Major dement chemistry of Lower Cretaceous igneous rocks of the Mecsek Mountains (Southern Hungary), I.

Transcription

1 ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 80. Budapest, 1988 p Major dement chemistry of Lower Cretaceous igneous rocks of the Mecsek Mountains (Southern Hungary), I. by Sz. H A R A N G I, Budapest Sz. HARANGI: Major element chemistry of Lower Cretaceous igneous rocks of the Mecsek Moun tains (Southern Hungary), I. Annls hist.-nat. Mus. natn. hung : Abstract Available chemical analyses of Lower Cretaceous volcanic rocks of the Mecsek Mts. (S Hungary) were statistically evaluated. Sixty-eight analyses of the total of 359 were selected accor ding to the following criteria: + H 0 < 3%, C 0 < %. The Fe 0 /FeO ratio were standardized to 0.. Based on the selected data and using 3 methods (Cox et al. 1979, D E L A ROCHE et al. 1980, TAS diagram) the Mecsek volcanics were classified into 4 groups : basaltic rocks (picrite, basanite, basalt), transitional rocks (basaltic andésite), alkaline transitional rocks (trachybasalt, basaltic trachyandesite, trachyandesite) and intermediate-acidic rocks (andésite, phonolite, trachyte). Among the basaltic-andesitic rocks the tholeiitic character was found to predominate. Average chemical composition of each rock-types is given. Using univariate statistical methods, petroche mical character of these rocks was determined. The Mecsek volcanics bear features of continental rift magmatism, however, the ratio of tholeiitic rocks is somewhat high. 3 I n t r o d u c t i o n Investigations on the Lower Cretaceous igneous rocks of the Mecsek Mts. in southern Hungary have been carried out for more than one hundred years. The first detailed petrographical and petrochemical investigation was made by MAURITZ (1913). Characters of the submarine volcanism were described by B I L I K (1983), who distinguished effusive rock types (hyaloclastite. pillow lava, massive lava, lava breccia, pillow breccia, etc.). He stressed the alkaline character and continental nature of the volcanism. Discrimination analyses (EMBEY-ISZTIN 1981) corroborated the intraplate affinity and relationships with continental rift magmatism. Studies on pyroxenes of the alkaline basalt trachybasalt trachyandesite phonolite series (Dobosi 1986, 1987) also indicate intraplate magmatism and alkaline magma, differentiated by low-pressure fractional crystallisa tion. The subvolcanic phonolite is a product of the Lower Cretaceous volcanic activity (VICZIÁN 1971), being the acidic, alkali-rich differentiate of the alkaline basaltic magma. The first data on the major element composition were published by MAURITZ (1913). Further geochemical analyses were carried out to help the detailed survey of the Mecsek Mts. in the 1960s, and part of them were published in the series "Explanations to the 1 : geological maps of the Mecsek Mts.". The chemical analyses were made in the Komló Laboratory of the National Geologi cal Prospecting and Drilling Company (OFKFV) by É. Pánczél, G. Csordás, M. Vigh, G. Csajághy. and in the Chemical Laboratory of the Hungarian Geological Institute by L. Jankovich and L. Soha. The data are deposited in the Documentation Department of the Hungarian Geological Institute. A n a l y t i c a l d a t a The results of 359 chemical analyses were collected and examined; only a minor part of them have been published (MAURITZ 1913, NAGY et al. 1978, BILIK et al. 1978, VICZIÁN 1971). The unpublished data are not accompanied by petrographical descriptions and the names of the rocks, raising several problems during evaluation. Therefore the conclusions of the present paper are exclusively based on the chemical data; classification of the rocks was made ac cording to the normative composition. Classification of the Mecsek igneous rocks is hindered by the almost total absence of fresh rocks ; most of them suffered alteration, such as submarine alteration, influence of host rocks on dykes and weathering. The often high CaC0 content may be due to the assimilation of carbonate rocks by the rising magma. The first step of the analyses was to delete volatile-rich samples. Generally accepted criteria of fresh rocks are: + H 0 «=.0% and C 0 < 1.0%. However, only 18 samples fulfilled this require ment. As this small number of data is not enough to characterize the types of igneous rocks in the Mecsek, we modified the criteria. The following conditions were applied: a) the sum of the compo nents would be between 98 and 10%; b) total volatile content ( + H 0, - H 0, C O j would be less 3

