燕山构造带中段早白垩世盆地特征

燕山构造带中段主要包含3个早白垩世盆地,即滦平盆地、凤山盆地、石人沟盆地.通过对盆地的沉积相分析、古水流的恢复以及盆地构造-沉积演化研究,认为燕山构造带中段早白垩世盆地发育分为三个阶段,即早期火山喷发阶段、中期强烈断陷阶段和晚期填平阶段.早期发育强烈的火山作用,形成以酸性火山岩为主的张家口组;中期盆地主体呈半地堑状,受单一边界主断层控制,盆地相互独立,盆地边缘以冲积扇砾岩和扇三角洲砂岩、砾岩沉积为主,盆地中心为湖泊细粒沉积.古流向和物源恢复结果证明,盆地沉积物主体来自于北部和/或西部的变质岩基底.盆地构造沉降和沉积充填过程主要受边界正断层的控制,断层下盘基底岩石的抬升与盆地边界正断层活动相关,从而成为盆地主要的物源区.

Early Cretaceous Basin Characteristics in the Middle Segment of Yanshanian Stuctural Belt

There were three Early Cretaceous basins(Luanping Basin,Fengshan Basin and Shirengou Basin) in the middle segment of Yanshanian stuctural belt.According to sedimentary facies analysis,paleo-current directions,provenance and tectono-sedimentary evolution,the Early Cretaceous basin evolution in the belt can be divided into three stages.The first stage is featured by vigorous volcanic eruptions and developed Zhangjiakou Formation which consists of acid igneous rock.The second is characterized by extensional subsidence.The third is basin filling stage.During second stage the basins were mainly asymmetric half-graben,which were separately controlled by single fault.Alluvial fan and fan delta are dominated basin marginal areas,while fine-grained lacustrine sediments were well developed in the basin centre.Sediments mainly came from metamorphic basements on the north and/or west,only small proportion from southeastern margin,as indicated by restored paleo-current directions and provenance.Tectonic subsidence and deposition sedimentation were primarily controlled by basin border normal faults.Uplift of basement rocks of the footwall was due to the tilting of border faults and became main provenance areas.