Browsing by Author "Yaliniz M.K."
Now showing 1 - 10 of 10
Results Per Page
Sort Options
Item Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey(Elsevier B.V., 1998) Floyd P.A.; Yaliniz M.K.; Goncuoglu M.C.Plagiogranites associated with the Sarikaraman ophiolite of the Central Anatolian Crystalline Complex, Turkey, closely resemble other plagiogranites from supra-subduction zone-type ophiolites of Neotethys. The ophiolite is remarkable in displaying a higher proportion of the plagiogranite suite (ca. 10% by volume) than is usually associated with such bodies. The Sarikaraman plagiogranites are represented by intrusive sheets and netvein trondhjemites largely developed at the top of the upper gabbros and as multiphase dykes within the sheeted dyke complex. The plagiogranite dykes are considered to feed extrusive silicified rhyolites associated with the basaltic lavas in the volcanic section of the ophiolite. Field relations suggest that the trondhjemites were probably generated from the roof section of a dynamic and evolving gabbroic magma chamber. Both the deep-seated trondhjemites and the volcanic rhyolites constitute the Sarikaraman plagiogranite suite. Geochemically there is complete overlap between the intrusive trondhjemites and extrusive rhyolites, which are characterised by (MORB-normalized) low HFS element contents with small negative Nb-Ta anomalies and variably enhanced LIL element abundances. Unlike other plagiogranites, however, the Sarikaraman suite is not characterized by consistently low K2O contents; a feature that reflects the variable mobilization of the LIL elements under lower greenschist facies conditions. The REE are uniformly enriched relative to the basic components of the complex, but have similar normalized patterns exhibiting mild light REE depletion. In terms of their origin, the initial or most primitive plagiogranite melts could have been generated by either fractional crystallization (70-85% of clinopyroxene-feldspar ± amphibole) or partial melting (5-15% batch melting) of a gabbroic 'source material', although only the first process can produce most of the range of the plagiogranite compositions. As a group the plagiogranites exhibit some degree of internal variation which can be generated by further fractionation largely dominated by feldspar with minor apatite and amphibole. © 1998 Elsevier Science B.V.Item A geotraverse across northwestern Turkey: Tectonic units of the Central Sakarya region and their tectonic evolution(2000) Göncüoǧlu M.C.; Turhan N.; Şentürk K.; Özcan A.; Uysal S.; Yaliniz M.K.In the Central Sakarya area of Turkey there are two main Alpine continental units, separated by a south verging ophiolitic complex which represents the root zone of the Izmir-Ankara Suture Belt. The Central Sakarya Terrane in the north includes two 'Variscan' tectonic units in its basement. The Sogut Metamorphic rocks represent a Variscan ensimatic arc complex and the Tepekoy Metamorphic rocks are characteristically a forearc-trench complex. The unconformably overlying Triassic Sogukkuyu Metamorphic rocks correspond to a part of the Karakaya Formation and are interpreted as a Triassic rift basin assemblage. These units are unconformably overlain by a transgressive sequence of Liassic-Late Cretaceous age that represents the northeastward deepening carbonate platform of the Sakarya Composite Terrane. The middle tectonic unit (the Central Sakarya Ophiolitic Complex) comprises blocks and slices of dismembered ophiolites, blueschists and basic volcanic rocks with uppermost Jurassic-Lower Cretaceous radiolarite-limestone interlayers. Geochemical data from basalt blocks suggest mid-ocean ridge basalt (MORB)- and suprasubduction-type tectonic settings within the Neotethyan Izmir-Ankara Ocean. The southern tectonic unit includes basal polyphase metamorphosed clastic rocks (Somdiken Metamorphics), intruded by felsic and basic dykes and overlain by thickbedded marbles. This assemblage is unconformably overlain by continental clastic rocks gradually giving way to thick-bedded recrystallized limestones, cherty limestones and pelagic limestones intercalated with radiolarites, and finally by a thick high pressure-low temperature (HP-LT) metamorphic synorogenic flysch sequence. This succession is identical to the passive continental margin sequences of the Tauride Platform. It is suggested that this passive margin was subducted during the Late Cretaceous in an intra-oceanic subduction zone and affected by HP-LT metamorphism. The emplacement of the allochthonous oceanic assemblages and the collision with the Central Sakarya Terrane was complete by the end of the Cretaceous.Item Petrology and geotectonic significance