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

Subduction 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...

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Main Authors: Hamahashi, Mari, Screaton, Elizabeth, Tanikawa, Wataru, Hashimoto, Yoshitaka, Martin, Kylara, Saito, Saneatsu, Kimura, Gaku
Other Authors: Earth Observatory of Singapore
Format: Article
Language:English
Published: 2020
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Online Access:https://hdl.handle.net/10356/143268
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-1432682020-09-26T21:31:03Z Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone Hamahashi, Mari Screaton, Elizabeth Tanikawa, Wataru Hashimoto, Yoshitaka Martin, Kylara Saito, Saneatsu Kimura, Gaku Earth Observatory of Singapore Science::Geology Costa Rica Subduction Zone Cocos Ridge Subduction Subduction 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. Published version 2020-08-18T04:57:44Z 2020-08-18T04:57:44Z 2017 Journal Article Hamahashi, 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:10.1002/2016gc006577 1525-2027 https://hdl.handle.net/10356/143268 10.1002/2016gc006577 2-s2.0-85024391619 7 18 2601 2616 en Geochemistry, Geophysics, Geosystems © 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. application/pdf
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic Science::Geology
Costa Rica Subduction Zone
Cocos Ridge Subduction
spellingShingle Science::Geology
Costa Rica Subduction Zone
Cocos Ridge Subduction
Hamahashi, Mari
Screaton, Elizabeth
Tanikawa, Wataru
Hashimoto, Yoshitaka
Martin, Kylara
Saito, Saneatsu
Kimura, Gaku
Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
description Subduction 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.
author2 Earth Observatory of Singapore
author_facet Earth Observatory of Singapore
Hamahashi, Mari
Screaton, Elizabeth
Tanikawa, Wataru
Hashimoto, Yoshitaka
Martin, Kylara
Saito, Saneatsu
Kimura, Gaku
format Article
author Hamahashi, Mari
Screaton, Elizabeth
Tanikawa, Wataru
Hashimoto, Yoshitaka
Martin, Kylara
Saito, Saneatsu
Kimura, Gaku
author_sort Hamahashi, Mari
title Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
title_short Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
title_full Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
title_fullStr Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
title_full_unstemmed Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone
title_sort normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the costa rica subduction zone
publishDate 2020
url https://hdl.handle.net/10356/143268
_version_ 1681057804370051072