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Linking Alpine deformation in the Aar Massif basement and its cover units – the case of the Jungfrau-Eiger Mountains (Central Alps, Switzerland)

This paper is available in a repository.
This paper is available in a repository.

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Abstract

The NW rim of the external Aar Massif was exhumed from ~ 10 km depth to its present position at 4 km elevation above sea level during several Alpine deformation stages. Different models have been proposed for the timing and nature of these stages. Recently proposed exhumation models for the central, internal Aar Massif differ from the ones established in the covering Helvetic sedimentary units. By updating pre-existing maps and collecting structural data, a structural map and tectonic section was reconstructed. Those were interpreted together with micro-structural data and peak metamorphic temperature estimates from collected samples to establish a framework suitable for both basement and cover. Temperatures at deformation ranged from 250 °C to 330 °C allowing for semi-brittle deformation in the basement rocks, while the calcite dominated sediments deform ductile at these conditions. Although field data allows to distinguish multiple deformation stages before and during the Aar Massifs rise, all related structures formed under similar P, T conditions at the investigated NW rim. We find that the exhumation occurred during 2 stages of shearing in the Aar Massif basement, which induced in the sediments first a phase of folding and then a period of thrusting, accompanied by the formation of a new foliation. We can link this uplift and exhumation history to recently published large-scale block extrusion models.

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