Geophysical constraints on exhumation mechanisms of high-pressure rocks: the Saxo-Thuringian case between the Franconian Line and Elbe Zone

Abstract

Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Granulite Massif, Erzgebirge) are investigated using a variety of geophysical methods (seismic reflection and refraction survey, magnetotelluric studies, gravity modelling). The Saxonian Granulite Massif and the Erzgebirge are not a continuous feature, as can be seen from discontinuous reflections, offset of upper-crustal seismic refraction velocity layers, and crustal resistivity increasing towards the Erzgebirge. Their juxtaposition during the evolution of two Variscan-age thrust wedges may have controlled this geometry. The earlier thrust wedge emplaced the supracrustal Erzgebirge HP nappes from the southeast to the northwest onto the Saxo-Thuringian Basin, whereas the later one propagated southwards and uplifted the Saxo-Thuringian granulites from deeper levels. To the southwest, the granulites are observed at shallow depth as far as the Franconian Line; to the southeast they extend down to the Moho, or they continue at mid-crustal levels. The granulites beneath the Saxo-Thuringian Belt can only have originated in one of two subduction zones: either through 'subduction erosion' and subsequent underplating of parts of the Saxo-Thuringian Plate from the north, or by intracrustal plug flow of overheated material from the southeast.

Geological interpretation of gravity profiles through the Karlovy Vary granite massif (Czech Republic)

“…The Rhenohercynian lithosphere was subducted under the Saxothuringicum, which was in turn overthrust by the rocks of the Moldanubian zone. The subductions were active in Late Devonian to Carboniferous time (Krawczyk et al, 2000). Franke (1989) classified the Teplá-Barranian unit as a part of the Moldanubian zone.…”

Control of paths of quaternary volcanic products in western Bohemian Massif by rejuvenated Variscan triple junction of ancient microplates

“…It has been investigated by several refraction and reflection profiles (e.g., Trappe and Wever, 1990;DEKORP, 1994;Krawczyk et al, 2000;Hrubcová et al, 2005;Grad et al, 2008) which imaged a highly reflective, about 4-6 km thick, lowermost crust of the ST. Reflection profile 9HR of Tomek et al (1997) showed a distinct inclined underthrusting of the ST crust beneath the TB.…”

Post-collisional melting of crustal sources: constraints from geochronology, petrology and Sr, Nd isotope geochemistry of the Variscan Sichevita and Poniasca granitoid plutons (South Carpathians, Romania)

“…The first phase can be correlated to the development of the Saxo-Thuringian belt marked by two successive thrust events. The first occurred during the Saxo-Thuringian-Tepla-Barrandian collision (340-320 Ma) and the second during the Saxo-ThuringianRheno-Hercynian collision that ended at c. 310 Ma (Krawczyk et al 2000). We could with advantage refer, following Cavazza et al 2004, to (1) with the collisional climax between the Hunic and Hanseatic terranes with Laurussia at c. 340 Ma followed by a period of lateral displacement accompanied by major plutonism and (2) an Alleghenian orogeny with the collisional climax between Gondwana and Laurentia at c. 300 Ma, also followed by an important magmatic event attaining the Early Permian.…”