Despositional Provenance Analysis of the Jinjiahe Phyllite from Sanchazhi Area (Lueyang County) in Mianlue Tectonic Belt of South Qinling, Shaanxi: Evidence from Detrital Zircon U-Pb Dating

A set of rock assemblage is exposed in the Sanchazi area, Mianlue tectonic belt of Southern Qinling orogenic belt, which is consist of gray-black carbonaceous sericite-quartz-phyllite, gray-white sericite-quartz-phyllite, intercalated with gravelly sericite-phyllite, dolomitic limestone, siliceous rock and carbon-siliceous slate. In order to explore their formation age and provenance, we conducted LA-ICP-MS U-Pb dating on detrital zircons from the gravelly sericite-dolomite-quartz-phyllite and sericite-dolomite-quartz-phyllite in Jinjiahe area. The obtained zircon U-Pb ages can be divided into three groups:Neoproterozoic age group (678~966Ma), with main age peak at 781Ma for sample ML1259-TW3 and 865Ma for sample ML1261-TW1, respectively; Mesoproterozoic age group (1122~1432Ma):and Palaeoproterozoic-Archaean age group (1944~2824Ma). The minimum age groups of detrital zircons for two metamorphic detrital rocks are 678~736Ma (average age of 725Ma) and 771~775Ma (average age of 773Ma), respectively. Combined with the regional geological records, we propose that the provenance of clastic debris in the sedimentary strata was mainly sourced from the Neoproterozoic magmatic rocks within the Mianlue tectonic belt, the Bikou block, and the Hannan-Micangshan complex in the northwestern margin of the Yangtze block. The maximum depositional age of the studied meta-sedimentary rocks is not later than Nanhua Period, and it may give insights into the post-collision-cracking stage of the Mianlue tectonic belt and the northwestern margin of the Yangtze block during the mid-late Neoproterozoic period (800Ma~).