Central Anatolian Ophiolite Research Articles

Timing of the subduction initiation and ophiolite emplacement of the inner Tauride Ocean: Insight from the Pınarbaşı ophiolite in Central Türkiye

Late Cretaceous ophiolites are widespread in southern Türkiye, including the Tauride Belt Ophiolites and the Central Anatolian Ophiolites. Here, we report new geological, geochemical, geochronological, and zircon isotopic data from ophiolitic rocks of the Pınarbaşı ophiolite (Eastern Tauride Belt). The Pınarbaşı ophiolite forms incomplete sequences, with its mantle section dominated by serpentinized harzburgite and chromitites, while the crustal section comprises ultramafic and mafic cumulates. Whole-rock and mineral chemistry data suggest a supra-subduction zone origin. LA-ICP-MS zircon U-Pb age of 88.2 ± 0.4 Ma (MSWD = 0.84) was obtained from a plagiogranite dyke cutting serpentinized peridotite of the Pınarbaşı ophiolite. Another, U-Pb zircon crystallization age of 96.8 ± 0.6 Ma (MSWD = 1.53) was obtained from a plagiogranite dyke within the mélange of the Pınarbaşı ophiolite. Hafnium isotope compositions of these zircons (εHf(t) = +26.4 to +3.1) suggest a depleted to slightly enriched mantle source. The formation ages of the crustal rocks (gabbro, plagiogranite, and dolerite) of the Cretaceous ophiolites in the Tauride Belt from this and previous ophiolite occurrences, suggest that supra-subduction zone ophiolites in the Inner Tauride Ocean formed during the period ∼101–87 Ma. On the other hand, the peak metamorphism of the metamorphic sole rocks is reported to have occurred around ∼104 Ma. According to all available petrogenetic and geochronological data, it is considered that the supra-subduction zone crust developed shortly (∼ 3–4 Myr) after the initiation of intra-oceanic subduction and this lasted ∼10–15 Myr.

Conditions and timing of incorporation of ophiolite into orogenic crust during oblique convergence, Central Anatolia

Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern, highest grade part of the CAO, raising questions about the tectonic relationship of the ophiolite to underlying metasedimentary and plutonic rocks. New geochronology results show that the 40Ar/39Ar hornblende age of amphibolite-facies metagabbro in the high-grade metamorphic part of the CAO is ~ 87 Ma, similar to hornblende ages from amphibolite in the underlying Nigde metamorphic/plutonic massif. Biotite in a deformed quartzofeldspathic rock associated with high-grade meta-ophiolitic rocks yielded an 40Ar–39Ar age of ~ 78 Ma, similar to biotite ages from the Nigde Massif. Hornblende in gabbro from unmetamorphosed CAO yielded an older 40Ar/39Ar age of ~ 90 Ma, similar to the previously determined crystallization age of the ophiolite. These data indicate that the southern part of the ophiolite was incorporated into and therefore metamorphosed and deformed with the orogenic mid-crust now exposed in the Nigde metamorphic–plutonic complex, whereas the northern, unmetamorphosed part of the ophiolite was obducted onto the continent. This distinct difference in different parts of the ophiolite may indicate oblique collision or irregularities in the continental margin, resulting in part of the ophiolite being incorporated into the orogenic crust and subsequently exhumed and cooled with it, and another part being obducted.

Tectonic evolution and paleogeography of the Kırşehir Block and the Central Anatolian Ophiolites, Turkey

In Central and Western Anatolia two continent-derived massifs simultaneously underthrusted an oceanic lithosphere in the Cretaceous and ended up with very contrasting metamorphic grades: high pressure, low temperature in the Tavsanli zone and the low pressure, high temperature in the Kirsehir Block. To assess why, we reconstruct the Cretaceous paleogeography and plate configuration of Central Anatolia using structural, metamorphic, and geochronological constraints and Africa-Europe plate reconstructions. We review and provide new 40Ar/39Ar and U/Pb ages from Central Anatolian metamorphic and magmatic rocks and ophiolites and show new paleomagnetic data on the paleo-ridge orientation in a Central Anatolian Ophiolite. Intraoceanic subduction that formed within the Neotethys around 100–90 Ma along connected N-S and E-W striking segments was followed by overriding oceanic plate extension. Already during suprasubduction zone ocean spreading, continental subduction started. We show that the complex geology of central and southern Turkey can at first order be explained by a foreland-propagating thrusting of upper crustal nappes derived from a downgoing, dominantly continental lithosphere: the Kirsehir Block and Tavsanli zone accreted around 85 Ma, the Afyon zone around 65 Ma, and Taurides accretion continued until after the middle Eocene. We find no argument for Late Cretaceous subduction initiation within a conceptual “Inner Tauride Ocean” between the Kirsehir Block and the Afyon zone as widely inferred. We propose that the major contrast in metamorphic grade between the Kirsehir Block and the Tavsanli zone primarily results from a major contrast in subduction obliquity and the associated burial rates, higher temperature being reached upon higher subduction obliquity.

