric com monly ob served in the rocks of this zone also re - sults from this sinistral shear ing ep i sode. The C-sur faces are par al lel to the pre vi ously de vel oped ax ial pla nar fo li a - tion con nected with the for ma tion of asym met ric folds, so the new mylonitic fo li a tion mim ics the pre-ex ist ing sur - faces of discontinuity. The sinistral shear ing led to the de vel op ment of the sec ond gen er a tion of asym met ric folds with steep ax ial sur - faces (Fig. 21f). The asym met ric folds of the pre vi ous gen - er a tion vis i ble in rocks of the ZSSSZ also have steep ax ial sur faces, but their axes are ori ented al most par al lel to the strike of the pen e tra tive fo li a tion (Fig. 17). The axes of the later-de vel oped folds plunge at a high an gle to wards the NW, and are gen er ally per pen dic u lar to the min eral stretch ing lineation. The asym met ric folds with steeply plung ing axes some times adopt the form of an an gu lar folds, indicating that their development continued beyond the transition from ductile to brittle deformation condi - tions. At a late stage of the struc tural evo lu tion of the rocks in the ZSSSZ, due to short en ing oc cur ring par al lel to the shear zone (in a NE SW di rec tion), con ju gate crenulations and chev ron folds de vel oped. The ori en ta tion of the an gu - lar fold axes re veals two max i mums, at 50/70 and 260/75 (Fig. 20). Par al lel to these axes, a crenulation lineation de - vel oped, vis i ble as small (up to two milimeters of am pli - tude) wrin kles on the fo li a tion planes. DIS CUS SION ON DATA FROM THE STRUCTURAL ANALYSIS The com par i son of the struc tural se quences es tab - lished for the rocks of the leptite se ries shows that, ir re - spec tive of the lo cal ity within the OSD, the de vel op ment of their struc tural re cord took place in the same tec tonic re gimes. Ta ble 11 pres ents a com par i son of the tec tonic re - cord com ing from the stud ied rocks out crop ping in each of the above-de scribed re gions of the OSD. The vivid con trast in the dom i nant style of de for ma - tion re corded by the rocks in the ZSSSZ and the rest of the OSD area re sults from the steep en ing of the fo li a tion planes caused by the bend ing of the rock masses, which must have been con tem po rary with or slightly later than the de vel op ment of the shear zone. This in ter pre ta tion is proved by the con stancy in the ki ne matic re cord, in di cat - ing the same sense of shear, re gard less of the ori en ta tion of the fo li a tion planes. If the fo li a tion planes ob served in the rocks of the ZSSSZ reached their steep po si tion due to fold - ing post-dat ing the NNE SSW shear ing ep i sode, then, on the op po site limbs of such folds, re verse shear senses would be ob served. This is not the case in the rocks of this zone. That asym met ric folds with axes ori ented at high an gles (some times al most per pen dic u lar) to the NNE SSW trending min eral stretch ing lineation only in the ZSSSZ can be ex plained by a strain par ti tion ing pro cess, the symp toms of which were re cog nised in the rocks of the ZSSSZ for the first time by Cymerman (1996). This pro cess led to the de - vel op ment of pure shear and sim ple shear do mains. Asym - met ric folds with steeply ori ented axes oc cur in do mains where pure shear pre vails. Anastomosing zones non-co ax i - ally de formed un der sim ple shear con di tions sur round these pure shear do mains. The con clu sion can be drawn that the main phase of de for ma tion in the ZSSSZ caused both the NNE SSW di rected shear ing and the steep en ing of fo li a tion planes. This zone-form ing deforma- tional ep i - sode strongly over printed the ear lier tec tonic re cord, which on the ba sis of the above-de scribed rem nants cor - re lates well with that es tab lished for the leptites from the other OSD re gions. Apart from the spe cif ics of the ZSSSZ leptites, an other prob lem that needs ad dress ing con cerns the pri mary ori en - ta tion of the ax ial planes of the intrafolial folds be long ing to the oldest recognisable generation. Due to the transposi - tion of the fo li a tion planes and their later re ac ti va tion dur - ing shear ing, it is very hard to es tab lish the pri mary an gu - lar re la tion ships be tween the two old est pla nar struc tures vis i ble in rocks of the Stronie For ma tion. One of these struc tures de vel oped as an ax ial pla nar fo li a tion of intrafolial root less folds, and the other as the ax ial pla nar fo li a tion of asym met ric folds. Some clues about the steep ori en ta tion of the old est fo li a tion can be read from the microstructural anal y sis of the mica schists of the Stronie For ma tion. Gar nets com ing from the hinge parts of the asym met ric folds with flat-ly ing ax ial sur faces have in clu - sions ar ranged in sur faces cre at ing high an gles with the later-de vel oped ax ial pla nar fo li a tion. More over, most of the gar nets, in spite of their ori en ta tion rel a tive to the fold

