桂北龙胜硅质岩的地球化学、Si-O同位素特征及沉积环境研究
Geochemical and Si-O isotopic characteristics and sedimentary environment of the siliceous rocks in the Longsheng area of the northern Guangxi,China
陈忻 1沙鑫 2阮青锋 2于海燕2
作者信息
- 1. 桂林理工大学地球科学学院,广西桂林 541004
- 2. 桂林理工大学地球科学学院,广西桂林 541004;广西隐伏金属矿产勘查重点实验室,广西桂林 541004
- 折叠
摘要
本文通过对桂北龙胜地区出露的硅质岩进行系统的地球化学及Si-O同位素分析以探讨其成因、物质来源及其沉积环境意义.结果表明,龙胜硅质岩的SiO2含量为92.09％～99.27％,Si/Al值为412.93～3841,Al2O3/(Al2O3+Fe2O3)值为0.03～0.58,Al/(Al+Fe+Mn)值为0.04～0.66;MnO/TiO2值为0.43～26.64;∑REE为0.20～2.37,LREE/HREE值为 1.76～11.18,U/Th值为 1.31～18.52.龙胜硅质岩的球粒陨石标准化配分模式呈右倾型,显示Eu负异常,且Ce具有较强正异常,北美页岩和澳大利亚后太古宙页岩标准化配分模式呈平坦型,具有较强的Eu正异常和较弱的Ce负异常特征;Th、U、Pb、Nb、Ta、Hf、Rb等不相容元素严重亏损,表明龙胜硅质岩是热水沉积成因;龙胜硅质岩δ30Si的值为-0.36‰～0.78‰,δ18O值为17.42‰～18.24‰,说明其为大陆边缘-半深海环境下沉积而成的热水成因硅质岩.综合分析认为,龙胜硅质岩沉积于765～760 Ma的新元古代,同时期大规模的岩浆活动以及裂谷盆地的形成与演化,指示龙胜硅质岩在热水沉积作用下形成,且沉积于大陆边缘海-半深海盆地之间.
Abstract
Based on systematically detailed geochemical and Si-O isotopic analyses of siliceous rocks outcropped in the Longsheng area of the northern Guangxi in this paper,we have explored the genesis,material sources and significance of the depositional environment of the Longsheng siliceous rocks.The results suggested that the Longsheng siliceous rock samples have SiO2 contents ranging from 92.09％to 99.27％,Si/Al ratios ranging from 412.93 to 3841,Al2O3/(Al2O3+Fe2O3)ratios ranging from 0.03 to 0.58 Al/(Al+Fe+Mn)ratios ranging from 0.04 to 0.66,MnO/TiO2 ratios ranging from 0.43 to 26.64,∑REE contents ranging from 0.20 to 2.37 LREE/HREE values ranging from 1.76 to 11.18,and U/Th ratios ranging from 1.31 to 18.52.There are negative Eu anomalies and relatively strong positive Ce anomalies in their chondrite-normalized REE distribution patterns,but relatively strong positive Eu anomalies and relatively weak negative Ce anomalies in their flat NASC(North American shale composition)-normalized and PAAS(Post-Archean Australian shale)-normalized REE patterns.The serious depletion of incompatible trace elements,such as Th,U,Pb,Nb,Ta,Hf,Rb,etc.,suggests that the Longsheng siliceous rocks are of the hot-water depositional origin.The Longsheng siliceous rocks have δ30Si values varying from-0.36‰ to 0.78‰ and δ18O values varying from 17.42‰ to 18.24‰,indicating that they are the hot-water sedimentary siliceous rocks deposited in the semi-abyssal environment of the continental margin.Comprehensive analysis shows that the Longsheng siliceous rocks were deposited at 765～760Ma of the Neoproterozoic era.The large-scale magmatic activities and the formation and evolution of rift basins during the same period imply that the Longsheng siliceous rocks were formed by the hot-water deposition and were deposited in the area between the continental marginal sea and the semi-abyssal basin.
关键词
硅质岩/地球化学/Si-O同位素/沉积环境/龙胜地区Key words
siliceous rock/geochemistry/Si-O isotopes/sedimentary environment/Longsheng area引用本文复制引用
基金项目
国家自然科学基金资助项目(42262006)
广西自然科学基金资助项目(2022GXNSFBA035595)
广西科技计划项目(桂科AD19110048)
桂林理工大学科研启动基金资助项目(GUTQDJJ2017101)
出版年
2024
NETL
NSTL
万方数据