东秦岭—大巴山逆冲推覆构造与油气远景

THRUSTING NAPPE STRUCTURE AND OIL-GAS POTENTIAL IN EASTERN QINLING AND DABA MOUNTAIN

扬子北缘有4套性质不同的原型盆地,即被动大陆边缘盆地(Pt3-O),周缘前陆盆地(D-C)、拗拉槽盆地(P-T),陆内前陆盆地(T3-K1)。扬子板块北缘古生代盆地经历了4期构造变动,但是对扬子北缘古生代盆地构造起决定作用的是晚加里东运动和晚印支—燕山期构造运动,而早、中海西期构造变动和晚海西至早印支期构造变动相对较弱。计算南秦岭-北大巴地区褶皱、应变、逆冲断层叠覆缩短量为918.8km。扬子北缘构造变形趋势由北向南从强变弱,由深变浅,形成了a)被动大陆边缘盆地构造变形样式构造组合:同斜褶皱—韧性逆掩构造组合,单向冲断—褶皱构造组合;对褶皱—逆冲构造组合;b)前陆盆地构造变形样式:斜歪褶皱-逆冲构造组合与等倾褶皱-逆冲构造组合;c)拗拉槽构造变形样式:等倾褶皱-对冲构造组合。川东北区发育4套烃源岩,主力烃源岩为下寒武统碳质板岩、上奥陶统-下志留统黑色硅质、泥质岩及二叠系碳酸盐岩和泥质岩、上三叠-下侏罗统湖沼相泥质岩。燕山晚期随着大巴山褶皱冲断带不断向南的推进,并对前期的北东向构造产生叠加改造,形成多层次的叠加褶皱。喜马拉雅运动以来区内的构造形变进一步加强,北西向构造进一步发育成型,形成现今的构造景观。大巴山逆冲推覆构造带构造变形在横向具分带性,在垂向上具分层性。在大巴山前,

In the northern margin of Yangtze Plate, there are 4 types of prototype basin, the passive continental edge basin (Pt_3-O), the peripheral foreland basin (D-C), the aulacogen basin (P-T), and the intracontinental foreland basin (T_3-K_1). The Paleozoic basin in the northern margin of Yangtze Plate has experienced 4 stages of tectonic event, among which the Late Caledonian orogeny and Late Indosinian-Yanshan movement play an important role, while the Early-Middle Hercynian orogeny and the Late Hercynian-Early Indosinaian orogeny are relatively weak. The superimposition shortening of the fold, strain and thrust fault in the Southern Qining-Daba area is 918.8km. The structural defrormation trend of the northern margin of Yangtze Plate changes from strong to weak and deep to shallow from the north to the south. This gives birth to: (1) structural deformation compositon of passive continental edge basin, i. e. isochinal fold-dustile thrust structural composition; unilateral thrust-fold structural composition; symmetical fold-thrust structural composition. (2) structural deformation compositon of foreland basin, including inclined fold-thrust and isoclinal fold-thrust structural composition. and (3) structural deformation of aulacogen, i. e. isoclinal fold-ramp structural compositon.Four systems of hydrocarbon source rock are found in the east of Sichuan. The main hydrocarbon source rock is the Lower Cambrian carbonaceous slate, Upper Ordovician-Lower Silurian black silicon and argilloaceous rock, Perminan carbonate rock and argillaceous rock, and Upper Triassic-Lower Jurassic limnetic argillaceous rock.In the final phase of Yanshan Movement, the fold thrust belt in Daba Mountain continues to move southward, and causes superimposition on the former north-east structure, forming multilayered superimposed fold. Since the Himalayan orogeny, the structural deformation in this area has been further strengthened, and the north-west structure comes into shape, which results in the present-day structure. The structural deformation of thrusting nappe structure in Daba Mountain is zonal crossuise and stratified vertically. In Daba Mountain, there exist 3 stratified decreases from noth to south. This forms 3 unbalanced layers. Different structural belts have different petroleum potential, since the series of strata involved in the deformation are different. The sturctural defromation intensity of thrusting fold structural belt is obviously weaker than that of imbricate thrusting belt. Vertically, the shallow deformation is strong while the deep deformation is weak. The shallow and deep structure are usually different. The upper deformation layer is not good reservoir. The lower layer broad and gentle, with fracture disappearing in the Silurian slips, can serves as good reservoir for oil and gas. Here is the new field for future exploration. The gentle fold structural belt, with least deformatin and newest exposure, has the best conditon for oil-gas reservation. It is the main area for petroleum exploration.