阿拉善地块雅布赖盆地“跷跷板式”负反转构造特征及成因分析

Characteristics and Origin of the“Seesaw Type”Negative Inversion Structure in the Yabulai Basin of the Alxa Block

雅布赖盆地位于阿拉善地块之上,自中生代以来进入板内构造演化阶段。区内侏罗系沉积受北东走向逆冲断层控制,形成了南东逆冲、北西超覆的挤压拗陷型盆地,发育以叠瓦式、背冲式、对冲式的逆冲断层组合样式以及冲起背斜、断背斜等挤压褶皱构造样式,挤压应力来源于鄂霍次克洋和古太平洋向欧亚板块俯冲产生的双侧挤压作用。下白垩统沉积受雅布赖山前正断层控制,形成了北西断陷、南东超覆的伸展断陷型盆地,发育阶梯式、多米诺式、共轭式等正断层组合样式,应力来源于太平洋板块俯冲后撤作用。侏罗纪形成的挤压拗陷盆地与早白垩世形成的伸展断陷盆地沉降方向相反,两者反向超覆沉积叠加形成了“跷跷板式”的负反转盆地。新生代以来受印度板块向欧亚大陆板块俯冲、碰撞作用的影响导致北大山断裂向北逆冲推覆在侏罗纪盆地之上,并使雅布赖山前断层发生左行走滑变形。构造物理模拟实验证实双侧差异挤压与单侧伸展叠加作用是形成雅布赖盆地构造格局的主控因素。

The Yabulai Basin is located in the Alxa Block and experienced intra-plate tectonic events since the Mesozoic Era.The Jurassic sediments are controlled by the NE-SW reverse faults,forming a compressional depressed basin with reverse fault patterns including imbricate fans,back-thrust,ramp structure,pop-up anticlines,and faulted anticlines.This compressional stress originated from the subduction of the Okhotsk Ocean and the Paleo-Pacific Ocean beneath the Eurasian plate.Lower Cretaceous sedimentation is controlled by the Yabulai normal fault,forming an extensional faulted depression basin with northwest faulting and southeastern overlap.Fault assemblages such as stepped,domino,and conjugate styles developed,and stresses resulting from the rollback of Pacific plate subduction.The Jurassic compressional basin and the Cretaceous extensional basin superimposed in opposite directions to form a“seesaw type”negative inversion structure.Since the Cenozoic Era,the subduction and collision of the Indian Plate with the Eurasian continental plate has caused the Beidashan fault to thrust northward over the Jurassic basin,leading to the sinistral slip of the Yabulai piedmont fault.The results of analogue models show that the superposition of bidirectional compression and unidirectional extension is the main factor controlling the structural patterns in the Yabulai Basin.