Introduction: Characteristics and tectonic settings of mélanges, and their significance for societal and engineering problems

Wakabayashi, John; Dilek, Yıldırım

doi:10.1130/2011.2480(00)

Cited by 26 publications

(19 citation statements)

References 16 publications

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“…Amongst the fluids present within the fault are methane and free hydrocarbons, perhaps migrating parallel to the fault after the fault captured organic-bearing lozenges of organic-rich rock (D. KIRSCHNER, pers. Comm., 2011;WIERSBERG and ERZINGER 2011) and was also connected to a deeper source of mantle-derived methane (KENNEDY et al 1997;KHARAKA et al 1999;WIERSBERG and ERZINGER 2011;WAKABAYASHI and DILEK 2011). Thus the SAFOD site sampled a remarkably complex region of phyllosilicate-rich, serpentine-bearing sheared rock that experienced significant organic-rich and water-rich fluids that altered the deformed rocks over its history.…”

Section: Discussionmentioning

confidence: 99%

“…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: 99%

Section: Discussionmentioning

confidence: 99%

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 nearcoastal region of the former forearc broadly coincides with the surface distribution of the serpentinite tectonic blocks and slivers and diapirs in forearc crustal rocks (Figure 2) as well as 'sedimentary' or 'mud' serpentinites that were thought to be part of a mélange of serpentinites erupted on the seafloor in the oceanic basins (Barnes et al 2013), like those observed in some modern subduction zones, such as the Marianas (Fryer et al 1985;Murata et al 2009;Wakabayashi 2011). Field relations in California indicate some of the diapiric or fault-bounded serpentinites were emplaced in the late Cenozoic (Bailey and Everhart 1964;Dickinson 1966;Coleman 1971Coleman , 1977Coleman , 2000Murata et al 1979;Page et al 1999;Wakabayashi 2004Wakabayashi , 2005Wakabayashi , 2012Wakabayashi and Dilek 2011;Wakabayashi et al 2010). The common local occurrence of blocks of mantle peridotite, blueschists, and/or eclogites in such Neogene emplacements suggest that these serpentinite bodies may have originally come from deep crustal and/or mantle depths and were entrained with serpentinite ascent during the formation and lengthening of the San Andreas Fault System.…”

Section: Tectonics Of California Serpentinite In Light Of This Modelmentioning

confidence: 99%

A large mantle water source for the northern San Andreas fault system: a ghost of subduction past

2014

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Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest, USA is cold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to the south in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with the creation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25 Ma by serpentine dehydration into the crust above. This deep, long-term water source could facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad region above the wedge. Moreover, the location and breadth of the water release from this model gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely plays a role in the occurrence of non-volcanic tremor (NVT) that has been reported along the SAFS in central California. This process of water release from mantle depths could also mobilize mantle serpentinite from the wedge above the dehydration front, permitting upward emplacement of serpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected from tectonically emplaced serpentinite blocks along the SAFS show mineralogical and structural evidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also lead to tectonic mobility along other plate boundaries that succeed subduction, such as other continental transforms, collision zones, or along present-day subduction zones where spreading centers are subducting.

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“…These metamorphic rocks are characterized by blockin-matrix feature, typical of tectonic mélange (e.g. Festa et al, 2012;Raymond & Bero, 2015;Silver & Beutner, 1980;Wakabayashi & Dilek, 2011;Wang, Kusky, et al, 2013).…”

Section: Geological Settingmentioning

confidence: 99%

Paleozoic subduction of the southern Dunhuang Orogenic Belt, northwest China: metamorphism and geochronology of the Shuixiakou area

et al. 2018

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Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnetbearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610-690 °C and 6.5-10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720-750 °C and 13.4-14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630-730 °C and 3.8-7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438-398 Ma.

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Introduction: Characteristics and tectonic settings of mélanges, and their significance for societal and engineering problems

Cited by 26 publications

References 16 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

A large mantle water source for the northern San Andreas fault system: a ghost of subduction past

Paleozoic subduction of the southern Dunhuang Orogenic Belt, northwest China: metamorphism and geochronology of the Shuixiakou area

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