Zircon and apatite as tools to monitor the evolution of fractionated I-type granites from the central Great Xing’an Range, NE China

Abstract

It is widely accepted that granitic melts can be highly evolved, however, the effective records of this process are usually obscure, especially for the exsolution and evolution of volatiles. We present a comprehensive investigation on zircon and apatite from less to highly fractionated granites from the central Xing’an Range, NE China, in order to reveal the mineral records for the evolution processes of granitic melt. Petrographic, whole-rock and mineralogical geochemical investigations indicate that the three granites are co-magmatic and experienced different degrees of fractionation. The variations of zircon morphology, textures and geochemical compositions reflect the progressive evolution of granitic melts from volatile-undersaturated to oversaturated conditions. The significantly decreased Raman spectra intensities imply that the zircon crystals experienced increased radiation damages and hydrothermal alteration during the fractionation of granitic magma. Correspondingly, apatite textures transform from fluid-inclusion-free to fluid-inclusion-rich stage with increasing F/Cl ratios during the magmatic evolution, implying that the segregation of isolated fluid phase in the fractionating magma. Accordingly, we conclude that the textural and compositional evolution of zircon and apatite can be regarded as efficient tools for recording granitic magma evolution.