本文關鍵詞： 南海北部陸緣 流紋巖 中、新生代 基本特征　出處：《中國地質大學(北京)》2017年碩士論文　論文類型：學位論文

【摘要】：位于多個板塊交匯區(qū)的南海,在地質歷史中經歷了復雜多變的演化過程,晚中生代以來先后經歷了古南海的閉合和現代南海的開裂。南海北部的大陸邊緣,在晚中生代和早新生代具有完全不同的構造性質并存在從活動大陸邊緣向被動陸緣的重大構造轉換。本文基于對瓊南、茂名、和三水等地不同地質時期流紋巖的專題研究,通過年代學、巖相學、地球化學和構造背景的綜合分析,取得以下重要認識:南海北部陸緣存在有多種類型流紋巖,流紋巖的噴發(fā)年代有所不同,瓊南地區(qū)流紋巖一般產出于早白堊世(121Ma~98Ma),茂名盆地、長塘盆地等地區(qū)歸屬于晚白堊世(100Ma~96.8Ma),它們可能對應于活動陸緣背景,唯有三水地區(qū)流紋巖樣品經分析產出于新生代(63.9Ma~28.5Ma),相當于被動陸緣裂解的時代;在巖石巖相學方面,茂名盆地、興寧盆地、海南島等地流紋巖樣品斑晶常見石英、斜長石,酸性程度大于三水盆地;三水盆地流紋巖斑晶中石英含量較少,長石多被風化破碎,且斜長石微晶呈定向-半定向排列;在地球化學特征方面,茂名盆地、海南島等地流紋巖屬于過堿質高鉀鈣堿性系列,輕重稀土分餾程度高,具有輕微的Eu負異常,富集Th、U、K等大離子親石元素,而虧損Nb、Ta等高場強元素;三水盆地樣品呈現出由過鋁質高鉀鈣堿型向過堿質高鉀鈣堿性系列流紋巖過渡,其輕重稀土總量遠大于茂名盆地、海南島等地樣品,但輕重稀土分餾不明顯,具有強烈的Eu負異常,與典型的大陸裂谷堿性流紋巖具有較好的一致性,富集Rb、Th、U等大離子親石元素與Ta、Nb、Zr、Hf高場強元素;研究表明,茂名盆地、海南島等地流紋巖具有典型的會聚陸緣火山弧的特征,而三水盆地流紋巖則表現出鮮明的板內或造山期后背景;兩系列巖石雖然同為殼源,但前者巖漿源區(qū)深度卻大于后者,且茂名盆地和海南島巖漿源區(qū)不均一,呈輕微的混合或混染現象,反映出典型會聚陸緣巖漿作用的復雜性;與處于著名的古太平洋俯沖條件下的浙閩地區(qū)流紋巖相比,茂名、海南島等地的流紋巖在巖石地球化學特征、巖石成因,以及構造演化階段等方面,都表現出系統性的差異性。
[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.
【學位授予單位】：中國地質大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P588.141
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本文編號：1528310