The İspendere ophiolite forms part of the Tauride active continental margin assemblage in SE Anatolia. The ophiolite exhibits an intact oceanic lithosphere section and is intruded by Late Cretaceous calc-alkaline granites. The ophiolite comprises mantle tectonites, ultramafic to mafic cumulates, isotropic gabbros, isolated diabase dykes, a sheeted dyke complex, plagiogranite and volcanic rocks. The volcanics and the sheeted dyke complex exhibit (1) similar rare earth element patterns, with flat to light rare earth element depletion (La-Yb) N ¼ 0.71-1.14 and 0.65-1.22, (2) negative Nb anomalies and (3) flat-lying high field strength element trends. These features differ from a typical Normal-Mid Ocean Ridge Basalt fractionation trend and could have resulted from c. 15% partial melting of a previously depleted mantle source. The whole-rock chemistry and the mineral chemistry of the ultramafic to mafic cumulates [high Ca plagioclases (An 89 -81 ), magnesian olivines (Fo 88 -81 ) and clinopyroxenes (Mg# 90 -83 )] show that the primary magma of the plutonic suite is compositionally similar to modern island arc tholeiites. The available evidence suggests that the İspendere ophiolite formed at a northerly supra-subduction zone spreading centre of the Southern Neotethys, between the Taurides and the Bitlis-Pütürge metamorphic units, during the Late Cretaceous. Comparison with the adjacent Göksun, Kömürhan and Guleman ophiolites suggests that the İspendere ophiolite represents part of a single regional-scale sheet of oceanic lithosphere that was accreted to the base of Tauride active continental margin where it was cut by arc-type magmatic rocks.
Post-collisional granitoid plutons intrude obducted Neo-Tethyan ophiolitic rocks in central and eastern Central Anatolia. The Bizmişen and Ç alt plutons and the ophiolitic rocks that they intrude are overlain by fossiliferous and flyschoidal sedimentary rocks of the early Miocene Kemah Formation. These sedimentary rocks were deposited in basins that developed at the same time as tectonic unroofing of the plutons along E-W and NW-SE trending faults in Oligo-Miocene time. Mineral separates from the Bizmişen and Ç alt plutons yield K-Ar ages ranging from 42 to 46 Ma, and from 40 to 49 Ma, respectively. Major, trace, and rare-earth element geochemistry as well as mineralogical and textural evidence reveals that the Bizmişen pluton crystallized first, followed at shallower depth by the Ç alt pluton from a medium-K calcalkaline, I-type hybrid magma which was generated by magma mixing of coeval mafic and felsic magmas. Delta 18 O values of both plutons fall in the field of I-type granitoids, although those of the Ç alt pluton are consistently higher than those of the Bizmişen pluton. This is in agreement with field observations, petrographic and whole-rock geochemical data, which indicate that the Bizmişen pluton represents relatively uncontaminated mantle material, whereas the Ç alt pluton has a significant crustal component.Structural data indicating the middle Eocene emplacement age and intrusion into already obducted ophiolitic rocks, suggest a post-collisional extensional origin. However, the pure geochemical discrimination diagrams indicate an arc origin which can be inherited either from the source material or from an upper mantle material modified by an early subduction process during the evolution of the Neo-Tethyan ocean.
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