Abstract
The age of the emplacement of the Ronda Peridotites has been widely debated during recent decades, and ages ranging from the Palaeozoic to the early Miocene have been proposed, although most of the current interpretations suggest an Oligocene-Miocene age. In this article, we describe two meta-sedimentary formations (the lower one formed by detrital sediments and the upper one by marbles) that were unconformably deposited over the Ronda peridotites and now record low-grade metamorphism. The detrital formation contains layers of acidic rocks with an age of 269±9 Ma and the overlying marbles are assumed to be Triassic. The existence of these unconformable formations over the peridotites is crucial for the dating of the exhumation of the latter. The presence of peridotite clasts in the detrital formation indicates that peridotites were exposed during the Permian and other data suggest that peridotites were exhumed during the late Carboniferous. During the Alpine cycle, the peridotites operated as an element situated at the bottom of the tectonically higher Alpujarride/Sebtide unit (the Jubrique unit) and forming part of it, then being incorporated to the Alpine thrusts of this unit.
Highlights
Orogenic peridotites are variably sized pieces of the upper mantle that are exposed in mountain belts
Most articles related to the Ronda massif in the Betics are based on an exclusive Alpine scenario, whereas most articles devoted to the Beni Bousera massif in the Rif favour a mixed Variscan+Alpine origin
(2013), tectonically located under the peridotites, we have found a magmatic formation and two metasedimentary formations in the same area, all located over the peridotites, in agreement with the previous description and cartography of Chamón Cobos et al (1978) and Piles Mateos et al (1978a and b)
Summary
Orogenic peridotites are variably sized pieces of the upper mantle that are exposed in mountain belts They are unique objects for realistic large-scale models of the Earth’s geochemical and tectonic evolution (Griffin et al, 1999) as well as for interpreting the tectonic evolution of particular orogens (Liou et al, 2007 and references therein). The Ronda (and the Beni Bousera) peridotites form two of the largest outcrops of orogenic peridotites in the world The time of their crustal emplacement and exhumation is debated, opinions varying from prePalaeozoic to Alpine ages. Most authors interpret the peridotites as h aving been exhumed during the Oligocene-Miocene (see Platt et al, 2013 for a Review) This hypothesis, as well as those supporting a Variscan age, is based mainly on: a) petrological and mineralogical studies; b) isotopic dating; and c) tectonic considerations and models explaining the evolution of the Western Mediterranean. The significance of some tectonic units previously defined in this area is discussed and a new model for the evolution of the Cordillera in their western zone is proposed
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