of plagiogranite from the Sarikaraman Ophiolite (Central Anatolia, Turkey)(2000) Yaliniz M.K.; Floyd P.A.; Göncüoǧlu M.C.Plagiogranites within the supra-subduction zone (SSZ) type Sarikaraman Ophiolite (SO), Central Anatolia, are very fine to coarse grained leucocratic rocks with a range of occurrences as simple narrow fracture infilling to wide complex zones of net-veining or agmatites with numerous, partly assimilated enclaves of gabbro and dolerite. Petrographically, they are characterized by the textures ranging from hypidiomorphic granular to granophyric intergrowths of quartz and plagioclase. Geochemically, major and trace elements data revealed that the plagiogranites belong to the typically low-potassium series of ophiolitic complexes and show similar geochemical characteristics with the Ocean-Ridge Granites. They are characterized by 10-20 times enriched flat chondrite REE patterns with a negative Eu anomalies relative to mafic component in the SO. This confirms the cogenetic nature of the plagiogranites and indicates progressive fractionation in the Sarikaraman mafic magma. Field observations coupled with major-element and trace element chemistry support to a model by which the plagiogranites of SO could be formed as a fractional crystallization of Sarikaraman basaltic magma in SSZ setting, like the other eastern Mediterranean ophiolitic plagiogranites such as Troodos, Pindos, and Oman.Item Geochemical character and tectonic environment of Neotethyan ophiolitic fragments and metabasites in the Central Anatolian Crystalline Complex, Turkey(2000) Floyd P.A.; Göncüoǧlu M.C.; Winchester J.A.; Yaliniz M.K.The Central Anatolian Crystalline Complex (CACC) or Kirsehir Block is part of the metamorphosed leading edge of the Tauride-Anatolide Carbonate Platform. It contains oceanic remnants derived from the Neotethys Ocean (Izmir-Ankara-Erzincan branch) which separate it from the Sakarya microcontinent. Two tectonic units are distinguished: an amphibolite facies Mesozoic 'basement', dominated by platform marbles, over which is thrust a younger fragmented Upper Cretaceous ophiolite sequence. Three metabasite horizons were sampled to reconstruct the development of the oceanic components: (1) fragmented Upper Cretaceous (90-85 Ma) stratiform ophiolitic members comprising gabbros, sheeted dykes, basalt lavas and pelagic sediments thrust over all other units; (2) a tectonised admixture of basite, ultramafic and felsic blocks in an ophiolitic melange (Upper Cretaceous matrix) thrust over the basement metamorphic rocks; and (3) amphibolites concordant with 'basement' marbles and minor pelagics of the largely (?)Triassic Kaleboynu Formation in the lower part of the carbonate platform. Metabasalts and metagabbros from isolated fragments of the stratiform ophiolites form geochemically coherent groups and indicate the influence of a subduction component during their development. It is considered that the suprasubduction zone ophiolites record the association of a tholeiitic arc and an adjacent back-arc basin with more mid-ocean ridge basalt (MORB)-like compositions. Metabasite blocks within the tectonised ophiolitic melange slice are MORB like, together with minor ocean island basalt (OIB) and island arc basalts, and may be tectonically related to ophiolitic units within the accretionary wedge of the Ankara Melange. Concordant amphibolites of the Kaleboynu Formation are largely OIB types and reflect an early ensialic rifting stage of the Tauride-Anatolide Carbonate Platform. Small ocean basins also developed at this time, as recorded by the presence of MORB and associated pelagics. The CACC block, together with parts of the Ankara Melange, are considered to represent oceanic lithosphere (comprising both early spreading centre and latter subduction-influenced crust) and continental carbonate platform that were subsequently ejected from an accretionary-subduction complex on collision with the Sakarya microcontinent.Item Formation and emplacement ages of the SSZ-type Neotethyan ophiolites in Central Anatolia, Turkey: Palaeotectonic implications(John Wiley and Sons Ltd, 2000) Yaliniz M.K.; Göncüoglu M.C.; Özkan-Altiner S.