2 than 5%; c) within this limit +H 0 content would be less than 3%; d) C0 content would be less than %. Ninety percent of the selected analyses showed less than 1 % C0 content. The 68 analyses, selected according to the above criteria, are suitable for statistical studies to obtain an overview on the volcanic rock types. However, due to these self-imposed restrictions, some known rock types are missing from the evaluation: essexite (TAKÁTS 1933) and augitite (Szilágyi 1981). The Mecsek igneous rocks are mostly characterized by high Fe /FeO ratio. In 9% of the selected analyses it is higher than 0.5 % due to subsequent oxidation. The degree of oxidation strongly influences the CIPW norms (Cox et al. 1979) : oxidation increases saturation, but decreases normative pyroxene and olivine content. That is why Fe /FeO values are standardized for oxidated samples. Several methods are applied, usually the Fe /FeO = 0. correction is preferred (HUGHES & HUSSEY 1979). This correction was carried out for samples with less than 54% Si0 content. The next step was correction for volatiles, recalculating the data for volatile-free composition. These corrections influence CIPW norms and M-value ( = 100. Mg + /Mg + +Fe + ) in the following way: Fe /FeO standardization: normative quartz and magnetite decreases, while normative diopside, hypersthene and olivine contents appear or increase ; the THORNTON TUTTLE Differentiation Index decreases, the colour index increases, M value decreases, while normative plagioclase composition ( = 100 an/an -fab) remains constant (in q- or hy-normative rocks). Recalculation of the composition to volatile-free composition does not cause significant changes, like the former correction: normative calcite disappears, while the other components slightly increase. 5r BAS 0- PMO 15 SAN 10 BTA PIC BSN TCP TBA AND TRA TAN Fig. 1. Percentage distribution of volcanic rock-types of Mecsek Mts.: PIC = Picrite, BSN = Basanite, BAS = Basalt, BAN = Basaltic andésite, TBA = Trachybasalt, TEP = Tephrite, BTA = Basaltic trachyandesite, TAN = Trachyandesite, AND = Andésite, Tra = Trachyte, PHO = Phonolite, O = samples, which can't be ranged into either of these rock-types.

3 Petrochemical classification of igneous rocks in the Mecsek Mts. Besides phonolite the Mecsek Lower Cretaceous volcanic rocks were denominated as "trachydolerites" until the end of 1960s. MAURITZ (1913) distingusihed a high-silica "typical" and a low-silica "limburgitoid" group within the trachydolerites. BILIK (1966) revised the trachydolerite name and proposed the application of alkaline basalt, or considering their appearance alkaline diabase name. No more detailed studies were carried out on /o 40 f OT 10 TH OT CA A8 TD DSN FA AA TSA Fig.. Percentage distribution of basaltic and andesitic rock-types of Mecsek Mts. : AB = Alkali basalt, OT = ol-tholeiite, TH = Tholeiite, QT = q-tholeiite, FA = Feldspathoidal andésite, TA = Tholeiitic andésite, CA = Calc-alkaline andésite, TD = Tholeiitic dacite.

4 the petrochemistry of the Mecsek igneous rocks, however, we know that there are several kinds of rocks in the Mecsek: augite diabase, alkaline diabase, albite diabase, spilite, augitite and several rock types: basalt, trachyte, essexite, phonolite. DOBOSI (1987) published brief petrographical descriptions of alkaline basalts, trachybasalts, trachyandesites and phonolites. A detailed study of the phonolite was carried out by VICZIÁN (1971). A new system for the classification and nomenclature was put forward by the IUGS Subcommission on the Systematics of Igneous Rocks (STRECKEISEN 1979). Among others the term "diabase", applied for altered basalts was rejected. The classification was based on the modal mineralogical composition, plotted on a QAPF diagram. We know that modal composition cannot be well determined for some volcanic rocks (due to the presence of microcrystalline or vitreous groundmass), therefore classification must be based on chemical composition. STRECKEISEN & L E MAÎTRE (1979) suggested the application of the Barth- Niggli norms for volcanic rocks classification, providing a diagram constructed from the fields of the QAPF diagram based on a large number of analytical data. The latter method is not widely applied; classification methods are rather based on Si0 vs. Na. 0+K 0 Si0 Fig. 3. Si0 vs. AN diagram for volcanic rocks of Mecsek Mts. : 1 = basanite, = basalt, 3 = tephrite, 4 = trachybasalt, 5 = basaltic trachyandesite, 6 = basaltic andésite, 7 = andésite, 8 = trachyandesite, 9 = trachyte, 10 = phonolite; I = basaltic rocks, II = transitional basaltic-andesitic rocks, III = alkaline transitional basaltic-andesitic rocks, IV = intermediate-acidic rocks

