Trace elements and growth patterns in quartz: a fingerprint of the evolution of the subvolcanic Podlesí Granite System (Krušné hory Mts., Czech Republic)


Authors: Müller A, Kronz A, Breiter K

Published in: Bulletin of Geosciences, volume 77, issue 2; pages: 135 - 145; Received 18 March 2002; Accepted in revised form 7 May 2002;

Keywords: granite, Krušné hory Mts., quartz population, magma evolution, residual melt, trace elements, zoned quartz,

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The Podlesí Granite System (PGS) in the Western Krušné hory Mts., Czech Republic, represents a suite of late-Variscan, highly fractionated rare-metal granites. Based on textural studies and cathodoluminescence five igneous quartz populations can be distinguished in the stock granite and the more evolved dyke granite hosting line rocks (layered granites). Trace element profiling by electron probe micro-analysis (EPMA) gives evidence for three main crystallisation stages: (1) the zoned quartz phenocrysts representing the early stage of magma evolution in the middle crust, (2) the stockscheider quartz and groundmass quartz of the stock granite reflecting the subvolcanic solidification conditions of the stock granite, and (3) the zoned snowball quartz and comb quartz of the dyke granite crystallised from a highly evolved, residual melt. Ti and Al in quartz show a general temporal trend reflecting the evolution of the magma: decrease of Ti and increase of Al. The increase of lithophile elements (Li, Na, Al, P, K) and of the water content in the magma, the decrease of Ti, crystallisation temperature and pressure are assumed to be predominantly responsible for the trend. High Al in quartz (>500 ppm) may also result from high crystal growth rate. The textural varieties of the PGS in general are not a product of metasomatic overprinting, but a product of crystallisation of different fractionated melts.