Dating of Precambrian metasedimentary rocks and timing of their metamorphism in the Soursat Metamorphic Complex (NW IRAN): Using LA-ICP-MS, U-Pb dating of zircon and monazite

Abstract

Soursat Metamorphic Complex (SMC) in west of Takab city is one of the polyphase metamorphic terrenes in northern Sanandaj-Sirjan metamorphic belt of Iran. The SMC composed mainly of metasedimentary rocks associated with granitic intrusions. Based on metamorphic rocks, two metamorphic phases could be separate in the complex. M1 is representative of regional metamorphisms which varies from greenschist to amphibolite facies and consists of mica-schist, garnet-schist, staurolite-schist, kyanite- schist, fibrolite-schist, garnet amphibo‌lites, marble, gneiss. M2 is contact metamorphism with clear outcrop just in the central of SMC and overprinted on M1. This phase consists of andalusite-schist, cordierite-schist and Actinolite- schist. SMC is in tectonic contact with Precamb‌rian to Paleozoic sedimentary rocks which make it difficult to date it based on stratigraphy. In this study, U-Pb dating of zircons and Monazites used in order to find the ages of deposition and metamorphism of metasediments in SMC. U-Pb dating of zircons from a staurolite-schist in the complex by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded a maximum Precambrian depositional age of 605±43. Monazites were also dated from a garnet-schist using the same technique and yielded a 238U/206Pb age of 61±8 which is interpreted as the age of the regional metamorphism. Based on these ages, metasedimentary protoliths of the SMC are deposited at the same time as the surrounding essentially unmetamorphosed Precambrian-Cambrian sedimentary rocks and regional metamorphism occurred later in Paleocene and could be related to the orogenesis during the collision of Arabian plate with Iranian block and closure of Neotethys.