Geomorphology and mechanisms of subduction erosion in the sediment-starved Mariana convergent margin

Subduction erosion, commonly occurring in convergent margins, serves as a key mechanism for effective recycling of materials into the deep subduction. Subduction of bathymetric highs is widely recognized as a critical factor of subduction erosion of the forearc. The Mariana margin is an often-cited example of a tectonically erosive zone, with numerous topographic features such as seamounts, ridges, horsts, and grabens. However, few studies have attempted to determine the regional subduction erosion regime. By combining high-resolution bathymetric data and multichannel seismic profiles, this study analyzed the seafloor roughness, forearc taper angle, accretionary prism, and forearc topography to reveal evidence of subduction erosion at the Mariana margin. The subduction of rough seafloor (seamounts, horsts, and grabens) has accelerated the erosion process of the sediment-starved (<1 km) Mariana margin. In addition to causing depressions and landslides on the inner trench slope, this erosive process resulted in a flat forearc topography, which in turn may have induced a steeper forearc slope and taper angle. The arc-trench distance also shows a strong negative correlation with subduction erosion along the Mariana margin. The involvement of fluid inhibits the erosive process by favoring the development of a smooth surface along the plate interface. Our results suggest that tectonic erosion at the Mariana margin is jointly due to three mechanisms: seamount subduction, horst and graben subduction, and hydrofracturing. This integrated erosive process corresponds to a long-term subduction erosion rate of the submerged forearc of 7–8 km3/km/Myr, significantly lower than those calculated along the other global convergent margins.