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

Abstract

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 Izmir-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. (C) 2007 Elsevier Ltd. All rights reserved.