La deformación varisca en el sector oriental del Sistema Central

Abstract

At present, it is still not clear what are the processes that led to the construction, transformation and dismantling of the oro- genic crust in each of the sectors of the Variscan Orogen. The metamorphic basement of the western sector of the Iberian Peninsula was configured during the Variscan Orogeny. In this work we describe the set of Variscan structures and provide a qualitative estimate of their development metamorphic conditions in the eastern sector of the Central System (Hiendelaen- cina) in order to reconstruct the tectonothermal evolution of said sector and identify the processes that affected this part of the orogen hinterland. The first phase of deformation (D 1) developed E-verging folds and an axial plane foliation (S1) under prograde metamorphic conditions, from the chlorite zone (upper sections) to probably that of the kyanite (lower sections). D1 structures are well preserved in the upper structural levels but occur as mineral relicts in the lower levels. D1 represents crustal thickening at the beginning of Variscan continental collision. The second phase (D2) formed a sub-horizontal main foliation in the lower structural levels of the region (S2), under conditions that vary from the chlorite zone in the upper parts to partial melting in the lower parts. S 2 is a crenulation cleavage in the upper structural levels (better preserved D1 structures), and a schistosity and gneissic banding formed within a top-to-the-SSE ductile shear zone in the lower levels. The inferred flat-lying primary geometry for S2 and said shear zone combined with its thermal imprint (normal telescoping of isogrades and lithostratigraphy) suggests an extensional character for the shear zone, that is, D2 attenuates the previous crustal over-thickening and favors vertical thermal reequilibrium. The third phase of deformation (D3) produces upright folds in all previous structures and a subvertical crenulation cleavage throughout the region (S3). D 3 represents a new phase of thickening as continental collision proceeds.