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Cutting through the Lower Permian Wurzen monotonous intermediate (drilling B1/19S near Grimma, Saxony): Fabrics, facies, and geochemistry

The Late Paleozoic North Saxon Volcanic Complex, situated east of the city Leipzig (Germany) hosts two nested caldera systems: the Rochlitz (RVS) and the slightly younger Wurzen Volcanic System (WVS). In addition to the voluminous Wurzen caldera fill ignimbrite, the WVS also comprises small-volume precursor eruptions (e.g. Cannewitz ignimbrite), whose classification as a post-climactic eruption of the RVS or as an initial eruption of the WVS remains uncertain. This study includes modal and geochemical investigations along an almost completely cored 648 m long profile through the deposits of the WVS at Großsteinberg (Grimma, Saxony). The observed depth-dependent and continuous changes in modal composition and geochemistry within the caldera ignimbrite facies suggest a close genetic relationship between the Cannewitz and the Wurzen ignimbrites. We, therefore, propose the new name Cannewitz member to emphasise the affiliation to the WVS. Characterised by a rhyolitic composition and low crystallinity (ca. 30.9 vol%), the Cannewitz member represents the initial eruption of the WVS from a rhyolitic cap of the magma chamber. During the continuous volcanic activity, the transition to the crystal-rich (up to 50.4 vol%) monotonous intermediate Wurzen ignimbrite, fed by a voluminous trachydacitic magma chamber, occurred. Based on the newly established minimum thickness of the caldera filling in the drilling, the erupted minimum volume could be recalculated to 838 km3. The resulting volcanic explosivity index of 7 qualifies the WVS as a supereruption.

Details

Author
Victoria Kühnemann1, Alexander Repstock2, Christoph Breitkreuz1, Hripsime Gevorgyan1, Bernhard Schulz1, Rosa Bögle3
Institutionen
1TU Bergakademie Freiberg, Germany; 2Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie (LfULG), Germany; 3Basalt-Actien-Gesellschaft, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/er7h-kz16