| 右江盆地内基性岩脉年代学和地球化学研究 |
| 邢朗彰
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| 导师 | 胡瑞忠
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| 2017
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| 学位授予单位 | 中国科学院研究生院
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| 学位授予地点 | 北京
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| 学位名称 | 硕士
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| 学位专业 | 地球化学
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| 关键词 | 右江盆地
煌斑岩
辉绿岩
锆石定年
岩石地球化学
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| 其他摘要 | 右江盆地位于我国西南滇黔桂接壤区，为金沙江—红河—马江缝合带东侧扬子地块内从泥盆纪以来发育起来的沉积盆地。盆地内岩浆岩出露不多，但可为理解右江盆地的形成演化过程提供重要信息。右江盆地中广泛分布卡林型金矿床，这些矿床的形成是否受岩浆活动驱动，是未解决的重要科学问题。本文在野外地质调查的基础上，采用岩石学、矿物学、LA-ICP-MS锆石U-Pb同位素年代学和岩石地球化学等方法，较系统地研究了贵州扁脚地区煌斑岩和广西隆林-西林地区辉绿岩的年代学、岩石成因、成岩构造背景及其与金成矿的关系，取得以下主要认识。（1）煌斑岩斑晶矿物主要为黑云母(10-25%)和辉石(5-10%)，基质主要为正长石(60-70%)，属于云煌岩。其中含岩浆成因球粒，球粒由正长石和方解石及少量氟碳钙铈矿等独立稀土矿物组成。煌斑岩中的其他副矿物主要有含钛磁铁矿、方解石和磷灰石。煌斑岩SiO2含量在基性岩范围内，含碱量高，属于钙碱性煌斑岩系列。微量元素Nb、Ta、Ti、Zr、Hf呈现负异常，Sr、Ba、K、Th、U等正异常，大离子亲石元素富集，高场强元素亏损。高度富集轻稀土元素，轻重稀土元素分馏明显。煌斑岩的岩浆锆石年龄为86.7±1.7 Ma，形成于晚燕山期，与区域内的碱性超基性岩以及右江盆地内的中酸性岩脉和盆地周边分布的花岗岩体基本上在同一时期形成。这些煌斑岩形成于华南岩石圈伸展的大环境下，是富集地幔部分熔融产生的原始岩浆在上升过程中同化少量地壳物质的产物。（2）广西隆林-西林地区辉绿岩的TiO2为3.0 %左右，为典型高钛辉绿岩，微量元素蛛网图以及稀土元素配分图上呈现与OIB型玄武岩一致的组成特征。其形成时代为255.2±2.7 Ma，与峨眉山大火成岩省的形成时代一致，是峨眉山地幔柱活动的产物，其岩浆源区为石榴子石稳定区域。这些特征说明，峨眉山大火成岩省的空间分布范围至少可扩大到广西隆林-西林地区。（3）右江盆地内的基性岩脉按年龄大致分为两期：形成于260Ma左右的晚古生代辉绿岩，在右江盆地南边出露较多，是峨眉山大火成岩省的组成部分；形成于90 Ma左右的晚燕山期煌斑岩等基性岩脉，主要分布在右江盆地北边和东边。这两期基性岩脉分别早于和晚于右江盆地中卡林型金矿的成矿时代。因此，至少这两期的基性岩浆活动与右江盆地中的金成矿没有成因上的直接联系。; The Youjiang Basin is located in Yunnan, Guizhou and Guangxi regions，in southwest China. The location of it is between the Jinsha River - Honghe - Majiang suture zone and the Yangtze plate, and it was developed from Devonian to Triassic. The magmatic rocks in the basin are not much exposed, but they can become an important source for understanding the evolution of the Youjiang basin. There are many carlin type gold deposits distributed in the basin. But whether the formations of these deposits were driven by magmatic activity or not is still an important unresolved scientific issue. Based on the field geological survey, this paper systematically studied the lamprophyres in Bianjiao area of Guizhou province and diabases in Longlin-Xilin area of Guangxi province, by means of mineralogy, zircon LA-ICP-MS U-Pb isotopic chronology, and geochemistry. Mainly have the following understanding:（1）The main porphyry minerals are biotite(10-25 %) and pyroxene (5 %), the matrix is mainly (60 -70 %), it belongs to the minette. There are some magmatic pellets that consist of orthoclase, calcite and a small amount of independent rare earth minerals such as parisite. The sub-minerals in lamprophyre are calcite, magnetite, and apatite. The content of SiO2 in the lamprophyre was within the range of basic rock, and the content of alkali is high. The contents of Nb, Ta, Ti, Zr and Hf are negative. There are significantly fractionation between light rare earth elements and light and heavy rare earth elements. The age of the lamprophyre was 86.7 ± 1.7 Ma, it was formed in the late Yanshanian period, and is same to the alkaline ultrabasic rocks in the region and the acid rocks in Youjiang basin or close to Youjiang basin. The lamprophyres were formed in the environment of South China lithosphere extension. They were the products of partially melting of enriched mantle, and experienced some crustal assimilation when its magma rising.(2)The diabases in Longlin-Xilin area of Guangxi were typical high-Ti diabase, the TiO2 of it was about 3%. It had the same distribution trend with OIB basalt in trace elements and rare earth elements. The age of it was 255.2±2.7 Ma which was same to the Emeishan large igneous province. It was the product of Emeishan mantle plume, and its magma was derived from the garnet stable mantle. All of these illustrated that the distribution of Emeishan large igneous province can expend to Longlin-Xilin area of Guangxi.(3)The mafic dykes in Youjiang basin can be classified into two parts according their ages: Diabases formed in late Permian (~260 Ma), it was more exposed in the south of the Youjiang basin and was a part of the Emeishan large igneous province. Mafic dykes formed in late Yanshanian (~90 Ma), they were mainly distributed in the north and east of Youjiang basin. But the ages of them were earlier or later than carlin type gold deposits in Youjiang basin. So, they had no direct genetic link with the gold deposits in Youjiang basin at least. |
| 学科领域 | 矿床地球化学
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| 语种 | 中文
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| 文献类型 | 学位论文
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| 条目标识符 | http://ir.gyig.ac.cn/handle/352002/7569
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| 专题 | 研究生_研究生_学位论文
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推荐引用方式
GB/T 7714 |
邢朗彰. 右江盆地内基性岩脉年代学和地球化学研究[D]. 北京. 中国科学院研究生院,2017.
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