Identification of Chrysotile in Local Soil at Beypinari Village (Sivas-Turkey) Regarding Mine and Health Issue

Abstract Asbestos is dangerous for health and is forbidden to use in Turkey, but villagers who live in rural eastern part still use it especially for their home for insulation purposes and even as a substitute for baby powder. Therefore, geological and chemical properties of this type of soil, which is near the settlement, should be characterized and identified from the point of view of health. Beypinari asbestos deposits are located at Beypinari village, about 90 km southeast of Sivas, Turkey within Central Anatolian Ophiolites. Therefore, in the present study, the existence of chrysotile in Beypinari asbestos deposit were characterized and identified by mineralogical analysis and by major, trace, REE analysis. The results show that the samples contain different amount of calcite mineral, the main mineral being chrysotile.

Geological, petrological, and geodynamical characteristics of the Karacaali Magmatic Complex (Kırıkkale) in the Central Anatolian Crystalline Complex, Turkey

Mafic and felsic igneous rocks in the Karacaali Magmatic Complex (KMC) in the northwestern margin of the Central Anatolian Crystalline Complex (CACC) are classified into 4 groups: i) granitoid pluton including granite, granodiorite, and monzonite; ii) a few meter-scale porphyritic microgranite enclaves within the hybrid rocks; iii) hybrid rocks formed by mixing/mingling of mafic lavas (basaltic/diabasic/lamprophyric), anorthositic, and/or rhyolitic lavas; iv) diabasic dykes/veins within the granitoid pluton. Major element composition of the granitoid pluton and porphyritic microgranite enclaves within the hybrid rocks indicate subalkaline, calc-alkaline, and mostly I-type characteristics. These rocks are mainly peraluminous with aluminum saturation index > 1, but mainly between 1 and 1.1, indicating transitional peraluminous. On the tectonomagmatic discrimination diagrams (Y vs. Nb and (Y+Nb) vs. Rb diagrams), all the granitic and monzonitic rock suites from the complex fall mostly in the VAG+Syn-COLG and VAG fields respectively, suggesting arc-related origin. On the R1 vs. R2 tectonic diagram, the granitic rocks display distribution from preplate collision to syncollision field, but quartz-monzonitic samples plot within the postcollision uplift field. Based on limited geological, petrographic, and geochemical results, the tectonomagmatic evolution of the KMC can be summarized as follow: i) initiation of subduction of the Inner Tauride oceanic lithosphere beneath the CACC during the Late Cretaceous time; ii) underplating of partial melts derived from subducted slab and/or mantle wedge, which provided enough heat for partial melting of the mafic lower crust and generation of granitic magma; iii) slab detachment following the continent–continent collision that resulted in tensional forces within the overlying continental crust, which allowed the intrusion of the granitic magma to the upper crust, also cutting the central Anatolian ophiolites, from the Late Cretaceous to most likely the Paleocene time. The hybrid rocks formed by mixing/mingling of the mafic, anorthositic, and/or rhyolitic magmas most likely indicate their injection into a partly crystalline granitic magmatic system just after crystallization of granitic magma in the upper crust. However, this model is open to discussion and needs to be investigated using isotope data in future studies.

^{207}Pb-^{206}Pb, ^{40}Ar-^{39}Ar and Fission-Track Geothermochronology Quantifying Cooling and Exhumation History of the Kaman-Kırşehir Region Intrusions, Central Anatolia, Turkey