28 28 M. MURTEZI Ta ble 11 Cor re la tion of tec tonic re cord com ing from rocks of the leptite series and sur round ing mica schists out crop ping in four re gions dis tin guished in the OSD. ZSSSZ Z³oty Stok-Skrzynka Shear Zone Def. ZSSSZ Krowiarki Mts. D5 D4 D3 D2 D1 No struc tures F4 poorly marked open folds, conjugate crenulations and chevron folds S4 steep ax ial sur faces of chev ron folds L4kor crenulation lineation S3 steep shear bands, close to par al lel to the S2 sur faces F3 shear folds L3m stretch ing lineation S2 steep pen e tra tive ax ial pla nar fo li a tion F2 folds with shal lowly plung ing axes L2i rarely vis i ble in ter sec tion lineation S1 folded pri mar ily steep fo li a - tion F1 rare intrafolial fold rel ics Bystrzyckie Mts. (Gniewoszów area) F5 chev ron folds F5 chev ron folds S5 steep ax ial sur faces of chev ron S5 steep ax ial sur faces of folds chevron folds L5kor crenulation lineation L5kor crenulation lineation F4 com monly vis i ble open folds S4 weakly de vel oped ax ial cleav - age (vis i ble only in mica schists) S3 flat ori ented shear bands (semi-parallel to S2) L3m stretch ing lineation su per - im posed on the L2i in ter sec - tion lineation S2 flat-lying, penetrative axial pla nar fo li a tion F2 tight folds with shal lowly NE and NW plung ing axes L2i in ter sec tion lineation - well vis i ble on the F2 folds hinges L2m stretch ing lineation (E-W) S1 folded steep fo li a tion F1 intrafolial fold rel ics F4 com monly vis i ble open folds S4 weakly de vel oped ax ial cleav - age (vis i ble only in mica schists) S3 flat ori ented shear bands (semi-parallel to S2) L3m stretch ing lineation cut ting un der high an gles (up to 90 ) lineation L2i S2 flat-lying, penetrative axial pla nar fo li a tion F2 tight folds with shal lowly W and WNW plung ing axes L2i in ter sec tion lineation well vis i ble on the F2 folds hinges S1 folded pri mar ily steep fo li a - tion Orlickie Mts.(Zieleniec area) F5 chev ron folds S5 steep ax ial sur faces of chev ron folds L5kor crenulation lineation F4 rarely vis i ble open folds S3 flat ori ented shear bands (semi-parallel to S2) L3m stretch ing lineation cut ting un der high an gles (up to 90 ) lineation L2i S2 flat-lying, penetrative axial pla nar fo li a tion F2 tight folds with shal lowly W and WNW plung ing axes L2i in ter sec tion lineation - well vis i ble on the F2 folds hinges S1 folded pri mar ily steep fo li a - tion Chem i cal group: BBL bi o tite-bear ing leptite; MT Mt. Wapnisko metatrachyte; ML mas sive leptites. Lo cal ity: BM Bystrzyckie Mts.; KM Krowiarki Mts.; ZSSSZ Z³oty Stok-Skrzynka shear zone; OM Orlickie Mts; LSMU L¹dek-Snie nik Meta mor phic Unit structures, incorporate traces of an internal Si foliation ori - ented obliquely to the later-de vel oped ex ter nal fo li a tion Se. Microstructural anal y sis re vealed that some of these gar - nets are syntectonic porphyroblasts de vel oped dur ing the formation of the flat-lying metamorphic foliation (Fig. 21g). The rest of the gar nets oc cur ring in the mica schists, which have a straight in clu sion pat tern (Fig. 21h), can be ei - ther syntectonic with the old est fold ing, or intertectonic with re spect to the two suc ces sive fold ing stages. This con - cept for the steep ori en ta tion of the old est meta mor phic fo - li a tion is also sup ported by the style of fold ing lead ing to the for ma tion of the asym met ric folds with flat-ly ing ax ial sur faces. This style is clearly vis i ble in the leptites from Kozia Hala near Zieleniec in the Orlickie Mts., where the struc tural im age of the strongly folded rock in di cates buck - ling of com pe tent lay ers in duced by the ver ti cally act ing forces. This is tes ti fied to by the steep ori en ta tion of the en - vel op ing sur faces of asym met ric folds vis i ble in the leptites from this lo cal ity. This flat ten ing led to the pro gres sive de - for ma tion of the rocks un der pure shear con di tions. The de formed rocks, de pend ing on their po si tion rel a tive to the main axes of the re gional strain el lip soid, could have been ex posed to flat ten ing, stretch ing or a se quence of suc ces sive flat ten ing and stretch ing (or vice versa). The lo cal stress field could have caused a non-co ax ial de for ma tion of some por tion of rock. This can ex plain the oc cur rence of curved in clu sion trails ob served in the gar nets formed dur ing flat - ten ing. Par al lel ism of the fo li a tion planes de vel oped at dif - fer ent stages of the de for ma tion of the Stronie For ma tion would then be a re sult of a re-fold ing of the steep pri mary fo li a tion and their re ori en ta tion on the limbs of the asym - met ric folds hav ing flat-ly ing ax ial sur faces. When those asym met ric folds be came iso cli nal, the