Tectonic Characteristic And Analysis Of Petroleum Geological Conditions In The Motianling Area

Based on the field geological survey,combined with structure geology,petroleum geology,sedimentology and so on.,the paper makes a comprehensive analysis to the Motianling area,such as its structural location,tectonic characteristic,tectonic evolution,petroleum geological conditions and so on.Motianling area is located in N32°-34°,E103°-107°,across the Sichuan,Shaanxi and Gansu provinces,with an area of ten thousands square kilometers.It is separated from the Songpan-Garze tectonic zone by the western Minjiang fault zone,adjacent with the west Qinling tectonic zone for the north Maqu-Lueyang fault zone,approach to the Longmenshan tentonic zone for the south Qingchuan-Pingwu fault zone,so its tectonic feature is like a triangle zone.The area exposed Indo-Chinese Epoch granites,and its distribution generally along the NEE,geochemical analysis shows that the rock is volcanic arc syn-collisional granite.Overall,the study aera is a duplex anticline,and could be divided into three sub-fold belt:Bikou duplex anticline,Xuebao ding-Huanglong fold belt and Maoxian-Fangshi fold belt.The three structural sections through the Motianling structure zone,show that,this aera form fold deformation,the anticline north limbs more reversed,the axial incline to the south.And the fold belt develop series of imbricated thrust fault.So these features indicate that this area suffer from south to north compression.The study of the fault systems show that the Motianling structure zone suffer from different direction compressions in the geological period.The structural deformation of the study area can be divided into the basement and cover deformation.The cover deformation perform thrust nappe structure and the extensional detachment.The fold deformation impact by the rock competent.The weak competent strata form close,asymmetrical and overturned fold.And with the strong competent strata,the deformation is weak,symmetric and broad.Since the Archaeozoic era,the Motianling area experienced Jinning-Caledonian -Hercynian-Indo chinese-Yanshanian-Himalayan tectonic activites,divided into three main stages of tectonic evolution:①The evolution of the old basement and trough from the Archaean to the early late Proterozoic.②The polycyclic evolution of Pan-Yangtze continent from late Proterozoic to Paleozoic.③The tectonic evolution of Mesozoic era. Through the stratigraphic development,geology structure section,analysis of the samples tested,the study area develop of the Silurian shale and carbonaceous shale Source Rock mainly,Upper Paleozoic carbonate reservoirs,the Triassic mudstone caps.And form of the source-reservoir-cap combination:Silurian～Devonian(source rocks)-Devonian～Triassic(reservoir)-Triassic(regional cap).From the development of source-reservoir-cap combination,oil-gas show and tectonic activity,the study area has some oil-gas prospect,and could find the favorable structure position within the Xuebaoding-Huanglong fold belt.