5 (Cox et al. 1979; LE BAS et al. 1986). The IUGS Subcommission suggested the application of the TAS (total-alkali-silica) diagram for the classification of volcanic rocks. SABINE and co-workers (1985) examined the influence of alteration on the TAS-diagram classification, and good correlation was observed between the petrographical and chemical nomenclature, except for strongly altered and rare rocks. DE LA ROCHE and co-workers (1980) suggested a chemical variation diagram containing the main cations. Their method provides more information than the Si0 alkali diagrams considering 3 components only. Classification of the Mecsek volcanics based on modal composition raises problems, therefore we need chemical classification, too. Besides the TAS diagram, plots of Cox et al. (1979) and DE LA ROCHE et al. (1980) were applied for the classification of the Mecsek rocks. As the latter one contains more rock names, some rock types were amalgamated for the purposes of the comparison (basalt = alkaline basalt, basalt and tholeiite; trachybasalt = hawaiite and mugearite; andésite andésite and latiandesite; phonolite = phonolite and trachypohonolite). Plotting the corrected compositions on the three diagrams,, we found that there is a 90% agreement between the TAS and Cox's classification, and 80% between the TAS and DE LA ROCHE'S classification. Summing up the results, the Mecsek volcanic rocks were ranged into 11 groups (Fig. 1), while the relations of the 5 samples with any of the groups is unclear, therefore these ones were excluded from the calculation of average compositions. In spite of the large number of rock types, 4 groups are easily separated: basaltic rocks (picrite, basanite, basalt); transitional rocks (basaltic andésite); alkaline transitional rocks (trachybasalt, basaltic trachyandesite); intermediate-acidic rocks (andésite, trachyandesite, phonolite, trachyte) (Figs 3 and 4). Na>0+ rco Fig. 4. Na 0 +K 0 vs. Si0 diagram for volcanic rocks of Mecsek Mts. (discrimination curve after MACDONALD & KATSURA 1974). A = Alkalic field, Th = Tholeiitic field (symbols are explained in Fig. 3).

6 Average chemical composition of each rock types are shown in Table 1. CIPW norms were calculated from the average composition. Comparing these average values with published ones (LE MAÎTRE 1976; DE LA ROCHE et al. 1980), we can observe high Ti0 and total iron, and relatively low A1 contents. Most of the Mecsek volcanics are of basaltic-andesitic composition, and a more detailed classification is proposed here. MIDDLEMOST (1975) suggested the joint application of Na 0 Si0 and K 0 Si0 diagrams to distinguish between alkaline and subalkaline characters. If the point of the sample lies in the alkaline field in both diagrams, the rock is alkaline, if it lies in the subalkaline field in both ones, then the sample is subalkaline. If one of the plots indicates subalkaline, while the other one indicates alkaline composition, we have a transitional basalt. About half of the Mecsek samples belong to the transitional group, while a quarter of them is alkaline, and another quarter is subalkaline. Tephrites, basanites, some basalt samples, trachybasalts (hawaiite) and basaltic trachyandesites belong to the alkaline group. To distinguish between potassic or sodic character, the samples were plotted on the K 0 Na 0 diagram (MIDDLEMOST 1975) (Fig. 5). More than half of the samples are of potassic composition, but the potassium enrichment may be connected to submarine alteration, the K being concentrated in clay minerals. WILKINSON (1986) has based the classification of basaltic and andesitic rocks (AN > 30) on normative plagioclase composition, Si0 saturation, A1 content and K 0/Na 0 ratio. More than half of the Mecsek volcanics belong to the andésites (norm. plag. AN = 100 an/an+ab < 50), while most of the basaltic rocks display tholeiitic character (Fig. ). Within the andesitic rocks the tholeiitic character is prevalent. However, we should note that the tholeiitic character does not imply genetic classification; we can only say that petrochemically the investigated rocks are of tholeiitic (subalkaline) character. Comparing the average compositions of each groups (Table ) with the averages provided by W'ILKINSON (1986), we can observe that Ti0 content is higher, while A1 content is somewhat lower in the Mecsek samples. According to the K 0/Na 0 ratio these belong to the middle to low K/Na type. K 1 fx I High K-series N. _ / + / K-series + \ / + V. + * N. - * SS Na-series \ 0 1 t 1 I e Na 0 Fig. 5. K 0 vs. Na 0 diagram (after MIDDLEMOST 1975) for basaltic-andesitic rocks of Mecsek Mts. Annls hist.-nat. Mus. natn. hung., 80, 1988