folded lay ers were of course par al lel to their ax ial sur faces on both of their limbs. The change able vergence of the asym met ric folds oc cur ring over the en tire OSD area is an other proof of their de vel op ment hav ing been con nected with the subvertical flat ten ing of the rock masses. The later shear ing in an NNE SSW di rec tion was het - erogeneous and occurred along zonally privileged surfaces of het er o ge ne ity in her ited af ter the ear lier stages of de for - mation. THE SUC CES SIVE STAGES OF DE FOR MA TION The meso- and micro struc tures re cog nised in the rocks of the leptite for ma tion and sur round ing mica schists were grouped in five sets at trib uted to five con sec u tive deformational ep i sodes. Start ing from subvertical flat ten ing, the dis tin guished ep i sodes should be treated rather as mark ers of changes in the style of de for ma tion dur ing one con tin u - ous tectono-meta mor phic cy cle, than as ut terly sep a rated stages in the tectono-meta mor phic evo lu tion of the rocks of the Stronie For ma tion. The dis tin guished stages D1

29 ACID META VOL CAN IC ROCKS 29 through D5 are of re gional char ac ter, but the in ten sity of the de for ma tions at trib uted to a given stage sig nif i cantly var ies over the OSD area. Ta ble 11 pres ents a cor re la tion of the mesostructures at trib uted to each of the five tec tonic stages. D1 is the old est mesostructurally doc u mented deformational ep i sode of the rocks of the leptite series. The struc tures de vel oped dur ing this stage are pre served in the leptites and mica schists across the en tire OSD area. These are the rarely vis i ble intrafolial F1 folds and meta mor phic S1 ax ial pla nar fo li a tion. The ge om e try of the F1 folds, which have N S trending shal lowly dip ping axes, as well as the most prob a bly near ver ti cal ori en ta tion of the S1 sur - faces in di cates that stage D1 was con nected with short en - ing act ing ap prox i mately in an E W di rec tion. This in ter - pre ta tion is con sis tent with the view pre sented by Dumicz (1976, 1988, 1995), ac cord ing to which the F1 folds de vel - oped in the field of tan gen tial com pres sion. Short en ing in this stage pro duced tight to iso cli nal folds. The relic char ac - ter of these struc tures, de scribed by elaÿniewicz (1976, 1978), causes dif fi cul ties in dis tin guish ing D1 as a sep a rate tec tonic ep i sode. So far, it is im pos si ble to de cide whether this stage, to gether with the sub se quent stages, be longs to one tectono-ther mal event, or should be treated as a rem - nant of an ear lier tectono-meta mor phic ep i sode, sep a rated from the later ones by an un spec i fied time gap. D2 had the stron gest in flu ence on the ob served tec - tonic char ac ter is tics of the stud ied rocks from the Bystrzyckie and Orlickie Mts. in the west ern part of the OSD and the Krowiarki Mts. in the LSMU. The de for ma tion of this stage lead to the de vel op ment of asym met ric F2 folds with flat-ly ing ax ial sur faces. The D2 fold ing re ori ented the orig i nally steep S1 sur faces bring ing them into their mod - ern subhorizontal po si tion. Thus the S1 sur faces be came par al lel with the newly de vel oped S2 ax ial pla nar fo li a tion. An an gu lar re la tion ship be tween these sur faces can be still ob served in the hinge parts of the F2 folds, where the L2i in ter sec tion lineation can also be seen. Stretched quartzofeldspathic ag gre gates, ori ented ap prox i mately per pen dic - u lar to the F2 fold axes and ob served along their limbs, de - fine the L2s min eral stretch ing lineation. The for ma tion of this E W trending lineation is con nected with the D2 flat - ten ing and fold ing, and is treated as the re sult of a flex ural slip along folded lay ers. I see no rea son for qual i fy ing this lineation as a fea ture de vel oped prior to or af ter the D2 fold ing. A very strong ver ti cal short en ing dur ing the D2 fold ing caused buck ling of the more com pe tent leptitic lay - ers sur rounded by duc tile mica schists. As this pro cess con - tinued, shearing between slipping layers of different com - pe tences lead to the for ma tion of par a sitic folds and stretch ing of min eral ag gre gates ori ented par al lel to the ax - ial sur faces of the newly de vel oped folds. As will be shown later, the de vel op ment of the D2 folds took place un der peak metamorphic conditions. The formation of garnets, which along their E W sec tions re veal curved trails of in - clu sions, is con nected with these E W di rected move - ments. My ob ser va tions con cur with the sce nario pro posed by Dumicz (1976, 1988, 1995), who as sumed that the tran - si tion be tween D1 and D2 was con nected with a change in the re gional stress field from the ini tial tan gen tial com pres - sion to com pres sion act ing in a ver ti cal di rec tion. The D3 deformations most