Material transfer and subduction channel segmentation at erosive continental margins: Insights from scaled analogue experiments

Abstract

Whereas tectonically erosive convergent margins make up nearly 60% of all present-day convergent margins, processes and amounts of material transfer and recycling remain enigmatic. Removal of material from the frontal forearc leaves no features which could be imaged seismically or probed through drilling. Only a few scaled laboratory analogue experiments have analyzed material transfer at convergent margins characterized by long-term subduction erosion and none has focused on processes and amounts of material transfer and recycling.Therefore, in this study, we attempt to identify potentially relevant parameters controlling material transfer in brittle, tectonically erosive forearcs. This is addressed by a series of sandbox experiments performed with granular materials. We here mainly focus on the amount of sediment that can be transported downdip through the subduction channel (SC).We analyzed our experiments with regard to the evolution of internal and basal material transfer, material transfer mode patterns, wedge geometry and SC evolution. To achieve a truly erosive scenario, we built a large initial wedge representing the brittle forearc, featuring a moderately high-friction basal detachment, and composed of “strong” granular material. There was no incoming material. The slope of the wedge initially had a critical taper. Through opening a subduction gap (SG), the wedge was subject to rear material loss.Our observations point to a close interaction between SC segmentation and wedge deformation. Basal erosion mainly took place beneath the middle-upper slope. Our experiments confirmed the strong influence of the SC on the wedge evolution. A larger amount of material loss led to the development of a SC with an inhomogeneous distribution of velocities along the base of the wedge, segmenting the SC and slope geometry. The latter was comparable to observations in natural forearcs, which are segmented into lower, middle and upper slopes.