7 n lor 3 310, 15 CBO 6-10 Q] n,,n TO 0 «t ffi.rp- - hnüfl Ma 0 10; ; 30 K 0 lor 0? 10 ^ ru [ r K 0/Wa 0 Mm ili ml nrni, "~ri I~r~i t 1»..I. * * ,8 Î \ 14 U6 18 n 15- MgO n 30* i l 0 P o 5 IC m S ' ,8 Fig. 6. Histograms of major element components of volcanic rocks in Mecsek Mts. (N = 68).

8 Petrochemically the igneous rocks of the Mecsek Mts. form an alkaline (alkaline basalt trachybasalt basaltic trachyandesite phonolite) series and a subalkaline (tholeiitic ) transitional series (tholeiite basaltic andésite?trachyte). Chemistry of the igneous rocks in the Mecsek Mts. If we have many samples and even more chemical analyses, statistical treatment of data cannot be avoided. In this paper only univariate statistical methods are applied. Histograms were constructed for all oxides and some characteristic ratios, expressing the characteristic frequency distribution of the oxides; besides, the maximum values are usually characteristic for the rock types (Fig. 6). Si0 (x/average value) = 53.71, SD (standard deviation = 5.35): there are three maxima in the Si0 distribution of the Mecsek volcanics (43-50, and Si0 %), corresponding to a basic a transitional basaltic-andesitic and an intermediate-acidic group, in accordance with the results of classification. TiO, (x =.88, SD = 1.45): the examined compositions show extremely high Ti0 contents, indicating intraplate volcanism. Phonolite contains average amount of Ti0 only. Defining a small class width (0.5) for the histogram, phonolites (0-0.5%), trachytes (1-1.5%), andésites (-3%) and basalts (> 3%) can be easily separated. A minor peak between 4.5 and 6.0% shows the location of Ti-rich basalts from the Jánosipuszta area. A1 (x = 14.76, SD = 3.3): AI contents are somewhat lower than published average values, except for the phonolites. Especially low values have been observed in andésites and trachytes. Applying 0.5% class width in the histogram, a low A1 (11-14%) group was observed, containing iy-tholeiites and alkaline basalts among the basaltic rocks. FeO tot (x = 10.18, SD = 3.76): total Fe contents are high in basaltic and andesitic groups; a significant positive excursion was observed in transitional intermediate rocks (trachybasalts). Phonolites and trachytes show lower FeO tot content. MgO (x = 4.3, SD =.96): Mg-poor phonolites (0-1.5%), and alkaline basic rocks, containing pyroxene and olivine, with higher MgO content (basanite, alkaline basalt, ol-tholeiite) (MgO =-7%) are separated. K 0 Fig. 7. K 0- Ti0 - P 0 5 diagram (after PEARCE et al. 1975) for basaltic-andesitic rocks of Mecsek Mts. Oc = Oceanic field, Cont = Continental field.

