Formation of sedimentary and tectonic mélanges during seamount subduction: new insights from analog modeling

This study presents three sets of scaled ‘sandbox’ experiments designed to understand the formation of mélanges during seamount subduction, focusing, in particular, on the role of talus aprons and moat basins, i.e., loose block accumulations around seamounts formed on the seafloor prior to subduction. In the first set of experiments, subduction of a single seamount increases wedge taper, inducing slumping of previously accreted material and producing sedimentary mélanges. Increasing the slab dip enhances off-scraping of material from the seamount's leading side, deposition on the rear side, and apron incorporation into the wedge interior. The second set simulates the subduction of a seamount chain, leading to wedge thickening, increased mass wasting, and the formation of a layered unit between the seamounts. The third set models oceanic plateau-wedge interactions, resulting in increased mass wasting on the wedge's surface and the formation of sedimentary mélanges. Loose blocks are deposited along the plateau surface and incorporated into the wedge along shear zones, creating tectonic mélanges. In conclusion, our results indicate that sedimentary and tectonic mélanges form during seamount subduction, especially from the surrounding talus. Sedimentary mélanges are deposited at the wedge surface through sliding and mixing of blocks with a terrigenous matrix, while the tectonic mélanges result from intense shear deformation inside the wedge, along the seamount/wedge interface. When compared with seismic profiles across modern accretionary wedges, our findings also suggest that the often-observed chaotic reflections may represent previously unrecognized seamount-derived mélanges, however, their type is difficult to establish just from geophysical data. • Thirteen analog experiments simulate subduction of seamounts surrounded by aprons. • Seamount aprons are a key prerequisite for mélange formation. • Sedimentary, tectonic and polygenetic mélanges form variably above seamounts. • Mélange formation is highly dependent on the geometry of the subduction zone. • Analog modeling may contribute to detection of mélanges in seismic profiles.