The Kaman-Kırşehir region intrusions were generated in a post-collisional extensional setting following Cenomanian-Turonian docking of an oceanic island arc, comprising the supra-subduction zone (SSZ) Central Anatolian ophiolite (CAO), onto the Tauride-Anatolide Platform (TAP). These granitoids have been named, from N to S, the Çamsarı quartz syenite, Hamit quartz syenite, Bayındır nepheline-cancrinite syenite, Durmuşlu nepheline-nosean-melanite syenite porphyry and Baranadağ quartz monzonite. They intrude the crustal metasediments of the Central Anatolian Crystalline Complex (CACC) and CAO and are unconformably overlain by Upper Paleocene to Lower-Middle Eocene sediments. The single-zircon ^{207}Pb-^{206}Pb evaporation age of the Çamsarı unit is 95.7±5.1 Ma; those of the Hamit and Baranadağ units are indistinguishable with a weighted mean of 74.3±4.5 Ma. The amphibole ^{40}Ar-^{39}Ar ages of the Hamit and Baranadağ units are almost identical with a weighted mean of 72.7±0.1 Ma. The apatite fission-track age vs elevation plot for the Çamsarı, Hamit, Durmuşlu and Baranadağ samples reveals rapid exhumation (>1 km/Ma) between ~57 and ~61 Ma, consistent with the results of track-length modelling. This Early-Middle Paleocene rapid exhumation is thought to result from uplift triggered by continent (TAP) - continent (Eurasian plate; EP) collision following the closure of İzmir-Ankara-Erzincan (İAE) ocean that also initiated the formation of peripheral foreland basins in central Anatolia.

Geochemical Comparison of Ultramafic-Mafic Cumulate Rocks from the Central Anatolian Ophiolites, Turkey

Ophiolites, formed during closure of the Neo-Tethyan ocean, are widespread in Turkey and have been extensively studied. In addition to ophiolites showing recognizable stratigraphic sequences, numerous massive and layered gabbroic masses occur as isolated outcrops in the Central Anatolian Crystalline Complex. An example from the Akcakent region ranges from gabbro to diorite; another, from the Kustepe area, is characterized by dunite, wehrlite, troctolite, olivine gabbro, clinopyroxene gabbro, clinopyroxene hornblende gabbro, uralite gabbro, and fine-grained gabbro. Samples from both regions display adcumulate and orthocumulate textures and show low-K and subalkaline characters; they are enriched in some LILE (e.g., Sr, Rb, K, Ba) and depleted in HFSE (e.g., Ta, Nb, Zr, Ti) relative to N-MORB. Petrological data, negative Ta, Nb, Zr, Ti anomalies, and ratios of elements such as Ba/Nb and La/Nb indicate a suprasubduction setting for the central Anatolian ultramafic-mafic rocks, suggesting that both rock types may have formed in a backarc setting.

Timing of post-obduction granitoids from intrusion through cooling to exhumation in central Anatolia, Turkey

The Middle to Late Cretaceous central Anatolian granitoids intrude the supra-subduction zone-type central Anatolian ophiolite and medium- to high-grade metasediments of central Anatolian crystalline complex and are overlain by Late Palaeocene to Early/Middle Eocene sediments. Their single-zircon 207Pb– 206Pb evaporation ages define three clusters: (1) Cenomanian–Turonian (weighted-mean age: 94.9 ± 3.4 Ma), (2) Turonian–Santonian (85.5 ± 5.5 Ma) and (3) Campanian (74.9 ± 3.8 Ma). Their hornblende and biotite 40Ar– 39Ar and K–Ar cooling ages cluster around 80–65 Ma. The close hornblende and biotite ages reflect rapid exhumation of a mid-crustal section during the Campanian–Maastrichtian. Early to Middle Palaeocene (57–62 Ma) apatite fission-track age clusters date the tail end of this exhumation episode. It is proposed that the central Anatolian granitoid melts were generated in a post-collisional extensional setting following the docking of an oceanic island arc onto the Tauride–Anatolide platform. Campanian–Maastrichtian to Early/Middle Palaeocene rapid exhumation event is considered to result from continent–continent collisions between Eurasian plate and the Tauride–Anatolide platform along the İzmir–Ankara–Erzincan suture zone.

A GEOCHEMICAL ATTEMPT TO DISTINGUISH FOREARC AND BACK ARC OPHIOLITES FROM THE “SUPRA-SUBDUCTION” CENTRAL ANATOLIAN OPHIOLITES (TURKEY) BY COMPARISON WITH MODERN OCEANIC ANALOGUES

