Petrogenesis of the Carboniferous Ghaleh-Dezh metagranite, Sanandaj–Sirjan zone, Iran: constraints from new zircon U–Pb and40Ar/39Ar ages and Sr–Nd isotopes

Abstract

AbstractThe Ghaleh-Dezh metagranites in the northern Sanandaj–Sirjan Zone (SaSZ) in western Iran are found in a 0.5 km long by 0.3 km wide unit emplaced within the older Precambrian basement. New zircon U–Pb ages confirm that crystallization and emplacement of the protolith of the metagranites occurred at 312 ± 10 Ma and 298 ± 17 Ma in the Upper Carboniferous (Pennsylvanian) – Early Permian, which is consistent with the ages of recently discovered Palaeozoic granites in the northern SaSZ. The studied metagranitic body has been metamorphosed at lower greenschist facies and deformed in ductile–brittle regime due to subsequent reheating events during the Mesozoic. The rocks are metaluminous to slightly peraluminous granites with an A2-type affinity. Initial87Sr/86Sr ratios andεNd(t) contents vary from 0.7037 to 0.7130 and −0.70 to 0.34, respectively.143Nd/144Nd(i)values for the granitic rocks are fairly uniform at ∼0.5123. The geochemical and isotopic evidence indicates that these rocks were generated from a mantle magma with crustal contamination and fractional crystallization. Rb–Sr isochron and40Ar/39Ar K-feldspar ages are 274 Ma and 60–70 Ma, respectively. The older event,c.270 Ma, was likely related to the opening of Neotethys, whereas the younger ages likely relate to collisional events in the region during the closure of Neotethys.