Clay-Mineral Provenance, Sediment Dispersal Patterns, and Mudrock Diagenesis in the Nankai Accretionary Prism, Southwest Japan

Underwood, Michael B.; Pickering, Kevin T.

doi:10.1346/ccmn.1996.0440304

Cited by 41 publications

(28 citation statements)

References 87 publications

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“…These findings are also consistent with previous work elsewhere in the Nankai region, which identified removal of K and Cl by alteration of volcanic ash well above the basement at Ocean Drilling Program (ODP) Site 808 (Masuda et al, 1993;Underwood and Pickering, 1996). Additionally, at ODP Sites 808, 1173, and 1177, as well as at Sites C0011 and C0012, anomalous porosity and other properties are caused by small amounts of amorphous silica cement…”

Section: Summary: Ash Layers and Trends In Alterationsupporting

confidence: 91%

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

et al. 2018

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We examine the importance of dispersed volcanic ash as a critical component of the aluminosilicate sediment entering the Nankai Trough, located south of Japan's island of Honshu, via the subducting Philippine Sea plate. Multivariate statistical analyses of an extensive major, trace, and rare earth element data set from bulk sediment and discrete ash layers at Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 quantitatively determine the abundance and accumulation of multiple aluminosilicate inputs to the Nankai subduction zone. We identify the eolian input of continental material to both sites, and we further find that there are an additional three ash sources from Kyushu and Honshu, Japan and other regions. Some of these ash sources may themselves represent mixtures of ash inputs, although the final compositions appear statistically distinct. The dispersed ash comprises 38 ± 7 weight percent (wt%) of the bulk sediment at Site C0011, and 34 ± 4 wt% at Site C0012. When considering the entire sediment thickness at Site C0011, the dispersed ash component supplies 38000 ± 7000 g/cm 2 of material to the Nankai subduction system, whereas Site C0012 supplies 20000 ± 3000 g/cm 2 . These values are enormous compared to the ~2500 g/cm 2 (C0011) and ~1200 g/cm 2 (C0012) of ash in the discrete ash layers. Therefore, the mass of volcanic ash and chemically equivalent alteration products (e.g., smectite) that are dispersed throughout the stratigraphic succession of bulk sediment appears to be up to 15-17 times greater than the mass of discrete ash layers. The composition of the dispersed ash component at Site C0011 appears linked to that of the discrete layers, and the mass accumulation rate for dispersed ash correlates best with discrete ash layer thickness. In contrast, at Site C0012 the mass accumulation rate for dispersed ash correlates better with the number of ash layers. Together, the discrete ash layers, dispersed ash, and clay-mineral assemblages present a complete record of volcanism and erosion of volcanic sources; and indicate that mass balances and subduction factory budgets should include the mass of dispersed ash for a more accurate assessment of volcanic contributions to large-scale geochemical cycling.

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Section: Summary: Ash Layers and Trends In Alterationsupporting

confidence: 91%

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

et al. 2018

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“…60 wt.%)29, probably owing to a difference in the clay mineral provenance30. The geological and physical properties in a fault zone should be sampled by drilling into subduction faults at multiple trench-parallel sites.…”

Section: Discussionmentioning

confidence: 99%

Near-trench slip potential of megaquakes evaluated from fault properties and conditions

Hirono

Tsuda

Tanikawa

et al. 2016

Sci Rep

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Near-trench slip during large megathrust earthquakes (megaquakes) is an important factor in the generation of destructive tsunamis. We proposed a new approach to assessing the near-trench slip potential quantitatively by integrating laboratory-derived properties of fault materials and simulations of fault weakening and rupture propagation. Although the permeability of the sandy Nankai Trough materials are higher than that of the clayey materials from the Japan Trench, dynamic weakening by thermally pressurized fluid is greater at the Nankai Trough owing to higher friction, although initially overpressured fluid at the Nankai Trough restrains the fault weakening. Dynamic rupture simulations reproduced the large slip near the trench observed in the 2011 Tohoku-oki earthquake and predicted the possibility of a large slip of over 30 m for the impending megaquake at the Nankai Trough. Our integrative approach is applicable globally to subduction zones as a novel tool for the prediction of extreme tsunami-producing near-trench slip.

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“…Maintenance of high porosity within the USB facies as seen at 1173 is not observed. At both Sites 1174 and 808, smectite to illite transformation has progressed significantly, with maximum values of illite in mixed-layer I-S reaching $70% at the base of the sediment section at Site 1174, and $80% at Site 808 [Underwood and Pickering, 1996;Steurer and Underwood, 2003]. …”

Section: Geologic Settingmentioning

confidence: 99%

Evaluation of in situ smectite dehydration as a pore water freshening mechanism in the Nankai Trough, offshore southwest Japan

Saffer

McKiernan

2009

Geochem Geophys Geosyst

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[1] Pore water freshening has been observed within sediments near the trench at numerous subduction zones. Constraining the relative contributions of long-distance updip flow of freshened fluids and in situ clay dehydration holds important implications for margin-scale fluid flow but remains unresolved because the evolution of pore water chemistry expected due to in situ clay dehydration and the budget of fresh water release have generally not been carefully quantified. Here, we address this problem at the wellstudied Nankai Trough offshore SW Japan, where Deep Sea Drilling Project and Ocean Drilling Program drilling have sampled the sedimentary section along two transects: the Muroto transect and the Ashizuri transect, located $100 km southwest along strike. Broad low-chloride anomalies with minimum concentrations significantly below typical seawater values were documented along the Muroto transect at Sites 1173, 1174, and 808 and indicate progressive freshening with increasing burial. In contrast, freshening at Site 1177 along the Ashizuri transect ($24 km seaward of the trench) is characterized by a series of sharp excursions from seawater values. We use a one-dimensional model to simulate sedimentation, thermal history, clay dehydration, and chemical diffusion, in order to quantify the component of pore water freshening attributable to in situ smectite dehydration. We find that simulated reaction progress is in close agreement with observations. The peak magnitude of pore water freshening is reasonably well predicted within the lowermost $150 m of the section but consistently underpredicted at intermediate depths. The residual pore water freshening profiles (not explained by smectite dehydration) reach peak magnitudes of $50-75 mM and approximately straddle the décollement at Sites 1174 and 808. We suggest that these residuals may reflect either an additional in situ dehydration process or a contribution from updip fluid migration along the fault. Our conclusion differs from that of previous studies, which have suggested that most of the observed geochemical anomaly could be generated by in situ smectite dehydration with as little as 15 wt% initial smectite. This substantial discrepancy is readily explained by the high sensitivity of pore water freshening to assumed porosity at the time of dehydration.

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Clay-Mineral Provenance, Sediment Dispersal Patterns, and Mudrock Diagenesis in the Nankai Accretionary Prism, Southwest Japan

Cited by 41 publications

References 87 publications

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

Near-trench slip potential of megaquakes evaluated from fault properties and conditions

Evaluation of in situ smectite dehydration as a pore water freshening mechanism in the Nankai Trough, offshore southwest Japan

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