The Stolpen Volcano in the Lausitz Volcanic Field (East Germany) - volcanological, petrographic and geochemical investigations at the type locality of basalt

Abstract

The ~30 Ma Stolpen Volcano near Dresden (Saxony) is situated at the western margin of the Lausitz Volcanic Field. It forms a small isolated basaltic hill, the famous Stolpen Castle Hill, penetrating the granodioritic basement of the Lausitz Block and is worldwide the type locality for the term 'basalt', as coined by Agricola (1546). The volcano has always been interpreted as subvolcanic crypto-or lava dome. New geological mapping, dip measurements of the basaltic columnar jointing and the first evidence of scoria for the Stolpen Volcano allow for a new interpretation of the volcanic edifices. On this basis the structure is best described as a maar crater volcano filled by a 110 m thick basanitic lava lake. According to genetic classification, it is a complex monogenetic volcano formed in three phases: (1) a phreatomagmatic diatreme phase with a maar crater, (2) a scoria cone phase with the final basanitic lava lake filling, and (3) a post-volcanic phase with neotectonic uplift, denudation and exposure of a basaltic hill since c. 1.3 Ma. The volcano reconstruction indicates an ongoing change in the eruption style from phreatomagmatic (phase 1) to eruptive and, finally, effusive processes (phase 2) without significant gaps between the eruption episodes. The only difference appears to be caused by a variable water supply during the magma ascent and volcanic eruption. New mineralogical (QAPF) and geochemical (TAS) investigations of the Stolpen lava samples reveal that the Stolpen Hill is not built by a basalt, but basanite trending toward a nephelinite, following the current nomenclature. Microscopic analyses also provide evidence of magma mingling, such as nephelinite melt enclaves, and show local lava contamination by the country-rock granodiorite, also supported by the presence of quartz xenocrysts. The combined field observations, petrography and geochemical data indicate overall heterogeneity of the Stolpen lava. Therefore, the Stolpen Castle Hill is not-in a scientific sense-a suitable type locality for either basalt or basanite. However, the outcropping volcanic rocks as well as their scientific and historical importance undoubtedly give relevance to Stolpen as a type locality for basaltic volcanic rocks in a broader sense.

Phreatomagmatic vs magmatic eruptive styles in maar-diatremes: a case study at Twin Peaks, Hopi Buttes volcanic field, Navajo Nation, Arizona

“…The lava lakes then cooled slowly over decades (Wright and Peck 1978;Cas and Wright 1988;Tazzieff 1994), during which joints formed perpendicularly to the cooling surface (DeGraff and Aydin 1987). Joints patterns on both peaks are typical of lava lakes formed within a crater (Tietz et al 2018).…”

“…Another possibility is that the eruptive regime progressively switches from phreatomagmatic to magmatic. If a late magmatic phase of the eruption lasts long enough, the syn-eruptive maar crater could be filled (or over-filled) by a scoria cone Vazquez 1998) or a lava lake (e.g., Martin and Németh 2002;Kereszturi and Németh 2011;Hencz et al 2017;Latutrie and Ross 2018;Tietz et al 2018), so that the final landform at the end of the eruption would not necessarily be a maar, even if there is a diatreme under it. Williams (1936) studied both the HBVF and the older Navajo volcanic field further north.…”

Characterisation and Evaluation of Columnar Basalt Geoheriatge in Thailand: Implication for Geotourism Management in Post-Quarrying Area

“…This work also determines the origin of basalt, both the columnar joint and the platy joint, linking with their engineering properties, which is interesting. According to the lava flow, the initial cooling from the surface, and its sudden change in temperature to form hard rock, will result in the lava to contract and create a tensile force more significant than the surrounding expansion, and hence isotherms are assumed to be perpendicular to the direction of the columns (Hetenyi et al 2012, Tietz et al 2018, Hamada, Toramaru 2020, Li, Liu 2020. The lava that lies beneath the earth cools slowly; the crack extends down the magma until its pull is equal to its expansion, which causes a columnar joint inside and a platy joint on the surface (Mallet 1875, Middlemost 1975.…”

The origin of the term ’basalt’

“…However, probably no geologist ever started to think where this term actually comes from. On the occasion of the Basalt 2017 conference held in Kadaň (Czech Republic) and the investigation of the Stolpen Volcano (see Tietz et al 2018, in this issue), the history of the word 'basalt' was examined more closely. The term was coined in 1546 by Georgius Agricola (1494-1555) in a short caption in De Natura Fossilium -an early modern era text representing the first attempt to scientifically classify minerals, rocks and fossils -referring to 'ashgrey marbles 1 ' at the Stolpen Castle Hill near Dresden (Saxony, Eastern Germany):…”