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dc.contributor.authorHamahashi, Marien_US
dc.contributor.authorScreaton, Elizabethen_US
dc.contributor.authorTanikawa, Wataruen_US
dc.contributor.authorHashimoto, Yoshitakaen_US
dc.contributor.authorMartin, Kylaraen_US
dc.contributor.authorSaito, Saneatsuen_US
dc.contributor.authorKimura, Gakuen_US
dc.identifier.citationHamahashi, M., Screaton, E., Tanikawa, W., Hashimoto, Y., Martin, K., Saito, S., & Kimura, G. (2017). Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone. Geochemistry, Geophysics, Geosystems, 18(7), 2601-2616. doi:10.1002/2016gc006577en_US
dc.description.abstractSubduction of the buoyant Cocos Ridge offshore the Osa Peninsula, Costa Rica substantially affects the upper plate structure through a variety of processes, including outer forearc uplift, erosion, and focused fluid flow. To investigate the nature of a major seismic reflector (MSR) developed between slope sediments (late Pliocene-late Pleistocene silty clay) and underlying higher velocity upper plate materials (late Pliocene-early Pleistocene clayey siltstone), we infer possible mechanisms of sediment removal by examining the consolidation state, microstructure, and zeolite assemblages of sediments recovered from Integrated Ocean Drilling Program Expedition 344 Site U1380. Formation of Ca-type zeolites, laumontite and heulandite, inferred to form in the presence of Ca-rich fluids, has caused porosity reduction. We adjust measured porosity values for these pore-filling zeolites and evaluated the new porosity profile to estimate how much material was removed at the MSR. Based on the composite porosity-depth curve, we infer the past burial depth of the sediments directly below the MSR. The corrected and uncorrected porosity-depth curves yield values of 800 ± 70 m and 900 ± 70 m, respectively. We argue that deposition and removal of this entire estimated thickness in 0.49 Ma would require unrealistically large sedimentation rates and suggest that normal faulting at the MSR must contribute. The porosity offset could be explained with maximum 250 ± 70 m of normal fault throw, or 350 ± 70 m if the porosity were not corrected. The porosity correction significantly reduces the amount of sediment removal needed for the combination of mass movement and normal faulting that characterize the slope in this margin.en_US
dc.relation.ispartofGeochemistry, Geophysics, Geosystemsen_US
dc.rights© 2017 American Geophysical Union. All rights reserved. This paper was published in Geochemistry, Geophysics, Geosystems and is made available with permission of American Geophysical Union.en_US
dc.titleNormal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zoneen_US
dc.typeJournal Articleen
dc.contributor.researchEarth Observatory of Singaporeen_US
dc.description.versionPublished versionen_US
dc.subject.keywordsCosta Rica Subduction Zoneen_US
dc.subject.keywordsCocos Ridge Subductionen_US
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