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Structure of the Tectonic Front of the Western Alps: Control of Fluid Pressure and Halite Occurrence on the Decollement Processes

Abstract : This study focuses on the respective role of (1) the occurrence and the nature of evaporitic layers and (2) the fluid pressure conditions on the decollement processes and the structure of the foreland fold and thrust belt of the Western Alps. The decollement in the Jura Mountains is predominantly localized in halite-bearing layers. Anhydrite-bearing units which are not associated to halite are not hosting major decollement. The shift of decollement level between Mid-Triassic halite unit and Upper Triassic halite unit has induced local tectonic subtractions and, elsewhere, tectonic duplications at depth. Available fluid pressure measurements show that fluids are not overpressured in the Jura. Even below the salt decollement, they remain in hydrostatic conditions. South of the Jura, the absence of halite is correlated with no efficient role of the Triassic layers in terms of decollement. The available pressure measurements show that the decollement is associated with high overpressure. Because of the low friction of halite, the Jura thrust wedge shows a narrow angle (3°–4°). The relatively high friction behavior of the decollement south of the Jura is responsible for stacks of tectonic units associated with a relatively wide angle of the tectonic wedge (12°–13°). The structural change between the Chartreuse and Vercors massifs is not controlled by the properties of the decollement but by the change of thickness of the sedimentary pile involved in the tectonic wedge. The change of thickness is controlled by paleogeographic heritage during Jurassic and Cretaceous times.
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Submitted on : Thursday, June 3, 2021 - 5:32:02 PM
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Eric Deville. Structure of the Tectonic Front of the Western Alps: Control of Fluid Pressure and Halite Occurrence on the Decollement Processes. Tectonics, American Geophysical Union (AGU), 2021, 40 (4), pp.e2020TC006591. ⟨10.1029/2020tc006591⟩. ⟨hal-03248807⟩



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