MASCLE, JEAN, Centre National de la Recherche Scientifique, Villefranche-Sur-Mer, France
ABSTRACT: New Constraints on the Tectonic of the Eastern Mediterranean Sea from Recent Marine Geophysical Surveys
Aspects of the initial stages of a continental collision between European and African plates have been documented during recent geophysical surveys of the Eastern Mediterranean basin conducted during the 1990s. Details of the seafloor and tectonic deformation along the Mediterranean Ridge, and surrounding margins, including the Nile deep sea fan, seem to point in that direction. The Eastern Mediterranean Sea represents a unique opportunity for studying the beginnings of such a collision between the passive margins of a major plate (Africa), locally acting as a continental indenter against the active margin of another plate (Europe). More wide-angle data, deep-penetrating multichannel seismic data, and ODP drilling data are, however, crucial to obtain in the future, to better assess the nature and the architecture of the underlying lithosphere, the styles of sedimentary deformation, and the consequences on fluid releases. Such data will make it possible to establish a geodynamic pre-collision model.
The Mediterranean Ridge is itself a large accretionary prism between Africa and southern Europe. In three dimensions, as well as in shaded views and on acoustic imagery, the area clearly shows several major structural provinces, well characterized by distinct bathymetric features and trends. Seismic data also show strongly contrasted tectonic structures. There are at least three recognizable main domains: the African continental slope to the south, the southern Crete margin and bordering trench system to the north, and the Mediterranean Ridge in the middle. The data so far demonstrate clear differences in seafloor morphology and elevation and a strong contrast in structures and sedimentary architecture of the Mediterranean Ridge east and west of 240 E. The region to the east has an average water depth of 2400 m, and its outer domain consists of an eastward widening folded belt crosscut by a fault system and rooted by Messinian salt deposits. The region to the west involves the possible incipient collision of the plates. It lies just north of the Cyrenaica promontory on the African continental margin and has an average water depth of just 1700 m. Undulating structural trends were observed there that approximately parallel the southern Mediterranean Ridge front along the African slope more than 60 km away. These observations suggest that the western part of the Mediterranean Ridge is being affected by the onset of a collision between the Cyrenaica-Africa continental margin (acting as an indenter) to the south and the underlying thinned edge of the Cretan margin to the north.
The data also illustrate a widespread occurrence of mud volcanoes and mud flows, particularly along the northern Mediterranean Ridge border. These features are clearly related to backthrusting and transcurrent faulting. This new set of data is currently changing our understanding of tectonic and related processes generated in a pre-continental collision setting. They should, as well, help to better understand several aspects of former collisions that occurred particularly in this area during the Alpine evolution. An approximately 15-20 minute video from deep dives performed on the Mud volcano fields, by 2000 m of water depth, can be shown in connection with this presentation.
AAPG Search and Discovery Article #90910©2000-2001 AAPG Distinguished Lectures