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Deducing the magma evolution of the Upper Carboniferous Tharandt Caldera (Saxony, Germany) by geochemical and mineralogical constraints

Voluminous pyroclastics are known to be formed in catastrophic caldera-forming eruptions. The reconstruction of the magma’s origin and lithospheric evolution beneath such calderas is still a challenging task in igneous petrology and volcanology. Probably one of the most interesting areas for studying volcanic activities is the Late Paleozoic of central Europe. Here, the deeply eroded Tharandt Caldera of the eastern Erzgebirge is one of the oldest volcanic edifices, comprising two crystal-rich rhyolitic ignimbrites, a vitrophyre, and microgranites.

In the present study, the pyroclastic record is characterized using a multifarious approach including whole-rock and µ-XRF analyses on fiamme, as well as electron microprobe data of glass and phenocrysts. Based on the results, the pyroclastic sheet within the caldera distinguished two rhyolitic ignimbrite units, the Lips Tullian and Mohorn members. The densely welded Mohorn member (welding degree VI) includes a vitrophyre, which can be interpreted as a rheomorphic diapir.

Thermometry of the ignimbritic members yield crystallization at 835 to 840°C for K-feldspar, apatite at 900 to 920°C, and zircon at 765°C to 800°C. It should be noted that the low zircon saturation temperature of 755°C in the vitrophyre shows that the agglutination and rheomorphism processes occurred in a short period during the eruption. The applied barometers unravel magma bodies in different lithospheric levels: an upper crustal magma body (5 to 10 km, PQtz = 1.2 to 3 kbar), a middle crustal magma body (20 km, PQtz = 5.6 kbar), and a lower crustal magma body (30 km, PQtz = 9 kbar).

Details

Author
Markus Aurelian Baessler1, Alexander Repstock2, Lutz Hecht3, Hripsime Gevorgyan4, Sabine Gilbricht4
Institutionen
1Freie Universität Berlin, Germany;Leibnitz-Institut für Evolutions- und Biodiversitätsforschung, Museum für Naturkunde Berlin; 2Geological Survey and Geophysics, Saxon State Office for Environment, Agriculture and Geology, Dresden; 3Leibnitz-Institut für Evolutions- und Biodiversitätsforschung, Museum für Naturkunde Berlin; 4Institute for Mineralogy, TU Bergakademie Freiberg
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/mn4q-az30