Turbidite Sedimentation in the Nankai Trough as Interpreted from Magnetic Fabric, Grain Size, and Detrital Modal Analyses

Taira, Asahiko; Niitsuma, Nobuaki

doi:10.2973/dsdp.proc.87.112.1986

Cited by 65 publications

(87 citation statements)

References 6 publications

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“…The amount of detrital smectite derived from subaerial weathering of volcanic rocks is relatively small. Our provenance interpretations for the fine-grained sediments reinforce previous contentions of Taira and Niitsuma (1986), who suggested that the sand-sized sediment came largely from the Japan Alps, which had formed in the collision zone between the Izu-Bonin arc and the Honshu arc ( Fig. 1).…”

Section: Clay Mineralogy and Diagenesissupporting

confidence: 78%

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Underwood¹,

Pickering²,

Gieskes³

et al. 1993

Proceedings of the Ocean Drilling Program

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This paper presents a synthesis of data from X-ray diffraction analyses of clay minerals and X-ray fluorescence analyses of bulk mudstones from Ocean Drilling Program Site 808. The samples come from three closely spaced holes drilled through the toe of the Nankai accretionary prism offshore Shikoku, Japan. Detrital assemblages of clay minerals are unusually uniform throughout the Nankai trench-wedge facies. Illite is the most abundant detrital clay mineral, followed by chlorite, smectite, and traces of kaolinite. Relative percentages of smectite increase within the upper subunit of the Shikoku Basin stratigraphy. This subunit contains abundant layers of volcanic ash, and the corresponding change in clay mineralogy probably was caused by synvolcanic weathering in source areas during the Pliocene, together with in-situ alteration of disseminated glass shards within the Shikoku Basin.At a depth of ~555 mbsf, the detrital and/or authigenic smectite component begins its transformation to illite/smectite mixed-layer clay. With increasing depth below this horizon there is a monotonic increase in illite interlayers. The onset of illitization occurs at an estimated temperature of ~65°C. Ordered (R = 1) illite/smectite interlayering first appears at depths of -1220 mbsf (<2-µm size fraction) and -1100 mbsf (<0.2-µm size fraction). The depth interval of the smectite-to-illite transformation coincides with a reduction in pore-water chlorinity; however, the absolute abundance of smectite appears to be insufficient to account for the changes in aqueous chemistry via in-situ dehydration reactions. Instead, significant volumes of diluted pore water probably were transported to Site 808, either from sources located deeper in the accretionary prism (where bulk mudstone porosities are lower) or from lateral sources where mudstones originally deposited in the Shikoku Basin may contain higher percentages of smectite. Significantly, we did not detect any anomalies in clay mineralogy or clay-mineral diagenesis within or near the décollement zone (945-964 mbsf).X-ray fluorescence analyses show that hemipelagic muds and mudstones at Site 808 are chemically uniform throughout most of the section. There are no geochemical perturbations, for example, within the décollement zone. Data from interbeds of volcanic ash demonstrate that the chemical effects of mud/ash dissemination and/or in-situ alteration of pyroclastic material are limited. In addition, ash layers are chemically heterogeneous within Unit III and Subunit IVa, which indicates that tephra was transported from a variety of andesitic to rhyolitic sources on the Japanese Islands during the Pliocene. In contrast, Miocene rocks of Unit V display a clear chemical divergence (little mixing) between rhyolitic tuffs and interbeds of multicolored mudstone.The most significant geochemical anomaly at Site 808 occurs well below the décollement zone between 1087 and 1111 mbsf. Variegated mudstones in this interval contain unusually high ratios of MgO/Al 2 O 3 , Fe total /Al 2 O 3 , Mn...

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Section: Clay Mineralogy and Diagenesissupporting

confidence: 78%

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Underwood¹,

Pickering²,

Gieskes³

et al. 1993

Proceedings of the Ocean Drilling Program

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“…The provenance must be from a polymictic province. The data agree well with Taira and Niitsuma's (1986) tabulation and support their inference on the Suruga Trough-Fuji River drainage source (Fig. 48, Sedimentary Petrology section, Site 808 chapter).…”

Section: Mineralogy and Diagenesissupporting

confidence: 75%

Sediment Deformation and Hydrogeology at the Nankai Accretionary Prism: Synthesis of ODP Leg 131 Shipboard Results