intensively influenced the rocks of the ZSSSZ, giv ing rise to its de vel op ment as a sinistral strike-slip zone. At this stage, in the rocks of this zone, F3 folds with steep, NW-plung ing axes, and the NE SW trending subhorizontal L3m min eral stretch ing lineation formed. L3m, un like the F3 folds, can be ob - served in rocks of the Stronie For ma tion across the en tire are of the OSD. This lineation con sti tutes a re cord of a zonal shear ing with top-to-the NNE ki ne mat ics man i fest - ing it self in rock from the en tire study area. Cor re la tion of the sinistral shear ing along steep ened fo li a tion planes ob - served in the rocks of the ZSSSZ with the NNE-di rected thrust ing ob served in the stud ied rocks com ing from the rest of the OSD area is sup ported by sim i lar i ties in the con - di tions of meta mor phism as cer tained us ing min eral parageneses de vel oped at this stage of the tec tonic evo lu - tion. The de for ma tions of this stage in the en tire OSD area, af ter orogenic up lift in duc ing subvertical short en ing of the D2 struc tures, took place un der low-p con di tions but still under a considerably high temperature. The continuous con ver gence of the col lid ing geo log i cal units the OSD to the west and the Moravo-Silesian Zone of the Bruno-Vistulicum to the east led to the for ma tion of shear zones, in which the rock masses were sub mit ted to ex ten sion. The ZSSSZ was cre ated at this stage as a zone of strain ac cu mu - la tion. Squeez ing of the rocks in the NE part of the OSD into a bay bor dered by the K³odzko meta mor phic unit with the de vel op ing in tru sion of K³odzko-Z³oty Stok granitoids to the west and the Moravo-Silesian Zone to the east led to de for ma tions in the transpressional re gime caus - ing the steep en ing of the S2 fo li a tion planes and si mul ta - neous NE SW shear ing ob served in the rocks of the ZSSSZ. The de for ma tions as signed to D4 oc cur ring un der con di tions of de creas ing duc til ity were con nected with a con tin u a tion of this con ver gence. The lack of space that pri mar ily in duced steep en ing and shear ing now led to NE SW di rected short en ing and the for ma tion of deformational struc tures in semi-brit tle and brit tle con di - tions (F4 an gu lar folds and L4 crenulation lineation). D4 is also re spon si ble for the for ma tion of the open and con cen tric F4 folds that are very char ac ter is tic for the rocks from the Krowiarki Mts.. The axes of these folds shal lowly dip to wards the NNW or SSE. An ex am ple of the su per po si tion of an open F4 fold on a tight F2 fold, com monly vis i ble in the rocks of the leptite series from the Krowiarki Mts., is pre sented in Fig ure 3f. The de for ma - tions of this stage also have a dis tinct re cord in the stud ied rocks from the Gniewoszów area in the Bystrzyckie Mts., where open folds with axes plung ing to wards the NE are common. Deformational struc tures be long ing to the last dis tin - guished set, as signed to D5, are vis i ble in the stud ied rocks out crop ping through out the OSD area with the ex cep tion of the ZSSSZ. The short en ing of the OSD rocks in a NW SE di rec tion led to the de vel op ment of an gu lar folds with, depending on the local orientation of the penetrative fo li a tion, NE, SW or SSW plung ing axes. The steep ori en - ta tion of the NE SW trending fo li a tion planes in the

30 30 M. MURTEZI Fig. 22. P-T pseudosections in KFMASH (+mu+q+h 2 O) for sam ples Sk19 (a) and K10/a (b). The meth ods and data are pre sented in the text. ZSSSZ pro tected the rocks of this zone from the D5 de for - mation. P-T RE CORD OF THE LEPTITES AND THE ADJACENT MICA SCHISTS P-T pseudosection Two sam ples (Sk19 for the ZSSSZ and K/a for the Krowiarki Mts.) were cho sen as be ing the most rep re sen ta - tive for their ar eas of or i gin with re gard to their min eral com po si tion and struc tural re cord. The use of the mea - sured bulk rock com po si tion as rep re sen ta tive of the chem - ical environment from which the metamorphic minerals grew im plies the as sump tion that the ma jor el e ment mo bil - ity during metamorphism was insignificant for P-T calculations. The mod elled phase re la tion ships are dis played in fig - ure 22. As the protolith of the stud ied rocks has a sil icarich, volcano-sedimentary affinity, in both cases muscovite, quartz and a pure H 2 O fluid phase were as sumed to be pres ent in ex cess. Al though cor di er ite is ab sent in sam ples Sk19 and K/a, pseudomorphous ag gre gates of fine grained micas af ter this phase were ob served in some sam ples com - ing from the ZSSSZ, so this min eral was in cluded in the cal - cu la tions for Sk19. The ob tained to pol ogy of divariant and trivariant fields is quite sim i lar for each sam ple. The gar net isograd oc curs at 580 C and about 7 kbar for Sk19 and at 560 C and 5.5 kbar for K/a. Gar net is sta - ble