万洋山-诸广山加里东期花岗岩的物质来源——Ⅰ.Sr-Nd-Pb-O多元同位素体系示踪

本文系统的Sr-Nd-Pb-O多元同位素体系示踪结果表明,万洋山-诸广山加里东期花岗岩类岩石是典型的壳型花岗岩,由区内未出露的中元古基底重熔形成,源岩的物质组成不均一.     

中国某些花岗岩的Sr-O同位素体系

花岗岩类岩石δ~(18)O和~(87)Sr/~(86)Sr初始比值的关系可分为四种类型:封闭结果型:呈近于垂直的短线;硅铝物质重熔型:呈负相关关系;壳幔混合型:呈正相关关系;水-岩交换型:基本为无相关。     

万洋山-诸广山加里东期花岗岩的物质来源——Ⅱ.同位素多维空间的拓扑分析

Sr-Nd-O-Pb~3六维同位素空间的拓扑分析结果表明,万洋山-诸广山加里东期花岗岩的源岩主要由三端元物质组成,混合模式判别证明花岗岩是由三端元组分不同比例混合的产物,多元同位素体系和元素地球化学综合示踪研究表明,这三端元地壳成分为陆源沉积物、地槽沉积物和蚀变的基性火山岩。     

Source Rocks of the Caledonian-Age Granitoid Rocks in Wanyanshan-Zhuguangshan, Southeast China (Ⅱ)——Topological Analysis in Isotopic Multispace

Topological analysis in Sr-Nd-O-Pb_3 six-dimensional isotopic space suggests that the source rocks of the Caledonian-age granitoid rocks in Wanyangshan-Zhuguangshan, southeast China, comprise three end-member components. Isotopic mixing model discrimination indicates that the granitoid rocks were produced through mixing of the three componentsin varying proportions. Comprehensive study of multiple isotopic systems and geochemistry of the granitoid rocks suggests that the three end-member components were crustal rocks which are continent-derived sediments, geosycline sediments and altered basic volcanic rocks.     

SOURCE ROCKS OF THE CALEDONIAN-AGE GRANITOID ROCKS IN WANYANGSHANZHUGUANGSHAN, SOUTHEAST GHINA (Ⅰ)——EVIDENCE FROM Sr-Nd-Pb-O ISOTOPIC CONSTRAINTS

Based on the systematic study by means of Sr-Nd-Pb-O isotopic constraints, the Caledonian-age granitoid rocks from Wanyangshan-Zhuguangshan, southeast China, were derived from the regional unexposed basement rocks of middle Proterozoic in age, belonging to the crust- (S-) type granite. Their source rocks were chemically and isotopically heterogeneous, and probably composed of more than two dominant end-members.     

“南永1井”礁相碳酸盐C,O,Sr,Pb同位素组成及其古环境意义探讨

“南永1井”礁相碳酸盐的O,C同位素组成可分为四段,它们的δ~(18)O(‰)和δ~(13)C(‰)平均值分别为:(Ⅰ)-5.0,-0.5;(Ⅱ)-7.7,-5.3;(Ⅲ)-6.4,-2.8;(Ⅳ)1.3,2.1.(Ⅱ)段的δ~(18)O值波动曲线以变化频率低、幅度小为特征,与布容期冰期-间冰期存在对应关系;(Ⅲ)和(Ⅳ)段的δ~(18)O和δ~(13)C值之间有正相关,在成因上与白云石化有关。△~(87)Sr和Pb同位素组成同样存在四分的特点。整个钻孔岩芯中△~(87)Sr的最大值和最小值以及全部正值都出现在第Ⅱ段。第Ⅳ段的Pb,sr同位素均呈现变化波动频繁的特点,在白云石化阶段有高μ值的Pb带入。礁相碳酸盐的O,C,Sr和Pb同位素组成记录了南海第四纪古气候、古环境变迁的历史。     

SR-O ISOTOPE SYSTEM OF SOME GRANITOIDS IN CHINA

Four of Sr- O isotope types can be observed in the graphs of δ~(18)O vs. (~(87)Sr/~(86)Sr)_i accord-ing to our data: (i) closed-system crystallization type: nearly short- vertical line withsimilar initial Sr isotope ratios and small changes of δ~(18)O values(<3‰); (ii) sialic materialremelting type: negative correlations without mantle end member; (iii) crust-mantle contam-ination type: a variety of mixing hyperbolas or straight lines with positive slopes: (iv)water-rock exchange type: irregular distribution.