The Application of Quartz Cathodoluminescence in Study of Igneous Rock

Cathodoluminescence is an effective technical method for studying microstructure of igneous quartz. By taking granite porphyry from the Jiama Porphyry Copper Deposit in Tibet for example, this paper briefly introduces the image characteristics of scanning electron microscope cathodoluminescence (SEMCL) and optical microscope cathodoluminescence (OMCL), and summarized the application of quartz cathodoluminescence in study of igneous rock. The relatively stable and bluedominant CL of zoned phenocrysts is principally related to variation of Ti content in quartz, which is a function of the crystallization temperature. The Al/Ti ratio of igneous quartz increases with progressive magma differentiation, as Ti is more compatible, compared to Al, Li, K, Ge, B, Fe, P during magma evolution. CL does not only show the various structures of earlymagmatic quartz and latemagmatic quartz, such as growth zone boundaries, resorption surfaces and growth embayment, it also reveals secondary CL structures of quartz (e.g. microfracturing). It is difficult to observe these phenomena by general optical microscopes. The microstructures of crystals provide important information of melt source and evolution. Combining the study of trace elements along with the analysis of quartz textures and melt inclusion inventories may reveal detailed PTt paths of magma evolution. This study shows that quartz is a sensitive indicator for physicchemical condition changes during the evolution of silicarich magma.