花岗岩成因类型的判别分析

DISCRIMINATION OF GENETIC TYPES OF GRANITOID ROCKS

花岗岩类可以划分为M、I、S和A型四大成因类型。本文通过对澳大利亚东南部典型的I型、S型、A型花岗岩和我国新疆西准噶尔蛇绿岩套中M型花岗岩的判别分析,提出了根据实际矿物含量、岩石化学成分和微量元素丰度确定花岗岩成因类型的判别方法,对其参加判别分析的68个样品的回判准确率分别高达94.1％、97.1％和98.5％。因此,该法是对目前广泛采用的确定花岗岩成因类型的各种地球化学参数或图解法的重要补充。

In this paper the petrological features of four types(I-type, S-type, A-type and M-type) of granitoid rocks are summarized. Then discrimination coefficients for each type are computerized from 68 detailedly studied samples. Among them 11 are of M-type granites from ophiotite suites in Westorn Junggar, NW China (Ma Hongwen, 1990), 20 of I-type and 20 of S-type granites from Kosciusko Batholith, SE Australia (Hine et al. 1978), and 17 of A-type granites from Gabo and Munbulla suites, SE Australia (Collins et al. 1982). It is found that the mean value of modal contents, bulk chemical compositions, and trace element concentrations in the four types of granitoid rocks are all at 99％ confidence level different from each other. From the discrimination coefficients, the 68 samples are well classified into their genetic types by their modal content, bulk composition, and trace element concentration criteria, respectively. It indicates that this method has advantage in determining the genetic types of granitoid rocks. Comparison of the four genetic types of granitoid rocks with both magnetite series/ilmenite series granitoids from Ishihara (1977) and tectonic environment groups of granitoid rocks from Pearce et al. (1984) are also discussed.