川东北须家河组凝灰岩形成时代及其物源区研究OA

The Late Triassic is a key era in the sea-land transition of Sichuan Basin:its sedimentary strata not only record the evolution of Sichuan Basin,but also reflect vital structural Indosinian events.This study focuses on tuff intercalations of the Xujiahe Formation(T3x)in the Qilixia section,which is located in the northeastern Sichuan Basin.The sedimentary age and magmatic source of the tuff were determined,and its geological significance was explored using petrology,geochemistry,and zircon U-Pb chronology.LA-ICP-MS zircon U-Pb dating yields an age of(205.9±1.5)Ma for the tuff,corresponding to the Norian-Rhaetian stages(Late Triassic).In combination with the"floating"astronomical timescales,the Xujiahe Formation has a sedimentary age of 210.1～204.2 Ma.The south Qinling orogenic belt is the origin of the volcanic materials that make up the tuff,which have been closely linked to the melting of continental crust during plate subduction.This assertion is supported by the geochemical characteristics of the tuff and its nearby igneous rocks,including their formation age,the direction of the prevailing mega-monsoon circulation,and the regional distribution of late Triassic igneous rocks.It is determined that the Xujiahe Formation exhibits a sedimentary age distribution that is"old in the west and new in the east"in Sichuan Basin,which may be attributed to the spatiotemporal heterogeneity of the terrigenous detrital supply.