Tectonic Evolution And Formation Mechanism Of Hetian Paleo-uplift In Tarim Basin

Hetian paleouplift is the main replacement region of oil-gas exploration in Tarim Basin.In this article,the nonuniform structural pattern and scale of Hetian paleouplift and its adjacent areas are analyzed by means of outcrop in the field,drilling and logging information and seismic data.By combining the features of stratum distribution,the intensity and migration rule of the paleouplift are studied based on cycle analysis method.The paleostructure framework of Hetian paleouplift and its adjacent areas at the period of transformation are restored with the paleostructure restoration technolog.And primary discussion is carried out on the formation mechanism of Hetian palaeohigh.This paper holds that the Palaeozoic unconformities in the southwestern Tarim Basin are mainly distributed in Southwestern Depression.From Bachu uplift to Maigaiti slope and to front belts of Kunlun Mountains,the unconformities develop strongly and the degree of superposed unconformities increases gradually.Under the control of the fault structure activities,Mesozoic and Cenozoic unconformities mainly develop in Bachu uplift and its peripheral regions.Angular unconformities develop inside Bachu uplift along the fault belt and disconformities and low angular unconformities develop in the south of Bachu uplift.The development and distribution of unconformities in the study area is associated with the evolution of Hetian paleouplift.The denudation thickness from Cambrian to Ordovician increased gradually with the largest denudation area in Yecheng-Hetian areas,reflecting the inherited development of the palaeohigh.The maximum denudation position shifted eastward from Silurian to Middle Devonian,which was related to the rise of the palaeohigh in the east and drop in the west.Because of the disappearance of Hetian palaeohigh and the rise of the west of Bachu uplift,Hetian paleouplift shifted towards Bachuuplift.Cenozoic denudation was mainly located at Bachu uplift,which was related to Bachu-Markit tectonic inversion.Structural restoration shows that Hetian paleouplift exist since the formation of Precambrian basement,and the evolution process consists of six stages,i.e.Initial basement uplift stage,Early-Middle Cambrian syn-sediment uplift stage,Late Cambrian-Ordovician inherited uplift stage,Silurian-middle Devonian strong uplift stage,Late Devonian-Permian initial disappear stage and Mesozic-Cenozoic tectonic inversion stage.During Early-Middle Caledonian,Hetian paleouplift was NW-NWW trending,with its high topographical located in the southwest of the study area;In early Hercynian,the trending of the paleouplift with a nose-like shape changed to nearly EW;At late Hercynian,this structure was gradually buried until topographically disappear.And the Himalayan period completely disappears.In conclusion,Hetian paleouplift inherits its general feature since the formation in early Paleozoic,but also shows local migration and spatial expansion characteristicsThe effect of the pre-existing faults at the basement,tectonic event at the periphery of basin,detachment layer and regional structure has together controlled the formation and evolution of Hetian palaeouplift.The faults at the basement makes the Hetian palaeouplift develop in the southwest depression,lying in NW or nearly EW.The extrusion stress caused by the closing of Kunlun ocean basin and Altyn-Tagh ocean basin,plate collision and uplift at the orogenic belt are the main power origin of the formation of palaeohigh.As far as regional detachment layer,the middle Cambrian gypsolyte has adjusted the diversion migration and transformation difference of palaeohigh at different periods.And the regional structural inversion effect takes the fracture at the south margin of Bachu uplift as the hinge to accelerate the burial and disappearance of Hetian palaeouplift in the Cenozoic ear.