Akademik Veri Yönetim Sistemi
LITHOS, cilt.326, ss.39-70, 2019 (SCI-Expanded)
We provide geochronological (zircon U-Pb) and geochemical data (whole rock major and trace elements, Sr-Nd-Pb isotopes, mineral compositions, zircon trace elements) for Late Cretaceous I- and A-type granitoids and associated gabbros from three areas (Dereli, Sebinkarahisar, Divrigi), along a north-south traverse in eastern Turkey from the northern part of the Eastern Pontides Orogenic Belt to the Anatol ide-Tauride Block, and from two locations (Sokmen and Pimalli) that are situated away from the traverse line. Our aim is to interpret the tectonic environment in which the granitoids formed. Late Cretaceous plutonic activity began similar to 90 Ma and continued uninterruptedly for about 20 my. The Dereli suite and the Asarcik intrusion at Sebinkarahisar are 1-type granitoids; the others are A-type granitoids. The A-type classification of these rocks is ambiguous; they are A-typerelative to other coeval granitoids in eastern Turkey. The Sebinkarahisar, Murmana (Divrigi), and Pirnalli granitoids evolved primarily by closed-system fractional crytallization. At Sebinkarahisar, I- and A-type intrusions are isotopically indistinguishable, and must share the same source. Open system, AFC processes affected the other granitoids. Crustal components contributed to all of the granitoids. The Dereli granitoids have an old component (1.2 < T-DM < 1.75 Ga) that is unusual among Turkish igneous rocks. No mantle component is recognizable in the A-type granitoids, but the low SiO2 content of some granitoids requires a mantle-derived component. Arc-like geochemical features may be inherited from a mid-crustal source component, in addition to contributions from the arc environment active at the time of magmatism. A petrogenetic relation cannot be demonstrated between the Divrigi gabbros and their contemporaneous granitoids. The gabbros require a subcontinental lithospheric mantle source. Trace elements in zircon track fractional crystallization paths within suites, and faithfully map the arc-related petrogenesis of the granitoids, but do not mirror trace element distributions in zircons from other A-type suites. Available data indicate that Late Cretaceous plutonic activity began at about similar to 90 Ma in both the northern part of the Eastern Pontides Orogenic Belt and the southern part of the Anatolide-Tauride Block. Magma compositions began to change at ca. 80 Ma, and transformed successively into high-K I-type and shoshonitic A-type activity, and magmatism continued until similar to 70 Ma. We interpret this 20 my interval to be the subduction-dominated, arc-construction phase in the Eastern Pontides. The distribution of I-type magmas in eastern Turkey is best explained by double-sided, initially shallow-angle subduction of Paleo- and Neo-Tethyan lithospheres, with subsequent steepening of the subducted slabs leading to an extensional regime and the generation of A-type magmas. This hypothesis also explains the origin of Late Cretaceous I- and A-type Central Anatolian granitoids. (C) 2018 Elsevier B.V. All rights reserved.