Structural synthesis: correlation of structural fabrics, velocity anisotropy, and magnetic susceptibility data .

Byrne, Timothy, Brückmann, Warner, Owens, William, Lallemant, Siegfried and Maltman, alex (1993) Structural synthesis: correlation of structural fabrics, velocity anisotropy, and magnetic susceptibility data . Open Access Proceedings of the Ocean Drilling Program: Scientific Results, 131 . pp. 365-378.

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Structural, physical property, and magnetic data from Ocean Drilling Program Site 808 in the Nankai Trough, Japan, indicate
that both sediment loading and plate convergence have driven dewatering and consolidation in this region. Evidence for this
interpretation is provided by a migrated seismic reflection profile, computed tomography of core-scale structures, magnetic
susceptibility and P-wave velocity data, and experimental studies of Site 808 samples. These data also show that the strain
(including volume change) resulting from plate convergence is partitioned into both penetrative deformation structures as well
as more discrete, core-scale structures with finite displacements. These core-scale structures range from relatively subtle, kink-like
deflections of the primary phyllosilicate fabric to sharp discontinuities with probable displacements much greater than the
dimensions of the core barrel. Although all of the structures acted at least in part as dewatering conduits, evidence of concentrated
fluid flow in this region of the prism is limited to a narrow interval almost 150 m above the décollement (located at between 946
and 965 mbsf). This interval correlates with the middle of a hemipelagic sequence above the décollement that appears to have
thinned, apparently through dewatering, relative to a more seaward section. Thinning and dewatering appear to have been induced
by deposition of a more clastic sedimentary sequence (the outer marginal trench-wedge sediments) that grades upward into a
coarse-grained trench-fill sequence. Importantly, the hemipelagic sequence below the décollement appears to have thinned very
little, suggesting that these sediments are underconsolidated and overpressured. This interpretation is consistent with porosity
measurements from below the décollement. Microscopic and submicroscopic studies of sediments from within the décollement
record a cyclic deformation sequence of displacement-brecciation-porosity collapse and compaction that may also reflect
deformation of an overpressured sequence. Finally, the structural, physical property, and magnetic data also yield kinematic and
geometric results consistent with the present convergent vector between the Philippine Sea Plate and Eurasia. These data indicate
a shortening direction that trends between 308° and 315°, consistent with plate convergent vectors that trend between 310°
and 314°.

Document Type: Article
Keywords: Structural geology; acoustical methods; anisotropy; body waves; consolidation; correlation; decollement; elastic waves; geophysical methods; geophysical profiles; geophysical surveys; Leg 131; Leg 132; lithofacies; magnetic susceptibility; Nankai Trough; North Pacific; Northwest Pacific; Ocean Drilling Program; ODP Site 808; P-waves; Pacific Ocean; paleomagnetism; physical properties; plate convergence; seismic profiles; seismic waves; strain; stress; surveys; velocity; West Pacific
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: No
Open Access Journal?: Yes
ISSN: 1096-7451
Projects: ODP
Date Deposited: 03 Mar 2016 08:53
Last Modified: 25 Oct 2016 12:06

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