Characteristic mineralogy of the Zhutishi granite: Implication for petrogenesis of the late intrusive granite

摘要

Many late intrusive granites with strongly peraluminous composition and fine-grained texture occur as stocks or apophysis in the Dadongshan main intrusive granite located in NW Guangdong Province. This paper reports the results of a petrogenetic study of some characteristic minerals (zircon, muscovite and andalusite) from the Zhutishi granite, one of the late intrusive granites in the Dadongshan granite. It is observed that the typological pattern of zircon population in the Zhutishi granite differs significantly from that in the Dadongshan granite, and that muscovite and andalusite, only found in the Zhutishi granite, are of magmatic origin. Therefore, this paper considers that the Zhutishi granite was unlike to be produced through crystal fractionation from the Dadongshan granitic magma as reported by previous authors, but is related closely to the formation of the Dadongshan granite. The hydrothermal fluid, produced by differentiation of the Dadongshan granitic magma at deep magmatic chamber, would penetrate into the source rock of the Zhutishi granite, and make it enriched in H2O and Al2O3; and the decompression after the ascent of the Dadongshan granitic magma in extension regime promotes partial melting of the source rock of the Zhutishi granite, and produces the strongly peraluminous granitic magma. The model proposed in this paper seems to be more reasonable to explain the spacio-temporal relationship between the late intrusive granites with strongly peraluminous feature and the main intrusive granite with metaluminous feature.