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Master Thesis

Analyse structurale et métamorphique des métasédiments de la zone Briançonnaise au SE du Pelvoux (Briançon, Guillestre, Alpes Occidentales). Premières estimations Pression - Température

Abstract : The study of the pressure-temperature (P-T) conditions recorded by the rocks is important to the understanding of the formation of mountain range. In the internal part of the Western Alps, near Briançon and Guillestre, the metamorphic footprint appears relatively weak with only few metamorphic minerals associated. These observations are consistent with the lack of P-T data. We conducted in two selected areas (Clarée and Guillestre) a combined structural, petrological and thermobarometric study in order to define the deformation phases and to propose P-T conditions for the D1 event. The development of thermobarometric methods involving the local equilibria for chlorite-phengite assemblage provides new tool for the study of these low-grade metamorphic areas. Three structural phases are identified in the Guillestre area: (1) A top-to-the-north shearing direction corresponding to the nappe stacking, (2) a westward-thrusting direction associated to the Brianconnais frontal thrust activity and (3) a late top-to-the-east thrusting direction. In the Clarée area, only a prograde D1 event without general orientations and an eastward D3 event can be characterized. We propose that the Clarée area in the “zone Houillère” records a pressure and temperature peak (D1) at 6.2 +/- 1 Kbar and 345 +/- 40°C. This first result in the French portion of the “zone Houillère” is consistent with other estimations and shows an intermediate geothermic gradient between subduction and collision. This event corresponds to the stacking of the Briançonnais cover and probably occurred between 37 and 34 Ma. In the “nappes briançonnaises” at Guillestre, the metamorphic peak (D1) is estimated at 5.8 +/- 1.7 Kbar and 280 +/- 60°C. This result shows a low metamorphic grade compared to the Vanoise cover, which illustrates the eastern position of this sample in the Briançonnais frontal thrust.
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Submitted on : Tuesday, January 12, 2010 - 10:20:18 AM
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Pierre Lanari. Analyse structurale et métamorphique des métasédiments de la zone Briançonnaise au SE du Pelvoux (Briançon, Guillestre, Alpes Occidentales). Premières estimations Pression - Température. Géochimie. 2009. ⟨dumas-00446125⟩

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