广西凭祥中三叠世盆地沉积特征与构造属性分析  

Sedimentary Characteristics and Tectonic Setting of the Middle Triassic Pingxiang Basin, Guangxi

作　　者：宋博[1] 闫全人[1] 向忠金[1] 陈辉明[1] 马铁球 杨广元 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]湖南省地质调查院,长沙410011 [3]内蒙古第二水文地质工程地质勘查院,内蒙古鄂尔多斯017000

出　　处：《地质学报》2013年第4期453-473,共21页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40872147和41102141);中国地质调查局项目(编号1212011085415)共同资助的成果

摘　　要：凭祥中三叠世盆地位于印支地块与华南地块碰撞拼合的缝合带内,记录了沿华南地块南缘展布的古特提斯分支洋盆俯冲闭合、印支地块与华南地块碰撞拼合的过程。本文通过大比例尺实测地质剖面,详细测量了凭祥盆地沉积相序及其组合变化,分析了不同相序的沉积环境及其物源,并探讨了盆地构造属性。结果表明,凭祥盆地主要充填有深水盆地相、浊积扇相和三角洲相等不同环境的沉积物。中三叠世期间盆地呈现为一系列因碰撞拼合作用形成的构造高地间夹深谷的岩相古地理面貌。深水盆地相以发育大套深灰色泥页岩和裹夹碎屑流沉积为特征,碎屑流沉积发育于构造高地陡坡一侧。浊积扇相以发育槽模、正粒序、爬升波纹层理、包卷层理、双向交错层理、透镜状层理、平行层理为特征。三角洲相以发育大型板状交错层理、潮沟、厚层透镜状砂体和砖红色泥岩为特征,类似发育于俯冲汇聚环境下的牙买加型扇三角洲,可能发育于构造高地缓坡一侧。沉积作用分析表明,主要存在碎屑流、浊流等重力流作用,并识别出底流作用。古水流分析表明存在向南和向北两个方向的物质搬运。岩相学特征表明盆地砂岩成分成熟度和结构成熟度均较低,物源为再旋回造山带或碰撞造山带。本文研究结果认为:凭祥盆地是一个伴随古特提斯分支洋盆俯冲闭合而被强烈改造的残余弧前盆地,时空上与之相配套是北泗组岛弧型流纹斑岩。该弧盆系统可能于晚二叠世末开始发育,中三叠世末结束沉积充填,暗示印支地块和华南地块最终于中三叠世碰撞拼合。The middle-Triassic Pingxiang basin,located within the suture of Indochina and South China blocks, records the closure of the Paleo-Tethys and the collision of the Indochina and South China blocks. Based on the detailed analyses of the geological sections, sedimentary facies, and provenance of this basin were systematically studied in this paper, and then the tectonic setting of this basin was also discussed. Our new results indicate that the sediments of the Pingxiang Basin are dominated by deep-water basin facies, turbidite fan facies and delta facies deposits. A series of tectonic rises and deep valleys were developed during Middle-Triassic because of subduction and collision. The deep-water basin, which is composed of dark-grey mudstone with debris flow interlayers, is formed on the steep slope of the tectonic rises. The turbidite fan facies is characterized by flute cast, normal-graded bedding, climbing ripple lamination, convolute lamination, bidirectional cross bedding, lenticular bedding and parallel bedding. The delta facies, characterized by large tabular cross bedding, tidal creek deposits, thick lenticular sandbody and brick red mudstone, is similar to the Jamacia-type fan delta that is developed in a subduction-related tectonic setting, which probably occurs in a gentle slope of the tectonic rises. Sedimentation analysis indicates that the deposits are predominantly produced by debris flow, turbidity current, additionally, and bottom current. Paleocurrent flow suggests material is transported to north and south. Petrography features show that the sandstones, which have low compositional maturity and textural maturity, derived from recycled orogen or collisional orogen. Our result suggests that Pingxiang basin, considered as a synchronal product with arc-type rhyolite (the Beisi Formation), is an intensively modified remnant forearc basin that resulted from the closure of the Paleo-Tethys ocean. The sedimentation started in late-Permian and ended in the late stage of mid-Triassic, implying that the fi

关 键 词：凭祥盆地 沉积相序 残余弧前盆地 古特提斯 

分 类 号：P512.2[天文地球—地质学] P548