Structures et cinématique liées á la mise en place des péridotites de ronda (cordilléres bétiques, espagne)

Abstract

In the westernmost part of the Betic Chain, the Ronda ultrabasic massifs are allochthonous slabs formed by alpine-type péridotites, mainly lherzolites. Two plastic deformations are preserved in these Iherzolitic massifs, related to their hot emplacement. The Ronda péridotites, in the Sierra Alpujata massif show a well-preserved dynamothermal aureole beneath peridotites, that allows an interpretation of the chronological relationship between these two plastic deformations. The inner part of the Sierra Alpujata massif is composed of plagioclase lherzolites which bear a high temperature (∼ 1100 0C) — low stress deformation as show by their fabrics and coarse-grained porphy roclastic textures. In contrast, the outermost parts are mainly composed of spinel lherzolites, often with mylonitic textures, in which a new deformation of low temperature (∼ 800 °C) — high stress (1-2 Kb) is imprinted. This second deformation is also imprinted in the dynamothermal aureole. The oldest deformation would affond to mantle flow beneath a continental rift, whereas the second one could be ascribed to thrusting of the still hot mantle slab over the continental crust. Kinematic criteria of shear sense from Betic-Rifian peridotites demonstrate the oroclinal origin of the Arc of Gibraltar. © Masson, Paris, 1987.