over most of the P-T range above 6 kbar and C. Be cause the Mn con tent was left out of the cal cu la - tions, the pres sures ob tained for parageneses con tain ing gar net may have been over es ti mated. Nev er the less, the cal - culated pseudosections are consistent with the petrological observations. The pres ence of tiny staurolite and chlorite in clu sions in the core of some gar nets from Sk19 is con sis tent with pseudosection-pre dicted paragenesis chl-st, pre ced ing the growth of gar nets. In Sk19, grt-chl-st could have been the sta ble as sem blage dur ing gar net core growth, and grt-bt-st dur ing rim growth (Fig. 23b, c). Fol low ing the growth of the gar nets, the bt-st as sem blage was re placed by bt-and (Fig. 23d). An da lu site blasts from Sk19 con tain in clu sions of strongly resorbed staurolites. The ear li est re cog nis able paragenesis in some sam ples from the Krowiarki Mts. is chl-cld-st. It is vis i ble de fin ing the S1 fo li a tion as in clu sions in gar nets; how ever, in K/a, only relicts of chloritoid can be ob served as in clu sions sit u - ated close to the cen tres of the gar nets (Fig. 23a). The K/a gar nets grew in the parageneses: grt-chl-st and grt-bt-st (Fig. 23a). The tran si tion be tween those equi lib ria took place dur ing the in crease in tem per a ture ac com pa ny ing the syntectonic gar net for ma tion (Fig. 21g). The lack of bi o tite as in clu sions in the gar nets from K/a is likely to be a pres er - va tion prob lem, rather than re flect ing a real ab sence from the assemblage during garnet growth. Subsequent paragen e ses (bt-st and chl-st) can be ob served in the ma trix. Garnet composition and abundance contours Match ing the pre dicted min eral com po si tion and abun dance with the real rocks will al low for a more pre cise de ter mi na tion of their P-T his tory. Fig ure 24 pres ent parts of the cal cu lated pseudosections with plot ted con tours of Fe/(Fe+Mg) and pre dicted abun dances for gar nets. The X Fe con tours for both sam ples are in gen eral par al - lel to those for gar net abun dance. In the divariant field grt-chl-st, the con tour lines are nearly par al lel to the pres - sure axis, whereas in the grt-bt-st field, they be come close to par al lel to the tem per a ture axis. The amount of Fe in - cor po rated in the gar net de creases with in creas ing tem per -

31 ACID META VOL CAN IC ROCKS 31 Fig. 23. (a) The in clu sion of chlorite and chloritoid de fin ing the S1 fo li a tion planes vis i ble here can scarcely be found in the in ner parts of the gar nets from the mica schists of the Krowiarki Mts. The S2 fo li a tion is de fined by the in clu sion of quartz and il men ite, which are con tin u ous out side of the gar net where staurolite can also be found, ar ranged along the S2 fo li a tion planes. (b) A gar net from a mica schist from the Z³oty Stok-Skrzynka Shear Zone (ZSSSZ) with curved in clu sion trails in its outer part; it de vel oped syntectonically to D2. (c) The meta mor phic peak paragenesis of gar net, bi o tite and staurolite from a mica schist of the ZSSSZ. (d) Asymmetric pressure shad ows around an an da lu site blast de vel oped synkinematically dur ing D3 sinistral shear ing in the mica schists of the ZSSSZ, out crop - ping near the con tact with the Javornik granitoids. a ture and pres sure. Gar net abun dance re veals the op po site trend. The ob tained con tour plots yield valu able in for ma - tion for the qual i ta tive P-T path that might have been fol - lowed by the real rocks Sk19 and K/a. Quan ti ta tive de lin - ea tion of the P-T his tory of these rocks re quires the com - par i son of pseudosection in for ma tion with the mea sured garnet composition. The gar nets from Sk19 have a core com po si tion with X Fe = c. 0.88, which can be found on the grid in the grt-chl-st sta bil ity field at about 7 10 kbar and C (Fig. 24a). This re sult con curs with the pres ence of chlorite in clu sions in the gar net core and very small in clu sions of staurolite found in two of the Sk19 gar nets. Un for tu nately, par tic u larly in the grt-chl-st field, the gar net abun dance con tours cut the com po si tion con tour at a very low an gle, which does not al low for a more pre cise de ter mi na tion of pres sure. The compositional step ping, vis i ble in the gar net zonation pro files for Sk19 (Fig. 4), could be an ef fect of the tran si tion from the grt-chl-st to the grt-bt-st sta bil ity field, where a de crease in pres sure re sults in a low er ing of the X Fe value ac com pa nied by a de crease in the amount of gar net in paragenesis. The modal pro por tion of about 1.5% gar net ob served in this sam ple is prob a bly the ef fect of a re ac tion cross ing grt+chl = st+bt. The core com po si tion of the gar nets from K/a is char - ac ter ised by X Fe = c The con tour of this value bound the grt-chl-st field from the low-t side at about kbar and 570 