Subduction erosion along the Middle America convergent margin

Abstract

‘Subduction erosion’ has been invoked to explain material missing from some continents along convergent margins¹. It has been suggested that this form of tectonic erosion removes continental material at the front of the margin or along the underside of the upper (continental) plate^2,3,4. Frontal erosion is interpreted from disrupted topography at the base of a slope and is most evident in the wake of subducting seamounts^5,6. In contrast, structures resulting from erosion at the base of a continental plate are seldom recognized in seismic reflection images because such images typically have poor resolution at distances greater than ∼ 5 km from the trench axis. Basal erosion from seamounts and ridges has been inferred^7,8, but few large subducted bodies—let alone the eroded base of the upper plate—are imaged convincingly. From seismic images we identify here two mechanisms of basal erosion: erosion by seamount tunnelling and removal of large rock lenses of a distending upper plate. Seismic cross-sections from Costa Rica to Nicaragua indicate that erosion may extend along much of the Middle America convergent margin.