Abstract

The process of extension in the Massif Central Rift (MCR) is discussed through the synthesis of available geological data. The MCR is 200 km wide and its overall geometry is best described as two opposite half-grabens arranged on both sides of a smaller symmetrical graben. This striking mirror symmetry is thought to result from the Oligocene extension during which sedimentation took place. Volcanism occurred later during the Miocene and is restricted to the west of the whole extensional province. Analogue modelling reveals that the geometry of the sedimentary basins may be interpreted in term of failure of the brittle upper-part of the lithospheric mantle during passive rifting. The most significant data strongly suggest that the initiation of the rift is due to farfield stresses acting on the lithosphere (i.e. stress-generated or passive rift) and does not result from an ascending mantle plume (i.e. plume-generated or active rift).

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