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1 Lithos 113 (2009) Contents lists available at ScienceDirect Lithos journal homepage: Mid-ocean ridge and supra-subduction geochemical signatures in spinel peridotites from the Neotethyan ophiolites in SW Turkey: Implications for upper mantle melting processes E. Aldanmaz a,, M.W. Schmidt b, A. Gourgaud c, T. Meisel d a Department of Geology, University of Kocaeli, Izmit 41040, Turkey b Institute of Mineralogy and Petrology, ETH, 8092 Zurich, Switzerland c Département de Géologie, Université Blaise Pascal, CNRS-UMR 6524, OPGC, 5 rue Kessler, Clermont-Ferrand Cedex, France d Department of General and Analytical Chemistry, University of Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria article info abstract Article history: Received 17 November 2008 Accepted 5 March 2009 Available online 21 March 2009 Keywords: Mantle geochemistry Mantle melting MORB SSZ Ophiolites Turkey The Lycian and Antalya ophiolite complexes in SW Turkey represent fragments of oceanic lithosphere emplaced following the closure of the Neotethys Ocean during the Late Cretaceous. The peridotites from both of these ophiolites have compositions ranging from relatively undepleted lherzolites to highly depleted harzburgites and display a diverse suite of geochemical signatures indicative of both anhydrous, mid-ocean ridge (MOR)-type and hydrous, supra-subduction zone (SSZ)-type melting regimes. Whole-rock major and trace element systematics and mineral chemistry indicate that the MOR- and SSZ-type peridotites represent the residues from 5 9% and 13 25% of mantle melting, respectively, and display evidence for a multi-stage evolution of an oceanic lithosphere. Olivine orthopyroxene spinel equilibria indicate that the clinopyroxenebearing, MOR-type peridotites are moderately reduced with their oxygen fugacity (fo 2 ) ranging from 2.22 to 1.44 log units relative to the FMQ (fayalite magnetite quartz) buffer and are similar to abyssal peridotites, while more refractory, SSZ-type harzburgites and dunites (b4% modal clinopyroxene) are more oxidized with their higher oxygen fugacity (FMQ 0.72 to +1.02). The latter can readily be explained by interaction with oxidizing melts/fluids originating from a subducted slab in a SSZ environment. Precise determination of trace element compositions of residual clinopyroxenes by LA-ICPMS indicates that the SSZ peridotites are strongly depleted inti and HREE and enriched in Zr and LMREE, compared to the most depleted MOR-type peridotites. The results of quantitative model calculations show that moderate degrees of anhydrous mantle melting accounts for the composition of MOR peridotites, while SSZ peridotites are likely to have originated from hydrous, orthopyroxene-dominated remelting of previously depleted mantle. For the case of hydrous melting, it is inferred that flux of a slab-derived fluid component sustained further melting of MORB-depleted peridotite, resulting in higher degrees of depletions in the SSZ mantle than the anhydrous melting in the MOR setting. Interaction of SSZtype melts with depleted peridotites enriched the source mantle in more incompatible trace elements, resulting in elevated Zr/Ti and LMREE/HREE ratios in peridotites. The occurrence of both MOR and SSZ styles of melting regimes indicates that these ophiolites contain mantle residues from discrete stages of oceanic lithosphere generation Elsevier B.V. All rights reserved. 1. Introduction Peridotites from tectonically emplaced fragments of oceanic lithosphere are usually considered to represent variably depleted solid residues of oceanic upper mantle left behind after mantle melting and crust mantle segregation. Chemical data from these rocks and their constituting minerals constrain mantle processes such as melting, melt extraction and melt mantle interaction (e.g. Kelemen et al., 1992; Parkinson and Pearce, 1998; Batanova et al., 1998; Takazawa et al., Corresponding author. address: ercan.aldanmaz@dunelm.org.uk (E. Aldanmaz). 2003; Rampone et al., 2004), and contribute to our understanding of the original tectonic setting of lithosphere generation (Pearce et al., 2000; Bizimis et al., 2000; Barth et al., 2003). Oceanic lithosphere may originate in a variety of tectonic environments including mid-ocean ridge (MOR) and supra-subduction zone (SSZ) settings, these discrete genetic types being distinct in the geochemical and mineralogical characteristics of mantle residues. The significance of variable mantle processes on the chemical composition of melting residues has become increasingly evident in studies which emphasized that variable compositions of mantle rocks from different tectonic environments are the results of different styles of depletion and refertilization events, and that the combined effects of partial /$ see front matter 2009 Elsevier B.V. All rights reserved. doi: /j.lithos

2 692 E. Aldanmaz et al. / Lithos 113 (2009) melting and interaction with fluids shape the ultimate composition of mantle relicts (Kelemen et al., 1992, 1997; Niu et al., 1997; Suhr et al., 2003; Rampone et al., 2004). The ophiolite complexes across SW Turkey contain a number of lithosphere fragments that represent remnants of oceanic lithosphere emplaced during the closure of the Neotethyan oceanic realm (Dilek et al., 1999; Robertson, 2002). These relicts of lithospheric mantle were emplaced mostly onto the passive margin of the Gondwanaderived continental fragment, the Anatolide-Tauride Platform, as a result of the consumption of the Tethyan domain by a number of episodes of northward subduction and subsequent accretion of continental fragments during the Mesozoic. This suite of ophiolites provides the opportunity to examine upper mantle processes over a relatively wide range of degree of melting and subduction-induced mantle metasomatism. Bulk-rock and mineral chemical data indicate that the mantle section of the ophiolites in this area contain mantle residues with contrasting geochemical signatures indicative of both MOR and SSZ settings. The former setting is best documented in the moderately depleted lherzolites and harzburgites that are usually explained by simple melt extraction and depletion at oceanic ridges. The latter setting produced the more depleted and in part reactive harzburgite and dunite bodies (with abundant chromite deposits), the formation of which is commonly attributed either to further melting of depleted mantle by injection of hydrous melts above subduction zones (e.g. Kubo, 2002) or to melt solid interaction during melt percolation (e.g. Zhou et al., 1996; Morgan and Liang, 2002). In this study, we combine bulk-rock and mineral chemical studies of the mantle residues sampled from the ophiolite complexes of SW Turkey, to place constraints on the mechanisms effective during melting and melt extraction in the upper mantle, and on the possible role of subduction fluids (or melts) on mantle melting processes. We also evaluate geochemical data to constrain the original geodynamic setting of oceanic lithosphere generation. 