北山东南部早白垩世伸展构造变形:二维反射地震剖面解释与磷灰石裂变径迹测年的制约OA北大核心CSTPCD

[Objective]The Beishan Range occupies a key position in Central Asia.This study aims to deepen the understanding of the timing,intracontinental deformation processes,and their dynamic mechanisms in the Late Mesozoic on the southern margin of the Central Asian Orogenic Belt(CAOB).[Methods]We conducted detailed analyses of the Early Cretaceous extensional and earlier compressional structures in the southeastern Beishan Range through field geological observations,interpretation of 2D reflection seismic profiles,and apatite fission track thermochronology.[Conclusion]Field observations show that Lower-Middle Jurassic strata have been strongly deformed by numerous thrusts and folds.2D seismic reflection profiles reveal two NE-to NEE-striking normal faults.The Suosuojing fault is a SE-dipping low-angle listric normal fault,while the Wudaoming fault is a NW-dipping high-angle normal fault.These normal faults cut through the early-formed fold-thrust system,indicating a transition from contraction to extension.The Suosuojing and Wudaoming faults,respectively,define the northwestern and southeastern boundaries of the Early Cretaceous Zongkouzi basin.The Zongkouzi basin exhibits a graben geometry,with Lower Cretaceous strata displaying typical growth-strata relationships,suggesting that the normal faults were active during the late Early Cretaceous.Thermal history modeling results from apatite fission track data indicate that the footwall of the Suosuojing fault experienced rapid cooling between 132 and 110 Ma.This rapid cooling phase was closely related to the footwall exhumation during the normal slip of the Suosuojing fault.We argue that the Late Mesozoic intracontinental contraction-extension transition in the southeastern Beishan Range likely occurred between～133 Ma and～129 Ma in the late Early Cretaceous.The collapse of the thickened crust and coupled mantle upwelling triggered the Early Cretaceous extensional deformation in the southern CAOB.