Geological Record of Tectono-Thermal Event at Early Paleozoic and Its Tectonic Setting in West Segment of the North Qaidam

Zha Xianfeng; Gu Pingyang; Dong Zengchan; Chen Ruiming; Lu Zhongyuan

doi:10.3799/dqkx.2016.048

Abstract：It is a valid approach to explore the tectonic evolution and origin by comparative chronological research of the rocks in the northern margin of Qaidam basin characterized by outcropped basement rocks and frequent magmatic activities.Dakendaban Rock Group (DRG)is one of the dominant crystal basement rocks of Oulongbuluke block.A study was carried out on material composition,deformation and metamorphism of the banded migmatitic gneiss,biotite plagioclase gneiss,two-mica plagioclase quartz schist sampled from the DRG,and the gneissic quartz diorite that intruded the DRG.The zircons from DRG samples yield nearly unanimous two peak age of about 460 Ma and peak age of about 430 Ma by LA-ICP-MS zircon U-Pb isotopic analy-ses.Combined with the regional tectonic processes,we maintain that the age of about 460 Ma is the geological response to the tectono-magmatism caused by ultradeep continental subduction in the North Qaidam.The metamorphic age about 430 Ma is consistent with the crystallization age (429.0±4.1 Ma)of the gneissic quartz diorite.Combined the chronolgical data with geo-chronological analyses on the gneissic quartz diorite,and the zircon REE data from DRG samples,it proves that the metamor-phism of about 430 Ma is closely related to the homochronous tectono-thermal event.The obvious depletion of HFSE,including Nb,Ta,Zr,Hf,and the Pb enrichment demonstrate that the characteristics of the gneissic quartz diorite are related to the plate subduction which formed the active continental margin.This study provides important information for further revealing the tectonic properties and the evolution of the tectono-thermal event at Early Paleozoic in western Oulongbuluke bolck.