2. Geologic background Tectonically emplaced fragments of oceanic lithosphere in SW Turkey constitute a part of the Mesozoic Neotethyan ophiolites exposed across the circum-mediterranean region (Fig. 1a). The ophiolite belts range from the Alpine Apennine region through the Balkan Peninsula (Dinaride Hellenide Albanide ophiolites) to the easternmost Mediterranean (ophiolite belts in Turkey, Cyprus and Syria) and reflect the evolutionary stages of Neotethyan ocean basins from the Jurassic to the Cretaceous (Robertson, 2002; Dilek et al., 2007). Variable petrological and structural evidence from the ophiolites in the eastern Mediterranean indicate that they experienced rifting, sea-floor spreading and convergent margin evolution in a number of oceanic basins that are inferred to have developed within the Tethyan realm and have been closed following episodes of northward subduction (Dilek and Moores, 1990). The relatively well-preserved Neotethyan ophiolites in SW Turkey are exposed across the western Tauride Mountains which comprise a central relatively autochthonous carbonate platform unit, the Tauride autochthon, bordered by two allochthonous units, the Lycian Nappes to the west and the Antalya Complex to the east (e.g. Robertson, 2002). Each of these internally thrusted allochthonous units is made up of several sub-units containing relicts of oceanic lithosphere. The Lycian nappes consist of thrust sheets dominantly composed of carbonate rocks and are located in a large area between the Menderes metamorphic basement and a segment of the Mesozoic Tethyan platform (the Beydaglari carbonate platform) (Fig. 1b). These nappes are generally believed to have been derived north of the Menderes massif from the region of the Izmir Ankara suture (e.g. Collins and Robertson, 1998). They were emplaced on the Menderes massif during Eocene time and transported southeast over the Beydaglari carbonate platform during Miocene time (Fig. 1b). The nappes contain (1) thrust sheets of dominantly Mesozoic continental margin sediments; (2) a mélange-type accretionary complex; and (3) an upper thrust sheet of ophiolites (Collins and Robertson, 1998; Robertson, 2002). The Lycian ophiolite consists of a number of ultramafic bodies, whose original internal structures were largely disrupted during their emplacement as thrust sheets. The ophiolites are predominantly serpentinized harzburgites with minor lherzolite, podiform dunites and chromitites. Crustal lithologies are rather absent in the ophiolite, although they comprise a significant portion of the underlying mélange-type accretionary complex. 40 Ar/ 39 Ar geochronology on metamorphic soles (amphibolites and mica schists) from beneath the Lycian peridotites indicates a Late Cretaceous age (~91 94 Ma; Celik et al., 2006) for the tectonic displacement of the oceanic lithosphere. The Antalya complex comprises four types of units: (1) shallowmarine platform carbonates (Tauride carbonates); (2) basinal sequences with volcanic intercalations; (3) a mélange-type accretionary complex; and (4) an ophiolite, representing remnants of an oceanic lithosphere (Juteau et al., 1977; Dilek et al., 1999; Robertson, 2002). The remnants of oceanic lithosphere within the Antalya complex comprise an almost complete ophiolite succession (i.e. mantle tectonites, ultramafic to mafic cumulates and isotropic gabbro, sheeted dykes and sediments), although these rock associations are dispersed between several different tectonic slices (Juteau et al., 1977; Robertson, 2002). The original tectonic setting of formation for the Antalya ophiolite is still debated. Juteau et al. (1977) used the structural elements and petrogenesis of the layered crustal sequences to suggest an origin by spreading at a MOR setting, while some other studies proposed a SSZ origin within the southern branch of Neotethys (Robertson, 2002). No metamorphic sole has yet been reported beneath the Antalya ophiolite. The sole-type amphibolites from the associated mélange unit, however, yield ages (93 94 Ma; Celik et al., 2006) similar to those obtained from the soles of the Lycian ophiolites, indicating simultaneous underplating of oceanic lithosphere. 3. Sample description and petrography The samples used in this study were collected from the Lycian and Antalya ophiolite suites in SW Turkey as described above (Fig. 1). Care was taken to sample least serpentinized and most representative rocks from different mantle lithologies. The mantle portions of these two ophiolites are similar in terms of rocks types and petrographic characteristics. They are composed mainly of cpx-poor harzburgites, commonly interpreted as residues of partial melting of a lherzolitic mantle during mantle rise beneath active spreading centers (e.g. Nicolas, 1986). Small amounts of cpx-bearing harzburgites and lherzolites are observed along with the depleted harzburgites. In terms of the field relationships of different lithological types the mantle sections of these ophiolites display compositional heterogeneities. The main part of the mantle section in both ophiolites is composed of highly depleted harzburgites with b4% of modal cpx, but m-scale to 100-m-scale domains of cpx-bearing harzburgites and lherzolites with 4.5 to 9% modal cpx sparsely distributed in some parts of the ophiolites. The local gradations of depleted to cpx-bearing harzburgite and lherzolite show no systematic structural and geographical pattern, but are most commonly observed to the northwest of Koycegiz in the Lycian ophiolite and to the north of Tekirova in the coastal part of Antalya ophiolite (Fig. 1b). These cpxbearing peridotites usually form elongated lenses, mostly parallel to the tectonite fabric, or irregular patches in the cpx-depleted harzburgites, generally about 1 10 m long and 1 4 m wide, but up to several tens of meters in diameter. The occurrence of mantle residues with distinct mineral modes within a single thrust sheet of peridotite may be interpreted to reflect heterogeneous melt depletion in different parts of the mantle sections in these ophiolites.