The Central Anatolian Ophiolite (CAO) includes oceanic crust and mantle fragments and contains all the components of a typical ophiolitic sequence: metamorphic tectonites, cumulates, isotropic gabbros, plagiogranites, dolerite sheeted dykes, basaltic lavas and sedimentary cover. They are found as dismembered but partially preserved allochthonous bodies in the Central Anatolian Crystalline Complex (CACC) representing the metamorphosed passive northern edge of the Tauride-Anatolide Platform (TAP), central Turkey. Geochemically, the magmatic rock units of the CAO display part of a dominant co-magmatic differentiated series of island-arc tholeiites (IAT). In addition, IAT are overlain by a subordinate group of boninite-like basalts which are chemically and mineralogically intermediate between IAT and more depleted boninites. The variations in lava chemistry of the CAO reflect eruption of progressively more depleted magmas through time and point to diverse mantle source compositions and partial melting. Detailed chemical analyses of the magmatic units of the CAO revealed typical supra-subduction zone (SSZ) features with depleted high field strength elements (HFSE) and light rare earth elements (LREE: LaN/YbN: < 1) and enriched large-ion lithophile elements relative to normal mid-oceanic ridge (NMORB) and back-arc basin basalts (BABB). In this respect the CAO is similar to oceanic crust generated in the Izu-Bonin and Mariana fore arcs. A N-MOR or BAB spreading seems unlikely. However, progressive depletion in the lava sequence and absence of calc-alkali basalts and their differentiates indicate that the CAO formed at an initial stage of subduction from previously depleted MORB mantle (DMM) and oceanic lithosphere, prior to development of any island arc within the Vardar-I . zmir-Ankara-Erzincan (VIAE) ocean segment of Neotethys. Accordingly, a forearc setting proposed for the genesis of the CAO is inappropriate and misleading. It was generated above a short-lived north-dipping nascent intra-oceanic subduction zone during early-middle Turonian-early Santonian, then, it was rapidly emplaced southwards onto the CACC, soon after formation between post-early Santonian and pre-middle Campanian.

High-K, calc-alkaline I-type granitoids from the composite Yozgat batholith generated in a post-collisional setting following continent-oceanic island arc collision in central Anatolia, Turkey

The composite Yozgat batholith consists of a S-I-A-type granitoid association intruding the supra-subduction zone-type (SSZ-type) central Anatolian ophiolite and medium- to high-grade metasedimentary rocks of the central Anatolian crystalline complex. These rocks are unconformably covered by Palaeocene to Early Eocene sedimentary rocks. The I-type granitoids are the most common rock association of this huge batholith. In an area between the towns of Şefaatli and Yerkoy, the southwestern part of the batholith can be subdivided into five mappable units: the Akcakoyunlu quartz monzodiorite (mafic; hornblende K-Ar cooling ages of 77.6–79.3 Ma); the Cankili monzodiorite (mafic; hornblende K-Ar cooling age of 71.1 Ma); the Adatepe quartz monzonite (mafic; hornblende K-Ar cooling age of 68.0 Ma); the Yassiagil monzogranite (felsic; hornblende + biotite K-Ar cooling ages of 69.9–79.8 Ma) and the Karakaya monzogranite (felsic; hornblende + biotite K-Ar cooling ages of 71.3–77.0 Ma). All the lithological units, except the Karakaya monzogranite, include large K-feldspar megacrysts and various types of mafic microgranular enclaves in field outcrops, indicating mingling and mixing. In addition, microscopic textures showing the hybridization between the coeval mafic and felsic magma sources are present. Whole-rock major element geochemistry shows a high-K calc-alkaline, metaluminous, I-type composition with an aluminium saturation index (ASI) less than 1.10 and with CIPW diopside content in all the lithological units. Large ion lithophile elements (LILE), light rare earth elements (LREE), some high field strength elements (HFSE) (except Nb) enrichments and significant crustal contribution revealed by the oxygen and sulphur stable isotope compositions in the mafic and felsic I-type granitoid units are consistent with mafic lower crustal and metasomatized mantle sources the latter of which were metasomatized by earlier supra subduction zone (SSZ)-derived fluids during the development of the SSZ-type central Anatolian ophiolite.

207Pb– 206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey

207Pb– 206Pb single-zircon evaporation age determinations carried out on nine different granitoid units of central Anatolia, Turkey have yielded three distinct granitoid groups with different emplacement ages. These are (1) Cenomanian–Turonian granitoids, with a weighted mean age (wma) of 94.9 ± 3.4 Ma; (2) Turonian–Santonian granitoids, with a wma of 85.5 ± 5.5 Ma; and (3) Campanian granitoids, with a wma of 74.9 ± 3.8 Ma. The spatial and temporal relationships between the formation of the metamorphic sole of the supra-subduction zone-type Central Anatolian Ophiolite (SSZ-type CAO), crustal metamorphism of the Central Anatolian Crystalline Complex (CACC), and the emplacement of Cenomanian–Turonian to Turonian–Santonian granitoids indicate a geodynamic setting in which all these geological events occurred quasi-simultaneously in central Anatolia. Such a geodynamic setting is thought to be related to the Cenomanian–Turonian collision of the Tauride–Anatolide Platform (TAP) and an oceanic island arc, including the SSZ-type CAO. The Campanian granitoids appear to be the continuation of this collision-related protracted magmatism in central Anatolia.

