Structural record of polyorogenic pre-Alpine and Alpine deformations within a major thrust nappe close to a suture zone (Internal-External Zones Boundary of the central Betic Cordillera, S Spain)

Abstract

ABSTRACT The Malaguide Complex occupies the highest position in a thick-skinned Alpine thrust stack. It includes polydeformed, sedimentary and low-grade metamorphic rocks of Palaeozoic basements and their Meso-Cenozoic covers. NE of Granada the complex results severely sheared and stretched along the Betic suture zone in the metamorphic hinterland (orogenic backstop). The suture developed after the Burdigalian, due to oblique collision of the Alboran Domain (including the Malaguide Complex) with the South-Eastern Iberian Paleomargin. The orogenic evolution in the backstop region started with late Palaeogene to Early Miocene N-directed pre-collisional shortening and early thrust stacking, associated with low-grade metamorphism in the lowest Malaguide units increasing downwards into the underlying Alpujarride Complex. An accretionary prism developed at the expense of deep-marine (Flysch) sediments and the sedimentary covers of the Iberian and Alboran conjugate margins (External Zones and Frontal units, respectively). Later orogenic stages were characterized by SSE-directed back-folding and -thrusting in the Middle Miocene affecting both sides of the Betic suture related to dextral wrenching causing plurikilometric displacements. In this way, the suture evolved towards a several kilometres wide megashear zone (Cogollos-Diezma Corridor), prior to a final phase of SW-directed post-orogenic extension in the Late Miocene. Despite this protracted Alpine evolution, the Malaguide basements also preserve a record of orogenic activity during Late Carboniferous stages of the Variscan Orogeny in the form of a set of NE-SW trending folds with SE vergence and associated slaty cleavage, which are not found in the post-Carboniferous cover. The temperature conditions of this event (>300°C) in the less metamorphic Malaguide units are determined by colour alteration index (CAI) data from conodonts that have also allowed biostratigraphic dating of the Devonian-Carboniferous successions.