3 E. Aldanmaz et al. / Lithos 113 (2009) Fig. 1. (a) Simplified tectonic map of the Eastern Mediterranean region showing the distribution of Neotethyan ophiolites (modified from Dilek et al., 2007). Key to abbreviations: NAF=North Anatolian Fault; EAF=East Anatolian Fault; DSF=Dead Sea Fault; IASZ=Izmir Ankara Suture Zone; BZSZ=Bitlis Zagros Suture Zone. (b) Simplified geological map showing the distribution of ophiolite bodies in SW Turkey (modified from Okay et al., 2001).

4 Table 1 Whole-rock major oxide and trace element data for the representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO27 KO18 KO19 KO20 KO112 KO1 KO3 ANT1 ANT7 ANT8 KO7 KO10 KO110 Rock type Lhz Lhz Lhz Lhz Hzb Hzb Hzb Lhz Hzb Hzb Lhz Hzb Hzb Hzb Hzb Hzb Petrological type MOR MOR MOR MOR MOR MOR MOR MOR MOR MOR MOR MOR MOR SSZ SSZ SSZ Locality Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Tekirova Tekirova Tekirova Koycegiz Koycegiz Koycegiz Primary modal compositions (%) Oliv Opx Cpx Sp wt.% SiO TiO Al 2 O Fe 2 O MnO MgO CaO Na 2 O L.O.I Total ppm Sc Cr V Ni Co Cu Zn Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu E. Aldanmaz et al. / Lithos 113 (2009)

5 Sample name KO105 KO108 KO103 KO115 S33 S36 S37 MAR24 MAR30 ANT6 ANT9 ANT11 ANT31 ANT30 ANT33 ANT37 ANT3 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Du Petrological type SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ Locality Koycegiz Koycegiz Koycegiz Koycegiz Lake Salda Lake Salda Lake Salda Marmaris Marmaris Tekirova Tekirova Tekirova Tekirova Adrasan Adrasan Adrasan Adrasan Primary modal compositions (%) Oliv Opx Cpx Sp SiO TiO Al 2 O Fe 2 O MnO MgO CaO Na 2 O L.O.I Total Sc Cr V Ni Co Cu Zn Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu E. Aldanmaz et al. / Lithos 113 (2009)

6 696 E. Aldanmaz et al. / Lithos 113 (2009) Table 2 Olivine average major element compositions for the representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO27 KO18 KO19 KO20 KO112 KO1 KO3 ANT7 ANT8 KO7 KO10 KO110 Rock type Lhz Lhz Lhz Lhz Hzb Hzb Hzb Lhz Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO FeO MnO MgO CaO NiO Total Fo Sample name KO105 KO108 KO103 KO115 S33 S36 S37 MAR24 MAR30 ANT6 ANT9 ANT31 ANT30 ANT33 ANT37 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO FeO MnO MgO CaO NiO Total Fo Both ophiolites also include dunites forming discordant patches or layers parallel to the main foliation. In parts of the ophiolitic sections, abundant chromite deposits are accompanied by large elongated dunite lenses hosted in basal units of harzburgites. Contacts between the dunite lenses and their host harzburgites are mostly sharp but the dunite envelops around chromite bodies grade outward into harzburgite. The lherzolites and harzburgites from the two suites are moderately serpentinized with the degree of serpentinization ranging between ~30 and 65% and increasing from lherzolites to harzburgites. The two most common textures observed are protogranular and medium to coarsegrained porphyroclastic. Protogranular types have weakly deformed textures of olivine and orthopyroxene, such as undulose extinction or kink bands in olivine and kinked or distorted lamellae in pyroxenes. Porphyroclastic rocks contain orthopyroxenes that form isolated large crystals with often resorbed shapes. Clinopyroxenes in these rocks form either small crystals with strong lobate boundaries or, in some cases, small blebs exsolved from orthopyroxenes. Brown colored, holly leafshaped spinels are commonly observed in association with orthopyroxenes. In some rare cases, spinels constitute subhedral crystals at olivine grain boundaries. The dunites are the least serpentinized rocks (with the degree of serpentinization b30%) among the ultramafics. They display porphyroclastic to mylonitic textures, with minor clinopyroxene and disseminated spinel. Coarse olivine crystals are usually elongated and display undulatory extinction and strain lamella. They are, in most cases, surrounded by finegrained olivines exhibiting a mylonitic texture. The clinopyroxene is diopside and forms individual small crystals at olivine boundaries. The Table 3 Orthopyroxene average major element compositions for the representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO27 KO18 KO19 KO20 KO112 KO1 KO3 ANT7 ANT8 KO7 KO10 KO110 Rock type Lhz Lhz Lhz Lhz Hzb Hzb Hzb Lhz Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO CaO Na 2 O Total Mg# Cr# Sample name KO105 KO108 KO103 KO115 S33 S36 S37 MAR24 MAR30 ANT6 ANT9 ANT31 ANT30 ANT33 ANT37 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO CaO Na 2 O Total Mg# Cr#

