Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China
; Univ Hong Kong, Dept Earth Sci, Hong Kong, Hong Kong, Peoples R China
; Tianjin Inst Geol & Mineral Resources, Tianjin 300170, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
Intermediate-acid igneous rocks including volcanic and intrusive rocks with SiO2 > 56% can be divided into four types on the basis of their Sr and Yb contents: high-Sr and low-Yb type (Sr > 400 x 10(-6) and Yb < 2 x 10(-6)); low-Sr and Yb type (Sr < 400 x 10(-6) and Yb < 2 x 10(-6)), low-Sr and high-Yb type (Sr < 400 x 10(-6) and Yb > 2 x 10(-6)), and high-Sr and Yb type (Sr > 400 x 10(-6) and Yb > 2 x 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 x 10(-6) and Yb > 2 x 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 protolith; (3) granites formed at low pressure with plagioclase in residual phase (amphibolite 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-Yb 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.