“广西型花岗岩”有岩石学意义吗?——对《广西型花岗岩的地球化学特征及其构造意义》一文的质疑

Does the “uangxi_type granite” have any petrological significance?——A critique on “Geochemistry of the Guangxi_type granite and its tectonic implications”

对国内外30个实例的汇总表明,所谓"广西型花岗岩"不具备张旗(2014)所认为的岩石学和地球动力学意义。富Sr和Yb的"广西型花岗岩"在岩性包含了中性岩、酸性岩和过碱性岩,绝大多数具有负Eu异常。从岩石组合(系列)方面看,"广西型花岗岩"是钙碱性系列、碱性系列与A型花岗岩的"混杂"。"广西型花岗岩"可以是基性岩浆分离结晶或分离结晶+混染(AFC)、壳源岩石部分熔融等多种成岩机制的产物,斜长石是结晶相或残留相。对不同源岩的失水熔融相图的比较分析表明,花岗岩类的全岩Sr、Yb含量不是指示花岗质岩浆起源压力的可靠指标,张旗提出的以"Sr-Yb"为基础的花岗岩分类没有地球动力学意义。

Based on the compilation of 30 cases around the world, the author holds that the so-called ＂ Guangxi-type granite＂ does not contain the petrological and geodynamic significance as argued by Zhang Qi（ 2014）, who has proposed the nomenclature. The Sr and Yb enriched ＂Guangxi-type granites＂ are composed of intermediate to acid and peralkaline rocks in lithology, and most of them exhibit negative Eu anomalies. From the perspective of rock association（ series）, the so-called ＂Guangxi-type granite＂ is actually the mingling of calc-alkaline, alkaline, and A-type granite. In fact, the ＂Guangxi-type granite＂ can be generated by many petrogenetic mechanisms, including the fractional crystallization or assimilated fractional crystallization（ AFC） of mafic magma, and the partial melting of crustal sources, with the plagioclase as one of the crystallization or residual phases. The comparison of the phase diagrams from fluid-absent melting of common crustal source rocks shows that the whole-rock Sr and Yb content of granitic rocks cannot be regard as a reliable index to indicate the melting pressure of granitic magma. Accordingly,the ＂Sr-Yb＂ classification of granitic rocks proposed by Zhang Qi is useless for geodynamic study.