A recent phase of accretion along the southern Costa Rican subduction zone

Abstract

In 2011 we acquired a 3D seismic reflection volume across the Costa Rica margin NW of the Osa Peninsula to investigate the complex structure and the development of the seismogenic zone within the Costa Rica subduction zone in the vicinity of recent International Ocean Drilling Program (IODP) drilling. In contrast to previous interpretations, these newly acquired seismic images show that the margin wedge is composed of a layered fabric that is consistent with clastic sediments, similar to materials recovered from IODP drilling, that have been thrust and thickened into thrust-bounded folded sequences. These structures are consistent with a balanced sequence that has been frontally accreted in the context of an accretionary model. We interpret these sequences as sediment originally deposited on the subducting crust in a trench basin created by the southward migration of the Cocos-Nazca-Caribbean triple junction, and accreted

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

“…The rates and spatiotemporal distribution of deformation within the outer forearc of subduction zones have provided important insights into processes fundamental to how mass is distributed within subduction zone systems (e.g., Allmendinger et al, ; Clift et al, ; Dominguez et al, ; Laursen et al, ; Ranero & von Huene, ; von Huene & Scholl, ; von Huene & Ranero, ). 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, ).…”

Texture Development of Clay‐Rich Sediments Across the Costa Rica Subduction Zone

“…Correspondingly, we locally observed textures indicative of tectonically inclined, deformed and small‐scale folded sediments apart from the overall compaction texture record. In contrast, the two samples from greater depth, which are assumed to represent an earlier and larger accretionary prism by Bangs et al (), show only moderate tectonic reworking mainly expressed by tilted sediment blocks. Their weaker textures might be related to the original inheritance of these samples from the former incoming plate thereby backing the interpretation of earlier accretionary prism sediments of Bangs et al ().…”

“…In contrast, the two samples from greater depth, which are assumed to represent an earlier and larger accretionary prism by Bangs et al (), show only moderate tectonic reworking mainly expressed by tilted sediment blocks. Their weaker textures might be related to the original inheritance of these samples from the former incoming plate thereby backing the interpretation of earlier accretionary prism sediments of Bangs et al (). Further comparative texture studies in combination with compositional analysis might allow to systematically image the compaction and deformation across an active continental margin and to distinguish between portions of slope sediments, earlier tectonic erosion, or accretion.…”

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.…”

“…Seismic reflection images indicate that the upper plate in this region has a densely fractured slope margin, and a widespread high-amplitude major seismic reflector (MSR) separates more intensely deformed material below characterized by landward dipping reflectors, normal faults, thrusts, and folds, from younger slope sediments above where normal faults are abundant [Shipley et al, 1992;McIntosh et al, 1993;von Huene et al, 2000;Bangs et al, 2015Bangs et al, , 2016 (Figures 1b and 1c). The MSR exists above lithified sediments offshore Osa Peninsula [Expedition 334 Scientists, 2012a;Harris et al, 2013aHarris et al, , 2013bHarris et al, , 2013c (Figures 1b and 1c), whereas the unconformity exists above mafic units offshore Nicoya Peninsula to the north [Kimura et al, 1997;Vannucchi et al, 2001].…”