三塘湖盆地构造应力场特征

Stress Field Characteristics of Structures in Santanghu Basin

二叠系前陆盆地与中生界坳陷盆地叠置构成了三塘湖盆地主体,通过对二叠系和中生界两个主要构造层古构造形迹组合样式分析,认为海西运动期—燕山运动期三塘湖盆地一直处于从南向北挤压应力环境,区域应力场近南北向。海西运动期由于岔哈泉凸起砥柱作用,在马朗凹陷转变为旋扭应力场,从而形成帚状构造体系;燕山运动期条湖凹陷近于平行四边形的边界条件,使得近南北向区域应力场转变为直扭应力场,从而在凹陷北坡形成雁行式构造体系。盆地南缘自海西运动期以来始终处于北东向正压力作用的前缘地带,发育多个大型滑脱断层,形成一系列滑覆构造体系,这些构造体系或单列或叠置,尤其是马朗凹陷南缘,白衣山石炭系推覆体之下二叠系内多个滑覆构造体系叠置,构成三角构造带。三角带断层及裂缝极为发育,是形成裂缝性油气藏的有利区带。

Host formation in Santanghu basin is made up of Permian foreland basin superimposed with Mesozoic depression basin. It is considered that Santanghu basin was in a south-north compressional stress environment from Hercynian to Yanshanian stages, and the regional stress field was nearly south-north by analysis of the palaeostructural trackway patterns of Permian and Mesozoic. In Hercynian stage, the compressional stress field changed into rotational shear stress field in Malang sag, and thus led to the creation of brush structural system, due to the nuclear column effect of Chahaquan swell. In Yanshanian stage, the nearly parallelogram boundary of Tiaohu sag made the nearly south-north regional stress field turn into a normal shear one, hence an en echelon structural system formed at the north slope of the sag. The southern margin of the basin has always been in a frontal belt of north-east positive pressure since Hercynian stage, so many huge decollement faults and s series of gliding nappe systems with single-row or superimposed styles developed. In the southern margin of Malang sag, several superimposed gliding nappe systems exist in the Permian strata beneath Baiyishan Carboniferous nappe, forming striangle structural belt. With abundant faults and fractures, the triangle belt could be a favorable area for fractured reservoirs.