C. The con tin u ous, one-staged growth of gar nets from this sam ple is in di cated by the un dis turbed curved in clu sion trails through out the en tire grain. The lack of bi o tite as an in clu sion can in di cate that the growth of the K/a gar nets took place en tirely in the grt-chl-st sta - bil ity field. More over, in the case of this sam ple, gar net con sti tutes about 6% of the modal com po si tion of the rock, which can be cor re lated with the pre dicted amount of gar net of this com po si tion in the grt-chl-st field. Chlorite com monly oc curs as an in clu sion in the K/a gar - nets, while staurolite and bi o tite can only be found in the ma trix. Additional constraints from conventional geothermobarometry The few bi o tite in clu sions found in the Sk19 gar nets al - low for the ap pli ca tion of grt-bt geothermometry and

32 32 M. MURTEZI Fig. 24. The parts of the pseudosections for sam ples Sk19 (a) and K10/a (b) con toured for gar net abun dance and XFe val ues. grt-ms-bt-pl geobarometry. The cal i bra tions used and ob - tained re sults are listed in ta ble 12. In gen eral, the meta - mor phic peak con di tions were cal cu lated at 620 C and 8.5 kbar val ues ly ing in the grt-chl-st sta bil ity field. The cal - cu lated pres sure cor re lates well with the Si con tent in the white micas, the dis tri bu tion of which shows a max i mum at about 9 kbar, ac cord ing to phengite geothermometry. The con di tions for gar net rim for ma tion for K/a were also es tab lished us ing grt-bt geothermometry and grt-ms-bt-pl geobarometry. For this cal cu la tion, the com - po si tion of the gar net rims and con tact ing bi o tite grains from the ma trix were used. The ob tained val ues of about 7 kbar and 590 C, ly ing at the bor der of the grt-st-bt and the st-bt fields, can be treated as the con di tions of the meta - mor phic peak reached by this rock. In ad di tion, ta ble 12 pres ents the peak meta mor phic P-T con di tions ob tained by means of con ven tional geotherobarometry for a mica schist from the Bystrzyckie Mts. in the west ern part of the OSD. The tem per a tures and pres sures of peak meta mor phism ob tained for this sam ple (not ex ceed ing 540 C and 6.1 kbar) are con sid er ably lower than those es tab lished for sam ples com ing from the east ern part of the OSD. CORELLATION OF DE FOR MA TION AND META MOR PHISM (THE P-T-D PATH) The P-T path con structed for the ana lysed rock sam - ples, based on all the above-quoted in for ma tion, is pre - sented in fig ure 25. The struc tural and phase-equi lib ria lines of ev i dence show that the tectono-meta mor phic evo - lu tion of the Stronie For ma tion was that of early burial to a depth not exceeding upper amphibolite facies conditions, and sub se quent up lift con nected with subvertical short en - ing and flat ten ing strain. The old est struc tures de tect able in the stud ied rocks (F1 folds and meta mor phic S1 fo li a tion) are thought to have de vel oped in re sponse to E W subhorizontal short en - ing (Dumicz, 1979; elaÿniewicz et al., 2002; Romanova & Štipska, 2002) oc cur ring along the east ern part of the West Sudetes dur ing the Variscan orog eny. The tim ing of this ear li est ep i sode is un clear and can only be rel a tively con - strained. This short en ing must have started be fore the for - ma tion of the intertectonic gar net cores, de vel oped un der progressive P-T conditions, embracing inclusions defining the S1 fo li a tion. A sub se quent stage, dur ing which the over turned to re cum bent F2 folds de vel oped in the rocks of the Stronie For ma tion, took place at the on set of up lift. In its ini tial stage, it was ac com pa nied by an in crease in tem per a ture lead ing to the peak of re gional meta mor phism under upper amphibolite facies conditions. The subhorizontal, pla nar fab ric ob served within the augen Œnie nik gneiss es re lates to this tectono-meta mor phic event. The D3 sinistral shear ing is the later ep i sode caused by the fi nal ad ap ta tion of the tec tonic units tak ing part in the Variscan col li sion in the bor der land of the East and the West Sudetes. The lo cal verticalisation of the S2 fo li a tion planes ob served within this area is an ef fect of a pro gres sive E W short en ing, ac com pa nied by strong NNE SSW di - rected zonal shear ing. This shear ing was con nected with a re pet i tive in crease in tem per a ture. A very im por tant guide -