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-Izmir-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 intercalculated 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-Izmir-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 (C) 2000 John Wiley and Sons, Ltd.Item Petrology of the Kurancali phlogopitic metagabbro: An island arc-Type ophiolitic sliver in the Central Anatolian Crystalline Complex(2001) Toksoy-Köksal F.; Göncüoglu M.C.; Yaliniz M.K.The Kurancali metagabbro occurs as an isolated body in the central part of the Central Anatolian Crystalline Complex. It has been emplaced along a steep S-vergent thrust-plane onto the uppermost units of the Central Anatolian Metamorphics. The main body of the Kurancali metagabbro is characterized by distinct compositional layering. The layered gabbros comprise pyroxene and hornblende gabbros. Phlogopite-rich, plagioclase-hornblende gabbro occurs mainly as pegmatitic dikes intruding the layered gabbro sequence. The layered gabbros, in general, consist mainly of diopsidic augites, brown hornblendes, and plagioclase. Secondary phases are phlogopitic mica, brownish-green hornblende replacing clinopyroxenes, and fibrous, greenish actinolitic hornblende partially or completely replacing brown hornblende. The primary dark micas are phlogopitic in the range of phlogopite (57-70) and annite (30-43). The analyzed pyroxenes are diopsidic distinct groups of rocks; a less pronounced group of phlogopite gabbro with island-arc calc-alkaline affinities, and a dominating layered gabbro sequence with island-arc tholeiite characteristics. They are extremely enriched in LILE, indicative of alkaline metasomatism in the source region, and display geochemical features of transitional backarc-basin basalts (BABB)/island-arc basalts (IAB)-and IAB-type oceanic crust. Based on their geochemical similarities to modern island-arc basements, we suggest that the Kurancali metagabbro may represent the basement of an initial island arc, generated in a supra-subduction zone setting within the Izmir-Ankara branch of Neotethys.Item Petrology of the Kurancali phlogopitic Metagabbro: An Island arc-type ophiolitic sliver in the central Anatolian Crystalline complex(2002) Toksoy-Koksal F.; Goncüoglü M.C.; Yaliniz M.K.In the Central Anatolian Crystalline Complex (CACC), besides the ophiolitic bodies with more or less recognisable sequence and preserved magmatic pseudostratigraphy, there are many massive and layered gabbroic masses occurring as isolated outcrops. Most of these mafic rocks were interpreted as dismembered parts of an allochthonous ophiolitic assemblage (Yaliniz et al, 2000), derived from the northerly located Izmir-Ankara branch of the Alpine Neotethys. An overall supra-subduction zone genesis has been envisaged for the Central Anatolian Ocean (CAO). However, remarkable differences in the geochemical characteristics of different isolated outcrops suggest differences in the source areas and tectonic settings within the intra-oceanic subduction zone. One of these gabbro units, the Kurancali Metagabbro, occurs as an isolated body in the central part of CACC. It is thrust along a steep south vergent thrust-plane onto the uppermost units of the Central Anatolian Metamorphics (CAM). The main body of the Kurancali Metagabbro is characterised by a distinct compositional layering. The layered gabbros are represented by pyroxene and hornblende gabbros. Phlogopite-rich plagioclase-hornblende gabbro occurs mainly as pegmatitic dikes intruding the layered gabbro sequence. The layered gabbros in general consist mainly of diopsidic augites, brown hornblendes, plagioclase. Secondary phases are phlogopitic mica, brownish green hornblende replacing clinopyroxenes, and fibrous greenish actinolitic hornblende partially or completely replacing brown hornblende. The primary dark micas display phlogopitic composition within the range of annite30.13-42.60 and plogopite 69.9-57.4 The analysed pyroxenes are diopsidic (En32.3Fs18.5Wo49.1 - En34.9Fs17.9Wo48.2). The whole-rock geochemistry of the gabbros indicates the presence of two distinct groups of rocks; a subordinate group of phlogopite gabbro with island arc calc-alkaline affinity and a dominating layered gabbro sequence with island arc tholeiite characteristics. They are extremely enriched in LIL elements, indicative of an alkaline metasomatism in the source region and they display geochemical features of transitional back arc basin basalts (BABB)/island arc basalts (IAB)- and IABtype oceanic crust. Based on their geochemical similarities with modern island arc basements, we suggest that the Kurankali Metagabbro may represent the basement of an initial island arc, generated in a supra-subduction zone setting within the Izmir-Ankara branch of Neotethys.Item Geochemistry, tectono-magmatic discrimination and radiolarian ages of basic extrusives within the Izmir-Ankara Suture Belt (NW Turkey): Time constraints for the neotethyan evolution(2006) Göncüoglu M.C.; Yaliniz M.K.; Tekin U.K.The Daǧkuplu Mélange in the Central Sakarya Valley represents the northernmost outcrops of the Izmir-Ankara Suture Belt in northwest Anatolia. In addition to blocks and slivers of