Distal Multidirectional Contractional Salt Tectonics in the Deep-Water Northwest Mediterranean: Evidence from the PRO­GRES Cruise, North-Balearic Basin

Gaullier, Virginie¹, Laurence Droz², Marina Rabineau², Eliane Le Drezen³, Alain Normand³, Guy Rothwell⁴, A. Cattaneo³, C. Bonnel², F. Duval³, E. Le Roux³, Gwenael Jouet², Juan Baztan² (1) Université de Perpignan, Perpignan, France (2) CNRS, Plouzané, France (3) Ifremer Brest, Plouzané, France (4) Southampton Oceanography Center, United Kingdom

Plio-Quaternary tectonics in the Northwestern Mediterranean is dominated by gravity­driven gliding-spreading associated with thick Messinian evaporites, characterized by prox­imal extension, mid-slope translation, and distal shortening. In the North-Balearic Basin, the distal region comprises numerous circular or elongate diapirs whose rise was driven by combined shortening and sediment loading, rather than density inversion. Although these salt structures have been identified previously, very few high-resolution academic data were available until now to precisely determine their geometry and the associated structural fea­tures in the overburden. During the recent PROGRES cruise (R/V “Suroît”, July – August 2003) we collected bathymetric data and back-scattering imagery using SIMRAD EM300 multibeam sounding system, 3.5 kHz profiles (CHIRP) and 6-channels seismic lines over the deep-water North-Balearic Basin, including in and west of the Rhône deep-sea fan. Dip pro­files (2000-2900 m water depths) clearly illustrate the different salt provinces (upslope domain, with listric normal growth faults, salt rollers, and rollover folds; midslope region with broad undulations; and downslope province with salt-cored anticlines and diapirs). Distal shortening is concentrated in a highly-deformed belt comprising, first a huge salt­cored anticline, a squeezed, thick sediment depocenter, and, more distally, a very large salt emergent diapir. At least three regional unconformities have recorded successive salt tec­tonics pulses. Downslope, the overburden is less deformed, except along the flanks of diapirs, whose size and number decrease basinward. Strike lines also show contractional features, indicating that shortening was multidirectional and was mainly accommodated by squeezing salt ridges whose stems often are pinched off entirely.