Oxygen and sulfur isotope geochemistry revealing a significant crustal signature in the genesis of the post-collisional granitoids in central Anatolia, Turkey

Late Cretaceous granitoid rocks from central Anatolia comprise S-I-A-type plutons derived from the collisional stages of the Neo-Tethyan convergence system in central Turkey. These granitoids intrude the tectonic imbrication zone consisting of blocks of supra-subduction zone-type (SSZ-type) central Anatolian ophiolite and crustal metasediments which are present in the İzmir-Ankara-Erzincan suture zone. The plutons are overlain by Late Palaeocene-Early Eocene or younger detrital sediments. Granitoid formation is thought to be related to magma generation processes occurring in a post-collisional lithospheric detachment-related geodynamic setting that resulted from slab break-off or lithospheric delamination. Whole-rock S and quartz/feldspar O isotope data from these plutons yields a broad range of values, and both parameters indicate a nearly exclusively supracrustal origin for the S-type granites, as well as a significant crustal contribution in the genesis of the hybrid I-type and A-type granitoids. The more mafic I-type and A-type granitoid rocks of any given suite have lower S and O values, indicative of their larger degree of mantle component. The combined stable isotope geochemical compositions, when coupled with major, trace and REE geochemistry and regional geology, provide evidence that the significant crustal contribution originated from a metasomatized mantle layer which was affected by earlier SSZ-derived fluids, and then accreted into the subcontinental lithosphere as collision occurred. The partial melting of such a metasomatized mantle layer in a post-collisional extensional geodynamic setting, supplied either by the slab break-off or lithospheric delamination mechanisms, provided the significant crustal signature in the hybrid magmas of the Late Cretaceous I-type and A-type granitoids in central Anatolia, Turkey.

K–Ar age, whole-rock and isotope geochemistry of A-type granitoids in the Divriği–Sivas region, eastern-central Anatolia, Turkey

The bimodal, A-type Dumluca and Murmana granitoids consist of felsic monzonitic/syenitic and mafic gabbroic/dioritic and monzogabbroic/monzodioritic rocks, which were intruded into the Cenomanian–Turonian supra subduction zone-type Divriği ophiolitic mélange. New hornblende and biotite K–Ar dates yield cooling ages ranging from 72 to 77 Ma, and from 68 to 77 Ma for the felsic and mafic rocks, respectively, in the Dumluca and Murmana granitoids. Felsic and mafic rocks of these intrusions have a metaluminous, high-K alkaline composition, however, highly evolved members of the felsic rocks are peraluminous in character. Trace element geochemistry data indicate that mafic and felsic rocks have their own geochemical characteristics which show different sources. The combined evidence of the trace element, radiogenic and stable isotope geochemistry from the Dumluca and Murmana granitoids suggest that the mafic rocks were derived exclusively from an enriched mantle mafic magma (EM II), but the felsic rocks were derived from a hybrid felsic magma. The hybrid felsic magma was generated by the mixing of the mantle-derived mafic with another crustal-derived silicic melt. The composition of some mafic rocks from Murmana granitoid suite is thought to be derived from an enriched mantle source that may have been metasomatized by earlier subduction-derived fluids, thus carrying the subduction signature in the source material. The local and regional geology suggest an early Late Cretaceous post-collisional extension-related geodynamic setting, following the collision between the Tauride–Anatolide platform and an oceanic island arc comprising the supra subduction zone-type central Anatolian ophiolite.