33 ACID META VOL CAN IC ROCKS 33 Ta ble 12 Com pi la tion of the peak meta mor phic P-T con di tions ob tained for the mica schists from the dif fer ent lo cal i ties in the OSD using conventional geothermobarometry Re gion Sam - ple ZSSSZ Krowiarki Mts. Bystrzyckie Mts. Anal y sis - po si tion Si Ti Al Fe Mn Mg Ca Na K T ( C) Bt 12 - in clu sion in Gt Gt core Mu 2a - in clu sion in Pl Pl3.2 - core Sk19 Bt 11 - in clu sion in Gt Gt core Mu 3 - in clu sion in Pl Pl core Pl rim Sk27 Bt 4 - S2 foliation , K/a Ro7 Bt S2 foliation , Gt rim ,000 Mu 9 - S2 foliation Gt rim Mu 5 - S2 foliation Pl rim , Bt 1 - S2 foliation Gt rim Mu 2 - S2 foliation Pl 2 - rim Bt S2 foliation Gt rim Mu S2 foliation Pl 2 - rim Bt 4 - S2 foliation Gt rim Ro3d Mu 1 - S2 foliation Pl 2 - rim Bt 5 - S2 foliation Grt 3 - rim Mu 6 - S2 foliation Pl 4 - rim Gn1b Bt 1 - S2 foliation Gt 1 - rim Mu 1 - S2 foliation Pl 1 - rim + D (P&L) 617 (T) 581 (P&L) 602 (T) 588 (P&L) 614 (T) 580 (P&L) 603 (T) 575 (P&L) 592 (T) 583 (W&G) 545 (P&L 555 (T) 542 (W&G) 510 (P&L) 501 (T) 513 (W&G) 498 (P&L) 480 (T) 520 (W&G) 510 (P&L) 495 (T) 540 (W&G) The chem i cal com po si tions of the min eral as sem blages used for cal cu la tions are listed as cat ions per for mula unit (% of ox ides in bt and mu were re - cal cu lated for 22 O, in grt for 12 O and in pl for 8 O). The tem per a tures were cal cu lated us ing the grt-bt geothermometer ac cord ing to the fol low ing cal i bra tions: P&L Perchuk & Lavrenteva (1983); T Thomp son (1976); W&G Wil liams & Grambling (1990). The pres sures were cal cu lated us ing the grt-ms-bt-pl geobarometer (Hol land & Powell, 1990). ZSSSZ Z³oty Stok-Skrzynka Shear Zone P (kbar) line is pro vided by the synkinematic blasts of an da lu site in the mica schists near the con tact with the Javornik granitoids. The in creased ther mal gra di ent ac com pa nied by the lo cal plutonic ac tiv ity led to local ised mylonitisation of the rocks of the Stronie For ma tion, oc cur ring at tem per a tures reach ing 600 C. Dur ing this stage, the stud - ied rocks from the ZSSSZ were brought into the higher crustal lev els. The fi nal stage of the D3 duc tile shear ing took place at a depth cor re spond ing to a pres sure not ex - ceed ing c. 3.5 kbar. The shear ing of this stage en hanced the lin ear fab ric in the OSD gneiss es. SUMMARY The geo chem i cal char ac ter is tics of the OSD leptites in - di cate the as so ci a tion of their protolith with both an in ter - continental rift environment and an active continental mar gin. This may in di cate that an ensialic rift en vi ron ment con sid ered the place of or i gin for mag matic rocks dated at c. 500 Ma oc cur ring in the OSD (Pin & Marini, 1993; Floyd et al., 1996; Kryza & Pin, 1997) de vel oped due to ex - ten sion be hind a collisional zone of Lower Palaeozoic age.

34 34 M. MURTEZI Fig. 25. A sum mary of the P-T-d paths ob tained for the rocks of the Stronie For ma tion from two dif fer ent struc tural units of the LSMU: the Z³oty Stok-Skrzynka Shear Zone and Krowiarki Mts. The box rep re sents the peak-meta mor phic con di tions reached by the mica schists from the W part of the OSD. The sig na ture of an ac tive mar gin car ried by con ti nen tal crust rocks stretched and melted due to the in creased heat trans fer re sulted from an ear lier tectono-ther mal ep i sode. Such an ep i sode could have been as so ci ated with a Neopro tero zoic orog eny for the west ern Gond wana re gion re - ferred to as the Cadomian orog eny. It is com monly con sid - ered that the rocks cre ated in this orogenic belt have geo - chem i cal fea tures of an ac tive con ti nen tal mar gin (e.g. Grunov et al.; 1996, Raumer et al., 2001). The P-T-d path pre sented in this pa per en tirely re sults from a Variscan collisional ep i sode oc cur ring in the bor - der land of the West ern and the East ern Sudetes. The se - quence of the de for ma tions es tab lished for the stud ied rocks is in ter preted as an ef fect of the con tin u ous con ver - gence of crustal units in an E W di rec tion. The struc tural relicts of the early stage (D1) of this con ver gence oc cur in the form of rare intrafolial F1 folds and traces of steep S1 fo li a tion planes pre served as in clu sion trails in porphyroblasts. The sub se quent orogenic up lift (D2) was ac com pa - nied by the de vel op ment of bi-vergent tight to iso cli nal F2 folds re sult ing from subvertical short en ing and flat ten ing. As a re sult of the con tin u ous con ver gence and due to the lack of space, thrust ing took place along the edges of the colliding units. The final adaptation of the colliding crustal slices led to zonal lat eral oblique dis place ments. This lat ter event is treated as the cause of the dis tur bance in the isograd and iso therm pat tern ob served within the rocks of the Stronie For ma tion. It is also re spon si ble for zonal shearing, gen er ally tak ing place in a N S di rec tion. A model show ing the se quen tial de vel op ment of the OSD tec tonic ar chi tec ture dur ing a col li sion be tween the West and East Sudetes is pre sented in fig ure 26. The pre sented above P-T-d path in di cates that the max i mal burial of the rocks of the Stronie For ma tion did not exceed a depth corresponding with upper amphibolite fa cies con di tions. Sim i larly, the OSD gneiss es have doc u - mented the re cord of their meta mor phism in the same P-T