Seafloor expression of sediment extrusion and intrusion at the El Arraiche mud volcano field, Gulf of Cadiz

Abstract

The El Arraiche mud volcano field consists of eight mud volcanoes up to 255 m high and 5.4 km wide, located in the Moroccan margin of the Gulf of Cadiz at water depths between 700 and 200 m. Available data include detailed swath bathymetry over the entire area, dense grids of high‐resolution seismic data, very high resolution deep tow subbottom profiles, side scan sonar mosaics over the major structures, selected underwater video lines, and sediment samples. The main morphological aspects of the mud volcanoes are, from the margin toward the center, a subsidence rim or moat, the mud volcano slope, in some cases a deep crater, and a recent central mud dome at the top. The slope is characterized by radial outward sediment flow deposits or by a concentric pattern of terraces and steps. The sediment flow deposits can be divided into elongate outflows that accumulate at the base of the slope and short bulky outflow deposits that freeze on the steep slope. The crater hosts extruded sediment ranging from fluidized sand to mud breccia with centimeter‐ to meter‐sized rock clasts issued from several vents within the crater. The concentric slope terraces and the central mud dome are interpreted to result from several phases of uplift caused by sediment intrusion or shallow diapirism. The mud volcano growth is thus interpreted to result from a combination of extrusive and intrusive processes.