The Late Carboniferous deeply eroded Tharandt Forest caldera–Niederbobritzsch granite complex: a post-Variscan long-lived magmatic system in central Europe

Abstract

Samples and documentation of outcrops and drillings, facies analysis, whole rock geochemistry and radiometric ages have been employed to re-evaluate the Late Carboniferous Tharandt Forest caldera (TFC) and the co-genetic Niederbobritzsch granite (NBG) in the eastern Erzgebirge near Dresden, Germany. The c. 52 km2 TFC harbours strongly welded ignimbrites with a preserved minimum thickness of 550 m. Composition of initial fallout tephra at the base of the TFC fill, comprising lithics of rhyolitic and basic lava, and of silica-rich pyroclastic rocks, suggests a bimodal volcanic activity in the area prior to the climactic TFC eruption. The lower part of the TFC fill comprises quartz-poor ignimbrites, overlain by quartz-rich ignimbrites, apparently without a depositional break. Landslides originating from the collapse collar of the caldera plunged into the still hot TFC fill producing monolithic gneiss mesobreccia with clasts ≤ 1 m in a pyroclastic matrix. Aphanitic and porphyritic rhyolitic magma formed ring- and radial dykes, and subvolcanic bodies in the centre of TFC. Whole rock geochemical data indicate a high silica (most samples have > 73 wt% SiO2) rhyolitic composition of the TFC magma, and a similar granodiorite–granitic composition for the NBG. Based on drillings and caldera extent, a minimum volume of 22 km3 of TFC fill is preserved, the original fill is assumed at about 33 km3. This estimate translates into a denudation of at least c. 210 m during Late Paleozoic to pre-Cenomanian. Telescopic subsidence of the TFC took place in two, perhaps three stages. A possible TFC outflow facies has been completely eroded and distal TFC tuff has not been recognized in neighboring basins. New CA-ID-TIMS measurements on two TFC samples gave mean zircon ages of 313.4 ± 0.4 Ma and 311.9 ± 0.4 Ma; two samples from NBG resulted in 318.2 ± 0.5 Ma and 319.5 ± 0.4 Ma. In addition, for one sample of the ring dyke an age of ca. 314.5 ± 0.5 Ma has been obtained. These ages, together with field relations, allow for a model of a long-standing evolution of an upper crustal magmatic system (~ 5 Ma?), where pulses of magmatic injection and crustal doming alternate with magmatic quietness and erosion. Together with the Altenberg–Teplice Volcanic Complex, located some 10 km to the southeast, the TFC–NBG Complex represents an early post-Variscan magmatic activity in central Europe.

Two-phase late Paleozoic magmatism (~ 313–312 and ~ 299–298 Ma) in the Lusatian Block and its relation to large scale NW striking fault zones: evidence from zircon U–Pb CA–ID–TIMS geochronology, bulk rock- and zircon chemistry

“…11) suggests the existence of two well-established magmatic episodes following the Variscan orogeny (e.g., Tischendorf and Förster 1990;Pietranik et al 2013). Contemporaneously with the intrusion of the Koenigshain pluton and the amphibole-bearing granites of the Lusatian Block, the Karkonosze pluton (Kryza et al 2014b), the volcanic rocks of the Tharandt Caldera of the NE Erzgebirge (Breitkreuz et al 2021), and volcanic rocks interlayered within the Žacléř Formation of the Intra-Sudetic basin (Opluštil et al 2016a) were formed. The intrusion of the large granite plutons of the Western Erzgebirge and of the Niederbobritzsch pluton of the NE Erzgebirge occurred slightly earlier, between 322.9 ± 0.4 Ma and 314.1 ± 0.6 Ma (Tichomirowa et al 2019a;Breitkreuz et al 2021).…”

“…Contemporaneously with the intrusion of the Koenigshain pluton and the amphibole-bearing granites of the Lusatian Block, the Karkonosze pluton (Kryza et al 2014b), the volcanic rocks of the Tharandt Caldera of the NE Erzgebirge (Breitkreuz et al 2021), and volcanic rocks interlayered within the Žacléř Formation of the Intra-Sudetic basin (Opluštil et al 2016a) were formed. The intrusion of the large granite plutons of the Western Erzgebirge and of the Niederbobritzsch pluton of the NE Erzgebirge occurred slightly earlier, between 322.9 ± 0.4 Ma and 314.1 ± 0.6 Ma (Tichomirowa et al 2019a;Breitkreuz et al 2021). The intrusion of the Stolpen pluton and the formation of the volcano-sedimentary Weissig basin occurred simultaneously with and subsequently to the volcanic rocks of the Ilmenau Formation and preceding the deposition of the Oberhof Formation of the Thuringian Forest basin (Lützner et al 2021).…”

Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany: reconstruction of an intra-continental supereruption

“…1). In the Erzgebirge Block, the Mid-Carboniferous Tharandt Forest Caldera (Benek 1980) and Teplice-Altenberg Volcanic Complex (e.g., Breiter et al 2001;Breiter et al 2012;Breitkreuz et al 2021;Mlčoch and Skácelová 2010;Walther et al 2016, Casas García et al 2019 evolved. At the Carboniferous-Permian boundary further volcanic activity led to formation of the Meißen Volcanic (Benek et al 1977), the Chemnitz Basin with its petrified forest (Schneider et al 2012), and the North Saxon Volcanic Complex.…”