7 E. Aldanmaz et al. / Lithos 113 (2009) spinel is chromium-rich and occurs as subhedral and euhedral crystals with homogeneous chemical compositions. In some samples, chromian spinels exhibit rims of magnetite or chromian magnetite, developed during hydrothermal alteration. 4. Analytical techniques Whole-rock major oxide and trace element abundances of the peridotites (Table 1) were measured at the Department of General and Analytical Chemistry, Leoben University (Austria). In order to obtain representative major and trace element analyses of coarse-grained peridotites, rock powders were prepared from at least 2 kg of material and crushed to powders in a disk mill. Glass disks were prepared using Li 2 B 4 O 7 after the samples were dried at 110 C and heated to 1000 C to determine loss on drying and ignition. Major element concentrations were determined on glass disks with a wavelength dispersive X-ray fluorescence spectrometer (ARL Fisons Instruments 8410) and trace element concentrations were determined using inductively coupled plasma mass spectrometer (ICP-MS) after acid digestion. Major oxide analyses of spinels, olivines and pyroxenes from the peridotite samples were determined with two microprobes. Some of the samples were analyzed on a CAMECA SX100 electron microprobe at the Université Blaise Pascal (France), while another set of samples were analyzed on a JEOL JXA-8200 electron microprobe at ETH Zurich (Switzerland). Operating conditions for both sets of measurements were 15 kv accelerating voltage, 20 na beam current and s counting time depending upon the element. Synthetic and natural mineral standards were employed to obtain reliable results for the mantle phases analyzed in this study. Mineral analyses of peridotites represent average mineral compositions (Tables 2 5) within each polished thin section. Trace elements of clinopyroxenes were measured in-situ on polished thick sections (N80 μm) by LA-ICP-MS at ETH Zurich. Ablation was performed in a He atmosphere by an ArF Excimer laser (193 nm) with a pulse energy of 100 mj and a pulse repetition rate of 5 Hz. The ablated material was flushed in a continuous argon flow into the torch of an ELAN 6100 DRC ICP-MS. Analyses of a maximum of 10 unknowns were bracketed by measurement of an external standard (NIST SRM 610) to allow linear drift correction. To correct for differences in the ablation yield between standard and samples, 43 Ca and 30 Si were used as internal standards. For each cpx, 3 12 analyses were performed within the grain cores, average compositions are listed in Table Bulk-rock geochemistry 5.1. Major oxides The peridotites display a remarkably variable degree of fertility with a range of MgO from 40 to 48 wt.%. The MgO contents increase systematically from lherzolite to harzburgite to dunite and can be considered as an index of melt depletion (e.g. Parkinson and Pearce, 1998). Abundances of CaO and Al 2 O 3 range between and wt.%, respectively, and display well-defined inverse linear correlations with MgO. TiO 2 concentrations show convex downward trends reaching very low abundances at high MgO contents (Table 1; Fig. 2a c). Although some samples have fertile average major element compositions with CaO and Al 2 O 3 N2 wt.% and MgO b43 wt.%, the majority of the peridotites are moderately to highly depleted and are more refractory than fertile upper mantle (Fig. 2a b). This depletion trend, which is accompanied by a decrease of the modal abundances of clinopyroxene and increase of those of olivine, is, to a first order, consistent with the formation of the peridotites as mantle residues from variable extent of basaltic melt extraction (Fig. 2). The negative SiO 2 MgO trend that is steeper than expected for residues of partial melting, and the relatively higher FeO values for some of the samples, however, cannot be explained by simple mantle melting followed by melt extraction (Fig. 2d e). Similar characteristics in abyssal peridotites have been previously interpreted to have resulted from olivine addition (Kelemen et al., 1997; Niu et al., 1997) Trace elements The chondrite-normalized whole-rock REE patterns for the peridotites are shown in Fig. 3. Also plotted for comparison are Table 4 Clinopyroxene average major element compositions for the representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO27 KO18 KO19 KO20 KO112 KO1 KO3 ANT7 ANT8 KO7 KO10 KO110 Rock type Lhz Lhz Lhz Lhz Hzb Hzb Hzb Lhz Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO CaO Na 2 O Total Mg# Cr# Sample name KO105 KO108 KO103 KO115 S33 S36 S37 MAR24 MAR30 ANT6 ANT9 ANT31 ANT30 ANT33 ANT37 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO CaO Na 2 O Total Mg# Cr#

8 698 E. Aldanmaz et al. / Lithos 113 (2009) Table 5 Spinel average major element compositions for the representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO27 KO18 KO19 KO20 KO112 KO1 KO3 ANT7 ANT8 KO7 KO10 KO110 Rock type Lhz Lhz Lhz Lhz Hzb Hzb Hzb Lhz Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO Total Cr# Mg# F (% melting) a Fe +3/ Fe (FMQ) ΔlogfO Sample name KO105 KO108 KO103 KO115 S33 S36 S37 MAR24 MAR30 ANT6 ANT9 ANT31 NT30 ANT33 ANT37 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb SiO TiO Al 2 O Cr 2 O FeO MnO MgO Total Cr# Mg# F (% melting) Fe +3/ Fe (FMQ) ΔlogfO a from Hellebrand et al. (2001). calculated melting residues of fractional melting of a source similar to depleted MORB mantle (DMM). The samples have low total REE contents, with LREE abundances between 0.98 and 0.02 times chondrite whilst HREE abundances vary between 1.50 and 0.16 times chondrite. The small number of lherzolite samples in Fig. 3a are characterized by a slight LREE depletion (La N /Yb N = ) with a flat to slightly fractionated HREE segments (Sm N /Yb N = ; Fig. 3a), consistent with the theoretical assessment of the melting of an undepleted lherzolite source and a relatively