El colapso gravitacional del frente orogénico alpino en el Dominio Subbético durante el Mioceno medio-superiorel Complejo Extensional Subbético

Résumé

It is currently accepted that the External Betic Zone corresponds to a fold-and-thrust-system, verging toward the NO, Early-Middle Miocene in age. The revision and study of the Olistostromic (OU) and Castro del Río units and their relation with the Mesozoic-Tertiary paleomargen sediments are the main scope of this paper. Our work has lead to a new interpretation of the structure of a part of the External Betic Zone, concretely, the Subbetic Domain viewed from a different perspective.The OU is a chaotic breccia, dated as Middle Miocene (15-13 Ma) mainly nourished from the primitive Betic Orogenic Front, resulting afterwards in the South-Iberian Paleomargen - Alborán Crustal Domain intra-continental collision (Early-Middle Miocene). The OU may be typified as a mass wasting complex (MWC) in origin. The OU hosts mega-clasts of thousands metres in size (tectonosomes) provided also by the primitive Betic Front. The Castro del Rio Unit was deposited unconformably on the OU and the tectonosomes during the Late Serravallian-Early Tortonian (13 � 8,5 Ma). The whole OU, the tectonosomes and the Castro del Río unit, extended from 13 Ma and was further sealed by younger sediments toward the W, here named as the South Betic extensional complex (SEC). This gravitational context and the resulting extension must be considered as an expression of cortical readjustment in the Betic Chain from the Early-Middle Miocene. Rollback of an oceanic lithospheric slab subducted toward the E-SE and subsequent subcrustal delamination and intraplate volcanism developed in the western part of the chain is the model currently proposed to explain the westernmost Mediterranean geodynamic scenario.