| The southwest area of Tarim Basin is located in the combination of Tarim Basin and West Kunlun orogenic belt,which is one of the ideal places to study the Mesozoic Paleotethys tectonic evolution.Meanwhile,the Jurassic and Cretaceous systems in this area are also important target strata for oil and gas exploration.Therefore,it is of great theoretical value and practical significance to study the structure and process of basin-mountains in southwest Tarim Basin.At present,there are different understandings about the tectonic setting,tectonic attributes and basin-forming mechanism of Mesozoic basins in southwest Tarim Basin.Palaeozoic group of sw in the tarim basin and the Jurassic-cretaceous as the research object,the integrated use of field geological survey,regional geology,such as the construction of earthquakes with large section and parsing,the structure of the large section balance recovery and basin sedimentology and provenance analysis method,the system analysis of Cenozoic multiphase tectonic deformation in south-western region of space,on the basis of segmentation,Rebalancing by constructing section,focus on identifying and restore the south-western Mesozoic ancient tectonic deformation characteristics and spatial distribution,and from the Mesozoic basin provenance space-time evolution and sedimentary response to the point of view of Jurassic and cretaceous basin prototype and evolution,and then discusses the Mesozoic tectonic process in south-western relationship with the evolution of orogenic belt of the ancient tethys,made the following understanding:(1)The field geological survey and the construction and analysis of the geoseismic large section show that the multistage strong thrust-fold deformation has been widely developed since the Mesozoic,and three tectonic belts,namely,Wupoer,Sugete-Qimgen and Kekeya,can be divided from west to east according to the deformation characteristics.The Upoer structural belt is mainly characterized by long distance thrust imbricated structural deformation and developed backpack basin.Sugete-qimgen structural belt is mainly characterized by strike-slip oblique thrust-fold deformation.Kekeya structural belt is mainly prespread multilayer detachment thrust-fold deformation.(2)Based on the restoration of large section structure balance and previous studies,it is proposed that the paleo-arc-shaped thrust belt was developed in the southwest of Tarim Basin during the Triassic period.Among them,sugete-Qimgen area has the strongest thrust-fold deformation,characterized by three rows of n W-trending large anticlines and imbricated thin-skin thrust structures,which advance furthest to the basin.The second is kekeya structural belt,which is mainly thrust imbricated deformation.The pamir structural zone has the weakest deformation and locally developed thrust faults.The paleo-arcuate structure is quite different from the Cenozoic arcuate structure dominated by pamir spikes in space and deformation characteristics.(3)Triassic system is absent in southwest Tarim,jurassic-Cretaceous system is distributed in bands in piedmont.Analysis of sedimentological characteristics of geological outcrop section shows that the early-middle Jurassic basin is characterized by fan delta and lacustrine deposition,which reflects the characteristics of rapid subsidence,rapid denudation and filling of the basin.The detrital zircon U-Pb analysis of the Jurassic sandstones in the Kiziltao area shows that the Jurassic samples are mainly in the range of 370～1000 Ma,with a single age peak of 440 Ma,indicating that the samples are from the West Kunlun orogenic belt.The Cretaceous is characterized by braided river delta facies and shallow water deposits equal to rivers.Although the basin scope is significantly expanded compared with the Jurassic period,it is still confined to the foremountain Triassic fold and thrust belt.The detrital zircon geochronology of the Lower Cretaceous sandstones in the Qimgen area near the Kiziltao area shows that the age ranges from 200 Ma to 1100 Ma,and there are two main age peaks of 264 Ma and 420 Ma,indicating that the sandstones are filled with bivalent provenance from the orogenic belt and the intra-basin uplift.According to the statistical results and palaeocurrent recovery,south-western region of Mesozoic basin by Jurassic clastic source unidirectional provenance supply in the west kunlun mountains to the cretaceous period south-western basin inside and the transition of the west kunlun mountains of things bidirectional provenance supply,this shift is likely to indicate a torn basin from Jurassic to cretaceous depression basin,an important transformation.(4)Comprehensive analysis shows that the Southwest Tarim basin experienced three stages of tectonic evolution during Mesozoic: Triassic period,the west kunlun orogenic belt after strong tectonic compression,and significant with orogenic granitic magmatism,at the same time in the south-western piedmont region formed an arc fold thrust belt,developmental rows into the thrust belt-fold structure,including Sue gheit-achim root deformation region is the strongest,and present a high southwest and northeast low uplift terrain,The Paleozoic and Triassic strata in southwestern Tasmanian are subjected to denudation and planation.At the beginning of Jurassic,rifted basins developed,and the paleogeomorphology changed significantly.One side of the orogenic belt settled quickly and significantly,presenting a low paleogeomorphology in the southwest and high paleogeomorphology in the northeast.In the late Jurassic-early Cretaceous,the basin changed into a depression basin with a wide range of subsidence,but the sedimentation of the basin was still confined to the piedmont fold and thrust belt.The Triassic thrust fold deformation and jurassic-Cretaceous rift-depression basin in southwest Tarim basin evolved continuously in time and were closely associated with each other in space.It is suggested that the Southwest Tarim basin underwent a dynamic transition from synorogenic tectonic compression(Triassic)to post-orogenic tectonic extension(Jurassic-Cretaceous)in Mesozoic.This process may be a response to the dynamic evolution of the Paleotethys orogenic belt in the Western Kunlun Mountains. |
PDF Full Text Request