Mineral Reorientation and Slaty Cleavage in the Martinsburg Formation, Lehigh Gap, Pennsylvania

Holeywell, Roger; Tullis, Terry E.

doi:10.1130/0016-7606(1975)86<1296:mrasci>2.0.co;2

Cited by 78 publications

(26 citation statements)

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“…Depositional processes can produce preferred orientations of grains, which if preserved, can yield nonrepresentative estimates for March strains (Holeywell and Tullis, 1975;Etheridge and Oertel, 1979). If basal planes of clay-minerals are initially aligned subparallel to bedding, then further compaction will tend to accentuate the alignment, leading to exaggerated estimates of shortening.…”

Section: Discussionmentioning

confidence: 99%

Ductile Strains in Clay-Rich Sediments from Hole 808C: Preliminary Results Using X-Ray Pole Figure Goniometry

Morgan¹,

Karig²

1993

Proceedings of the Ocean Drilling Program

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Deformation within accreting and subducting sediments may occur through ductile as well as brittle modes, producing deformation fabrics defined by the preferred orientation of sedimentary particles. The method of X-ray pole figure goniometry is used to determine the clay-mineral fabric in hemipelagic sediments collected from Hole 808C within the Nankai accretionary prism toe during ODP Leg 131. Total finite ductile strains are estimated assuming the theory of March (1932) relating grain preferred orientation to strains.The resulting strains, adjusted to reflect volume changes in the sediments, suggest that accreting sediments have experienced up to 10% lateral ductile shortening while subducting sediments show little evidence for any lateral shortening. This suggests that the décollement serves as an important boundary between subducting and accreting sediments in the vicinity of Site 808. Vertical strains obtained here are lower than expected, especially for the deepest samples, possibly due to the effects of bioturbation during primary deposition and compaction, or to the breakdown of the March model at high strains. The results also suggest that sediment response to tectonic stress may vary with position, based on reversals in depth trends for strains and strain parameters at mid-depth. Further work is needed to expand these findings.This study shows that the method of X-ray pole figure goniometry can be useful for recognizing spatial variations in deformation fabrics and ductile strains in sediments within the toes of accretionary prisms.

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Section: Discussionmentioning

confidence: 99%

Ductile Strains in Clay-Rich Sediments from Hole 808C: Preliminary Results Using X-Ray Pole Figure Goniometry

Morgan¹,

Karig²

1993

Proceedings of the Ocean Drilling Program

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“…XTG is ideal for the quantification of fabric intensity in clay‐rich fault gouge because it provides information for large numbers of small particles in three dimensions, and the analysis and sample preparation are straightforward. The XTG technique has been used to quantify phyllosilicate fabric intensity in the following four basic areas: (1) Identifying the relative roles of compaction and authigenic mineral growth in the mud‐to‐shale transition [ Sintubin , 1994b; Curtis et al , 1980; Ho et al , 1999; Aplin et al , 2006; Day‐Stirrat et al , 2008]; (2) assessing the relative roles of mechanical rotation, dissolution, and neocrystallization of micas in the shale‐to‐slate transition [ Holeywell and Tullis , 1975; Tullis and Wood , 1975; Sintubin , 1994a; Ho et al , 1995, 1996, 2001; Jacob et al , 2000]; (3) Assessing the symmetry of the preferred orientation of micas in phyllonitic and mylonitic rocks [ O'Brien et al , 1987]; and (4) Quantifying phyllosilicate fabric intensities in clay‐rich fault gouges [ Yan et al , 2001; Solum et al , 2003, 2005; Schleicher et al , 2009]. The technique has also been used to study spatial variations of strain, on the mm to m scale, in phyllosilicate‐rich rocks [ Oertel and Curtis , 1972; Holeywell and Tullis , 1975; Curtis et al , 1980; van der Pluijm et al , 1994; Ho et al , 1995].…”

