Igneous Rock Anomaly Separation And Mesozoic Thickness Estimation Of Qiangtang Basin

Qiangtang Basin is developed at the east Tethys structure in Qinghai-Tibet Plateau with large potential of oil and gas.It's also the largest meso-neonatal residual basin in China within the orogenic belt with good natural gas hydrate formation conditions and prospecting potential.In order to understand the formation and sedimentary environment of gas hydrate in Qiangtang basin,it is necessary to delineate the thickness of the main hydrocarbon-generating layer,the Mesozoic sediments and its cap layer.Focusing on the thickness of Mesozoic,this research carried out the study on thickness estimation technique with gravity and magnetic anomalies and completed comprehensive inversion to the thickness of Mesozoic sediment in Qiangtang basin,which provides important evidence and data for gas hydrate potential assessment and subsequent exploration in the basin.Main work and progress gained by this research are as follows:(1)Based on gravity,magnetic and geological data collection and coordination of Qiangtang basin,gave the technical process of anomalous igneous rock stripping and Mesozoic sediment thickness estimation.Through the identification and stripping of igneous rock,the concealed and semi-cryptosphere of the Qiangtang Basin were delineated The igneous rocks are distributed and stripped of the gravity anomalies generated by the igneous rocks in the Tanggula Mountains area.The depth distribution of the Mesozoic top and bottom interfaces in the Qiangtang Basin was obtained by variable density constrained inversion,and then the Mesozoic sediment thickness distribution in the Qiangtang Basin was estimated.(2)Concentrated areas of concealed and semi-concealed igneous rocks in Qiangtang basin are Geladandong area to east of the basin and Tanggula Mountain area.Part of the igneous rock body at Tanggula Mountain area is exposed,and depth to the bottom is 5500 m.Its thickness varies from 200 m to 2000 m.The result is more accurate after the gravity anomaly of the igneous rocks are effectively removed.(3)Depth to the Mesozoic bottom in the northern part of Qiangtang basin variesfrom 2.5km to10 km,and this depth in the southern part of the basin changes between0.5km to 8.5km.Depth to the bottom of Cenozoic in the north part of Qiangtang basin changes from 0.1km to 1.5km,and it varies from 0 to 1km in the south part.(4)Thickness of the Mesozoic sedimentary strata in Qiangtang basin changes from 0 to 9.5km.And the main sedimentary areas of Mesozoic are located at Zangsegangri,Quedancuo,Bandao Lake,Puruogangri,Quemocuo,and Mugagangri,where Mesozoic sediment is greater than 6km thick.While thicker results in Zulken Wula Mountain and other areas are may not reveal the actual thickness due to incomplete removal of igneous anomalies.