small degree of melt extraction (~4 6%). Most of the cpx-bearing harzburgites, however, exhibit smoothly decreasing concentrations from HREE to MREE, but are enriched in LREE (La N /Sm N = ). LMREE profiles of these samples are inconsistent with simple melting residues. The cpx-poor harzburgites and dunites show concave patterns with fractionated HREE segments and have U-shaped REE profiles owing to pronounced LREE enrichments relative to MREE and HREE (Sm N /Yb N =0.02 to 0.62; La N /Sm N =2.06 to 43.48; Fig. 3b). Although the slopes of MREE-HREE, which is defined by decreasing trace element contents from the HREE to the MREE, are consistent with relatively large degrees of mantle melting (15 to 25%), the slopes and patterns of LREE cannot be explained by melting of a mantle source with any degree of fertility. Similar REE patterns are, in fact, widely observed in variably depleted mantle residues from different tectonic environments such as oceanic ridges and marginal basins and are usually interpreted as resulting from extensive interaction between LREE-enriched melt and strongly LREE-depleted residue (e.g. Suhr, 1999; Pearce et al., 2000; Niu, 2004). The variations of REE with the melt depletion index of Al 2 O 3 in Fig. 4 exhibit a more scattered distribution of Nd and Sm relative to Yb (for the cpx-poor harzburgites and dunites in particular), suggesting that elements with a higher degree of incompatibility are more affected by metasomatic processes (D Nd ND Sm ND Yb ). Overall the whole-rock REE patterns of the peridotites imply a multi-stage evolution; most of the peridotites have experienced reenrichment in highly incompatible LREE. This suggests that the peridotites have been metasomatized by strongly LREE-enriched liquids (hydrous fluids or melts). A more rigorous modeling of trace element evolution of the mantle phases during melting will be presented after describing mineral chemical characteristics of the peridotites. 6. Mineral chemistry 6.1. Major oxide variations of primary mantle phases The mineral compositions of spinel peridotites from SW Turkey are typical of mantle phases, and no significant within-sample variation was observed during analysis. Olivines from the two ophiolites are compositionally similar and homogeneous. They are Mg rich with a compositional range of Mg# [=molar Mg/(Mg+Fe tot )] from to (Table 2). The range of Mg#, as well as NiO ( wt.%) and MnO ( wt.%), is similar to those of olivines from abyssal peridotites and mantle relicts in ophiolites (e.g. Bonatti and Michael, 1989; Takazawa et al., 2003). Olivines in dunite and cpxpoor harzburgites have higher Mg# than in cpx-bearing harzburgites, consistent with a higher degree of melt depletion of cpx-poor mantle rocks. The CaO contents of olivines are very low (b0.02 wt.%) and show no correlation with Mg# of olivine. Orthopyroxenes are represented by enstatite with a compositional range of Wo En Fs The Mg#s vary from to 0.923, which are similar to or slightly, but constantly, higher than those of coexisting olivines, implying that the Fe Mg distribution between the two phases reflects complete chemical equilibrium (Fig. 5a). Orthopyroxenes in dunites and cpx-poor harzburgites have higher Mg# and SiO 2 content, and lower Al 2 O 3, TiO 2 and Na 2 O than in lherzolites and cpx-bearing harzburgites. The Cr 2 O 3 contents vary significantly from 0.03 to 0.89 wt.% with Cr#s exhibiting a welldefined correlation with melt depletion indices (Table 3). Both TiO 2

9 E. Aldanmaz et al. / Lithos 113 (2009) Table 6 Trace element compositions of clinopyroxenes (in ppm) in representative peridotite samples from SW Turkey. Sample name KO22 KO23 KO26 KO18 KO112 ANT2 ANT8 KO7 KO10 Rock type Lhz Lhz Lhz Hzb Lhz Hzb Hzb Hzb Hzb Petrological type MOR MOR MOR MOR MOR MOR MOR SSZ SSZ Locality Koycegiz Koycegiz Koycegiz Koycegiz Koycegiz Tekirova Tekirova Koycegiz Koycegiz Sc V Co Cu Zn Ga Sr Y Zr Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sample name KO108 KO103 KO115 S33 MAR24 MAR30 ANT31 ANT30 ANT33 Rock type Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Hzb Petrological type SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ SSZ Locality Koycegiz Koycegiz Koycegiz Lake Salda Marmaris Marmaris Tekirova Adrasan Adrasan Sc V Co Cu Zn Ga Sr Y Zr Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu and Al 2 O 3 decrease with increasing Mg# of orthopyroxene from 0.12 to 0.01 wt.% and from 5.13 to 1.04 wt.%, respectively. Clinopyroxenes are generally represented by TiO 2 and Na 2 O-poor diopsides with a compositional range of Wo En Fs The Mg# varies from to and displays a well-defined correlation with those of olivines (Fig. 5b). The Cr 2 O 3 contents increase significantly from 0.24 to 1.27 wt.% with increasing Mg#. The clinopyroxenes in most of the peridotites are characterized by increasing TiO 2 and Na 2 O, and decreasing CaO with increasing Al 2 O 3. TiO 2 and Al 2 O 3 of clinopyroxenes decrease from 0.23 to 0.01 wt.% and from 5.94 to 0.67 wt.%, respectively, but are not correlated with Mg# (Table 4). Non-systematic variation of Na 2 O and TiO 2 contents of clinopyroxenes with melt depletion indices such as clinopyroxene Mg# and whole-rock Mg# indicates that compositional features of some of the samples cannot be explained solely by simple partial melting. Spinels display a remarkably large variation in spinel Cr# [=molar Cr/(Cr+Al)] and form two compositionally distinct ranges. Spinels in the lherzolites and cpx-bearing harzburgites are aluminous with Cr# ranging between and 0.280, indicating a moderately fertile character. Compositions of these aluminous spinels are rather comparable to those in abyssal peridotites (Dick and Bullen,1984). Spinels in the cpx-poor harzburgites and dunites, on the other hand, are significantly depleted in aluminum with Cr# ranging from to and are compositionally similar to mantle spinels from plate convergence settings (Dick and Bullen, 1984; Parkinson and Pearce, 1998). A clear

