摘要
桂西巴马地区位于扬子克拉通西南边缘和峨眉山大火成岩省(ELIP)外部区域的交汇处,是研究桂西基性岩的岩石成因、构造环境及其与ELIP空间归属关系等科学问题的重要区域。本文对巴马基性岩进行了岩石学、地球化学、年代学及锆石Hf同位素分析研究。LA-ICP-MS锆石U-Pb定年结果显示,巴马地区那桃、乙圩和燕洞岩体的锆石^(206)Pb/^(238)U加权平均年龄约为260 Ma,属于晚二叠世基性岩。巴马基性岩具有低SiO_(2)、高TiO_(2)和MgO的特征,属于高Ti系列碱性玄武质岩石;富集轻稀土元素和大离子亲石元素,蛛网图解上呈现类似洋岛玄武岩(OIB)的地球化学特征。锆石ε_(Hf)(t)值(0.07~4.79)均为正值,Nb/La值(0.48~0.90)<1,说明未受地壳成分混染。巴马基性岩地球化学和锆石Hf同位素特征类似于ELIP高Ti玄武岩,同时具有比ELIP高Ti玄武岩更高的Ti/Y值(多在507~1286),表明巴马基性岩的母岩浆形成于部分熔融程度低(<8%)或深度超过3.5 GPa的厚岩石圈下含石榴石的地幔柱岩浆源区。巴马基性岩的形成主要与板内构造环境有关,属于ELIP的一部分。
Located at the intersection of the southwest edge of the Yangtze Craton and the outer region of Emeishan large igneous province(ELIP),Bama in western Guangxi is an important area for studying the lithogenesis,tectonic environment and spatial attribution relationship between the basic rocks of western Guangxi and ELIP.In this paper,petrology,geochemistry,zircon U-Pb chronology and Hf isotopic analysis of Bama basic rocks are studied.LA-ICP-MS zircon U-Pb data show that the weighted average age of zircon ^(206)Pb/^(238)U in the Natao,Yixu and Yandong basic rocks in Bama is-260 Ma,belonging to basic rocks of Late Permian.Bama basic rocks have the characteristics of low SiO_(2),high TiO_(2) and MgO,showing the high Ti series of alkaline basalts.They are enriched in light rare earth elements and large ionic lithophilic elements.The right-leaning distribution pattern of rare earth elements on spider diagram shows geochemical characteristics similar to those of oceanic island basalts(OIB).Theε_(Hf)(t)(0.07-4.79)of zircon is positive,Nb/La(0.48-0.90)<1,and seems nothing to do with crustal composition.The geochemical and zircon Hf isotope characteristics of Bama basic rocks are similar to those of the ELIP high-Ti basalt and have higher Ti/Y values than the ELIP high-Ti basalts,indicating that the parent magma of Bama basic rocks was formed in the source area of garnet-bearing mantle column magma under the thick lithosphere with a low degree of melt(<8%)or a depth of more than 3.5 GPa.The formation of Bama basic rocks is mainly related to the intraplate tectonic environment and a part of ELIP.This study provides new data for better understanding of the genesis and linkage for Bama basic rocks with ELIP.
作者
吴祥珂
梁国科
李玉坤
赵兵
蒋剑
尹庭旺
WU Xiangke;LIANG Guoke;LI Yukun;ZHAO Bing;JIANG Jian;YIN Tingwang(Research Centre of Granitic Diagenesis and Mineralization,China Geological Survey,Wuhan 430205,China;Guangxi Mineral Resources Reserve Evaluation Centre,Nanning 530023,China;Guangxi Institute of Geological Survey,Nanning 530023,China)
出处
《桂林理工大学学报》
CAS
北大核心
2023年第1期14-29,共16页
Journal of Guilin University of Technology
基金
中国地质调查局项目(DD20160034-06,121201009000150002)
中国地质调查局花岗岩成岩成矿地质研究中心开放基金项目(PMGR202007)
广西关键矿产资源深部勘查人才小高地项目(桂组通字〔2019〕85号)。
关键词
基性岩
年代学
锆石HF同位素
巴马
桂西
basic rock
geochronology
zircon Hf isotopic
Bama
western Guangxi
