Mesozoic-Cenozoic Basin-Mountain Relationships And Tectonic Evolution Process Of Southeastern Junggar

The southeastern margin of Junggar Basin consist of Yilinhebilgen Mountain,Chaiwopu Depression,Bogda Mountain and the northern tectonic belt of Bogda Mountain,presented the structure of which basins inlaid in mountain ranges,which from the distinctive complicated geological structure and the process of tectonic evolution.The research of the Mesozoic and Cenozoic deformation characteristic and tectonic evolution will be of great importance in revealing Mesozoic-Cenozoic inland deformation mechanism of the northern margin of Tianshan and enhancing oil-gas exploration in the area.This paper was based on the research of structural deformation features and sedimentary fillings with the southeastern margins of Junggar Basin,combine with the history of orogenic belt uplift,analyze the characteristics of tectonic evolution and discuss the evolution of the southeastern margin of the Junggar basin.The main conclusions are summarized as follows:1.Three phases of unconformity was identified at Chaiwopu Depression which is at the south of Bogda Mountain,it include the unconformity between Jurassic and Triassic(J/T),Paleogene and Jurassic(E/J),Pliocene and Miocene(N2/N1),confirm the Chaiwopu Depression mainly undergoes late Triassic?late Jurassic and late Miocene Three phases tectonic deformation at least:four phases of unconformity was identified at northern tectonic belt of Bogda Mountain,which include the unconformity between Jurassic and Triassic(J/T),Cretaceous and Jurassic(K/J),Paleogene and Cretaceous(E/K),Plioccne and Miocene(N2/N1),confirm the northern tectonic belt of Bogda Mountain mainly undergoes late Triassiclate Jurassic,late Cretaceous and late Miocene four phases tectonic deformation.2.The basic deformation structure of the southeastern margin of the Junggar basin was controlled by the northward extension of the deep detachment fault:Some basement-involved faults grew at the north margin of Yilinhebilgen Mountain when it pressing in north direction;extrusion stress northward spread to Bogda Mountain along the deep detachment fault,it formed back-thrust and fault-related fold at south Bogda Mountain;the thrusting still northward spread along the deep detachment fault,formed thrust faults and fault-related fold at north Bogda.The Overall structure of Chaiwopu Depression was a triangle zone which display the thrust faults is a north-south hedge.And the Bogda Mountain showed as a pop up structure with fan-shaped as a whole.3.The tectonic and sedimentary response model of middle-late Jurassic can be explained by top wedge deposition:middle-late Jurassic Bogda Mountain northern faults thrust intensively,Chaiwopu Depression and Bogda Mountain were uplifted as a whole and at the position of top wedge,which deposited thin fluvial deposition,in the meantime the northern tectonic belt of Bogda Mountain was at the position of Foredeep depression and deposited thick lacustrine deposition,the top wedge deposition result in the big depositional difference between south and north margin of Bogda Mountain;Since Pliocene the tectonic deformation showed as thrust intensively at north margin of Yilinhebilgen Mountain and north margin of Bogda Mountain,flexural subsidence was developed at mountain front,Pliocene and quaternary deposited thick at south and thin to north,show as foreland basin.Chaiwopu Depression maybe a piggy-back basin and the north area of Bogda Mountain northern tectonic belt was a Foredeep depression,4.Put forward the evolution process of the southeastern margin of the Junggar basin:The Triassic was deposited as depression sedimentation,the Bogda Mountain was a low uplift at late Triassic;early-middle Jurassic the study area was a extensional depression,middle-late Jurassic top wedge deposition was developed at southeastern of the Junggar basin which result in the big depositional difference between south and north margin of Bogda Mountain;During the Cretaceous Chaiwopu Depression was uplifted at high position,lack of Cretaceous,but Cretaceous was sedimentation at north mar(gin of Bogda Mountain;From Paleogene to Miocene the study area was deposited as depression sedimentation,Late Miocene the strata at north margin of Yilinhebilgen Mountain and north margin of Bogda Mountain developed flexural subsidence,Pliocene and quaternary deposited thick at south and thin to north,Chaiwopu Depression maybe a piggy-back basin and the north area of Bogda Mountain northern tectonic belt was a Foredeep depression.