10 700 E. Aldanmaz et al. / Lithos 113 (2009) Fig. 2. Variations of whole-rock SiO 2,Al 2 O 3, CaO, FeO and TiO 2 concentrations as a function of MgO in the peridotites from SW Turkey. The curves represent the residues of incrementally isentropic polybaric batch melting calculated using the MELTS thermodynamic approach. The curves correspond to melting pressures of 1.5, and 2.0 GPa. The major element variations are consistent with the calculated trends of experimental results for low-pressure (b1.5 GPa) partial melting of spinel lherzolites. compositional gap between these two petrological types in terms of spinel Cr# may indicate different petrogenetic histories. The extremely low TiO 2 (b0.01 wt.%) contents of the spinels from both our ophiolite suites attest to the residual nature of the samples. The Mg#s of spinels range from to Spinels in dunites and cpx-poor harzburgites have lower MgO, and higher FeO contents than in lherzolites and cpxbearing harzburgites (Table 5). The composition of residual phases in peridotites changes continuously during partial melting. For example, Fe contents of silicate minerals, and Al contents of spinel decrease with increasing degree of partial melting, whereas Mg of silicate minerals and Cr of spinel generally increase. Therefore, the Mg/Fe ratio or Mg# of silicate minerals, and Cr/Al ratio or Cr# of spinel are indicators of the degree of partial melting (e.g. Dick and Bullen, 1984; Arai, 1987, 1994; Hellebrand et al., 2001).

11 E. Aldanmaz et al. / Lithos 113 (2009) similar to the clinopyroxenes from other cpx-bearing peridotites of the same suite (Fig. 7a). Relatively higher M-HREE concentrations, which are close to equilibrium concentrations with MORB melt, suggest that these clinopyroxenes are not residues of simple melt extraction, but could be explained by crystallization of a trapped melt component. Clinopyroxenes from more depleted, cpx-poor harzburgites, exhibit significantly different REE patterns from those in the cpx- Fig. 3. Chondrite-normalized REE patterns for (a) the lherzolites and cpx-bearing harzburgites, and (b) the cpx-poor harzburgites and dunites from SW Turkey. Also plotted for comparison (the grey curves) is the range of model residual mantle compositions calculated using the modeling of near-fractional melting for different amounts of melt extraction (2% to 20% meting within thespinelstability fieldwiththe parameters described in Niu (2004)). Normalizing values are from Anders and Grevesse (1989). Fig. 6 illustrates the variations in mineral compositions in the peridotite samples employing Cr# in spinel vs. Mg# in coexisting olivine, all samples plotting within, or close to, the olivine-spinel mantle array (or residual peridotite array) defined by Arai (1994). Linear variation of the spinel Cr# and forsterite content of olivine indicates a residual origin of the peridotites. The relatively large range in spinel Cr# and olivine Mg# may result from a wide range of degrees of mantle melting. The two distinct ranges of spinel Cr#, represented by (1) lherzolites and cpx-bearing harzburgites and (2) cpx-poor harzburgites and dunites, possibly indicate mantle melting in different geotectonic settings Clinopyroxene trace element chemistry Clinopyroxenes from the spinel peridotites display two distinct ranges of compositions consistent with the whole-rock and mineral major element compositions of the rocks. Clinopyroxenes from the lherzolites and cpx-bearing harzburgites are characterized by strong LREE depletions (Sm N /Lu N = ) with flat HREE segments (Er N / Lu N = ; Fig. 7a b). These chemical characteristics closely resemble those of clinopyroxenes in abyssal peridotites (e.g. Johnson et al., 1990), the formation of which is usually explained by small degree melt extraction from a mantle source similar in composition to the MORB mantle. A small number of lherzolite samples from the Lycian ophiolites, however, contain clinopyroxenes with higher concentrations of incompatible trace elements than expected for melting residues. Trace element compositions of these clinopyroxenes show enrichments of 2 to 10 times those of clinopyroxenes from the least depleted lherzolites, although their normalized multi-element patterns are Fig. 4. Variations of chondrite-normalized concentrations of (a) Nd, (b) Sm, and (c) Yb with the melt depletion index of Al 2 O 3 for the peridotites from SW Turkey. The theoretical melt depletion trend was calculated using the parameters described in Fig. 3.

