摘要
研究表明,中酸性火成岩大致按照Sr=400μg/g和Yb=2μg/g的标志可以划分为4种类型,即高Sr低Yb(Sr>400×10-6,Yb<2×10-6)、低Sr低Yb(Sr<400×10-6,Yb<2×10-6)、低Sr高Yb(Sr<400×10-6,Yb>2×10-6)和高Sr高Yb(Sr>400×10-6,Yb>2×10-6)型。其中,从低Sr高Yb型中还可以分出非常低Sr高Yb(Sr<100×10-6,Yb>2×10-6)的一类。着重探讨了这5类花岗岩形成的源区深度问题,指出按照残留相组成和花岗岩Sr、Yb含量,可以将花岗岩形成的压力分为3或4个级别:①高压下与石榴子石平衡的花岗岩具有高Sr低Yb的特征;②中等压力下,残留相为麻粒岩相(斜长石+石榴子石+角闪石+辉石),花岗岩具低Sr低Yb或高Sr高Yb的特点(取决于原岩成分);③低压下,残留相有斜长石无石榴子石的花岗岩为低Sr高Yb类型的;④与蛇绿岩有关的在洋壳剖面浅部由辉长岩部分熔融形成的M型花岗岩可能是非常低压(高温)条件下形成的。
Intermediate-acid igneous rocks may be divided into four types on the basis of their Sr and Yb contents, i.e. high-St and low-Yb type （Sr〉400×10^-6 and Yb〈2×10^-6）, low-Sr and -Yb type （Sr〈400×10^-6 and Yb〈2×10^-6）, low-Sr and high-Yb type （Sr〈400×10^-6 and Yb〉2×10^-6） and high-Sr and -Yb type （Sr〉400×10^-6 and Yb〉2×10^-6）. In the low-Sr and high-Yb type, some granites can be grouped as very low-Sr and high-Yb type with Sr〈100×10^-6 and Yb〉2×10^-6. In addition, the very low-Sr and high-Yb type （Sr〈100×10^-6 and Yb〉2×10^-6） may be further separated from the third type. The variation in Sr and Yb contents of granite is related to the depth of the magma source. This paper focuses on the depths of the source regions of the five types of granite. According to the contents of Sr and Yb and composition of the residual facies, the pressures at which granite formed may be divided into four ranges and the characteristics of the granites formed in the four pressure ranges are as follows： ① granite formed at high pressures with garnet left in residual phase has high Sr and low Yb contents; ② granite formed at medium pressures with granulite facies（composed of plagioclage＋garnet＋amphibolite＋pyroxene） as the residual facies has low Sr and Yb or high Sr and Yb contents（depending on the composition of protolith）; ③granite formed at low pressures with plagioclase and no garnet in residual phase has low Sr and high Yb contents; and ④M-type granites related to ophiolites formed by partial melting of gabbro possibly at very low pressures and high temperatures at shallow oceanic crustal levels have very low Sr and Yb contents.
出处
《地质通报》
CAS
CSCD
北大核心
2006年第11期1274-1278,共5页
Geological Bulletin of China
基金
国家"973"项目(2002CB412601)
(G1999043206-05)
中国科学院知识创新工程基金(KZCX1-07和KZCX2-SW-119)资助。
关键词
花岗岩
分类
SR
Yb含量
地球化学
压力
granites
classification
Sr-Yb content
geochemistry
pressure
