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چکیده
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The oldest basement rocks of Iran, known as Late Neoproterozoic–Early Paleozoic granites, are exposed in the various regions. The Golpayegan and Shahrekord granites, which are exposed in the central region of the Sanandaj-Sirjan Zone (SaSZ) in western Iran, are considered as part of this basement. In this research, we focus on the oxygen‑hafnium (O-Hf) isotope ratios of zircon grains from two bodies. High δ18O values for zircon grains separated from both granites (MR 5–1: +8.81 to +9.51‰; H-55-P: +9.01 to +9.37‰) together with the presence of high-Al minerals, such as sillimanite, muscovite, garnet, and boron-rich minerals like tourmaline, imply a strong resemblance to the S-type granite for both meta-granites. In addition, the negative εHf(t) values (MR 5–1: − 15.4 to +0.9; H-55-P: − 10.9 to − 1.4) confirm that the origin magma was generated from the partial melting of supracrustal components such as graywacke, psammite, with some clay rich rocks such as shale. The wide range of Hf model ages (TDM2) in both granites (2.4 to 1.4 Ga) shows the heterogeneity of source components. The simultaneous injection of mafic dikes with OIB-like signature, coupled with the thinning of the continental crust (extension regime) and elevated temperatures in the shallow depths, likely served as a trigger for the partial melting of buried sediments and the production of felsic melts in a shallow depth. The findings of this research suggest that an extensional tectonic regime, accompanied by a subsequent rise in the geothermal gradient due to the continental crustal thinning and the injection of mafic melts into the upper crust, was a principal mechanism responsible for the partial melting of supracrustal materials at shallow depths within the northern Gondwana during Late Neoproterozoic to Early Paleozoic.
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