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引用本文:张 岚1,2 杨经绥2 熊发挥2 刘 飞2 周文达3,2. 雅鲁藏布缝合带巴尔蛇绿岩边部石英菱镁岩成因[J]. 中国地质, 2015, (5): 1443-1456.
ZHANG Lan1,2, YANG Jing-sui2, XIONG Fa-hui2, LIU Fei2, ZHOU Wen-da3,2. Origin of listwanite from Baer ophiolite, Yarlung Zangbo suture zone[J]. Geology in China, 2015, (5): 1443-1456(in Chinese with English abstract).
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雅鲁藏布缝合带巴尔蛇绿岩边部石英菱镁岩成因
张 岚1,2 杨经绥2 熊发挥2 刘 飞2 周文达3,21,2,3
1. 中国地质大学 (北京) 地球科学与资源学院,北京100083;2. 地幔研究中心,大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京 100037;3. 中国地质大学地球科学学院, 湖北 武汉 430074
摘要:
提要:石英(滑石)菱镁岩是基性岩、超基性岩与富CO2流体反应形成的一套硅化-碳酸盐化蚀变岩,常伴生金、汞、菱镁矿、碱金属矿化而在国外备受关注,但国内相关研究较薄弱。巴尔蛇绿岩位于西藏阿里地区,石英菱镁岩主要出露在蛇绿岩体东北边界,出露厚度约20 m,近北西西向延伸数千米。本文系统研究了雅鲁藏布缝合带西段巴尔蛇绿岩边部石英菱镁岩矿物学及地球化学特征。根据尖晶石镜下特征,划分为两个阶段:一阶段石英菱镁岩中尖晶石稳定存在,二阶段石英菱镁岩中尖晶石几乎全部蚀变(代表更强程度蚀变作用)。石英菱镁岩主要地球化学组成为SiO2、MgO及CO2,8件样品主量元素含量变化较大,SiO2/MgO比值波动较大,反映石英菱镁岩形成为非等化学过程。蛇纹石化橄榄岩与石英菱镁岩有着相似微量元素分布规律,表明同源性,但两者仍有较明显差异:两阶段石英菱镁岩LREE都较地幔橄榄岩略富集,从地幔橄榄岩到两阶段石英菱镁岩,HREE先亏损再略富集。微量元素标准化图解中,Sr在橄榄岩与石英菱镁岩中都为正异常,其含量随蚀变强度增强而增加。此外,两阶段石英菱镁岩均无Au、Hg矿化。
关键词:  巴尔石英菱镁岩  矿物学  地球化学  岩石成因
DOI:
分类号:
基金项目:国家自然科学基金重点项目(40930313)、中国地质调查局工作项目(12120114061801、12120114057701、12120114061501) 资助。
Origin of listwanite from Baer ophiolite, Yarlung Zangbo suture zone
ZHANG Lan1,2, YANG Jing-sui2, XIONG Fa-hui2, LIU Fei2, ZHOU Wen-da3,21,2,3
1. School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. CARMA, State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, Hubei, China
Abstract:
Abstract: Listwanite is a suite of silica-carbonate alteration products which are formed when CO2-bearing hydrothermal fluids meet and react with serpentinized mafic and ultramafic rocks. This alteration product is of great importance for its economic significance. Gold, mercury, magnesite and base metal deposits are often associated with listwanite. In China, Not enough attention has been paid to the petrogenesis of listwanite and related mineralization. This paper reports the study of listwanite occurring along the northeast edge of Baer ophiolite in the western part of the Yarlung Zangbo?suture (YZSZ). Baer ophiolite lies in Ngari Prefecture of southwest Tibet. The Baer listwanite crops out along the northeast boundary of the ophiolite with a width of ca. 20 meters and stretches a few kilometers in NWW direction. Based on the features of spinel under optical microscope, the authors recognized two stages of listwanite: Stage I listwanite contains spinel relicts while Stage II listwanite rarely contains spinel relicts. This means Stage II listwanite experienced more intense alteration. Geochemically, Baer listwanite is mainly composed of SiO2, MgO and CO2. 8 samples (containing 3 Stage I samples and 5 Stage II samples) show variation of major oxides, and the MgO/SiO2 ratios are not consistent, which implies that the listwanization was not an iso-chemical process. Baer peridotite and two stages of listwanites show similar trace elements distribution patterns. Both stages of listwanites show little enrichment of the LREE related to the protolith. From peridotite to two stages of listwanites, the behavior of HREE might have experienced depletion followed by slight enrichment. All samples show positive Sr anomalies and their values go up stage by stage. The values of Au and Hg in both stages of listwanites show that they have not been subjected to Au and Hg mineralization.
Key words:  Baer listwanite  mineralogy  geochemistry  petrogenesis