Comparative Research On Tectono-Thermal Evolution Of The Eastern And Western Kuqa Depression

The continuous collision between the southern margin of the Indian plate and the southern margin of the Eurasian plate during the Cenozoic led to the reactivation of the southern Tianshan Mountains and the formation of the Kuqa geodetic basin in the northern margin of the Tarim Basin.Because of its special tectonic position,there are abundant evolutionary records of the Southern Tianshan Mountains,and the study of these records is also the focus of long-term attention at home and abroad.However,previous studies on the thermal evolution history of the Kuqa area mainly focus on a certain tectonic unit or a certain section,but the systematic comparative studies on the east and west of the depression are few,and the studies on the tectonic-thermal evolution of the whole area are still insufficient.To enrich the data on tectonic-thermal evolution in the Kuqa Depression,it is necessary to make a comparative study of tectonic-thermal evolution in the east and west of the Kuqa Depression.Based on the above purposes,the present geothermal gradient and terrestrial heat flow distribution characteristics of Kuqa Depression are calculated and analyzed in combination with drilling temperature measurement data in the study area,and the burial-thermal history of the eastern and western Kuqa Depression is reconstructed.On this basis,the thermal history of typical core samples and outcrops of Kuqa Depression is recovered by combining apatite fission track and apatite(U-Th)/He.The meso-Cenozoic tectonic cooling events and thermal evolution history of source rocks in the eastern and western Kuqa Depression and its surrounding areas were revealed,and the following understandings were obtained:The present geothermal gradient of 0～5000m in Kuqa Depression is between16～28.6℃/km.The current earth heat flow value of Kuqa depression is between 40～50m W/m~2,which belongs to a low heat flow cold basin.The simulation results of the reverse fault show that the temperature of the reverse fault activity in this area changes from 25.6℃/km to 54.5℃/km at 1～10Ma,and the fault slip rate is the main reason affecting the temperature change.Apatite fission track and apatite(U-Th)/He thermal history simulation reveal three tectonic cooling events in the Meso-Cenozoic Kuqa Depression and its surrounding areas:Late Jurassic-Early Cretaceous(collision between Qiangtang and Lhasa plate),Late Cretaceous-Early Paleogene(collision between Kohistan-Dras Island arc and Lhasa terrane on the southern margin of Asia),Pliocene(collision between the southern margin of Eurasia plate and India plate).The paleo heat flow evolution in the Kuqa area can be divided into two modes:(1)The strata in the eastern Kuqa Depression continued to settle from Triassic to Neogene,and the earth heat flow decreased to 35 m W/m~2 at the lowest level,then increased rapidly and reached the maximum at present;(2)There was a tectonic movement in the western Kuqa Depression at the end of Paleogene which resulted in rapid subsidence.Most of the Jurassic source rocks in the Kuqa Depression were in the low maturity stage at the end of the Late Jurassic.At the end of the Late Cretaceous,Jurassic source rocks in the eastern and western Kuqa Depression entered the middle maturity stage.At present,most of the Kuqa depression is in the middle maturity stage,and the distribution characteristics are low in the east and high in the west.Combined with low-temperature thermochronology and drilling data,this paper reveals the tectonic-thermal evolution history of the eastern and western Kuqa depression and the thermal evolution history of the main source rocks in the Kuqa depression,which not only enriches the study of the thermal regime of the Kuqa depression but also has important significance for regional tectonic evolution and oil and gas resource exploration and evaluation.