Section: Clay Fabric Intensity Measurementsmentioning

confidence: 99%

Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution

et al. 2009

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[1] The role of phyllosilicate fabrics in fault gouge is a poorly understood component of the mechanical and hydrologic behavior of brittle fault zones. We present 90 fabric intensity measurements using X-ray texture goniometry on 22 natural clay-rich fault gouges from low-angle detachment faults (Death Valley area detachments, California; Ruby Mountains, Nevada; West Salton Detachment Fault, California) and the Peramola thrust in NE Spain. Natural fault gouges have uniformly weak clay fabrics (multiples of a random distribution (MRD) = 1.7-4.5, average MRD = 2.6) when compared to phyllosilicate-rich rocks found in other geologic settings. Clay fabric intensities in natural gouges do not vary significantly either as a function of tectonic environment or of dominant clay mineralogy in the gouge. We compare these natural samples with 69 phyllosilicate fabric intensities measured in laboratory experiments on synthetic clay-quartz mixtures. Clay fabric intensities from laboratory samples are similar to those in natural gouges (MRD = 1.7 -4.6), but increase systematically with increasing shear strain and normal stress. Total phyllosilicate content does not significantly affect clay fabric intensity. Shear strain is important for developing stronger fabrics; samples subjected solely to compression exhibit uniformly weak fabrics (MRD = 1.6 -1.8) even when compressed at high normal stresses (150 MPa). The weak fabrics found in natural fault gouge indicate that if anisotropic and overall low fault zone permeability allow elevated pore fluid pressures and fault weakening, this anisotropy must be a transient feature that is not preserved. Our data also reinforce the idea that clay fabric development in sedimentary rocks is primarily a function of authigenic mineral growth and not of compaction-induced particle rotation.

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“…The degree of cleavage development is proportional to the distance from the Martinsburg-Shawangunk contact, with uncleaved shales occurring O-70 m from the contact, pencil slates 70-100 m, and well-cleaved slates 100 m and beyond. Microstructural and X-ray texture studies (Holeywell and Tullis, 1975;Wintsch, 1978;Lee et al, 1986) have shown that chlorite and mica are sub-parallel to bedding in the shales and cleavage-parallel in the slates, and that the phyllosilicates mainly reorient via dissolution and new-growth during cleavage development. The relative proportion of bedding-parallel phyllosilicates decreases, and the relative proportion of cleavage-parallel phyllosilicates increases as cleavage develops.…”

Section: An Applicationmentioning

confidence: 99%

Composite magnetic anisotropy fabrics: experiments, numerical models and implications for the quantification of rock fabrics

1993

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Magnetic fabrics from rocks with multiple mineral-preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics. Our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and/or orientations of the individual mineral fabrics, and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks. These criteria include: (1) the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics, and (2) the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases, as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases.Composite magnetic fabrics are observed in the shales and slates of the Martinsburg Formation, Lehigh Gap, Pennsylvania. Modeling of the AMS (anisotropy of magnetic susceptibility) and ARMA (anhysteretic remanent magnetization anisotropy) behavior constrains the relative degree of anisotropy of the bedding-parallel and cleavage-parallel fabrics. In particular, ARMA model results allow a good estimate of magnetite fabric strength.We conclude that, in the presence of composite magnetic fabrics, quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric. Such determinations require knowledge of the mineral(s) that are responsible for the measured magnetic fabric and their behavior during deformation.

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Mineral Reorientation and Slaty Cleavage in the Martinsburg Formation, Lehigh Gap, Pennsylvania

Cited by 78 publications

References 0 publications

Ductile Strains in Clay-Rich Sediments from Hole 808C: Preliminary Results Using X-Ray Pole Figure Goniometry

Ductile Strains in Clay-Rich Sediments from Hole 808C: Preliminary Results Using X-Ray Pole Figure Goniometry

Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution

Composite magnetic anisotropy fabrics: experiments, numerical models and implications for the quantification of rock fabrics

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