range (Stawikowski, 2002; Stawikowski & Rhede, 2003; Gzeœkowiak & elaÿniewicz, 2002). The pre sented data shows a con sid er able de crease in the peak-meta mor phic con di tions from the east to the west of the OSD. This sup - ports a the ory about the key mean ing of the col li sion oc - cur ring along the east ern mar gin of the OSD in the tectono-meta mor phic evo lu tion of the unit. As the re sult of this east erly col li sion, near the con tact with the Silesian do main, the rocks of the Stronie For ma tion reached the highest P-T conditions of metamorphism at c. 9 kbar and 650 C. On the side of the Silesian do main, a set of tec tonic slices de vel oped, form ing the con ti nen tal accretionary wedge of Schulmann & Gayer (2000). The dextral shear senses ob served in the rocks of the Moravo-Silesian Zone and in the ad ja cent ZSSSZ can be ex plained by an in den ta - tion of the rock masses to wards the NE, due to an oblique col li sion. The lat eral dis place ment of the col lid ing units re - sulted in the jux ta po si tion of their mod ern con tact ing parts. The as cer tained strong geo chem i cal af fin ity of the OSD leptites and their equiv a lents from the Staré Mìsto group of the Moravo-Silesian Zone in di cates that both the units oc cu pied the same geotectonic po si tion dur ing the for ma tion of the leptites protoliths. The strong con trast be tween the P-T con di tions of meta mor phism es tab lished for the OSD eclogites and granu lites and those for the rest of the OSD rocks must be the ef fect of a tec tonic em place ment of the UHP rocks (Don, 1989; elaÿniewicz & Bakun-Czubarow, 2002; Grzeœkowiak & elaÿniewicz, 2002). The es ti mated peak meta mor phic con di tions for the eclogites and granu lites ex ceed a pres sure of 30 kbar at tem per a tures of C for the eclogites and C for the granu lites (Bakun- Czubarow, 1991, 1998; Kryza et al., 1996; elaÿniewicz & Bakun-Czubarow, 2002; Szczepañski et al., 2004). The data pre sented in this pa per proves that it is im pos si ble to con - struct a com mon P-T path for the whole of the OSD, con - trary to what is pre sented in Schulmann & Gayer s model (2000). When com par ing the pre sented se quence of tec tonic fea tures of the Stronie For ma tion with the struc tural re - cord of the OSD gneiss es, the main prob lem that has to be solved is the cor re la tion of the early constrictional fab ric of the por phy ritic Œnie nik metagranites with one of the above-de scribed tec tonic stages. As the N S trending lin ear fab ric is the old est struc ture re cog nis able within the Œnie nik gneiss es ( elaÿniewicz, 1988), its de vel op ment should be linked to the old est deformational event that can be re cog nised in the rocks of the Stronie For ma tion. Ac - cord ing to elaÿniewicz (1988), the con stric tion of the gneiss es was the re sult of a tec tonic es cape per pen dic u lar to the di rec tion of con ver gence. Un der such cir cum stances, a log i cal so lu tion is to con nect the for ma tion of the lin ear fab ric in the Œnie nik gneiss es with the D1 short en ing, lead ing to the de vel op ment of the up right F1 folds ob - served as rel ics in the rocks of the Stronie For ma tion. Al - though the data on the tim ing of the de for ma tion of the OSD-form ing rocks is re stricted, some cor re la tion based on the ex ist ing con straints is pos si ble. The rims on the zir - cons from the OSD gneiss es were dated by Turniak et al. (2000) at c. 342 Ma, and in ter preted as a re cord of migmatisation fol low ing mylonitisation. The Rb-Sr mica dat ing (Lange et al. 2002) con strains the min i mum age for the last mylonitisation of the OSD gneiss es at 340 Ma. The rel a -

35 ACID META VOL CAN IC ROCKS 35 Fig. 26. The model for the tec tonic evo lu tion of the OSD show ing the se quen tial de vel op ment of its ar chi tec ture dur ing the col li sion of the West and East Sudetes. (a) Short en ing and thrust ing in an E W di rec tion. In creas ing burial of the OSD rocks. (b) Orogenic up lift with subvertical short en ing and flat ten ing strain. At the on set of this stage, the rocks of the Stronie For ma tion reached their peak meta - morphic conditions in the upper amphibolite facies. (c) The fi nal ad ap ta tion of the tec tonic units tak ing part in the Variscan col li sion in the bor der land of the East and West Sudetes. The flat fo li a tion was zon ally trans posed into al most ver ti cal NE SW trending shear planes. The verticalisation of the fo li a tion planes in the Z³oty Stok-Skrzynka Shear Zone (ZSSSZ) was trig gered by the but tress ing ef fect of the MU. The op po site senses of shear in the ZSSSZ (sinistral) and in the rocks of the Silesian do main (dextral) re sult from the in dent - ing of the OSD to wards the NE. This tec tonic event oc curred be tween c. 348 Ma (synkinematic Javornik granitoids) and c. 300 Ma (post-tec tonic K³odzko-Z³oty Stok granitoids).