SUPERIMPOSED FOLDING AND OBLIQUE STRUCTURES IN THE PALAEOMARGIN-DERIVED UNITS OF THE CENTRAL BETICS (SW SPAIN)

Abstract

The Subbetic units consist of a deformed wedge of sedimentary rocks deriving from the South Iberian palaeomargin, in the westernmost segment of the Alpine-Mediterranean orogenic belt. In the central Betics, shortening produced folding, thrusting and nappe-stacking. The structural trend is NE-SW to ENE-WSW, and the internal structure of the thrust sheets, which shows no preferred vergence, is strongly controlled by the theology of the decollement level, a viscous layer of Triassic evaporites, and of the overlying carbonate rock sequence. The relationships of piggyback basin Miocene sediments with the main structures show that the latter developed during the Aquitanian-Burdigalian transition. Superimposed folding is described for the first time in the study area. The origin of the interference cannot be determined at present, but may be related to initially oblique structures refolded during progressive deformation. A revision of previously published palaeomagnetic data in the light of the data presented in this paper, in conjunction with a model of the structural evolution of the Subbetic units of the western Betics, permits us to establish milestones of the tectonic evolution of the external zones in the northern branch of the Gibraltar Arc.