Etapas de fallamiento neógenas en la mitad occidental de la depresión de Ugijar (Cordilleras Béticas)

Abstract

The geological structure of the western half of the Ugíjar Depression has been studied and the fauling of the intramiocene and later times is described in detail. The present contact zone between the Nevado-Filábrides and the Alpujárrides units (the Mecina Fault) is shown to be a shallow-angled, dextral, transtensile fault. It can be determined from the associated rock deformations in the Nevado-Filábrides, such as extensional crenulation c1eavage, cataclasites and folding, that the upper block is moving towards SW-SSW. As far as the later structures are concerned the following stages have been distinguished: firstly, folding with an ENE axis. followed by normal dextral faults trending E to ENE, then reverse faults and thrusts with the upper block moving firstly towards the SE and then to the E, folding with an ENE axis normal dextral faults trending E to ENE, and finally the appearance of other small faults trending N to NW. The principal thrust shows ramps and flats and gives rise to fault rocks which may attain some ten metres in thickness. The intersections between thrusts and normal dextral faults, which occurred before and after these, form a complex zone of slices at the northern border of the Depression. Two hypotheses are proposed in order to explain the different stages of faulting. In the first, the structures might be the result of a dynamic evolution including a positional alteration in the in the stresses. In the second, which is geometrical in character, the structures may well be due to dextral, transtensile and strike-slip displacements along the convexities of the Mecina Fault.