A型花岗岩的标志和判别——兼答汪洋等对“A型花岗岩的实质是什么”的质疑

The criteria and discrimination for A-type granites:A reply to the question put forward by Wang Yang and some other persons for “A-type granite:what is the essence?"

A型花岗岩是富硅、富碱、贫水的花岗岩类,地球化学上以贫Al、Sr、Eu、Ba、Ti、P为特征,形成于低压高温条件下,对源岩没有选择。A型(或南岭型)花岗岩的实质为:在低压下熔融的花岗岩类,大多产于地壳伸展减薄的构造背景。汪洋等(2013)举的几个国外A型花岗岩的实例笔者认为大多不是A型花岗岩,不形成于低压条件下。

A-type granites are silicon-, alkali-rich, water-poor granitoids, characterized geochemically by poor A1, Sr, Eu, Ba, Ti and P. A-type granites are formed under low pressure and high temperature conditions, and have no choice for source rocks. The essence of the A-type （or the Nanling type） granites lies in the melting of granitic magma under low pressure and their generation mainly in the tectonic setting of crustal extension and thinning. The several ＂A-type granites＂ abroad cited by Wang Yang et al. are actually mostly outside the cate- gory of A-type granites and were not formed under low pressure conditions.