南海扩张期后西北缘岩浆—构造活动解析

发布时间：2018-04-23 03:02

  本文选题：南海扩张期后 + 雷琼地区　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：南海扩张期后在其周边陆域特别是西北缘所发生的大规模岩浆活动系一重大的区域特色,它所代表的构造意义及深部过程值得予以重点关注。本论文以雷州半岛、琼北地区和越南昆嵩地区出露的晚新生代玄武岩为研究对象,在岩相学和地球化学工作的基础上,结合同时期区域断裂的展布特点和活动规律,就中中新世(~16Ma)南海扩张停止之后的区域地质过程提出新的认识。雷琼地区和越南昆嵩地区的玄武岩喷发年代接近,性质相似,富集大离子亲石元素(LILE),高场强元素(HFSE)和轻稀土元素(LREE),毫无争议地接近于板内成因。应用高Mg#值首先得到雷琼和昆嵩地区的原始岩浆组分,进一步依据原始岩浆组分中的MgO含量求得两地的地幔潜在温度分别为T雷琼 p=1552.02℃,T越南p=1546.70℃,其中,琼北的温度还得到橄榄石-熔体平衡计算方法的支持。这一结果显示,研究区与MORB相比较的ΔT值高达200~300℃,超过冰岛而逼近夏威夷的地幔潜在温度,暗示研究区存在堪与世界著名热点媲美的地幔柱,与近期地球物探资料所得到的结果基本吻合。源自下地幔的“海南地幔柱”的存在极为可能。南海西北缘陆缘断裂构造非常发育。中中新世以后南海停止扩张,正断层代替走滑断层成为区域断裂体系的主要元素。在越南,正断层主要呈N-S向展布,而在雷琼地区呈NW-SE向展布,它们都是地幔隆升后岩浆上升的主要通道。南海停止扩张后在其西北缘即本文研究区所显示的岩浆-构造活动构成的典型的主动型陆内裂谷体系,但这一体系的形成在时代顺序上与南海扩张并无关联。
[Abstract]:The large-scale magmatism occurring in the continental area around the South China Sea, especially in the northwestern margin, is a major regional feature after the expansion period of the South China Sea. The tectonic significance and deep process represented by the magmatism deserve to be paid more attention to. In this paper, the late Cenozoic basalt exposed in Leizhou Peninsula, Qiongbei area and Kunsong area, Vietnam, is taken as the research object. On the basis of petrographic and geochemical work, combined with the distribution characteristics and activity law of regional faults in the same period, A new understanding of the regional geological process following the cessation of South China Sea extension in Miocene is presented. The eruption age of basalt in Leiqiong area is close to that in Kunsong area of Vietnam, and its properties are similar. The rich large ion lithophile element LILEN, high field strength element (HFSE) and light rare earth element (LREE) are indisputably close to the intraplate origin. Using high Mg# value, the primitive magmatic components in the Leiqiong and Kunsong areas were first obtained, and the potential temperatures of the mantle in the two places were obtained from the MgO content of the original magmatic components, respectively, at 1552.02 鈩，

本文编号：1790131