Vermiculitization of Phlogopite in Metagabbro, Central Turkey

AbstractDioctahedral vermiculite occurs in an isolated metagabbro klippe (Kurançalı Metagabbro) that belongs to the Central Anatolian Ophiolites from central Turkey. Both the metagabbro and the structurally underlying high-grade metamorphic rocks are intruded by granitic rocks. The Kurançalı Metagabbro is characterized by its well-developed compositional layering, and the presence of vermiculitized phlogopiterich layers. Petrographic and mineralogie studies show that the primary mineral phases in the host rock are diopside, tschermakitic hornblende, Fe-rich phlogopite, and plagioclase. Secondary minerals are hornblende, actinolitic hornblende, Fe-rich phlogopite, and vermiculite. A two-phase history of alteration involving acidic weathering and alkaline metasomatism is suggested for the dioctahedral vermiculite and secondary Fe-rich phlogopite, respectively. The alteration of phlogopite to dioctahedral vermiculite proceeded both along cleavage planes and at crystal edges. The vermiculite is colorless to pale yellow with weak pleochroism and shows optical continuity with the parent mineral. Vermiculite flakes, analyzed semi-quantitatively by scanning electron microscope-energy dispersive analysis (SEM-EDS) and electron microprobe (EMP), are characterized by partially expanded interlayers, K depletion, and Mg and/or A1 enrichment. X-ray diffraction (XRD) and differential thermal analysis-thermal gravimetric (DTA-TG) analyses indicate that phlogopite is not a pure phase, although it is the dominant one. The XRD patterns show the presence of both dioctahedral vermiculite having dehydrated interlayers and hydroxy-Al interlayers, and interstratified phlogopite-vermiculite. The transformation of phlogopite to vermiculite is thought to represent an initial stage of weathering in an acidic environment.

FORMATION AND EMPLACEMENT AGES OF THE SSZ-TYPE NEOTETHYAN OPHIOLITES IN CENTRAL ANATOLIA, TURKEY: PALAEOTECTONIC IMPLICATIONS

Isolated outcrops of dismembered ophiolitic rocks occur as allochthonous units (Central Anatolian Ophiolites, CAO) in the Central Anatolian Crystalline Complex, which represents the metamorphosed passive northern edge of the Tauride- Anatolide Platform. Both stratigraphic observations and chemical data indicate that the CAO formed in a supra-subduction zone (fore arc) setting within the Vardar-Izmir- Ankara-Erzincan (VIAE) segment of the Neotethys. The epi-ophiolitic, sedimentary cover of the Sarikaraman Ophiolite, which is a representative unit of the CAO, is characterized by epiclastic, volcanogenic, deep-sea sediments, with the latter being intercalated with debris-flows. The most significant planktonic foraminiferal association found in the lowest pelagic member of this unit indicates an early-middle Turonian to early Santonian age. K/Ar data (81-65 Ma) collected from post-collisional granitoids intruding both the basement rocks and the Sarikaraman Ophiolite imply a post-early Santonian to pre-middle Campanian emplacement age for the CAO. The high volume of epiclastic volcanogenic sediments that occur alternated with both the pelagic limestones and the radiolarites of the CAO suggests that the depositional setting was a marginal sea adjacent to a volcanic arc. The occurrence of debris-flows indicates also that the depositional basin was affected by tectonism, that resulted in major slides and mass-gravity reworking of preexisting units and of arc-derived volcanics and sediments. The stratigraphy and the age of formation and obduction of the CAO were compared with other supra-subduction zone type ophiolites of both the eastern (Turkey) and the western (Greece) parts of the VIAE segment of the Neotethys. This comparison indicates that the western intraoceanic subduction is definitely older. Accordingly, we surmise that important transform faults were separating the continental micro-plates within the VIAE-ocean (e.g. the Tauride-Anatolide microplate) during the closure of this oceanic branch.

CLINOPYROXENE COMPOSITIONS OF THE ISOTROPIC GABBROS FROM THE SARIKARAMAN OPHIOLITE: NEW EVIDENCE ON SUPRA-SUBDUCTION ZONE TYPE MAGMA GENESIS IN CENTRAL ANATOLIA

The middle Turonian-early to Campanian Sarikaraman Ophiolite (SO) is one of the least dismembered ophiolitic units of the allochthonous Central Anatolian Ophiolites, and retains a recognizable pseudostratigraphy. The lowermost part of the SO is characterized by gabbros which are cut by random or en-echelon pegmatite veins. The clinopyroxenes within the isotropic gabbro sequence are small, colorless relicts with cloudy appearance. In most of the samples, they resulted completely replaced by successive generation of green to brown amphiboles. The EMP analyses of fresh clinopyroxenes from 5 selected samples display diopsitic to augitic compositions within the range of En45Fs5Wo49 to En50Fs9Wo41. They are Ca-rich (Wo41-49) and Na poor (Na2O<0.55) and characterized by high-Mg (Mg# = 81.4-91.19) and low-Ti (<0.68 wt %) contents. The composition of the SO clinopyroxene is characterized by low to very low values of Ti, and is thus similar to other well-known supra-subduction zone-type ophiolites, such as Troodos, Pindos, and Oman. When the concentration of clinopyroxene of the SO is compared to modern basalts formed in different settings (MORB, IAT and BON, Beccaluva et al., 1989), the SO samples match the island arc basalts, with some shift towards the boninite field. The most significant chemical characteristic of the clinopyroxene of the SO is the low-Ti content, which resulted 2-3 times lower of the values typically found in MORB basalts. The latter feature is also consistent with the generally low Ti content found in the basaltic lavas of the SO, and might indicate that the primary melt was probably formed by partial melting of a severely depleted upper mantle. In conclusion, the occurrence of a high-Mg and low-Ti magma constrains the formation of the Sarikaraman ophiolitic gabbro to a supra-subduction zone setting. The clinopyroxenes of the Sarikaraman Ophiolite show similar chemical compositions of other supra-subduction zone-type, Eastern Mediterranean ophiolites (e.g. Troodos, Varinous, Pindos and Oman ophiolites) that show island-arc affinity.

