Post-orogenic exhumation of high-grade rocks in the Sierra de los Filabres, SE Spain

Abstract

The Internal Betics (SE Spain) have experienced a complex structural and metamorphic history of burial during the Alpine Orogeny followed by (post-)orogenic exhumation of high-grade rocks. Traditionally, the Nevado-Filabrides and Alpujarride are the two tectonic units that are used to reconstruct the Alpine orogenic history of the Internal Betics, whereas at the same in the field the boundary between the two is defined by a Miocene detachment that has emplaced the Alpujarride on top of the Nevado-Filabrides. This study presents an improved tectono-stratigraphic column of the upper part of the Nevado-Filabrides with a special focus on the structural position of the (ultra-)mafic oceanic mantle derived rocks and quantitatively defines the relation between burial and exhumation shear zones in the eastern Sierra de los Filabres, located in the eastern part of the Internal Betics. Analysis of kinematic (micro-)structures shows that there is a ~45 degree difference between the direction of contraction (top-to-NW) and subsequent extension (top-to-W). Moreover, the detachment that accommodated the main displacement during extension did not exactly localize in the burial related shear zones but instead occasionally cross-cuts them. For this reason, on a local scale the detachment cannot be used as the boundary between the Nevado-Filabrides and Alpujarride. Alternatively, we propose that the (ultra-)mafic rocks observed in the Nevado-Filabrides represent an Alpine suture zone between the two units and therefore should be used as the boundary. The detachment creates a tectonic omission that cross-cuts this suture zone and in this way preserves slivers of low-grade Nevado-Filabrides in the hanging-wall and slivers of high-grade Alpujarride in the footwall. Simultaneous N-S compression perpendicular to the E-W extension has led to the formation of an E-W trending dome in which the high-grade Nevado-Filabrides and Alpujarride are exposed in the core and the low-grade equivalents at the margins.