Increasing Control of Crustal Tectonics on Salt Tectonics from Mediterranean examples

Abstract

International audienceThe deposition during the huge Messinian Salinity Crisis (MSC, 5.96 - 5.33 My) of a thick layer of evaporites and especially of a mobile halite unit (MU) has deeply influenced the architecture and evolution of the Mediter-ranean margins. The Mediterranean has characteristics that set it apart from most “classic” salt-bearing basins, where salt was deposited after (or right after) the rifting stage. Conversely, in the Mediterranean, salt was not related to a rifting event and it covers vast areas that are geodynamically active presently. These include regions of divergence (Tyrrhenian Sea), young or mature convergence (Algerian and Ligurian Margins, Ionian Sea, Mediterra-nean Ridge), oblique convergence (Eastern Cyprus Arc), and strike-slip (Levant Basin). Despite the progress in seismic processing, the strong acoustic impedance contrast between salt and sediments prevents an accu-rate seismic imaging of the sub-salt deep structures. Second, the evaporites act as a decoupling layer (thin-skinned tectonics) preventing the propaga-tion of the crustal structures towards the surface. Last, when crustal tecton-ics generates horizontal and vertical movements in the basement, these movements can trigger a gravitational response in the salt and its overbur-den, thereby blurring the deeper tectonic signal. In order to bypass these difficulties, we propose to use salt tectonics as a proxy to better constrain these deep structures both in terms of geometry and timing. Furthermore, the comparison between natural examples (seismic data) with analogue model-ling allows a better understanding of the margins’ structure and evolution. We present here a synthesis of several Mediterranean study cases in differ-ent geodynamical settings (divergence, convergence, strike-slip) with an in-creasing impact of the crustal tectonics on the salt tectonics. The complexi-ty and variety of its margins, along with the presence of a widely distribut-ed Messinian salt décollement, make the Mediterranean the perfect area to analyze salt deformation and its relationships with different tectonic styles, including the effects of crustal activity. Salt tectonics therefore provides a powerful tool to understand the deep crustal tectonics of the margins and to better constrain the timing of the crustal reactivation in the Mediterranean