Formation and emplacement ages of the SSZ-type Neotethyan ophiolites in Central Anatolia, Turkey: palaeotectonic implications

Isolated outcrops of ophiolitic rocks, termed the Central Anatolian Ophiolites, are found as allochthonous bodies in the Central Anatolian Crystalline Complex, that represent the metamorphosed passive northern edge of the Tauride–Anatolide Platform, central Turkey. In terms of pseudostratigraphic relationships of the magmatic units and their chemical designation, the Central Anatolian Ophiolites exhibit a supra-subduction zone (fore-arc) setting within the Vardar–İzmir–Ankara–Erzincan segment of the Neotethys. The epi-ophiolitic sedimentary cover of the Central Anatolian Ophiolites is generally characterized by epiclastic volcanogenic deep-sea sediments and debris flows intercalated with pelagic units. The richest and most significant planktonic foraminiferal association recorded from the lowest pelagic members infer a formation age of early–middle Turonian to early Santonian. K/Ar ages of post-collisional granitoids (81–65 Ma) intruding the basement rocks as well as the Central Anatolian Ophiolites suggest a post-early Santonian to pre-middle Campanian emplacement age. The marked high volume of epiclastic volcanogenic sediments intercalated with the pelagics of the Central Anatolian Ophiolite is suggestive of rifting in a marginal sea adjacent to a volcanic arc. Penecontemporaneous tectonism is reflected in repetitions in the stratigraphy and in debris flows, which result from major slides and mass-gravity reworking of pre-existing units and of arc-derived volcanics and sediments. Correlating the rock units and formation/obduction ages of the Central Anatolian Ophiolites with further supra-subduction zone type ophiolites in the eastern (Turkey) and western (Greece) parts of the Vardar–İzmir–Ankara–Erzincan segment of Neotethys we conclude that the intraoceanic subduction in the east is definitely younger and the closure history of this segment is more complex than previously suggested. Copyright © 2000 John Wiley & Sons, Ltd.

Geochemistry of Volcanic Rocks from the Çiçekdağ, Ophiolite, Central Anatolia, Turkey, and Their Inferred Tectonic Setting within the Northern Branch of the Neotethyan Ocean

Abstract The Central Anatolian Ophiolites (CAO) comprise a number of little studied Upper Cretaceous ophiolitic bodies that originally represented part of the northern branch of the Neotethyan ocean. The Çiçekdağ Ophiolite (CO) is an dismembered example of this ophiolite group that still retains a partially preserved magmatic pseudostratigraphy. The following units (bottom to top) can be recognized: (1) layered gabbro; (2) isotropic gabbro: (3) plagiogranite; (4) dolerite dyke complex; (5) basaltic volcanic sequence; and (6) a Turonian-Santonian epi-ophiolitic sedimentary cover. The magmatic rock units (gabbro, dolerite and basalt) form part of a dominant comagmatic series of differentiated tholeiites, together with a minor group of primitive unfractionated basalts. The basaltic volcanics mainly consist of pillow lavas with a subordinate amount of massive lavas and rare basaltic breccias. Petrographic data from the least altered pillow lavas indicate that they were originally olivine-poor, plagioclase-clinopyroxene phyric tholeiites. Immobile trace element data from the basalt lavas and dolerite dykes show a strong subduction-related chemical signature. Relative to N-mid-ocean ridge basalt the Çiçekdağ basaltic rocks (allowing for the effects of alteration) have typical suprasubduction zone features with similarities to the Izu-Bonin Arc, i.e. enriched in most large-ion lithophile elements, depleted in high field strength elements and exhibiting depleted light rare earth element patterns. The geochemical characteristics are similar to other eastern Mediterranean Neotethyan SSZ-type ophiolites and suggest that the CO oceanic crust was generated by partial melting of already depleted oceanic lithosphere within the northern branch of the Neotethyan ocean. The Çiçekdağ body, along with the other fragmented CAO, is thus representative of the Late Cretaceous development of new oceanic lithosphere within an older oceanic realm.