serpentinite, gabbro, blueschist, neritic and pelagic limestones, it includes blocks of basic volcanic rocks associated with radiolarian cherts, pelagic carbonates and mudstones. The preliminary geochemical data revealed the existence of a variety of basaltic rocks with magma types ranging in composition of MORB, IAT, OIB and CAB, in the mélange. The age of the radiolarian assemblage from a tectonic block of chert-mudstone alternation associated with OIB-type basalts within the mélange is assigned to early Berriasian - early Hauterivian, based on the co-occurrence of radiolarian taxa as Angulobracchia sp. cf. A. (?) portmanni, Godia nodocentrum, Pantanellium masirahense, Thanarla brouweri, Pseudoeucyrtis hanni, Svinitzium mizutanii, Mirifusus dianae s.l., Tethysetta boesii. Another block of chert-mudstone alternation associated with MORB-type basalts includes the following Cenomanian radiolarian fauna: Thanarla pulchra, Novixitus mclaughlini, Pseudodictyomitra pseudomacrocephala, Pseudodictyomitra tiara, Stichomitra communis. New findings from the Central Sakarya area combined with previous data of the authors reveal that the Izmir-Ankara Ocean started to open already in the Late Triassic. The formation of OIB-type intra-plate seamounts within the Izmir-Ankara Ocean began in late Bathonian and persisted until early Aptian. The the intra-oceanic subduction and the generation of supra-subduction-type volcanism started in early Santonian and the spreading-ridge of the Izmir-Ankara Ocean plate was not subducted until the Cenomanian.Item Geochemical characteristics of mafic lavas from the Neotethyan ophiolites in western Turkey: Implications for heterogeneous source contribution during variable stages of ocean crust generation(Cambridge University Press, 2008) Aldanmaz E.; Yaliniz M.K.; Güctekin A.; Göncüoǧlu M.C.The Late Triassic to Late Cretaceous age mafic lavas from the Neotethyan suture zone ophiolites in western Turkey exhibit a wide diversity of geochemical signatures, indicating derivation from extremely heterogeneous mantle sources. The rocks as a whole can be divided into three broad subdivisions based on their bulk-rock geochemical characteristics: (1) mid-ocean ridge basalts (MORB) that range in composition from light rare earth element (LREE)-depleted varieties (N-MORB; (La/Sm)N < 1) through transitional MORB to LREE enriched types (E-MORB; (La/Sm)N > 1); (2) the ocean island basalt (OIB)-type alkaline volcanic rocks with significant enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to normal mid-ocean ridge basalts (N-MORB); and (3) the supra-subduction zone (SSZ)-type tholeiites originated from arc mantle sources that are characterized by selective enrichments in fluid-soluble large ion lithophile elements (LILE) and LREE relative to the high field strength elements (HFSE). The formation of MORB tholeiites with variable enrichments and depletions in incompatible trace elements is probably related to the processes of crust generation along an oceanic spreading system, and the observed MORB-OIB associations can be modelled by heterogeneous source contribution and mixing of melts from chemically discrete sources from sub-lithospheric reservoirs. Evaluation of trace element systematics shows that the inferred heterogeneities within the mantle source regions are likely to have originated from continuous processes of formation and destruction of enriched mantle domains by long-term plate recycling, convective mixing and melt extraction. The origin of SSZ-type tholeiites with back-arc basin affinities, on the other hand, can be attributed to the later intra-oceanic subduction and plate convergence which led to the generation of supra-subduction-type oceanic crust as a consequence of imparting a certain extent of subduction component into the mantle melting region. Mixing of melts from a multiply depleted mantle source, which subsequently received variable re-enrichment with a subduction component, is suggested to explain the generation of supra-subduction-type oceanic crust. The geodynamic setting in which much of the SSZ-type ophiolitic extrusive rocks from western Turkey were generated can be described as an arc-basin system that is characterized by an oceanic lithosphere generation most probably associated with melting of mantle material along a supra-subduction-type spreading centre. © 2007 Cambridge University Press.Item A geochemical attempt to distinguish forearc and back arc ophiolites from the "supra-subduction" central anatolian ophiolites (Turkey) by comparison with modern oceanic analogues(2008) Yaliniz M.K.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-İzmir-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.