Late orogenic faulting and associated vein mineralisation in Saxothuringian metasediments – implications for crustal strength estimates

Author(s): Carlo Dietl, Ines Donhauser, Michel Bestmann, Lars Scharfenberg, Helga de Wall
Abstract: Palaeozoic metasediments, recovered from a well bore at the E’ margin of the Franconian Basin in NE Bavaria, give insight into the Variscan basement west of the Bohemian Massif. Quartz veins are abundant in the folded and cleaved pelitic to psammitic sequence. They are mainly restricted to coarse-grained massive metasandstone. The structural inven-tory of the quartz veins and cross-cutting relationships between them indicates their formation during three brittle deformation phases and corresponding fluid pulses at a depth of ca. 7 km. The metasandstone has a low porosity (1.1 to 1.5 vol-%) and is almost impermeable (permeability = 1.70e-17). Triaxial tests characterise the metasandstone as strong and very cohe-sive lithology (C₀: 185.52 MPa, S₀: 52.11 MPa) that can sustain high compressive stresses. Faulting and vein formation seem to be triggered by high fluid pressure which might have built up in the low permeable metasandstone. The most probable timing for fracturing and vein formation is shortly after the transition from compression to extension tectonics late in the orogenic history of the Variscides during orogenic collapse. At this changeover point effective stresses are decreasing, be-cause fluid pressure becomes more effective as driving force for (hydraulic) fracturing. The generated fracture structures (from vein to fault scale) are preferably orientated in N–S and NW–SE directions. Both orientations represent prominent and persistent regional fault trends in the area not only for Variscan structures but also for younger Permo-Mesozoic to Cenozoic strata of the Franconian Basin.
Organisation(s): Faculty of Earth Sciences, Geography and Astronomy, Department of Geology, Department of Lithospheric Research
External organisation(s): Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Gesteinslabor Dr. Eberhard Jahns
Journal: Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften
Volume: 173
Pages: 445-467
No. of pages: 23
ISSN: 1860-1804
DOI: https://doi.org/10.1127/zdgg/2022/0273
Publication date: 2022
Peer reviewed: Yes
Austrian Fields of Science 2012: 105106 Geodynamics
Keywords
ASJC Scopus subject areas: General Earth and Planetary Sciences
Portal url: https://ucrisportal.univie.ac.at/en/publications/ca333cc9-49fb-470c-8062-2d48cf4c41ed

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