Tectonic Evolution And Hydrocarbon Accumulation Conditions In Chuxiong Basin

Chuxiong Basin locates in the southwest margin of the Yangtze plate,as well as in the south of Sichuan-Yunnan rhombic block and in the southern section of SN strike central tectonic belt of China which is on the joint zone of the Tethys tectonic domain and the west coast Pacific tectonic domain.It is adjacent to the Simao-Indochina block westward and Songpan-Ganzi block northward,and bounded by the Red River Fault in Southwest,Xiaojinhe-Longmenshan Fault in the north and Xiaojiang Fault in the east.This special tectonic location means that the Chuxiong basin has experienced complex tectonic evolution during the opening and closing of the Tethys ocean.Since Mesozoic,the basin suffered from a pair of extrusion forces of northward direction from the Tethys tectonic domain and westward direction from the marginal Pacific tectonic domain,suffered from multi-age,multi-direction forces from periphery blocks.According to the problems of complex structure and low signal-to-noise ratio of seismic data origin from intense tectonic deformation of relict basin,several countermeasures or approaches are put forward in seismic data acquisition,processing and interpretation to improve the quality of seismic profiles and the reasonability of interpretation.For the characteristic that the different tectonic units of the basin which enclosed and cut by several lithospheric or crustal faults which experienced different tectonic evolution process independently,a model of complex rifting or multiple-causes rifting is put forward under the regional compressive stress background caused by the diagonal extrusion forces on the basement faults which can well explain the cause and formation mechanism of Chuxiong rift basin under the regional compressive tectonic background of late Triassic as well as the layer-block differentiation features of tectonic evolution process since Paleozoic.Based on the results of seismic data interpretation,the characteristics and evolution history of tectonic and its prototype in each tectonic stage of the basin are careful analyzed and discussed according to the depositional-structural features along with the peripheral tectonic evolution background.Several controversial geological questions are demonstrated,reasoned or answered during the study of tectonic evolution.It is stated that the prototype of the Chuxiong basin in late Triassic is a extensional basin rather than a foreland basin though it is bordered by the Jinshajiang-Red river collision belt after the conjunction of Indochina block and Yangtze Plate.The Red River Fault was mainly in strike-slip motion because of the small angle between the strike of the Fault and the movement direction of Indochina block,and didn't give rise to large scale mountain orogenesis.Thereafter,the Chuxiong Basin was evolved into a rifted basin in the SN directional extrusion forces in the late Indosinian period.It is also demonstrated that the existence of Kangdian rift system in Chuxiong basin in the early later Triassic;The abrupt change of sedimentary thickness in the region of Chuxiong-mouding originated from the pull-apart effects during the striking-slip movement of Chuxiong-jianshui Fault and Mouding Fault.The tectonic evolution plays an important controlling role on the hydrocarbon accumulation conditions of Chuxiong basin: Three intense extension period devoloped three sets of high-quality hydrocarbon source rocks.Multiple lifting movement gave rise to several sets of reservoir and cap rock.TheYanshan movement formed a large number oil and gas reservoir along with gentle folding and massive oil and gas migration which strongly refolded,adjusted and destroyed in the Himalayan movement.The characteristics of layer-block differentiation tectonic evolution determine the intensity of deformation in the later tectonic reworking and oil and gas preservation conditions of different units.Based on the comprehensive analysis,five favorable target areas are put forward in next oil and gas exploration.