Provenance of the Lower Jurassic pyroclastic sediments in the Zigui Basin:Implication for crustal thickening in the eastern Qinling orogenic belt

作     者：Rong CHAI Jianghai YANG Yuansheng DU Chengshan WANG 

作者机构：School of Earth Sciences and ResourcesChina University of Geosciences(Beijing)Beijing 100023China School of Earth SciencesChina University of Geosciences(Wuhan)Wuhan 430074China Chinese Academy of Geological SciencesBeijing 100037China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2024年第67卷第1期

页      面：196-207页

核心收录：

学科分类：070904[理学-构造地质学] 070903[理学-古生物学与地层学(含：古人类学)] 0709[理学-地质学] 07[理学] 0708[理学-地球物理学] 0705[理学-地理学] 

基　　金：This work was supported by the National Natural Science Foundation of China(Grant Nos.41888101,42102121,42122015) the China Geological Survey Project(Grant Nos.DD20230008,DD20221656) Guizhou Provincial Science and Technology Projects(Grant No.ZKGeneral 081). 

主　　题：Qinling orogenic belt Zigui Basin Late Triassic Detrital zircons Crustal thickening 

摘      要：The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt,accompanied by magma underplating and tectonic deformation.These processes potentially resulted in substantial crustal thickening and uplift of the Qinling orogen.However,due to the absence of igneous rock records from this period in the eastern section of the Qinling orogen,the changes in crustal thickness during this orogenic process have not been thoroughly investigated.A series of foreland basins emerged during the Early Mesozoic to the south of the East Qinling orogenic belt.These basins have preserved clastic sedimentary rocks derived from the uplift and erosion of the orogenic belt.These sedimentary records serve as crucial records to reconstruct the evolutionary history of the Qinling orogen.To further clarify the collisional orogenic process of the Qinling orogenic belt,this study conducted in situ volcanic lithic fragment geochemistry,detrital zircon U-Pb chronology and trace element composition analysis on the sandstones of the Lower Jurassic Tongzhuyuan Formation in the Zigui Basin.The results suggest that the sandstones,which exhibit a significant abundance of volcanic lithic fragments,has a characteristic detrital zircon age group of 250–200 Ma,indicating a major provenance from the Triassic volcanic rocks.Combined with regional correlation and paleocurrent analysis,the detrital zircon U-Pb age data show that the source area of volcanic rocks should be in the Qinling orogenic belt to the north of the basin.This interpretation is further supported by the Triassic granitic rocks exposed in the western part of the orogenic belt,representing the magmatism during the Triassic collisional orogenesis in the Qinling orogen.Based on the co-varying relationships between present-day crust thickness with the chemical compositions of granite rocks and zircons,the La/Yb ratio of volcanic lithic fragments in the Tongzhuyuan Formation and the Eu/Eu*ratio of detrital zircons with Triassic ages indicate that the Qinling orogen experienced crustal thickening during the Late Triassic,reaching its maximum thickness of 60–70 km at ca.220–210 Ma.This crustal thickening in the eastern Qinling orogen is temporally consistent with that in the western orogen as recorded by the Triassic granitic rocks and may be related to large-scale crustal shortening and magmatism during the collisional orogeny.