Scaly fabrics from Deep Sea Drilling Project cores from forearcs

Moore, J. Casey; Roeske, Sarah M.; Cowan, Darrel S.; Lundberg, Neil; Gonzales, Eugenio; Schoonmaker, Jane; Lucas, Stephen E.

doi:10.1130/mem166-p55

Cited by 86 publications

(65 citation statements)

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“…Given (1) the absence of metamorphism during deformation in the Ebro Basin, and (2) the feasibility of grain sliding and rotation as the mechanism responsible for phyllosilicate reorientation, we suggest that the preferred crystallographic orientation in these mudrocks formed when the sediment was only partially lithified and thus relatively soft. These deformation conditions are similar to those observed in accretionary wedges at convergent margins, where sediments are progressively dewatered and deformed by the development of tectonic fabrics at various scales (Moore, 1986). Thus, AMS studies could conceivably be able to characterize deformation stages in accretionary wedges, where other methods show little or no strain accumulation.…”

Section: A Mechanism For Grain-reorientationsupporting

confidence: 51%

Evolution of magnetic fabrics during incipient deformation of mudrocks (Pyrenees, northern Spain)

1999

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The anisotropy of magnetic susceptibility (AMS) of Eocene mudrocks from the Southern Pyrenean Foreland Basin documents the progressive development of tectonic fabrics in sediments that mesoscopically show no evidence for deformation. Two end members are observed: (1) a strong oblate fabric, with strong clustering of the minimum axes of susceptibility that is characteristic of depositional and compaction processes; and (2) a prolate magnetic ellipsoid with moderate to strong minimum axes girdle that reflects weak cleavage in the mudrocks. Low-temperature experiments and anhysteretic remanent magnetization reveal that the paramagnetic fraction dominates the AMS signal and thus, represent the preferred orientation of phyllosilicates. Characteristic stages of magnetic fabrics in mudrocks can be established and thus the AMS can be used as an indicator of cleavage development and intensity in mudrocks. The three stages of fabric development (early deformation, pencil structure and weak cleavage) reflect a process of increasingly preferred crystallographic orientation of the phyllosilicates that is evidenced by the change of distribution of the minimum susceptibility axes. This is particularly evident in the eigenvalues, which we plot on a Woodcock diagram that describes both shape and fabric strength, and allows different stages of deformation to be distinguished. Because appreciable depth during deformation (elevated temperatures and high confining pressures) can be ruled out, we propose that the sediments were wet and only partly lithified when the phyllosilicates became progressively reoriented. Thus, the observed fabric is explained as a result of the close interaction of deformation and diagenetic processes. Tectonically induced deformational fabrics formed while diagenesis progressed. Although the study area is a foreland basin, it offers a valuable analogue to active accretionary wedges. The application of AMS in these settings, where sediments are progressively dewatered through the development of fabrics, permits a similar quantification of fabric development and, eventually, of deformation. © 1999 Elsevier Science B.V. All rights reserved.

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Section: A Mechanism For Grain-reorientationsupporting

confidence: 51%

Evolution of magnetic fabrics during incipient deformation of mudrocks (Pyrenees, northern Spain)

1999

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“…The shallowly dipping surfaces are subparallel to the décollement dip and the dips of the discrete faults described below and are therefore inferred to be subparallel to the décollement shear plane. Assuming that these two fabric orientations represent shear surfaces (compare with Moore and Wheeler [1978], Moore et al [1986], and Labaume et al [1997]), shallowly dipping, shear plane-parallel surfaces are geometrically analogous to Y and more steeply dipping surfaces to P shears [Rutter et al, 1986]. Additional shear surfaces that could correspond to the R-orientation are not observed in the core face.…”

Section: Scaly Fabricmentioning

confidence: 99%

Structure and lithology of the Japan Trench subduction plate boundary fault

et al. 2015

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The 2011 Mw9.0 Tohoku‐oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ∼7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite‐rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ∼5–15m thick. Fault rocks recovered from within the clay‐rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity‐strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity‐weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

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“…Tectonic stresses almost certainly accentuate dewatering and lithification through such processes as "tectonic dewatering" (Moore et al, 1986) and "shear dewatering" (Bray and Kang, 1985). For example, in the Barbados accretionary wedge concentrated fluid flow and dewatering correspond directly with zones of tectonically induced faulting and scaly fabric development (Mascle, Moore, et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Structural Synthesis: Correlation of Structural Fabrics, Velocity Anisotropy, and Magnetic Susceptibility Data

Byrne¹,

Brückmann²,

Owens³

et al. 1993

Proceedings of the Ocean Drilling Program

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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°a nd 314°.

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Scaly fabrics from Deep Sea Drilling Project cores from forearcs

Cited by 86 publications

References 0 publications

Evolution of magnetic fabrics during incipient deformation of mudrocks (Pyrenees, northern Spain)

Evolution of magnetic fabrics during incipient deformation of mudrocks (Pyrenees, northern Spain)

Structure and lithology of the Japan Trench subduction plate boundary fault

Structural Synthesis: Correlation of Structural Fabrics, Velocity Anisotropy, and Magnetic Susceptibility Data

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