Bannock Basin,Sirte Abyssal Plain and Conrad Spur: structural relationships between Mediterranean Ridge and its western foreland and implications on the character of the accretionary complex (eastern Mediterranean) |
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Authors: | W Hieke A Camerlenghi M B Cita G A Dehghani N Fusi H B Hirschleber L Mirabile C Müller A Polonia |
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Institution: | 1.Lehrstuhl für Ingenieurgeologie (formerly: Lehrstuhl für Allgemeine, Angewandte und Ingenieur-Geologie),Technische Universit?t München,München,Germany;2.ICREA c/o Departament d’Estratigrafia, Paleontologia i Geociències Marines, Facultat de Geologia,Universitat de Barcelona,Barcelona,Spain;3.Dipartimento di Scienze della Terra ?Ardito Desio”,Università di Milano,Milan,Italy;4.Institut für Geophysik,Universit?t Hamburg,Hamburg,Germany;5.Dipartimento di Scienze Geologiche e Geotechnologia,Università di Milano-Bicocca,Milan,Italy;6.Istituto di Oceanologia,Istituto Universitario Navale,Naples,Italy;7.Rueil-Malmaison,France;8.CNR-ISMAR Sezione Geologia Marina,Bologna,Italy |
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Abstract: | In previous publications, the relationship between the Sirte Abyssal Plain as foreland and the Mediterranean Ridge as accretionary
complex was considered to be simple: the foreland is undeformed, the accretionary complex consumes the foreland, the Messinian
evaporites control the internal structure of the growing complex. The compilation of our own and published data results in
a more complex tectonic pattern and a new geodynamic interpretation. The Sirte Abyssal Plain is imprinted by extensional tectonics
which originated independently from and prior to the approaching process of accretion. The structural setting of the pre-Messinian
and Messinian Sirte Abyssal Plain is responsible for the highly variable thickness of Messinian evaporites. The foreland setting
in the Sirte Abyssal Plain also controls the internal structure of the Mediterranean Ridge, at least between the deformation
front and Bannock Basin, following sediment deformation within the accretionary wedge with a dominating inherited SW-NE orientation.
The taper angle of the post-Messinian Mediterranean Ridge is unusually small compared with other accretionary wedges. In the
studied area, within a distance of about 45 km from the deformation front, there is no appreciable dip in the décollement.
Therefore, the slope of the outer 45 km of the Mediterranean Ridge is considered to be caused only by gravitational spreading
of Messinian evaporites deposited on the slope of pre-Messinian accretionary wedge. As a consequence, the Mediterranean Ridge
underlying such slope is interpreted to belong to the foreland. The allochthonous evaporites overlie autochthonous evaporites
of the Sirte Abyssal Plain. The NE-dipping décollement (and thus of the true tectonically driven deformation front) is expected
to initiate at about the present position of Bannock Basin. The Sirte Abyssal Plain, the adjacent Cyrene Seamount and neighbouring
seafloor relief on the African continental margin are considered to be the product of tectonic segmentation of the continental
crust. |
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