History of mud diapirism and trigger mechanisms in the Western Alboran Sea

Abstract

The distribution and morphology of the mud diapirs in the Western Alboran Basin were studied using multichannel and high resolution seismic profiles (airgun). The diapirism in the Western Alboran Basin forms diapiric ridges and mud volcanoes. Three types of contact relationships between the diapirs and the sedimentary cover have been identified: (1) inverse-piercing contacts; (2) normal-fault contacts; and (3) subvertical contacts. These geometric relationships and the study of the sedimentary cover composed of six seismic units (Lower Miocene to Quaternary) allow us to establish the timing and the geodynamic framework under which the diapirism has evolved. The diapir distribution was controlled through the geodynamic evolution of the Alboran Basin related to extensive, compressive and strike-slip processes. Four phases of diapirism are proposed in order to explain the evolution of diapirism: reactive, active, passive and collapse phases. We establish an evolutionary model of diapirism from the Langhian to the present. Diapirism started in the Langhian-lower Serravallian controlled by extensional processes that allowed a reactive phase to develop. Upper Serravallian-lower Tortonian diapirism was characterized mainly by active diapirism induced by compressional and strike-slip processes. During the upper Tortonian-lower Messinian passive diapirism was predominant until the upper Messinian, when an active diapiric phase developed under a transtensive tectonic setting. Extensional processes continued acting during the Pliocene and Lower Quaternary in the Western Alboran Sea, inducing reactive diapirism though it was punctuated by several active phases. The Upper Quaternary was characterized by a generalised collapse phase linked to extensional processes that developed in many mud ridges, although mud volcanism and active diapirism was also favoured by differential loading produced by a contouritic drift.