Zircon U-Pb geochronology of Sr-Nd isotopes and petrogenesis of I-type reduced granitoids of Keybarkuh (Southwest of Khaf)


1 Department of Geological Sciences, University of Colorado, CB-399, Boulder, CO, USA

2 Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran

3 استان خراسان رضوی، مشهد، بلوار وکیل آباد، دانشگاه فردوسی مشهد، دانشکده علوم، گروه زمین شناسی،دکترمحمدرضا حیدریان شهری


The Keybarkuh area is situated in the northeast of the Lut block. The rock units of the area are the Paleozoic metamorphic rocks and the Cretaceous to Tertiary intrusions with granite to diorite composition. The intrusive rocks are divided into oxidant and reduced series. The reduced intrusive rocks are granite and granodiorite with hypidiomorphic granular texture. The main minerals consist of feldspars, quartz, muscovite and less biotite. The reduced intrusions are mostly moderate to high-K and mostly metaluminous. Their tectonic setting mostly plot in the boundary between subduction and continental collision. LREE enrichment relative to HREE is observed. The Eu negative anomalies and depletion of Sr and Ba can be attributed to the presence of residual plagioclase in a source and redox conditions. Depletion of Sr, Zr, Hf and Ti relative to Rb, K, La, Ce, Nd and Tb indicate the involvement of continental crust in generation of magma. The initial 87Sr/86Sr isotope ratio, initial 143Nd/144Nd isotope ratio and εNd values could be considered as representative of reduced continental crust derived magmas. The age of muscovite granite unit was determined 137 Ma, belong to the early Cretaceous (Valanginian), using zircon U-Pb method. Field observation (lack of exnolith), petrography (the presence of amphibole and lack of restite minerals), geochemical data (high-K calc-alkaline, metaluminous and radiogenic isotopes) and magnetic susceptibility (reduced type) indicate these intrusions are reduced I-type intrusive rocks resulting by partial melting of continental crust, which mostly show metagreywackes to amphibolite source.