EGU2020-2192
https://doi.org/10.5194/egusphere-egu2020-2192
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Full paleostress tensor determination: case of the Panasqueira Mine, Portugal.

Christophe Pascal1, Luís Jaques1, and Atsushi Yamaji2
Christophe Pascal et al.
  • 1Ruhr University Bochum, Germany (christophe.pascal@rub.de)
  • 2Graduate School of Science, Kyoto University, Japan

The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa and differential stress lower than ~20 MPa.

How to cite: Pascal, C., Jaques, L., and Yamaji, A.: Full paleostress tensor determination: case of the Panasqueira Mine, Portugal., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2192, https://doi.org/10.5194/egusphere-egu2020-2192, 2020.