9 CaO (x = 6.6, SD = 3.46) : CaO contents of phonolites and trachytes are conspicuously separated from those of the other groups (0- vs %). Higher than 8% values were observed in more basic samples. Na 0 and K 0 (x = 4.11, SD =.5 (Na 0) and x =.53, SD = 1.8 (K Q)): Besides the especially high alkali contents of phonolites, potassium content of the trachytes ( %) is considerable. On the K 0/Na 0 histogram we can see identical values for phonolites and for other groups, instead of the conspicuous separation observed on the histograms of all other oxides. It may indicate genetic relationships. Only the K-rich trachyte is separated. P 0 5 (x = 0.58, SD = 0,84): it displays an approximately monotonous decreasing log-normadistribution. Rock groups do not have characteristic P 0 5 contents, the values having a very high standard deviation. Tectonic position Open marine, carbonate sediments were deposited in the Late Jurassic Mecsek sea, topographical highs and lows were formed in the basin due to tectonic movements preceding magmatism. The volcanic activity may have begun during Late Jurassic time, paroxysm was reached during Valanginian and Hauterivian only. According to published observations the melt ascended to the surface through more or less parallel fractures in the continental crust. The volcanic rocks display alkaline character (BILIK 1983, EMBEY-ISZTIN 1981). Usually two methods are applied to distinguish between the alkaline and the subalkaline (tholeiitic) characters of the volcanic rocks. A swift and frequently applied process is plotting the data on Si0 alkali diagram. The analytical data of the Mecsek volcanics are equally distributed between the alkaline and the tholeiitic field (discrimination curve after MACDONALD & KATSURA 1964) (Fig. 4). Conspicuously, the basaltic andésites display mostly tholeiitic, while the basaltic trachyandesites alkaline character. Half of the basalts FeO t MgO Ai Fig. 8. (MgO- FeO tot - A1 discriminating diagram (after PEARCE et al. 1977) for basaltic-andesitic rocks (Si0 : 51-56%) of Mecsek Mts. OI = Ocean Island, CO = Continental, SCI = Spreading Center Island, OR = Orogenic, ORF = Ocean Ridge and Floor.

10 {basanites, alkali basalts and ol-tholeiites) belong to the alkaline, and half o f them to the tholeiitic field. Another method indicates alkaline character, i f i t contains normative nepheline. I t indicates subalkaline character for most o f the Mecsek volcanics, except phonolites, but part of them belong to the transitional ( o l - and/or hy-normative) group. Tectonic position may be determined by applying the discrimination diagram o f PEARCE (1976), which is mainly useful for high T i 0 and high K 0 rocks. A p p l y i n g this method E M B E Y T S Z T I N (1981) has shown the intraplate affinity o f the Mecsek volcanics. The analytical data examined by us, which fulfill the requirements o f Pearce, fall into the same field (WPB) without exception. The K 0 T i 0 P 0 triangular diagram (PEARCE et al. 1975) can be used to dis tinguish between continental and oceanic character. O f course, the exclusive application o f this method seldom yields acceptable results, because both K 0 and T i 0 can be enriched i n oceanic and continental volcanics. The Mecsek samples (bearing less than 0 % total alkalis o n the A F M diagram) display a scattered distribution, part o f them i n the continen tal, part i n the oceanic field. The latter contains the samples w i t h extremely high T i 0 content (Fig. 7). To make more detailed distinctions on the tectonic character, the M g O F e O A 1 0 diagram (PEARCE et al. 1977) was applied with good results on the basaltic andésites with 51-56% S i 0. Almost all the samples fall into the continental field (Fig. 8). Discrimination diagrams and chemical composition enable us to draw the conclusion that the Mecsek volcanics bear features o f a continental rift magmatism, compared with the products o f recent rifts (BARBERIet al. 198), but the ratio o f tholeiitic rocks is somewhat higher. This study is based on major element analyses, w i t h inherent uncertainties. Yet it can call attention to some problems which may be solved by other methods (trace element and R E E analyses). Besides studying the classification o f the Mecsek rocks based o n chemical analytical data, we should like to call attention to the unsolved problems i n geochemistry i n this area, hoping that further detailed studies w i l l follow. 5 t o t 3 References BARBERI, F., SANTACROCE, R., VARET, J. ( ) : Chemical aspects of rift magmatism I n : PÁLMASON, G. (ed.): Continental and oceanic rifts. Geodynamic Ser. 8: 3-58 B I L I K, I. (1966) : Problems of the nomenclature of the Lower Cretaceous volcanic rocks in the Mecsek Mts. (Hung, with English abstract) Ann. Rep. Hung. Geol. Inst, for : B I L I K, I. (1983): Lower Cretaceous submarine (rift) volcanism in South Transdanubia (South Hun gary) Proc. 17 th Assembly of the ESC, Budapest : B I L I K, I., HÁMOR, G., HETÉNYI, R. & N A G Y, I. ( ) : Explanation to the 1 : geological maps of Mecsek Mts., Kisbattyán (Hung.). Publ. Hung. Geol. Inst. (Budapest). Cox, K. G., BELL, J. D. & PANKHURST R. J. (1979): The interpretation of igneous rocks. London, Georg Allen and Unwin. D E L A ROCHE, H., LETERRIER, P., GRANDCLAUDE, P. & M A R C H A L, M. ( ) : A classification of volcanic and plutonic rocks using the R 1 - R diagram and major element analyses. Its relation ships with current nomenclature Chem. Geol. 9 : DOBOSI, G. (1986): Clinopyroxene compositions of some mesozoic igneous rocks of Hungary: the possibility of identification of their magma type and tectonic settings Ofioliti 1 1 : DOBOSI G. (1987): Chemistry of clinopyroxenes from the Lower Cretaceous alkaline volcanic rocks of the Mecsek Mountains, South Hungary. N. Jb. Miner. Abh. 156: EMBEY-ISZTIN, A. (1981): Statistical analyses of major element patterns in basaltic rocks of Hunga ry. Acta geol. hung. 4: HUGHES, C. J. & HUSSEY, E. M. (1979): Standardized procedure for presenting corrected Fe O /FeO ratios in analyses offinegrained mafic rocks N. Jb. Miner. Mh. 1: a

