南海北部陆缘中、新生代流纹岩基本特征研究

发布时间：2018-02-24 01:12

  本文关键词： 南海北部陆缘 流纹岩 中、新生代 基本特征　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：位于多个板块交汇区的南海,在地质历史中经历了复杂多变的演化过程,晚中生代以来先后经历了古南海的闭合和现代南海的开裂。南海北部的大陆边缘,在晚中生代和早新生代具有完全不同的构造性质并存在从活动大陆边缘向被动陆缘的重大构造转换。本文基于对琼南、茂名、和三水等地不同地质时期流纹岩的专题研究,通过年代学、岩相学、地球化学和构造背景的综合分析,取得以下重要认识:南海北部陆缘存在有多种类型流纹岩,流纹岩的喷发年代有所不同,琼南地区流纹岩一般产出于早白垩世(121Ma~98Ma),茂名盆地、长塘盆地等地区归属于晚白垩世(100Ma~96.8Ma),它们可能对应于活动陆缘背景,唯有三水地区流纹岩样品经分析产出于新生代(63.9Ma~28.5Ma),相当于被动陆缘裂解的时代;在岩石岩相学方面,茂名盆地、兴宁盆地、海南岛等地流纹岩样品斑晶常见石英、斜长石,酸性程度大于三水盆地;三水盆地流纹岩斑晶中石英含量较少,长石多被风化破碎,且斜长石微晶呈定向-半定向排列;在地球化学特征方面,茂名盆地、海南岛等地流纹岩属于过碱质高钾钙碱性系列,轻重稀土分馏程度高,具有轻微的Eu负异常,富集Th、U、K等大离子亲石元素,而亏损Nb、Ta等高场强元素;三水盆地样品呈现出由过铝质高钾钙碱型向过碱质高钾钙碱性系列流纹岩过渡,其轻重稀土总量远大于茂名盆地、海南岛等地样品,但轻重稀土分馏不明显,具有强烈的Eu负异常,与典型的大陆裂谷碱性流纹岩具有较好的一致性,富集Rb、Th、U等大离子亲石元素与Ta、Nb、Zr、Hf高场强元素;研究表明,茂名盆地、海南岛等地流纹岩具有典型的会聚陆缘火山弧的特征,而三水盆地流纹岩则表现出鲜明的板内或造山期后背景;两系列岩石虽然同为壳源,但前者岩浆源区深度却大于后者,且茂名盆地和海南岛岩浆源区不均一,呈轻微的混合或混染现象,反映出典型会聚陆缘岩浆作用的复杂性;与处于著名的古太平洋俯冲条件下的浙闽地区流纹岩相比,茂名、海南岛等地的流纹岩在岩石地球化学特征、岩石成因,以及构造演化阶段等方面,都表现出系统性的差异性。
[Abstract]:The South China Sea, which is located at the intersection of several plates, has undergone a complicated and changeable evolution process in geological history. Since the late Mesozoic, it has experienced the closure of the ancient South China Sea and the cracking of the modern South China Sea, and the continental margin of the northern part of the South China Sea. The late Mesozoic and early Cenozoic have completely different tectonic properties and there is a major tectonic transition from active continental margin to passive continental margin. This paper is based on a special study of rhyolite in different geological periods in Qiongnan, Maoming and Sanshui, etc. Based on the comprehensive analysis of geochronology, petrography, geochemistry and tectonic background, the following important understandings are obtained: there are many types of rhyolite in the northern continental margin of the South China Sea, and the eruption age of rhyolite is different. The rhyolite occurred in the early Cretaceous, Maoming basin, Changtang basin and so on, which belong to the late Cretaceous Ma100 Ma-96. 8 Ma-member, which may correspond to the active continental margin background. Only the rhyolite samples in Sanshui area were analyzed and produced in the Cenozoic age of 63.9 Ma-28.5 Ma-which is equivalent to the age of passive continental margin pyrolysis. In petrolithology, the porphyry quartz and plagioclase are common in rhyolite samples from Maoming basin, Xingning basin and Hainan Island, etc. The content of quartz in rhyolite porphyry in Sanshui basin is less than that in Sanshui basin, the feldspar is mostly weathered and broken, and the microcrystal of plagioclase is orientation-semi-directional. The rhyolite in Hainan Island belongs to a series of peralkalic high potassium calc-alkaline series with high fractionation degree of light and light rare earth elements with slight EU negative anomalies and enrichment of large ion lithophile elements such as Thu UK and depletion of high field strength elements such as NbTa-Ta. The samples of Sanshui basin show a transition from peraluminous high potassium calcium alkali type to peralkalic high potassium calcium alkaline series rhyolite. The total amount of heavy and heavy rare earth elements is much larger than that of Maoming basin and Hainan Island, but the fractionation of light and heavy rare earth elements is not obvious. There are strong negative EU anomalies, which are consistent with the typical continental rift alkaline rhyolite, and are rich in RbPU and Ta-NbsZrHf elements, the study shows that the Maoming basin is characterized by high field strength. The rhyolite in Hainan Island has typical characteristics of converging continental margin volcanic arc, while the rhyolite in Sanshui Basin shows a distinct intraplate or post-orogenic background. Although the two series of rocks are both crusts, the former magmatic source is deeper than the latter. The magma source areas of Maoming basin and Hainan Island are not uniform, showing a slight mixing or mixing phenomenon, which reflects the complexity of magmatism in typical convergent continental margin, and compared with the rhyolite of Zhejiang and Fujian regions under the famous paleo-Pacific subduction condition, Maoming, The rhyolite in Hainan Island shows systematic differences in petrogeochemical characteristics, petrogenesis, and tectonic evolution stage.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.141
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本文编号：1528310