Serpentinite matrix mélange: Implications of mixed provenance for mélange formation

Shervais, John W.; Choi, Sung Hi; Sharp, Warren D.; Ross, Jeffrey A.; Zoglman-Schuman, Marchell; Mukasa, Samuel B.

doi:10.1130/2011.2480(01)

Cited by 43 publications

(47 citation statements)

References 75 publications

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“…This buoyancy-driven origin requires a source of fluids at depth and extensive physio-chemical interactions to bring material from depth. Similar fluid-assisted processes of transporting serpentinite-bearing rocks from depth have been documented in accretionary prism mélange deposits of the Franciscan Formation (CLOOS 1984) or through volumetric expansion associated with serpentinization (PAGE et al 1999;SHERVAIS et al 2011).…”

Section: Discussionmentioning

confidence: 52%

“…Detailed investigation of the fault-related rocks reveals distinct compositional and structural features that are similar to rock collected from the three outcrop localities and at several other serpentinitebearing or serpentinite-derived exposures throughout central to northern California (COLEMAN, 1996;DIBBLEE, 1971;DICKINSON, 1966;MOORE and RYMER 2012;PAGE et al 1999;RYMER et al 2003;SHERVAIS et al 2004SHERVAIS et al , 2011SIMS 1988SIMS , 1990. Observations and sampling of the surface outcrops provide additional insight into the composition and spatial variability of the internal structure of the fault and related damage zones at SAFOD and the potential physical and chemical processes that may occur at the meter to sub-meter scale in the active SAF.…”

Section: Composition and Texture Of Safod Fault-related Rocksmentioning

confidence: 75%

“…3f; Table 2; KIRSCHNER et al 2008) due to enhanced permeability parallel to strike and reduced permeability perpendicular to the fault strands (WIERSBERG and ERZINGER 2011). Mélange fabrics may form through a variety of depositional and post-lithification processes, including tectonic folding and faulting, sedimentary and slope failure processes, and origin by vertically driven movements related to diapiric and/or volume expansion processes (BAILEY et al 1964;FESTA et al 2010;RAYMOND, 1984;SHERVAIS et al 2011;SILVER and BEUTNER 1980;VANNUCCHI et al 2003;WAKABAYASHI and DILEK 2011). Each process is associated with distinct rock textures and/or compositions that may reflect the style of deformation (COWAN 1985;RAYMOND 1984;VANUCCHI et al 2003).…”

Section: Discussionmentioning

confidence: 99%

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Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Bradbury

Davis

Shervais

et al. 2014

Pure Appl. Geophys.

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Abstract-We examine the fine-scale variations in mineralogical composition, geochemical alteration, and texture of the faultrelated rocks from the Phase 3 whole-rock core sampled between 3,187.4 and 3,301.4 m measured depth within the San Andreas Fault Observatory at Depth (SAFOD) borehole near Parkfield, California. This work provides insight into the physical and chemical properties, structural architecture, and fluid-rock interactions associated with the actively deforming traces of the San Andreas Fault zone at depth. Exhumed outcrops within the SAF system comprised of serpentinitebearing protolith are examined for comparison at San Simeon, Goat Rock State Park, and Nelson Creek, California. In the Phase 3 SAFOD drillcore samples, the fault-related rocks consist of multiple juxtaposed lenses of sheared, foliated siltstone and shale with blockin-matrix fabric, black cataclasite to ultracataclasite, and sheared serpentinite-bearing, finely foliated fault gouge. Meters-wide zones of sheared rock and fault gouge correlate to the sites of active borehole casing deformation and are characterized by scaly clay fabric with multiple discrete slip surfaces or anastomosing shear zones that surround conglobulated or rounded clasts of compacted clay and/or serpentinite. The fine gouge matrix is composed of Mgrich clays and serpentine minerals (saponite ± palygorskite, and lizardite ± chrysotile). Whole-rock geochemistry data show increases in Fe-, Mg-, Ni-, and Cr-oxides and hydroxides, Fe-sulfides, and C-rich material, with a total organic content of [1 % locally in the fault-related rocks. The faults sampled in the field are composed of meters-thick zones of cohesive to non-cohesive, serpentinite-bearing foliated clay gouge and black fine-grained fault rock derived from sheared Franciscan Formation or serpentinized Coast Range Ophiolite. X-ray diffraction of outcrop samples shows that the foliated clay gouge is composed primarily of saponite and serpentinite, with localized increases in Ni-and Cr-oxides and C-rich material over several meters. Mesoscopic and microscopic textures and deformation mechanisms interpreted from the outcrop sites are remarkably similar to those observed in the SAFOD core. Microscale to meso-scale fabrics observed in the SAFOD core exhibit textural characteristics that are common in deformed serpentinites and are often attributed to aseismic deformation with episodic seismic slip. The mineralogy and whole-rock geochemistry results indicate that the fault zone experienced transient fluid-rock interactions with fluids of varying chemical composition, including evidence for highly reducing, hydrocarbon-bearing fluids.

