THE 2-STAGE OPENING OF THE WESTERN-CENTRAL MEDITERRANEAN BASINS - A FORWARD MODELING TEST TO A NEW EVOLUTIONARY MODEL

The Algero-Provencal and the Tyrrhenian extensional basins developed i n two stages in a geodynamic setting characterized by the nearly N-S c onvergence between Africa and Eurasia. The spreading of the Provencal basin occurred in the early Miocene following a long period of rifting in the western Mediterranean area. A dramatic eastward shift of the a ctive extensional deformation resulted in the Tortonian to Quaternary opening of the Tyrrhenian basin. In a companion paper, Carminati et al . propose that: a trench retreat process in a geodynamic setting locke d by the continental collisions in the Alps and in the Betic chain is a viable mechanism for the late Oligocene-early Langhian opening of th e western Mediterranean; a Langhian slab detachment episode along the north African margin is likely to have caused the end of the trench re treat along this part of the boundary determining the end of active ex pansion in the western Mediterranean and the beginning of active exten sion in the Tyrrhenian basin. The objective of the present paper is to quantitatively test this proposed scenario. We calculate, by means of a thin shell model, the effects of these plate boundary reorganizatio ns on the European stress and strain field. We show that the two-stage opening of the western and central Mediterranean can be explained by the evolution proposed by Carminati et al, and that, in particular, th e eastward shift of the active extension which produced the terminatio n of the first opening stage and the beginning of the second is likely to have been triggered by the slab detachment episode along the north African margin. (C) 1998 Elsevier Science B.V. All rights reserved.