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Mineralogical Characteristics of Chlorites from Precambrian Metamorphic Rocks in Yidun Magmatic Arc of Qinghai-Tibet Plateau and Their Geological Implications(PDF)

《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]

Issue:
2018年第01期
Page:
36-48
Research Field:
基础地质与矿产地质
Publishing date:

Info

Title:
Mineralogical Characteristics of Chlorites from Precambrian Metamorphic Rocks in Yidun Magmatic Arc of Qinghai-Tibet Plateau and Their Geological Implications
Author(s):
TIAN Zhen-dong LENG Cheng-biao ZHANG Xing-chun YIN Chong-jun ZHANG Wei GUO Jian-heng TIAN Feng
1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, Guizhou, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China; 3. Guizhou Zhongdida Thermal Energy Technology Co. LTD., Guiyang 550000, Guizhou, China
Keywords:
mineralogy magmatic arc chlorite electron microprobe Precambrian metamorphic rock temperature-pressure condition Qinghai-Tibet Plateau
PACS:
P612
DOI:
-
Abstract:
Yidun magmatic arc, which is located in the southeastern margin of QinghaiTibet Plateau, is formed in Late Triassic by the westward subduction of Ganzi-Litang Paleo-Tethyan ocean. The study on Precambrian metamorphic rocks is lacking, which restricts better understanding of tectonic evolution progress and tectonic affinity in Yidun magmatic arc. Chlorites from Precambrian metamorphic rocks in Yidun magmatic arc are widespread developed. The detailed microscope observations and the analysis of mineral chemical compositions of the chlorites using electron microprobe were studied. The results show that all the chlorites belong to prochlorite, and their chemical compositions are controlled by pelites, suggesting they are formed in a relative reduced environment; the replacement of Si by AlIV is the main substitution in the tetrahedral site, while in the octahedral site, Mg is predominately replaced by Fe, followed by AlVI, indicating the chlorites are formed in the relative acid environment; the chlorites have lower Si contents, higher Fe, Mg and AlIV contents, meanwhile AlIV content is approximately equal to AlVI content, implying the chlorites are metamorphic origin and the result of the hydrolysis of biotites; the forming temperature estimated by the chlorites thermometer ranges from 352 ℃ to 443 ℃ (average at 404 ℃), and the pressure ranges from 0.57 to 0.90 GPa (average at 0.73 GPa) inferred from the phengites intergrowth with the chlorites, suggesting the metamorphic basement of Yidun magmatic arc undergoes mediumpressure type metamorphisms. Together with previous studies, Yidun magmatic arc has an affinity of Yangtze Block.

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Last Update: 2018-03-08