Taira¹,

Hill²,

Firth³

1991

Proceedings of the Ocean Drilling Program

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The Nankai accretionary prism is arguably the best-known clastic prism in the world. The main objective of ODP Leg 131 was to provide data on the deformational processes and associated hydrogeology of the prism. Such information can be incorporated into the existing geophysical and geological data set to characterize the evolution of sediments in this tectonic setting. The objective was approached by drilling Site 808, at which the frontal thrust and décollement of the prism toe were penetrated. Drilling also succeeded, for the first time in the history of ocean drilling, in penetrating the complete sedimentary sequence to basaltic basement, and with good core recovery. Both the frontal thrust and the décollement were clearly recognizable in the cored material. Bedding dips, faults, and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to northwest-southeast shortening. Below the décollement no significant deformation features were observed. Physical properties data show major discontinuities at the décollement, notably an increase in porosity below the décollement. This might indicate excess pore pressure in the subducted section. An increase in porosity below the frontal thrust is less marked and might reflect only the youthfulness of this feature. Attempts to make downhole measurements were severely hampered by unstable hole conditions, but useful constraints have been placed on the thermal regime, some calibration of laboratory physical properties to in-situ conditions has been provided, and in-situ stress and pore pressure were measured in the uppermost sediments. Evidence of channelized fluid flow is inconclusive because no vein structures were observed in the cores, no unequivocal geochemical anomalies indicative of flow were found, and thermal measurements are not significantly different from those predicted by a purely conductive heat-flow model. We conclude that dewatering probably occurs mainly through diffuse flow at this site.

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“…Early theoretical and laboratory studies indicate that AMS of studied rocks arises from the preferred orientation of elongate and flattened magnetic grains and could, therefore, be used as a measure of the degree and orientation of particle alignment, which in turn helps depicting palaeocurrent directions conditions [52] Hamilton and Rees 1970). Further comparative studies indicate that fabric and palaeocurrent estimated using AMS are in good agreement with those obtained from photometric, optical and other related methods [53][54][55].…”

Section: Magnetic Anisotropy and Rock Propertiessupporting

confidence: 58%

Stress analysis and tectonic trends of southern Sinai Peninsula, using potential field data analysis and anisotropy technique

Saleh

2012

Open Geosciences

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Abstract:The aim of the present work is to evaluate the stress direction and the tectonic trends of the study area using magnetic anisotropy and potential field data interpretations (Bouguer and aeromagnetic). The specific objective of the gravity and aeromagnetic interpretation is to establish the trend and depth of the structural configuration of the basement rocks. Horizontal gradient techniques could to delineate directions of deep sources and enabled tracing several faults, lineaments and tectonic boundaries of basement rocks. The trend analysis shows N40°-50°W, N10°-20°W and N10°-20°E which may be related to the Gulf of Suez, Red Sea and Gulf of Aqaba stresses. However, Euler Deconvolution technique was applied using the aeromagnetic data to provide reliable information about penetrated source depth (100 m and ∼10.0 km) and trends of the subsurface sources (principally in NW and NE directions). Moreover, representative 72 oriented rock samples have been collected from seven sites in the study area. The rock magnetic properties and magnetic anisotropy analysis have been determined for all the studied samples. The interpretation clearly defined magnetic lineation at all sites and anisotropy of magnetic susceptibility (AMS) parameters. The stress direction of the studied area has been evaluated using magnetic anisotropy and geophysical analysis. Generally the estimated geophysical data analysis (Bouguer and aeromagnetic) are well consistent with the AMS interpretations of this study. The results indicated that the directions of predominant faults and foliations are NW-SE (related to the Gulf of Suez and Red Sea rifting) which indicate that the main stress and tectonic trend is NE-SW, which is more predominant in southern Sinai region. Moreover, it is clear that, the studied area was affected also by less predominant sources trended in NE-SW direction, which related to the tectonic activity of Gulf of Aqaba. The least predominant is north 40°-50°east that is probably due to the Syrian Arc system. Finally, our results are extremely coincided with the previous stress directions derived from geological, seismological and tectonic analysis in northern Red Sea rift, Gulf of Suez and Sinai regions.

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Turbidite Sedimentation in the Nankai Trough as Interpreted from Magnetic Fabric, Grain Size, and Detrital Modal Analyses

Cited by 65 publications

References 6 publications

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Sediment Deformation and Hydrogeology at the Nankai Accretionary Prism: Synthesis of ODP Leg 131 Shipboard Results

Stress analysis and tectonic trends of southern Sinai Peninsula, using potential field data analysis and anisotropy technique

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