鲁西隆起晚中生代以来伸展断裂特征及形成机制

野外地质调查表明,鲁西隆起的伸展断裂十分发育,其构造样式复杂.主要形式为陡倾斜的伸展断裂和缓倾斜的滑脱断层组成的复合伸展断裂系统.陡倾斜的伸展断裂构成鲁西伸展断裂系的主体,是控制其南部凹陷沉积的边界断裂.断裂带中构造角砾岩、断层泥发育,并有小褶皱、擦痕等显示断裂活动的标志.缓倾斜的滑脱断层在鲁西隆起区广泛发育,分为深、浅两个层次,浅层次中最具规模的位于下寒武统与太古宇之间.滑脱面上盘的寒武系底部产生强烈的构造变形,褶皱和破碎带发育,下盘构造相对简单,仅挤压破碎.深层次滑脱断层发育在中地壳低速层处,控制着浅层次滑脱断层的形成与分布.构造应力场数值模拟结果显示,鲁西隆起的伸展断裂系统是由晚中生代以来两次大规模的伸展运动形成的,形成机制上,与中、新生代郯庐断裂的走滑活动、太平洋板块的俯冲以及岩浆上涌密切相关.

Characteristics and mechanism of Late Mesozoic extensional faults in West Shandong Uplift

Field survey performed in West Shandong Uplift indicates that extensional faults are well developed and characterized by complicated structural styles in West Shandong Uplift. The main structure style is the compound extensional fault system composed of high -angle faults and low -angle decollement faults. The high -angle faults, which dominate the sedimentation in the southern depression, constitute the main part of the extensional fault system in West Shandong Uplift. In the fault zone, there are dynamic breccia, fault clay, small folds and scraping trace making up signs of faulting activity. Regional decollement faults composed of shallow level faults and deep level faults were found in West Shandong Uplift. The most outstanding decollement faults of the shallow level are between Lower Cambrian and Archean and between Ordovician and Carboniferous. There are different structural deformational styles developed near the decollement surface: above it (in the lowermost part of the Cambrian) there occurred intense structure deformation resulting in folding and shattering, whereas the structures in the underlying Archean are relatively simple, only with extrusion and rupture. The decollement of the deep level controlling the formation and distribution of the shallow level decollement is mainly developed in the low-velocity layer of the crust. The result of the tectonic stress field numerical simulation shows that the extensional fault system has been formed by two stages of large scale extensional movement since Late Mesozoic. Mechanically, the extensional fault system is closely related to the Late Mesozoic-Cenozoic strike-slip activity of Tan-Lu fault zone, the subduction of the Pacific Plate and the magma upwelling.