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《Acta Petrologica Sinica》 2006-09
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Granite classification on the basis of Sr and Yb contents and its implications.

ZHANG Qi~1 WANG Yan~2 LI ChengDong~3 WANG YuanLong1 JIN WeiJun~1 JIA XiuQin~4 1.Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China 2.Department of Earth Sciences,The University of Hong Kong,Hnag Knag,China 3.Tianfin Institute of Geology and Mineral Resources,Tianjin 300170,China 4.Institute of High Energy Physics,Chinese Academy of Sciences,Beijing 100039,China  
Intermediate-acid igneous rocks including volcanic and intrusive rocks with SiO_256% can be divided into four types on the basis of their Sr and Yb contents:high-Sr and low-Yb type (Sr400×10~(-6) and Yb2×10~(-6));low-Sr and Yb type (Sr400× 10~(-6) and Yb2×10~(-6)),low-Sr and high-Yb type (St400×10~(-6) and Yb2×10~(-6)),and high-Sr and Yb type (Sr400×10~(-6) and Yb2×10~(-6)).In the low-Sr and high-Yb type,some granites can be grouped as very low-Sr and high-Yb type with Sr100× 10~(-6) and Yb2×10~(-6).It is therefore five types of granites on the basis of their Sr and Yb contents.The variation of the Sr and Yb contents of the granites are related to the depth of the magma source.With the contents of Sr and Yb and mineral assemblage of the residual magma,the pressure at which granite formed may have four ranges;(1)granites formed at high pressure with garnet left in the redisual phase,magma have high Sr and low Yb content;(2)granites formed at medium or higher pressure such as granulite facies (composed of plagioclage+garnet+amphibolite+pyroxene) have low Sr and Yb,or high Sr and Yb content,depending on the composition of protohth;(3)granites formed at low pressure with plagioclase in residual phase (amphibohte facies) have low Sr and high Yb contents,and(4)M-type granites related to ophiolite formed by partial melting of gabbro at shallower depth (2 to 5km) have very low Sr and Yb content.In general,most lecuogranites are of low-Sr and Yb type,whereas some syenite and shoshonite are high- Sr and high-Yh type.The lecuogranites in southern Tiebet may have formed at relatively high pressure.It is discussed in this study that the relationship between the composition of magma and formation depth,which is a preliminary work and need more evidence to approve.
【Fund】: 国家“973”项目(2002CB412601)、(G1999043206-05);; 中国科学院知识创新工程基金(KZCX 1-07和 KZCX2-SW-119)资助的项目。
【CateGory Index】: P588.121
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