11 LE BAS, M. J., LE MAÎTRE R. W., STRECKEISEN, A. & ZANETTIN, B. (1986): A chemical classification of volcanic rocks based on the total alkali-silica diagram. J. Petrol. 7: LE MAÎTRE, R. W. (1976): The chemical variability of some common igneous rocks. /. Petrol. 17: MACDONALD, G. A. & KATSURA, T. (1964): Chemical composition of Hawaiian lavas /. Petrol. 5: MAURITZ, B. (1913): Die Eruptivgesteine des Mecsekgebirges Jahr. kgl. ung. Reichan. 1: MIDDLEMOST, E. A. K. (1975): The basalt clan. Earth-Sci. Rev. 11: NAGY, L, HÁMOR, G., HETÉNYI, R. BILIK, I. & FÖLDI, M. (1978): Explanation to the 1 : geological maps of Mecsek Mts, Kisújbánya (Hung.). Publ. Hung. Geol. Inst. (Budapest). PEARCE, J. A. (1976) : Statistical analyses of major element patterns in basalts. /. Petrol. 17: PEARCE, T. H., GORMAN, B. E. & BIRKETT, T. C. (1975): The Ti0 K 0 P 0 5 diagram: a method of discriminating between oceanic and nonoceanic basalts. Earth Planet. Sei. Lett. 4: PEARCE, T. H., GORMAN, B. E. & BIRKETT, T. C. (1977): The relationship between major element chemistry and tectonic environment of basic and intermediate volcanic rocks. Earth Planet. Sei. Lett. 36: SABINE, P. A., HARRISON, R. K. & LAWSON, R. I. (1985): Classification of volcanic rocks of the British Isles on the total alkali oxide-silica diagram and the significance of alteration. Brit, geol. Surv. Rep. 17: 1-9. STRECKEISEN, A. ( 1979) : Classification and nomenclature of volcanic rocks, lamprophyres, carbonatites and melilitic rocks: Recommendation and suggestions of the IUGS Subcommission on the Systematics of Igneous Rocks. Geology 7: STRECKEISEN, A. & LE MAÎTRE, R. W. (1979): A chemical approximation to the modal QAPF classification of the igneous rocks. N. Jb. Miner. Abh. 136: SZILÁGYI, T. (1981): Lamprophyric dike rock in the coal exploratory borehole Komló-173 (Hung, with English abstract). Földt. Közi. 11: TAKÁTS, T. (1933): Essexit in the Mecsek Mts. (Hung.) Mat. Term.tud. Ért. 50: WILKINSON, J. F. G. (1986): Classification and average chemical composition of common basalts and andésites. /. Petrol. 7: VICZIÁN, I. (1971): Petrology of the Mecsek Mts. phonolites (Hung, with English abstract) Ann. Rep. Hung. Geol. Inst, for Author's address: SZABOLCS HARANGI Mineralogical and Petrographical Department Hungarian Natural History Museum H-1088 Budapest, Múzeum körút Hungary

