Trace elements and cathodoluminescence of igneous quartz in topaz granites from the Hub Stock (Slavkovsk� Les Mts., Czech Republic)

Abstract

Igneous quartz of the late-Variscan topaz-bearing granites from the Hub Stock (Slavkovský Les, Czech Republic) was investigated by cathodoluminescence (CL) and electron probe micro-analysis (EPMA) to demonstrate the intra-granular heterogeneity of growth patterns and trace element distribution in quartz. We show that EPMA is well suited for the in situ study of Al and Ti in zoned quartz, because of its high spatial resolution down to 5 µm in conjunction with the ability to combine spot analyses with CL imaging. In the quartz phenocrysts of the topaz granites high Ti is associated with blue luminescent growth zones. High Ti (>40 ppm) in quartz indicates a high crystallisation temperature and pressure. The groundmass quartz of the granites which is almost free of Ti, has higher Al than the phenocrysts which may reflect an increase of lithophile elements and water content in melt during the late magmatic stage. The occurrence of similar quartz phenocrysts in most of the late-Variscan granites and rhyolites of the Krušné Hory/Erzgebirge which intruded over a period of about 40 Ma points to a similar crystallisation environment and origin of the quartz phenocrysts in the lower to middle crust.