Terlemez quartz monzonite of Central Anatolia (Aksaray-Sarıkaraman): age, petrogenesis and geotectonic implications for ophiolite emplacement

The Terlemez quartz monzonite is one of the Central Anatolian Granitoids and is exposed to the east of one of the main granitoid belts trending in a NW–SE direction and situated at the western end of the Central Anatolian Crystalline Complex. The Terlemez quartz monzonite is medium- to coarse-grained with granoblastic texture. It is essentially composed of quartz, plagioclase, hornblende and K-feldspar and variable contents of biotite. It is mostly compact and massive, but close to the contact with the ophiolitic basic rocks it shows a chilled margin. It characteristically includes K-feldspar megacrysts up to 3 cm in width and 10 cm in length, and contains irregular, angular or sub-rounded micromafic granular enclaves as well as xenoliths and large ‘roof-pendants’ of gabbroic composition derived from the Sarıkaraman Ophiolite, which is the most representative member of the supra-subduction zone type of Central Anatolian Ophiolites. The Terlemez quartz monzonite is a calc-alkaline, metaluminous intrusion. It typically displays moderately developed negative Ba and Nb trace element anomalies and enrichment in light rare earth elements relative to heavy rare earth elements without any significant Eu, Sr and Ti anomalies. On the basis of field, petrographic and geochemical data, the Terlemez quartz monzonite has been classified as H-type (hybrid type), which requires significant input from a mantle-derived mafic magma. The intrusion represents the advanced stage of the post-collisional magmatism of the Central Anatolian Crystalline Complex. Unlike the other Central Anatolian Granitoids, the Terlemez quartz monzonite has a clear intrusive contact with the well studied Middle Turonian–Lower Santonian Sarıkaraman Ophiolite. The K-Ar hornblende age obtained from the quartz monzonite (81·5 ± 1·9 Ma) is interpreted as the intrusion age. These data suggest a post-Early Santonian to pre-Early Campanian emplacement age for the supra-subduction zone type of Central Anatolian Ophiolites. The data further suggest that the post-collisional magmatism in Central Anatolia post-dates the emplacement of fore arc-type ophiolites onto the passive margin of the Tauride–Anatolide platform. The very short time interval between the formation and emplacement ages of supra-subduction zone-type ophiolites seems to be a very typical feature of the fore arc-type Eastern Mediterranean Ophiolites. Copyright © 1999 John Wiley & Sons, Ltd.

Supra-subduction zone ophiolites of Central Anatolia: geochemical evidence from the Sarikaraman Ophiolite, Aksaray, Turkey

AbstractThe Central Anatolian Crystalline Complex (CACC), situated between the northern and southern oceanic strands of Neotethys, contain a number of little-studied ophiolitic bodies of late Cretaceous age that have a bearing on the Mesozoic development of this region. The pillow lavas and sheeted dykes of the Sarikaraman Ophiolite were originally a comagmatic differentiated series of vesicular, aphyric and olivine-poor, plagioclase—clinopyroxene phyric tholeiites, but now exhibit greenschist facies assemblages. A set of late dolerite dykes cross-cutting the whole volcanic sequence are more chemically evolved and were probably derived from a different source. Relative to N-MORB the lavas and dykes are enriched in some LIL elements (K, Rb, Cs, U, Th and Sr) and depleted in HFS elements (Nb, Ta, Hf, Zr, Ti and Y) and light REE. In terms of immobile elements the ophiolitic basalts have the broad chemical characteristics of island are tholeiites that were formed in a supra-subduction zone setting, whereas the late dykes are more akin to N-MORB. In this respect the Sarikaraman Ophiolite is similar to other ophiolites found in the eastern Mediterranean region and emphasizes the preservation of this particular environment in the CACC. If all the Central Anatolian Ophiolites (of which the Sarikaraman Ophiolite is one example) were derived via southward thrusting from the Vardar-Izmir-Ankara-Erzincan Ocean branch to the north, age relationships suggest that this segment of ocean crust was relatively short-lived before obduction onto the CACC.