12 Table 1. Average chemical composition, M-values, CIPW norms and Differentiation index (THORNTON-TUTTLE) of volcanic rock-types of Mecsek Mts. (Symbols are explained in Fig. 1) (* = standard deviation) BSN BAS TEP TBA BAN N SiO, TiO, Al O a Fe FeO MnO MgO CaO Na 0 K Ö P O (0.4)* 3.8 (0.4) (1.8).17 (0.1) (0.6) 0.16 (0.1) 9.0 (.0) (0.6) 3.04 (0.3) 1.17 (0.6) 0.44 (0.) (1.8) 4.5 (.09) 13.9 (1.9).13 (0.) (1.) 0.3 (0.) 7.30 (1.9) 9.66 (1.3).7 (0.4) 1.11 (0,3) 0.51 (0.7) (0.1) 3.69 (1.9) (1.) 1.95 (0.1) 9.76 (0.5) 0.1 (0.) 3.34 (0.8) 7.19 (0.6) 5.54 (0.8).08 (0.8) 0.58 (0) (0.7) 3.01 (0.5) 13.3 (1.4).76 (0.1) (0.8) 0.41 (0.1).4 (.1) 6.84 (0.4) 3.98 (0.3).03 (0.4) 0.08 (0.1) (1.) 3.18 (0.7) 1.84 (1.3).04 (0.4) 10.3 (1.9) 0. (0.) 4. (1.3) 9.3 (1.3).56 (0.9) 1.4 (0.4) 0.48 (0.4) M CIPW norms q _ or ab an ne wo di ! hy ol mt hm il tn ap D.I

13 Table 1, continuation. BTA TAN AND TRA PHO (0.9) (.9) (3.0) (1.9) (1.0) 3.9 (0.7).68 (0.4).50 (0) 1.1 (0.6) 0.3 (0.4) 14.8 (1.7) (0.5) (.) 1.05 (0.3) 0.44 (1.1) 1.75 (0.) 3.48 (1.0) 4.0 (1.6) 7.53 (.7) 3.00 (1.3) 8.81 (1.1).79 (1.) 8.41 (3.0) 0.8 (0.3) 1.51 (0.7) 0. (0.) (0.1) (0.1) 3.93 (0.9).5 (0.6) 3.59 (0.5).95 (1.0) 0.34 (0.4) 6.41 (0.7) 4.35 (.5) 5.73 (1.0) 1.67 (1.6) 1.18 (0.3) 3.48 (0.3) 5.76 (0.4) 3.06 (0.) 3.36 (1.4) 9.06 (0.9).67 (0.6).38 (0.9).14 (0.) 6.16 (3.1) 4.75 (0.3) 1.14 (0.6) 0.16 (0.) 0.78 (0.1) 0.69 (0.) 0.03 (0) _

14 Table. Average chemical compositions, M-values, CIPW norms and Differentiation Index (TKORNTON-TUTTLE) of basaltic-andsajic rock-types of Mecsek Mts. (Symbols are explained in Fig. ) (* standard deviation). AB or XI! QT TA C'A TD N Si (0.)* 48.7 (1.9) 5.45 (1.8) 5.99 (1.4) 5.54 (1.6) Ti (0.9) 4.1 (1.) 3.31 (0.5) 3.45 (0.7).87 (0.4).66 A (.0) (1.8) 1.13 (1.0) (1.5) 17.3 (0.1) 13.4 Fe (0.).11 (0.).36 (0.3) 1.97 (0.3) 1.6 (0.3) FeO (1.0) (1.) (1.3) 9.87 (1.5) 8.14 (1.3) 9.4 MnO (0.1) 0.37 (0.) 0.3 (0.1) 0.3 (0.1) 0.3 (0.) 0.49 MgO (1.4) 6.68 (1.5) 5.14 (1.) 4.19 (1.5) 4.36 (0.7) 3. CaO (1.4) (0.9) 9.19 (1.) 8.17 (1.7) 6.3 (0.4) 6.75 Na, (0.4).9 (0.1) 1.66 (0.6) 3.19 (0.5) 3.43 (0.3) 3.16 K (0.3) 0.97 (0.4) 0.9 (0.3) 1.81 (0.6).45 (0.) 1.88 P O (0.) 0.51 (0.3) 0.81 (0.6) 0.86 (0.8) 0.8 (0.1) 1.09 M CIPW norms J* q or ab an ne.5 di by Ol ml il ap D.I