Origin and dynamics of depositionary subduction margins

Abstract

Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a ''depositionary forearc,'' a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

Seamount chain–subduction zone interactions: Implications for accretionary and erosive subduction zone behavior

“…They interact with subduction zones-e.g., where the Louisville Ridge subducts at the Tonga-Kermadec trenchand it has been estimated that ~17% of the total length of modern subduction systems are subducting major high-relief features (Vannucchi et al, 2016). Raymond's (1984) map of global distribution of mélanges shows good correlation between mélanges and modern subducting seamount chains.…”

Plio‐Quaternary Outer Forearc Deformation and Mass Balance of the Southern Costa Rica Convergent Margin

“…There are competing models about the origin and history of the margin wedge at the location of the 3‐D seismic volume. Vannucchi, Morgan, Silver, et al () suggest that basal erosion has caused km‐scale subsidence, removal of basement, and replacement of the entire margin wedge by forearc‐derived sediments. However, Bangs et al () point out that the patterns of thrusting and folding visible within the margin wedge are similar to wedges in settings undergoing frontal accretion (e.g., Taiwan; Lester et al, ), and the overall seaward decrease in the amount of thrust displacement is consistent with this model (Davis et al, ).…”

“…The <∼200‐m‐thick sedimentary layers above this unconformity record progressive basin infilling from ∼1 Ma to present. Vannucchi, Morgan, Silver, et al () suggest that the rapid rate of sediment accumulation recorded within the uppermost slope sequence (1,035 m/Myr) is a consequence of subsidence that allows terrestrial sediments to accumulate in a basin without reaching the trench.…”

“…Over the last three decades, the forearc of the nonaccretionary convergent margin at Costa Rica (Figure ) has served as the focus of numerous investigations to understand the role of subducting bathymetry and a thinly sedimented plate on forearc evolution, including the Costa Rica Seismogenesis Project (CRISP) drilling expeditions (Harris et al, ; Vannucchi et al, ), onland field studies (Buchs et al, , ; Corrigan et al, ; Denyer et al, ; Gardner et al, , ; Fisher et al, , ; Vannucchi et al, ; Marshall & Anderson, ; Morell et al, ), and geophysical surveys (Bangs et al, ; Edwards et al, ; Hinz, ; McIntosh et al, ; Moore & Sender, ; Morell et al, ; Ranero & von Huene, ; von Huene et al, , ). Despite the voluminous data sets on outer forearc structure, subsidence history, and a record of slope sedimentation, there is no agreement on the processes that have shaped the Costa Rican outer forearc throughout the Plio‐Quaternary, such as the relative roles of basal erosion (e.g., Vannucchi et al, ; von Huene et al, ; Vannucchi, Morgan, Silver, et al, ; Vannucchi, Morgan & Balestrieri, ), shortening (e.g., Taylor et al, ), and surface exhumation (e.g., Edwards et al, ).…”

Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone

“…The sediment-dominated upper plate offshore Osa Peninsula hosts a complex system evolving through these multiple-phased events of uplift, erosion, and recent compression [e.g., Bangs et al, 2016;Vannucchi et al, 2016] that are well recorded near the MSR as examined in this paper. The MSR offshore Osa is distinct from the unconformity developed above the mafic units offshore Nicoya Peninsula to the north [e.g., Kimura et al, 1997;Vannucchi et al, 2001], and the variability along the trench could possibly be due in part to the effect of Cocos Ridge subduction to the south.…”