Magnetic fabrics in overthrusted terrains: example from the Buntsandstein Facies in the southern edge of the Axial Zone (Nogueres unit, Central Pyrenees)
Abstract
Magnetic fabrics in deformed domains are a source of information of the strain rate and the tectonic evolution of the rocks. The present study shows the results derived from the application of this methodological approach to the Permian-Triassic red beds in the western sector of the Nogueres unit and eastern sector of the Gavarnie thrust sheet (Central Pyrenees). From the structural point of view, the sampled domain constitutes a key area since it is located in the transition between the antiformal stack of the Axial Zone to the West, including non-overturned basement thrust sheets, and the têtes plongeantes domain of the Nogueres unit to the East. The latter comprises three folded thrust sheets, involving Stephanian, Permian and Triassic rocks, whose fronts define several synformal anticlines. Alpine cleavage is generally absent within the têtes plongantes domain but Triassic outcrops located North and West are affected by WNW-ESE-striking, North-dipping cleavage planes. Samples for the study of the anisotropy of magnetic susceptibility were collected from 31 sites, distributed throughout the different structural domains (in the têtes plongeantes domain and in the red beds unconformably overlying the Paleozoic, North and West of the Nogueres unit). Measurements of the magnetic fabric were made at room and low temperature (~77°K) with a KLY-3S susceptibility meter (AGICO, Czech Republic) that combined with a CS-3 apparatus was also used to perform thermomagnetic runs. Mean magnetic susceptibility (Km) in the sampled sites ranges between 35 and 221·10-6 S.I. It is lower in the sandstones (
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2012
- Bibcode:
- 2012EGUGA..14..823I