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Section: Discussionmentioning

confidence: 52%

Section: Composition and Texture Of Safod Fault-related Rocksmentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

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Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Bradbury

Davis

Shervais

et al. 2014

Pure Appl. Geophys.

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“…The South Fork Mountain Schist lies in tectonic contact with slivers of low-grade volcanic and siliciclastic rocks, which may be correlative with the mid-Jurassic Galice Formation of the Klamath Mountains (Jayko and Blake, 1986). These low-grade rocks are overlain Coas t R an g e F a u lt www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE in turn by a highly disrupted assemblage of ophiolitic rocks, which has been referred to as the Tehama-Colusa mélange (Hopson and Pessagno, 2004;Shervais et al, 2011). The Tehama-Colusa mélange lies in the same structural position relative to both the Franciscan and the overlying Great Valley sequence as the Coast Range ophiolite, but its affinities are controversial, and it lies in fault contact with the Great Valley sequence, which is tilted steeply east near the boundary.…”

Section: The Eastern Beltmentioning

confidence: 99%

Subduction, accretion, and exhumation of coherent Franciscan blueschist-facies rocks, northern Coast Ranges, California

Schmidt

Platt

2018

Lithosphere

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We present structural data and cross sections from four transects that together cover much of the Eastern Belt of the Franciscan accretionary complex. The westernmost, Middle Eel transect includes jadeite-lawsonite facies rocks (the Taliaferro Metamorphic Complex, TMC) intercalated with lawsonite-albite facies metagreywacke. The TMC shows subduction-related imbricate thrusting, refolded by upright folds with amplitudes of 100-1500 m, and it is cut by abundant normal faults that contributed to exhumation. East of the Coast Ranges divide, three linked transects along Thomes Creek cover the transition from lawsonite-albite facies metagreywackes to the blueschist facies South Fork Mountain Schist. The western section shows thick-bedded metagreywacke intercalated with broken formation, deformed by NWvergent folds and associated thrusts and pressure-solution cleavage, and intensively dissected by abundant low-angle normal faults. In the central section, thin-bedded metagreywacke, broken formation, and conglomerate show an early foliation and folds overprinted by E-vergent folds and crenulation cleavage. The South Fork Mountain Schist forms the easternmost section and records the most intense deformation. The dominant foliation is a differentiated crenulation cleavage that has been refolded by NW vergent folds with amplitudes of millimeters to hundreds of meters. Structural relationships in the South Fork Mountain Schist exposed in Cottonwood Creek farther north are similar to those in Thomes Creek, indicating that our observations have regional significance. All the contractional structures and ductile deformational fabrics in these transects formed under high-P low-T metamorphic conditions during subduction and accretion, and the dominant deformation mechanism was pressure solution. Exhumation was achieved primarily by intensive normal faulting on the outcrop scale, and normal sense motion on the Coast Range fault. This paper provides the first documentation of syn-subduction normal faulting within the Franciscan Complex.

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“…They may occur as subophiolitic or supra-ophiolitic (overlying the ophioltes) in origin, and their matrix may range in composition from serpentinite, serpentinite mud, greywacke, turbiditic rocks, and mud-shale (Dilek and Thy, 2006;Furnes et al, 2012;Phipps, 1984;Saleeby, 1984;Shervais et al, 2011). The final configuration and development of the structural architecture of ophiolitic mélanges are strongly controlled by ophiolite emplacement and collisional (arc-continent, continent-continent) processes (Dilek, 2006;Dilek and Furnes, 2011;Flower and Dilek, 2003;Furnes et al, 2012;Robertson et al, 2009).…”

Section: Part Vi: Ophiolitic Mélangesmentioning

confidence: 99%

Chaos and geodynamics: Mélanges, mélange-forming processes and their significance in the geological record

Dilek

Festa

Ogawa³

et al. 2012

Tectonophysics

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Serpentinite matrix mélange: Implications of mixed provenance for mélange formation

Cited by 43 publications

References 75 publications

Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Subduction, accretion, and exhumation of coherent Franciscan blueschist-facies rocks, northern Coast Ranges, California

Chaos and geodynamics: Mélanges, mélange-forming processes and their significance in the geological record

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