12 702 E. Aldanmaz et al. / Lithos 113 (2009) The peridotites from the entire suite display a strong correlation between mineral chemistry and HREE abundances of clinopyroxene. The strong negative correlation between Yb content in clinopyroxene and Cr# of spinel (Fig. 8) yields trends overlapping with the calculated melt depletion trend. Among the entire suite, the only exceptions include a few exsolved clinopyroxene blebs (in orthopyroxenes) present in the most depleted dunites, and clinopyroxenes present in the melt-metasomatized lherzolites within the lycian suite. Clinopyroxene grains in the former are extremely depleted in incompatible elements, while those in the latter slightly deviate from the melting trend with their relatively higher abundances of incompatible elements than predicted for simple melting (Fig. 8). In summary, REE, Zr, and Ti concentrations of clinopyroxenes from the highly depleted, cpx-poor peridotites are markedly different from the concentrations of these elements in abyssal peridotites, while clinopyroxenes from most of the cpx-bearing lherzolites and harzburgites have trace element patterns similar to those from abyssal peridotites. The highly depleted cpx-poor peridotites are characterized, in particular, by very low concentrations of trace elements, but by marked enrichments in the LREE and Zr relative to Ti and HREE. This type of enrichment has been commonly reported from ophiolite peridotites, and their origin are usually explained by either melt mantle interaction involving chromatographic fractionation of percolating melt (e.g., Bodinier et al.,1990; Batanova et al., 1998; Godard et al., 2000) or metasomatic interaction of subduction fluids with the mantle peridotites in SSZ melting regions (e.g. Parkinson and Pearce,1998; Bizimis et al., 2000; Batanova and Sobolev, 2000; Barth et al., 2003; Choi et al., 2008). 7. Petrogenetic considerations 7.1. Oxygen fugacity and mantle redox state during melting We have applied the oxygen barometer based on Fe Mg olivinespinel exchange (Ballhaus et al., 1991) to calculate oxygen fugacity for Fig. 5. The relationship between Mg# of olivine and pyroxenes of the peridotites from SW Turkey. The solid lines represent theoretical isothermal equilibrium lines for exchange reactions with different Fe/Mg distribution coefficients between olivine and orthopyroxene. bearing peridotites (Fig. 7c d). The majority of the samples have concentrations of the HREE which are significantly more depleted than the abyssal peridotite range. They are characterized by REE patterns with smoothly decreasing abundances from the HREE to the MREE, consistent with the residual origin of the samples. Additionally, they have significantly lower absolute abundances of H-MREE than the pyroxenes from the cpx-bearing peridotites, suggesting that they are residual to larger degrees of melt depletion than the cpx-bearing peridotites. The samples, however, exhibit various concentrations of clinopyroxene LREE (Fig. 7c d), some of which are depleted in LREE with a steep slope from middle to light REE, consistent with basaltic melt extraction, while others display U-shaped patterns in their middle to light REE segments owing mainly to significantly elevated concentrations of LREE compared to what could be expected for melting residues. The high field strength elements (HFSE) Zr and Ti in clinopyroxenes from the entire suite have low concentrations of ppm and ppm, respectively. Zr and Ti concentrations of clinopyroxenes from our cpx-bearing peridotites show marked depletions with respect to their neighboring REEs in normalized diagrams (Fig. 7a b). Clinopyroxenes from the cpx-poor peridotites have less pronounced negative Ti and Zr anomalies and are characterized by significant Ti/Zr fractionation (Fig. 7 c d). Fig. 6. Plot of spinel Cr# against olivine Mg# for the peridotites from SW Turkey. The approximate fields for abyssal (ocean ridge) peridotites (Dick and Bullen, 1984), the oceanic arc peridotites and passive continental margin peridotites (Pearce et al., 2000) are also shown for comparison. The olivine spinel mantle array and melting trend are from Arai (1994).

13 E. Aldanmaz et al. / Lithos 113 (2009) Fig. 7. Chondrite-normalized trace element compositions of clinopyroxenes for the peridotites from the Lycian (a c) and the Antalya (b d) ophiolites of SW Turkey. Normalizing values are from Anders and Grevesse (1989). Abyssal peridotite field is defined by the data from Johnson et al. (1990), Johnson and Dick (1992) and Hellebrand et al. (2001). the spinel peridotites. The calculations involve ferric iron contents of the spinels, which can be estimated with adequate precision from electron microprobe data using secondary standardization (e.g. Wood and Virgo, 1989). Calculated oxygen fugacities for the peridotites are given in Table 5 and illustrated in Fig. 9 where oxygen fugacity relative to the FMQ (fayalite magnetite quartz) buffer at 1.0 GPa is plotted against the Cr# in spinel. Most of the investigated lherzolites and cpx-bearing harzburgites from SW Turkey are moderately reduced (Fig. 9), with oxidation states similar to abyssal peridotites considered to be equivalent to present-day reduced oceanic mantle (e.g., Parkinson and Arculus, 1999). This, along with the absence of a clear correlation between fo 2 and spinel Cr# for the cpxbearing peridotites, indicates that the melting that produced these peridotites did not involve large amounts of water. A small number of lherzolite samples, i.e. those which contain clinopyroxenes with incompatible trace element concentrations greater than expected for melt residues, however, are significantly more oxidized with fo 2 between +0.5bFMQb+1.0. The more oxidizing conditions of these samples might be attributed to fluid solid interaction associated with the passage of more oxidizing metasomatic fluids, which increased the Fe +3 /ΣFe ratio of the spinel without altering their Cr/Al ratio significantly. The relatively more depleted, cpx-poor harburgites and dunites from SW Turkey, on the other hand, exhibit a positive correlation of Cr# with Δlogf FMQ O 2 (Fig. 9). As a whole, they form a compositional trend from the upper end of abyssal peridotites to the oceanic arc field. Among this largely depleted group, some samples have low oxygen fugacities, but the majority of the peridotites plot close to a compositional space represented by peridotites from oceanic arc and SSZ mantle.

