渤海湾中部中、新生代构造演化与潜山的形成

Mesozoic-Cenozoic tectonic evolution and buried hill formation in central Bohai Bay

渤海湾盆地是华北克拉通东部的晚中—新生代断陷盆地,其东部为西太平洋活动大陆边缘,经历了多期不同性质的构造运动叠加。目前对渤海湾地区中—新生代的构造期次划分及各期次构造运动的应力状态的认识仍存在较大的争议。潜山是盆地沉积之前就已形成的基岩古地貌山,后被新地层覆盖而成,潜山内幕所保留的先存断裂及潜山与上覆盖层之间的接触关系为研究盆地构造运动提供了依据。本文以渤中19-6潜山构造为例,基于三维地震资料的精细解释、结合相干剖面及钻井资料进行系统构造解析,建立渤中19-6潜山构造演化新模型,并探讨了华北克拉通东缘的区域构造演化。研究结果表明:(1)渤中19-6潜山构造西部以一系列S-N向雁列式正断层为界,断层东侧为隆起的渤中19-6潜山构造,西侧为低洼的沙南凹陷。古潜山最早形成于晚三叠世,早白垩世形成如今以S-N向正断层为界的东隆西降的潜山构造格局;(2)渤中19-6潜山构造西部边界S-N向断裂以及上覆地层中存在的E-W向断裂为两侧大型走滑带间雁列式断裂构造,是该潜山构造储层形成的重要控制因素;(3)该潜山受华北板块与扬子板块剪刀式闭合碰撞和古太平洋板块NNW向俯冲的多重影响,中生代以来,共经历了印支早期挤压隆起、印支晚期伸展改造、燕山早期左行压扭改造、燕山中期左行伸展改造、燕山晚期左行压扭改造、喜山期右行伸展埋藏6个阶段的发育演化。

The Bohai Bay Basin is a Late Mesozoic-Cenozoic faulted basin in the eastern North China Craton.Located in the continental active margin of the western Pacific Ocean,the Bohai Bay Basin experienced multi-stage tectonic movements of various types.Currently there is still much controversy over the divisions of tectonic stages and stress fields for each tectonic movement in the Bohai Bay Basin during the Meso-Cenozoic.Buried hill is a palaeogeomorphologic feature formed before the basin filled and then buried by new sedimentary cover.The pre-existing faults inside the buried hill and the contact relationship between the buried hill and the overlying new strata provide an evidence basis for studying the tectonic movement in the basin.Choosing the Bozhong 19-6 buried hill as an example,this paper proposes a new structural model for the buried hill,based on the 3D seismic interpretation and systematic structural analysis of coherent seismic profile and drilling data,and discusses the regional tectonic evolution of the eastern North China Craton.The current structural characteristics of the Bozhong 19-6 buried hill are:(1)The buried hill is bounded by a series of S-N-trending normal faults,which separates it to the east and the Shanan Depression to the west.The buried hill first appeared in the Late Triassic and formed in the Early Cretaceous.(2)The S-N-trending boundary faults and the E-W-trending faults within the buried hill are formed by the transpressive strain due to the regional strike-slip faults along either sides of the buried hill,which are the important controlling factors for the structural reservoir in the buried hill.(3)The buried hill,impacted by the scission-type collision between the North China and Yangtze Plates and the NNW-ward subduction of the Paleo-Pacific Plate,underwent six-stage tectonic evolution since the Mesozoic era:the Early Indosinian compression,the Late Indosinian extension,the Early Yanshanian sinistral transpression,the Middle Yanshanian sinistral transtension,the Late Yanshanian sinistral transpression,and the final Himalayan transtension.