南海北部陆缘晚三叠世—中侏罗世盆地沉积充填与构造背景研究

The “Yuedong marine basin” had formed during Late Triassic to Early Jurassic in the north continental margin of South China Sea（south china continental margin and continental shelf-slope of north South China sea）, undergone the transgression of sea water. The “Yuedong marine basin” might be a remain of proto-South China Sea as well as the northwest Kalimantan marine basin. We focus on the strata of Late Triassic to Middle Jurassic in this program, studying basin depositional filling, evolution and sea-level change, and analyzing the provenance, stratigraphic depositional response to the tectonic setting of “Yuedong marine basin”.We determine magmatic origin and geodynamic settings based on the study on igneous rocks, zircon U-Pb chronology and petrogeochemistry of Early Jurassic and Middle Jurassic in Guangdong province and Hainan island. We study clastic zircon U-Pb chronology and petrogeochemistry of mudstones from Late Triassic to Middle Jurassic of Guangdong area, analysing types and distributions of provenance, combining the provenance - sedimentary system with igneous rocks, to search the existing evidences of the continental margin volcanic arc or the subduction zone, identifying the tectonic setting. Under the guidance of from land to offshore, we take the relative sea level change as a “bridge” within the united framework of the regional tectonics and basin forming system, take the igneous rocks and zircon ages as the key point to determine structural-volcanic event, and realize the contrast between land’s basin formation and sedimentation and marine’s. This program not only can remodel dynamic mechanics and evolution of the north continental margin basins of the northern South China Sea from Late Triassic to Middle Jurassic, but also is significant to deepwater petroleum exploration in north South China sea.

南海北部陆缘（华南陆缘和南海北部陆架-陆坡区）在晚三叠世—早侏罗世遭受海侵，形成“粤东海盆”，其与“西北加里曼丹海盆”可能是“古南海”的残留。本项目以南海北部陆缘上三叠统—中侏罗统为研究对象，研究盆地沉积充填、演化与海平面变化规律，分析物缘区和构造背景的地层和沉积响应；研究广东省和海南岛早、中侏罗世火成岩锆石U-Pb年代学和岩石地球化学，揭示岩浆成因和地球动力学背景；研究广东地区碎屑锆石U-Pb年代学和泥岩岩石地球化学，分析物源类型与分布，综合物源-沉积体系与火成岩研究，寻找火山弧或俯冲带存在的证据，分析构造背景。在由陆及海思想指导下，在区域构造成盆体制框架内，以海平面变化作为连接陆海的纽带，以火成岩及锆石年龄为确定构造-火山事件的关键环节，实现陆区和海区盆地地层和沉积的对比。该研究不仅对于重塑晚三叠世—中侏罗世南海北部陆缘盆地动力学机制和演化，而且对于南海北部深水油气勘探具有重要意义。

本项目以南海北部陆缘（华南陆缘和南海北部陆架-陆坡区）上三叠统—中侏罗统为研究对象，综合地质、岩石地球化学、同位素、锆石U-Pb测年和地球物理解释等方法，开展以下研究并取得相应成果：1）晚三叠世—中侏罗世广东地区经历了一次海侵-海退过程，最大海侵发生在早侏罗世早期。上三叠统—中侏罗统可划分为12个Ⅲ级层序、5个Ⅱ级层序和1个Ⅰ级层序，并建立了层序地层格架。2）晚三叠世华南陆缘可分为西部和东部两个物源区。西部沉积物主要来自云开地体，东部沉积物主要来自武夷地体以及华南陆缘东部的下伏沉积地层。早侏罗世华南陆缘分为西部，中部和东部三个物源区。云开地体和海南岛为华南陆缘西部的主要供给源区；东侧隆升的武夷地体和南岭地区为华南陆缘东部沉积物提供了大量的碎屑物质；中部地区由于早侏罗世发生的海侵，发育广阔的浅海环境，海流和被海水淹没的水下河谷是主要的碎屑物质搬运路径。中侏罗世华南陆缘沉积物主要来自武夷地体和由古太平洋板块俯冲引起的一条岩浆弧。晚三叠世—中侏罗世华南陆缘处于伸展构造背景。3）海南岛勤赛地区发育一套辉长岩-闪长岩-二长岩-正长岩的侵入岩岩石组合。二长岩形成时代为179.0±2Ma，辉长岩形成时代为179.5±3Ma，均为早侏罗世晚期侵入岩。正长岩是由辉长岩分异演化形成的，二长岩和闪长岩是分异的中间产物，该套侵入岩形成于伸展背景下。粤东梅州霞岚的早侏罗世双峰式侵入岩属于伸展环境产物。4）南海北部陆架-陆坡区晚三叠—中侏罗世经历了一个海侵—海退过程。最大海侵发生在早侏罗世。上三叠统—中侏罗统可划分出12个Ⅲ级层序、5个Ⅱ级层序和1个Ⅰ级层序，并建立了层序地层格架。晚三叠世—中侏罗世南海北部陆架盆地为坳陷盆地。5）华南陆缘与北部陆架-陆坡区上三叠—中侏罗统是在Ⅰ级层序控制下发育的5个Ⅱ级层序和12个Ⅲ级层序。华南陆缘和北部陆架-陆坡区层序地层可进行对比，Ⅲ级层序是对比的基础。