14 704 E. Aldanmaz et al. / Lithos 113 (2009) Fig. 8. Compositional relationship between the Cr# of spinel and the Yb concentration of clinopyroxene in peridotites from SW Turkey. Partial melting trend is defined as a combination of changing the compositions of spinel (Hellebrand et al., 2001) and clinopyroxene (Johnson et al., 1990) with degree of partial melting within the spinel stability field. Numbers along the line are percent melting. Data sources for the approximate field of abyssal peridotites are as in Fig. 7. The peridotites, as a whole, display mineral chemical and phase equilibria characteristics indicative of formation in two distinct tectonic settings, i.e. typical mid-ocean ridge (MOR) and suprasubduction zone (SSZ) environments. Among these, lherzolites and cpx-bearing harzburgites from both the Lycian and Antalya ophiolites correspond to MOR peridotites, while cpx-poor harzburgites and dunites correspond to SSZ peridotites. In the following sections these two discrete types will be referred to as MOR- and SSZ-type peridotites. residue trends. Melting is modeled as incremental batch melting of spinel facies lherzolite, assuming no reaction between the mantle residue and extracted melt. Most of the clinopyroxenes from the least refractory MOR-type peridotites plot in the field of abyssal peridotites and can be modeled as residues after 5 to 9% anhydrous melting of a MORB source. A distinctive feature in a few lherzolite samples from the Lycian ophiolites, however, is their anomalous enrichments in immobile incompatible trace elements while they have clinopyroxenes with Ti and Dy contents similar to the MORB source. Such a characteristic is difficult to reconcile with simple melting, as the low degrees of melting (b5%) required for the high Ti and Dy contents of clinopyroxenes from these samples is not reflected by their spinel Cr#. These enrichments are most easily explained by some element addition probably through melt infiltration and possibly clinopyroxene crystallization from a trapped melt component. The chemical composition of these melt-impregnated lherzolites can therefore be interpreted in terms of interaction between ocean ridge magma and pre-existing oceanic lithosphere. High Al/Cr ratios of spinels from these lherzolites further indicate that this particular domain of oceanic lithosphere is the residue to relatively small degrees of melting (~7 8%). The interacting melt had a somewhat higher oxygen fugacity (+0.5bFMQb+1) and lower Cr# ( ) suggesting that it was compositionally similar to, but slightly more oxidized than MORB melt. The calculated melting trajectory for anhydrous melting of a MORB source (Fig. 10) predicts the composition of clinopyroxenes from the chemically undisturbed MOR-type peridotites, but fails to reconcile the composition of clinopyroxenes from more refractory, SSZ-type harzburgites and dunites. Clinopyroxenes from these highly depleted peridotites plot on the extension of the anhydrous melting trend towards lower abundances of Ti and Dy, suggesting that they are the residues of higher degrees of melting than the MOR peridotites. Experiments show that clinopyroxene disappears from the residual mineralogy after ~22% anhydrous melting and further melting would proceed with significantly decreased melt productivity (Johnson et al., 1990). In contrast, mantle fluxing by hydrous fluids or melts released from 7.2. Nature and extent of partial melting A number of studies have highlighted the well-defined correlation between the degree of partial melting and Cr# of residual spinels in mantle relicts sampled as ophiolites or abyssal peridotites (e.g. Dick and Bullen, 1984; Batanova et al., 1998; Hellebrand et al., 2001). On the basis of spinel Cr#, the MOR-type and SSZ-type peridotites from SW Turkey are represented by two distinct ranges of degree of melt extraction with a clear compositional gap between the two (Table 5; Fig. 6). These two distinct types can be explained in terms of 5 9% and ~13 25% of total melt extraction, respectively. The nature and degree of melt extraction for mantle residues may also be adequately determined employing high field strength element concentrations (Ti, Zr, Y, Al, HREE), i.e. with the elements least affected by post-melting processes and low-temperature alteration (e.g. Pearce et al., 2000; Niu, 2004). In fact, co-variations of these elements with each other and with melt depletion indices in most of our peridotite samples indicate that the concentrations of these elements were shaped primarily by mantle melting and were not significantly affected by secondary processes. In particular, relative abundances of these elements in residual clinopyroxenes from peridotites constrain the melting history of the rocks, as clinopyroxene is extremely resistant to alteration and preserves its high temperature chemical signatures even in severely serpentinised mantle relicts (e.g. Johnson et al., 1990). In this study, therefore, following the approach of Bizimis et al. (2000), we have quantified the extent of melt extraction using the HFSE and HREE variations in the peridotite clinopyroxenes. On a plot of Ti vs Dy (Fig. 10), we compared the compositions of the peridotite clinopyroxenes from SW Turkey with calculated melt Fig. 9. Plot of ΔlogfO 2 (FMQ) against Cr# of spinel for the peridotite samples from SW Turkey. The approximate fields for abyssal (mid-ocean ridge) peridotites, arc peridotites and continental (margin) peridotites are shown for comparison (Parkinson and Pearce, 1998). Solid and dashed arrows denote the trends for residual peridotite compositions interacting with MORB and SSZ melts respectively. The data are consistent with two distinct origins for the peridotites: (1) formation as residues after melting in reduced conditions for the lherzolites and cpx-bearing harzburgites; and (2) formation by interaction between lithospheric mantle protoliths of ocean ridge and SSZ magmas for the cpx-poor harzburgites and dunites.