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Stress induced by the Mio-Pliocene Alpine collision in northern France

MURIEL ROCHER, MARC CUSHING, FRANCIS LEMEILLE and STÉPHANE BAIZE
Bull. Soc. Géol. Fr., 2005, t. 176, n 4, pp. 319-328

Document type > *Article de revue

Keywords > earthquakes, rift/fault

Research Unit > IRSN/DEI/SARG/BERSSIN

Authors > BAIZE Stéphane, CUSHING Edward, LEMEILLE Francis, ROCHER Muriel

Publication Date > 01/09/2005

Summary

ln most rocks, tectonic stress induces crystalline deformation, such as mechanical twinning. The inverse analysis of calcite twinning allows reconstruction of both directions and values of the paleostress tield. The Etchecopar inverse method using calcite twinning has been improved in this paper, lowering the uncertainties on the calculated stress values. Calcite was sampled in the foreland of the western Alps, along a SE-NW section from the Jura Mountains to the Isle of Wight. The calcite twinning inversion has identified the successive Cenozoic tectonic events, named "Pyre­nean" compression, "Oligocene" extension and "Alpine" compression. The distribution of the Mio-Pliocene Alpine orogenie stress was specified. This stress field varies in terms of stress regime, directions and values. The horizontal principal stress trends E- Win southern France, WNW in the centre, and NW in the North, which can be attributed to the Alpine indenter phenomenon. The tectonic stress regime roughly corresponds to a pure compression in the Jura and rapidly evolves to the NW to a strike-slip state of stress, then beyond the Paris basin's centre to a perpendicular extension. Unlike the Pyrenean or Appalachian foreland stress, the Alpine dif­ferential stress does not significantly decrease from the Jura front to the far field (30 to 25 MPa). Moreover, stress values vary from one area to another, low in the Burgundy high, fractured and uprising du ring this tectonic event, and high in Paris basin centre, poorly fractured and subsiding during this event. Three possible explanations are proposed : variation in crust thickness, crustal buckling during the Mio-Pliocene, and pre-existing fractures


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