川北旺苍地区梁山组碎屑锆石物源分析及其大地构造背景OA

The Early Permian is an important tectonic transition period for the Yangtze Block.This study explores the provenance and geotectonic setting of the Lower Permian Liangshan Formation in the Wangcang area of north Sichuan Basin,based on the geological survey,U-Pb dating,and trace element analysis of detrital zircons.Results show that:(1)Most of the detrital zircons from the Liangshan Formation in the Wangcang area have rounded shapes,clear zoning,and Th/U ratios between 0.01 and 2.9,enrichment of heavy rare earth elements,depletion of light rare earth elements,positive Ce anomalies,and negative Eu anomalies.Their U-Pb ages are mainly distributed in four intervals:1 100-850 Ma,850-700 Ma,600-500 Ma,and 500-400 Ma.(2)The detrital zircons of the Liangshan Formation are mostly of magmatic origin,with sources mainly derived from granitic and mafic rocks.The geotectonic setting of the source area is inferred as an island arc,with three stages of crustal thinning and two stages of thickening during 1 000-400 Ma.(3)The geotectonic setting of the Liangshan Formation in the study area reflects a collision-dominated environment transitioning to extensional,with primary provenance from recycled underlying sedimentary strata and the northern Hannan-Micangshan micro-block.No external plate sources are evident.Compared to southern Guizhou,the Wangcang detrital zircon ages are more diverse,indicating regional differences in provenance.This study establishes the detrital zircon age spectrum of the Liangshan Formation in the northwestern margin of the Upper Yangtze Block,clarifies its provenance and tectonic setting characteristics,and provides a basis for reconstructing Early Permian paleogeography and geotectonic evolution of the Yangtze Block.