From a mountain belt collapse to a sedimentary basin development: 2-D thermal model based on inversion of stratigraphic data in the Paris Basin

摘要

The thermal, mineralogical and mechanical behaviour of the lithosphere determines the genesis and evolution of sedimentary basins (subsidence amplitude, geometry of sediment bodies, sedimentary processes). Using the large stratigraphic database available for the Paris Basin, we constrain the lithosphere thermal evolution, thickness, and rigidity as well as the mechanism that gave birth to this wide intracontinental basin. The thermal subsidence calculated with a two-dimensional thermal model is adjusted to the estimated tectonic subsidence by optimization of three parameters (extension profile, crustal thickness profile, and average mantle heat flow). The best fits for the Paris Basin lithosphere are obtained for a mantle heat flow of similar or equal to 23 mW m(-2) and for an elastic thickness lower than 20 km (preferred value: T-c = 5 km). Two mechanisms for the origin of the basin subsidence have been tested: a pure extensional collapse of the Variscan Belt and a delamination of the mantle lithosphere at the end of Carboniferous. It appears that, in both cases, inverted extension factors are large, in the range betais an element of [1.2; 1.85] in the first case, and in the range betais an element of [1.0; 1.85] in the second case. Both cases involve the presence of a thick Variscan crustal wedge and a mountain belt elevation of 1500-3500 m located in the Paris Basin centre. The maximum extensional rates are obtained in the centre part of the basin. In addition, lithospheric delamination at around 300 Ma allows for both crustal and mantle melting in agreement with the widespread existence of Permian bimodal magmatism in France. At the end of extension, the basin centre kept a high elevation of about 1000 m before subsiding around 40 My later below sea-level. (C) 2004 Elsevier B.V. All rights reserved.