燕山中元古代裂谷早期同沉积断裂活动及其对事件沉积的影响

THE EARLY SYNSEDIMENTARY FAULTING OF THE MESO-PROTEROZOIC YANSHAN RIFT AND ITS INFLUENCE ON EVENT SEDIMENTATION

在早期长城纪演化阶段 ,燕山中新元古代裂谷盆地构造拉张活动明显 ,它控制了整体沉积相带的展布 ,并在强烈活动期引发了一系列事件沉积。长城纪时期的古构造活动主要以 4种方式影响盆地的充填 ,即同沉积断裂活动、构造掀斜 ,轴部强烈拗陷和整体的均衡沉陷。其中 ,同沉积断裂活动在长城纪盆地演化过程中具有突发性或脉动活动的特点 ,记录了古地震、碳酸盐滑塌沉积和碎屑浊流沉积 ,并诱发火山活动形成火山碎屑重力流等地质事件。盆地的古水流、地层格架及特征沉积相带等分析显示 ,盆地主体展布为NE向 ;燕山元古代裂谷向外海出口的位置应处于中朝准地台的北部 ;现今所见崇礼—承德—北票EW向断裂在长城纪大部分时期对盆地的沉积充填没有明显影响。

The principal part of the Meso Neoproterozoic Yanshan Rift Basin is located in Hebei and Liaoning provinces of North China. An obvious rifting of the Yanshan Basin occurred in the early stage of the Mesoproterozoic, named Changchengian about 1800～1400 Ma. Sedimentary fills of the basin during this period are earliest deposits within the covering strata after formation of the crystalline basement of the Archaeozoic-Paleoproterozoic. The Changchengian of the early Mesoproterozoic mainly consists of five Formations, namely, Changzhougou, Chuanlinggou, Tuanshanzi, Dahongyu and Gaoyuzhuang Formations. During the Changchengian the palaeotectonic activities of the basin controlled the basin fillings in four ways, that is, synsedimentary faulting, structural tilting, and intent subsidence in basin axis and equilibrium subsidence in entire basin. In particular, the synsedimentary faulting, characterized by abrupt or pulsing activities, controls the distribution of main facies belts of the basin. During the intense periods of the basin, the synsedimentary faulting also caused a series of event depositions, such as palaeo seismic records, carbonate slumping, clastic turbidites, and volcanism-induced volcanic turbidite deposits. Analyses of palaeocurrent, stratigraphic framework, and special facies belts show that the main axis of the basin is along NE direction. The outlet position, towards open sea, of the intracontinental rift basin probably was located in the north part of the Sino Korea Paraplatform and the basin infilling during the Changchengian was not obviously affected with the E W direction (from Chicheng to Beipiao) faulting.