Institute of Geology AS CR, v. v. i.
Medium-sized research center which main purpose is to gain, interpret and integrate the knowledge of the Earth System.
Interpretation of the Teplice Caldera history based on the LA-ICP-MS study of quartz crystal zoning
The Altenberg–Teplice Caldera (eastern Krušné Hory/Erzebirge) is the largest Variscan volcano-plutonic complex in the Bohemian Massif. It is composed of co-magmatic volcanics (peraluminous basal rhyolite and associated dacite, overlying three units of subaluminous Teplice rhyolite and granite porphyry) and plutonic granites (two intrusions of A-type granites). In this study, the internal structures and trace-element distributions within quartz grains were investigated using a laser ablation ICP-MS combined with a hot-cathode and scanning cathodoluminescence analysis. The trace-element distribution in quartz from the granite porphyry and rhyolite demonstrates a distinct zoning: the core is poor in Ti, the rims are enriched in Ti, and the trends recorded for Al are opposite. The quartz from granites is mostly homogeneous. Based on the chemical composition of quartz and its zoning, we assume that the quartz crystals began to crystallize in the primary deep-seated magma chamber with a pressure of 10 kbar and a temperature of 750 °C. The early stage was followed by the subsequent adiabatic ascent into a shallow magma chamber (estimated by the Ti-in-quartz thermobarometry at approximately 700 °C, 2 kbar), during which crystal rims rich in Ti formed and then extruded. After the caldera collapse, part of the magma intruded as granite, and in the environment of the residual melt rich in water and flux agents, late quartz grew in the form of snowball quartz with an increased Al content and decreased Ti content. Our study is the first attempt, in the international scale, to interpret the evolution of magmatic caldera based on the chemical composition of quartz. This methodology is resistant to chemical changes, which affect other rock-forming minerals during post-magmatic alterations.
Reference: Breiter, K. - Svojtka, M. - Ackerman, L. - Švecová, K.: Trace element composition of quartz from the Variscan Altenberg-Teplice caldera (Krušné hory/Erzgebirge Mts, Czech Republic/Germany): Insights into the volcano-plutonic complex evolution. Chemical Geology.327, 9 (2012), 36–50.
Contact: RNDr. Karel Breiter, PhD., +420 233087210, breiter
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