大陆花岗岩的地球动力学意义

大陆花岗岩的地球动力学意义是一个有争议的话题。笔者认为,花岗岩可分为大洋和大陆两个系列,产于洋盆内及其边缘的花岗岩属于大洋系列,产于大陆内(不包括造山带)的花岗岩属于大陆系列。大洋系列花岗岩最重要的地球动力学意义是判断花岗岩形成的构造环境;大陆系列花岗岩最重要的地球动力学意义是判断地壳状况,包括花岗岩形成时的地壳厚度和温度状况。花岗岩按照Sr-Yb含量可分为埃达克型、喜马拉雅型、浙闽型、广西型和南岭型5类。产于大陆内的不同类型的花岗岩与其形成的深度有关:埃达克型花岗岩富Sr贫Yb,与榴辉岩相处于平衡,产于加厚的地壳;喜马拉雅型花岗岩贫Sr和Yb,与麻粒岩相处于平衡,产于较厚的地壳;浙闽型(贫Sr富Yb)和广西型(富Sr和Yb)花岗岩与角闪岩相处于平衡,产于正常或较薄的地壳;南岭型花岗岩也与角闪岩相处于平衡,地壳厚度最薄。喜马拉雅型花岗岩属于低温系列,浙闽型花岗岩为中或高温系列,广西型和南岭型花岗岩属于高温系列。埃达克型花岗岩则可以出现在各个温度系列。应用花岗岩分类可以恢复古代地壳厚度和下地壳底部温度状况,还可以追踪某些地区随时间变化地壳厚度和温度变化的情况和趋势。

Geodynamic implications of continental granites

The geodynamic implications of continental granite remain a controversial topic. The author believes that the granite can be divided into two series of ocean and continent. The granite produced in the ocean basin and the edge belongs to the ocean series, whereas the granite produced in the continent belongs to continental series. The most important geodynamic implications of ocean series granite is to distinguish tectonic settings, the same of continent series is to judge the crust thickness and temperature conditions. Granite can be divided into Adak-type, Himalaya-type, Zhemin-type, Guangxi-type and Nanling-type on the basis of Sr-Yb content. Different types of granite are related to the granite formation depth: Adak-type granite rich in Sr and poor in Yb is in equilibrium with eclogite facies and produced in the thickening crust; Himalaya-type granite with poor Sr and Yb is in equilibrium with granulite facies and produced in thick crust; Zhemin-type poor in Sr and rich in Yb and Guangxi-type rich in Sr and Yb are in equilibrium with amphibolite facies and produced in normal or thin crust; Nanling-type granite is also in equilibrium with amphibolite facies and produced in the thinnest crust. Himalaya-type granite belongs to the low temperature series, whereas Zhemin- type granite to the middle or high temperature series; Nanling-type and Guangxi-type belong to the high temperature series. Adak-type granite can appear in each temperature series. The application of classification of granite can restore ancient crustal thickness and temperature conditions at the bottom of the lower crust and can also trace changes of the situation and trend of the change of crustal thickness and temperature with time in some regions.