The Study Of Mesozoic-Cenozoic Tectonic Evolution In Eastern Qaidam Basin

The Qaidam Basin had a complex tectonic evolution history.The surrounding three plates played important roles in controlling tectonic reconstruction and tectonic evolution of the basin.Based on the field geological,drilling and seismic data,this research study structural styles,fracture characteristics,paleo and present tectonic stress field in eastern Qaidam Basin and its adjacent areas by means of a variety of geological methods.Also,ANSYS is used to primarily simulate the tectonic stress field which could be predict fracture zone and oil-favored areas.Finally,dynamic mechanism of tectonic deformations in eastern Qaidam and tectonic evolution process since the Mesozoic were discussed:(1)Eastern Qaidam Basin tectonic types can be divided into 3 styles: compression tectonic style,strike-slip style and extending tectonic style.(2)The sequences of the development of the fractures are roughly determined: netted fractures filing with mud?near vertical and oblique crossing filling with calcite?horizontal with mud?near vertical with mud.Diagenetic netted fractures developed in the Early Hercynian-Indosinian.All the structural fractures developed mainly in the Late Hercynian-Indosinian,Yanshanian and Late Himalayan.(3)Olongbluke convex part is the low potential areas for oil and gas.This low potential area is conducive to the migration and accumulation of oil and gas and forming anticlinal hydrocarbon reservoir.(4)Qaidam Basin has undergone five stages in sedimentary structural evolution-Cenozoic including since Mesozoic:(1)From the Late Permian to Triassic,the basin was uplifted and eroded by NE-SW direction compression.(2)At the Early-Middle Jurassic stage,the N-S direction extension led to some differential settlement zone such as the Delingha depression.Both Altyn Tagh fault and eastern Qaidam showed left lateral slip;(3)From the Late Jurassic to Cretaceous compression inversion stage,the stress field turned to NE-SW direction compression in the Cretaceous.Altyn Tagh fault took place left lateral slip while the eastern basin simply thrusted onto the Qilian Mountains by compression;(4)At the Paleogene compressive rift-depression stage,Altyn Tagh fault showed strongly left lateral slip and the eastern Qaidam experienced right lateral slip under the component along NW-SE direction because of the N-S direction compression;(5)From the Neogene to Quaternary,the basin experienced intensive N-S direction compression which reached to the maximum in the late Himalayan period and laid the tectonic framework of the basin.