南海北部陆缘新生代岩浆活动及构造意义

发布时间：2018-04-17 13:59

本文选题：南海北部陆缘 + 火成岩　；参考：《中国科学院研究生院(海洋研究所)》2014年博士论文

【摘要】：南海及其周边广泛发育的火山活动记录了南海演化以及相关的深部动力学过程的重要信息,开展南海火成岩的研究对于理解南海地区张裂陆缘的构造性质、海底扩张、壳幔作用、以及资源效应均有重要的科学意义。本文利用2D/3D地震资料,并参考最新的钻井和大洋钻探资料以及重磁数据,结合区域地质背景,重点研究了南海北部陆缘火成岩的地震特征,分析了岩浆岩的几何产状、形成时间和分布规律。讨论了火成岩的形成机制,南海北部大陆边缘的类型及构造性质以及地幔柱对裂后岩浆活动的影响。取得以下成果:1)建立火成岩识别标准,在南海北部识别出两大类火成岩-侵入型和喷出型,并精细刻画各类火成岩体的地震反射特征。根据能量的强弱,进一步将侵入型分为刺穿型和隐刺穿型。根据外形特征,进一步将喷出型分成平顶海山和尖顶锥状海山。统计了各类火成岩体在南海北部分布的数量和规模。在地震数据包含的可分辨尺度信息的前提下,总结了三种判别火成岩形成时期的标准。据此,将南海北部陆缘岩浆活动分为三期,并讨论各期次的分布规律;2)分析本区岩床复合体的组合形式和形成机制,指出本区岩床复合体几何产状多为碟状,以个体或互相结合的方式在白云凹陷西部下中新统中广泛分布。判断形成时间为15.5Ma,表明海底扩张结束后,残余岩浆将裂谷期断层作为岩浆通道,深部大岩床成为其上小岩床的根部岩浆供给。岩浆通过水平不连续面,由内岩床放射性的向外岩床提供岩浆,形成新的岩床;3)总结四点支持南海北部陆缘为非典型岩浆匮乏型大陆边缘的证据:南海北部陆缘存在接近洋壳广泛的分布于下陆坡并明显集中在向海一侧的岩浆岩带;存在与裂谷盆地相关的高角度铲式断层,并终止于断凹转换面S23.8即存在裂后延迟;OCT处地壳厚度明显减薄;裂谷期间没有地幔柱的作用和影响。讨论晚中新世以来出现在琼东南盆地,莺歌海盆地及西沙海区的异常热沉降与岩浆活动的关系;4)刻画自晚燕山期至今岩浆活动演化图,表明南海北部陆缘的岩浆作用受太平洋板块俯冲和欧亚碰撞共同影响。讨论海底扩张结束后,地幔柱可能作为主导因素影响着岩浆活动的发生时间和规模。结合海南地幔柱半径小、上升速度慢、温度低等特点分析其引起大规模岩浆活动延迟的原因。
[Abstract]:The extensive volcanic activity in and around the South China Sea records the important information of the evolution of the South China Sea and related deep dynamic processes. The study of the igneous rocks in the South China Sea is useful in understanding the tectonic properties of the extensional continental margin in the South China Sea and the undersea expansion.Crust-mantle interaction, as well as resource effects, are of great scientific significance.Based on the 2D/3D seismic data, the latest drilling and ocean drilling data and gravity and magnetic data, combined with the regional geological background, the seismic characteristics of igneous rocks in the northern continental margin of the South China Sea are emphatically studied, and the geometric occurrence of magmatic rocks is analyzed.Formation time and distribution.The formation mechanism of igneous rocks, the types and tectonic properties of the continental margin in the northern part of the South China Sea and the influence of mantle plume on post-rift magmatic activity are discussed.The following results are obtained: 1) establish the igneous rock identification standard, identify two major types of igneous rocks-intrusive and ejection types in the northern part of the South China Sea, and characterize the seismic reflection characteristics of various igneous rocks in detail.According to the strength of energy, the invasive type is further divided into piercing type and implicit piercing type.The ejection type is further divided into flat-topped seamounts and pointed conical seamounts according to their shape characteristics.The quantity and scale of distribution of various igneous rocks in the northern part of the South China Sea are calculated.On the premise of the discernible scale information contained in seismic data, three criteria for distinguishing igneous rocks are summarized.Based on this, the magmatic activity in the northern margin of the South China Sea is divided into three stages, and the distribution of each stage is discussed. (2) the assemblage form and formation mechanism of the rock bed complex in this area are analyzed, and it is pointed out that the geometric occurrence of the rock bed complex in this area is mostly disheveled.It is widely distributed in the lower Miocene in the west of Baiyun sag.The judging time of formation is 15.5Ma. it shows that the residual magma takes the rift fault as the magmatic channel and the deep rock bed becomes the root magma supply of the upper and smaller rock bed after the undersea expansion.Magma passes through horizontal discontinuities, providing magma from the radioactive inner rock bed to the outer rock bed,The formation of a new rock bed 3) summarizes the evidence that the northern margin of the South China Sea is an atypical magmatic deficient continental margin: the northern margin of the South China Sea has a magmatic belt close to the oceanic crust and widely distributed on the lower slope and obviously concentrated on the seaward side;There are high-angle shovel faults related to rift basins, and the crust thickness is obviously thinned at post-crack delay Oct when it terminates at S23.8, and there is no effect of mantle plume during the rift.The relationship between anomalous thermal subsidence and magmatic activity in the Yinggehai basin and Xisha sea area since the late Miocene is discussed.It shows that the magmatism in the northern margin of the South China Sea is influenced by the subduction of the Pacific plate and the Eurasian collision.It is discussed that the mantle plume may be the dominant factor influencing the occurrence time and scale of magmatic activity after the undersea expansion.According to the characteristics of Hainan mantle plume, such as small radius, slow rising speed and low temperature, the reasons for the delay of large-scale magmatic activity are analyzed.
【学位授予单位】：中国科学院研究生院(海洋研究所)
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P736.1

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