Recent deformational state from morphological analysis of mud volcanoes in the Gulf of Cadiz (southwestern part of the Iberian Atlantic Margin)

Abstract

Information gathered from multibeam echosounders and seismic profiles in the Gulf of Cadiz show several morphological reliefs having circular to sub-circular shape having been associated to mud volcanoes. The distribution of mud volcanoes in this area can be related to fluids escapes (gases and water), comprising mud and rock blocks from a pressurized deep unit through structural discontinuities of the upper crust. They are located in a complex tecto-sedimentary wedge named Accretionary Wedge of the Gulf of Cadiz formed by African-Eurasian convergence and the westward Rifean-Gibraltar-Betic Arc. They are most frequent in four sectors: the Moroccan, the Guadalquivir Diapiric Ridge, the TASYO and Deep South Portuguese fields. They differ in size, shape, and presence of the mud flows. Statistical analysis of the regional-scale distribution and shape of the mud volcanoes provides new information about present-day stress filed. The volcano strain indicators show a robust recent direction of two main regional maximum horizontal stress SH striking N132E and N149E to N160E, as well as a three secondary stress field with a N050E, N090E and N175E to N045E trends. The analysis of mud volcano alignments indicates two main trends, N125E and N150E, and two secondary orientations, N070E and N095E. These results are congruent with the stress field established from focal mechanisms, borehole breakouts and mesofault population data.