Transient stripping of subducting slabs controls periodic forearc uplift

Abstract

Topography in forearc regions reflects tectonic processes along the subduction interface, from seismic cycle-related transients to long-term competition between accretion and erosion. Yet, no consensus exists about the topography drivers, especially as the contribution of deep accretion remains poorly constrained. Here, we use thermo-mechanical simulations to show that transient slab-top stripping events at the base of the forearc crust control upliftthen-subsidence sequences. This 100s-m-high topographic signal with a Myr-long periodicity, mostly inaccessible to geodetic and geomorphological records, reflects the nature and influx rate of material involved in the accretion process. The protracted succession of stripping events eventually results in the pulsing rise of a large, positive coastal topography. Trench-parallel alternation of forearc highs and depressions along active margins worldwide may reflect temporal snapshots of different stages of these surface oscillations, implying that the 3D shape of topography enables tracking deep accretion and associated plate-interface frictional properties in space and time.

Co‐location of the Downdip End of Seismic Coupling and the Continental Shelf Break

“…Noda (2016) proposed a classification of forearcs that is, particularly useful here to classify patterns of surface uplift rates, U struct , that result from the structural growth of the forearc, excluding the earthquake cycle. Forearcs can be categorized according to two characteristics: from extensional to contractional and from erosional to accretionary (with respect to mass fluxes across the subduction channel, not surface processes, Clift & Vannucchi, 2004; Menant et al., 2020; von Huene & Lallemand, 1990). Most forearc systems are either extensional and erosional or contractional and accretionary (Noda, 2016).…”

Numerical modeling of tectonic underplating in accretionary wedge systems

“…Finally, Menant et al (2019Menant et al ( , 2020 presented mantle-scale thermo-mechanical experiments focusing on the dynamics along the subduction interface and deep basal accretion. They argued that periodic underplating and the formation of thick duplex structures develop related to fluid-driven stress changes along the subduction interface beneath the accretionary wedge (Menant et al, 2019).…”

“…When uplifted rocks get exposed, erosion removes material from the top and thins the affected part. Furthermore, underplating-related steepening of the overall surface taper may eventually result in gravitational collapse and extensional tectonics above the affected region (Menant et al, 2020;Platt, 1986;Ruh, 2017). In this sense, both underplating and surface removal of material contribute to the overall wedge taper, which mechanically maintains a value between its critical minimum and maximum (Dahlen and Suppe, 1988).…”

Marine terraces of the last interglacial period along the Pacific coast of South America (1° N–40° S)

“…The thickness of sediment in the trench is an additional controlling factor on forearc architecture that may determine which areas of the continental margin are subjected to subduction erosion or accretion (Hilde, 1983;Cloos and Shreve, 1988;Menant et al, 2020). Our data shows that the accretionary part of the WSC (south of the intersection with the Juan Fernandez Ridge at 32.9°S) displays faster median uplift rates of 0.26 m/ka than in the rest of the WSC (Fig.…”