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现代地质 ›› 2021, Vol. 35 ›› Issue (04): 981-996.DOI: 10.19657/j.geoscience.1000-8527.2020.103

• 岩石学 • 上一篇    下一篇

桂西南早中生代流纹岩年代学、地球化学特征及地质意义

刘冬梅1(), 康志强1,2(), 杨锋1,2, 李岱鲜1   

  1. 1.桂林理工大学 地球科学学院,广西 桂林 541004
    2.桂林理工大学有色金属矿产勘查与资源高效利用协同创新中心, 广西 桂林 541004
  • 收稿日期:2020-08-14 修回日期:2020-11-12 出版日期:2021-08-10 发布日期:2021-09-08
  • 通讯作者: 康志强
  • 作者简介:康志强,男,教授,博士生导师,1979年出生,矿物学、岩石学、矿床学专业,主要从事岩石、矿床地球化学研究。Email: zk99201@163.com
    刘冬梅,女,硕士研究生,1996年出生,矿物学、岩石学、矿床学专业,主要从事岩石地球化学研究。Email: 2991038805@qq.com
  • 基金资助:
    国家重点研发计划项目(2020YFA0714804);国家重点研发计划项目(2016YFC0600407);国家自然科学基金项目(41863005);广西八桂学者项目(许继峰);广西研究生教育创新计划项目(YCSW2020169)

Geochronology and Geochemistry of Early Mesozoic Rhyolite in Southwestern Guangxi and Its Geological Significance

LIU Dongmei1(), KANG Zhiqiang1,2(), YANG Feng1,2, LI Daixian1   

  1. 1. School of Earth Sciences, Guilin University of Technology, Guilin, Guangxi 541004, China
    2. Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources, Guilin University of Technology, Guilin, Guangxi 541004, China
  • Received:2020-08-14 Revised:2020-11-12 Online:2021-08-10 Published:2021-09-08
  • Contact: KANG Zhiqiang

摘要:

印支期桂西南地区处于多板块构造交汇地带,其岩浆构造演化存在很大的争议。对桂西南十万大山盆地两侧酸性火山岩进行了系统的锆石年代学、全岩地球化学及Sr-Nd同位素地球化学研究。结果表明,十万大山盆地两侧酸性火山岩LA-ICP-MS锆石U-Pb年龄为240.5~248.4 Ma,形成于早三叠世。岩性主要为流纹岩,具有高SiO2、K2O、Al2O3及低的CaO、MgO特征,A/CNK=1.17~1.25,属于强过铝质高钾钙碱性-钾玄质系列岩石。微量元素整体上富集Rb、Th、U、Zr、Hf,而Sr、Nb、Ti和P元素亏损,稀土元素配分模式表现为轻稀土元素富集右倾型,轻、重稀土元素分馏显著,Eu中等负异常(δEu值为0.44~0.73);Sr-Nd同位素特征显示,样品具有较高的Sr初始值(0.706 21~0.719 51),低的εNd(t)值(-10.67~-9.72),其模式年龄为1.85~1.96 Ga,显示源区可能主要为古元古代的壳源物质。结合前人研究结果,认为研究区流纹岩是华南板块与印支地块后碰撞或碰撞晚期挤压热应力松弛的间隙环境下古老地壳变质泥岩部分熔融的产物。

关键词: 流纹岩, 年代学, 地球化学, 地质意义, 桂西南地区

Abstract:

The Indosinian southwestern Guangxi was located in the intersection of multiple tectonic plates, with it’s structure and evolution still being controversial. In this paper, systematic studies were carried out on zircon geochronology, whole-rock major and trace elemental, and Sr-Nd isotopic data of the felsic volcanic rocks on both sides of the Shiwandashan basin in southwestern Guangxi. LA-ICP-MS zircon U-Pb dating of the felsic volcanic rocks yielded 240.5-248.4 Ma, suggesting that the rocks were formed in the Early Triassic. The felsic volcanic rocks are mainly rhyolitic, characterized by high SiO2, K2O and Al2O3, and low CaO and MgO, belonging to high-K calc-alkaline and strongly peraluminous series with A/CNK=1.17-1.25. The rhyolite is enriched in Rb, Th, U, Zr and Hf, but depleted in Sr, Nb, Ti and P in the primitive mantle-normalized spider diagram. The chondrite-normalized REE patterns show slightly right inclining, LREE/HREE enrichment patterns, and moderate negative Eu anomalies (δEu=0.44-0.73). The rocks have relatively high (87Sr/86Sr)i(0.706,21-0.719,51) and low εNd(t) (-10.67 to -9.72), with model age of 1.85-1.96 Ga, suggesting a Paleoproterozoic crustal-derived magma source. Based on the previous studies, the rhyolite was emplaced at late/post-collisional setting after the main Indosinian collision between the South China and Indochina blocks.

Key words: rhyolite, chronology, geochemistry, geological significance, southwestern Guangxi

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