Seismic velocities, anisotropy, and shear‐wave splitting of antigorite serpentinites and tectonic implications for subduction zones

Ji, Shaocheng; Li, Awei; Wang, Qian; Long, Changxing; Wang, Hongcai; Marcotte, Denis; Salisbury, Matthew H.

doi:10.1002/jgrb.50110

Cited by 69 publications

(125 citation statements)

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“…Note that the temperature dependence of antigorite's bulk modulus can be directly calculated from that experimentally measured for shear modulus (see below) by taking a temperature-independent Poisson's ratio (an assumption which seems reasonable for antigorite; Christensen, 1996;Ji et al, 2013) and using conversions between elastic constants. Note that the temperature dependence of antigorite's bulk modulus can be directly calculated from that experimentally measured for shear modulus (see below) by taking a temperature-independent Poisson's ratio (an assumption which seems reasonable for antigorite; Christensen, 1996;Ji et al, 2013) and using conversions between elastic constants.…”

Section: Resultsmentioning

confidence: 99%

Low‐Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

David

Brantut

Hansen

et al. 2019

Geophysical Research Letters

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Laboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation ( QG−1) and associated modulus dispersion, with QG−1 increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite ( log10QG−1≈−1.5 at 550 °C and 0.01 Hz) than in olivine ( log10QG−1≪−2.0 below 800 °C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.

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Section: Resultsmentioning

confidence: 99%

Low‐Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

David

Brantut

Hansen

et al. 2019

Geophysical Research Letters

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“…The amphibole‐rich rocks display an average A p value (10.5% at 200 MPa, 9.5% at 600 MPa) higher than that of A s (8.8% at 200 MPa, 8.5% at 600 MPa). These anisotropy values, which are comparable to those of mica‐rich schists and phyllites [ Kern and Wenk , ; Barruol et al ., ; Godfrey et al ., ] as well as serpentinites [ Kern et al ., ; Ji et al ., ], are much larger than those for other categories of igneous and metamorphic rocks such as granite, diorite, gabbro, pyroxenite, peridotite, marble, felsic gneiss, and mafic granulite [ Ji et al ., , p. 616]. Metamorphic and deformed rocks that are anisotropic to ultrasonic waves should be also anisotropic at the scale of active and passive seismic experiments (lower‐frequency waves) because metamorphic and deformation fabrics are often pervasive for tens to hundreds of kilometers [ Brocher and Christensen , ].…”

Section: Discussionmentioning

confidence: 99%

A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole‐rich rocks

Shao

Michibayashi

et al. 2013

JGR Solid Earth

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A large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase. We have measured P and S wave velocities (Vp and Vs) and anisotropy of 17 amphibole‐rich rock samples containing 34–80 vol % amphibole at hydrostatic pressures (P) up to 650 MPa. Combined petrophysical and geochemical analyses provide a new calibration for mean density, average major element contents, mean Vp‐P and Vs‐P coefficients, intrinsic Vp and Vs anisotropy, Poisson's ratios, the logarithmic ratio Rs/p, and elastic moduli of amphibole‐rich rocks. The Vp values decrease with increasing SiO2 and Na2O + K2O contents but increase with increasing MgO and CaO contents. The maximum (≤0.38–0.40 km/s) and minimum S wave birefringence values occur generally in the propagation direction parallel to Y and normal to foliation, respectively. Amphibole plays a critical role in the formation of seismic anisotropy, whereas the presence of plagioclase, quartz, pyroxene, and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations (CPOs). The CPO variations cause different anisotropy patterns illustrated in the Flinn diagram of Vp(X)/Vp(Y)‐Vp(Y)/Vp(Z) plots. The results make it possible to distinguish, in terms of seismic properties, the amphibolites from other categories of lithology such as granite‐granodiorite, diorite, gabbro‐diabase, felsic gneiss, mafic gneiss, eclogite, and peridotite within the Earth's crust. Hence, amphibole, aligned by dislocation creep, anisotropic growth, or rigid‐body rotation, is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs, which contains rather little phyllosilicates such as mica or chlorite.

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“…Trench-parallel seismic anisotropy has been observed in the mantle wedge above subducting slabs (Long, 2013;Long and Silver, 2008;Smith et al, 2001), as well as below subducting slabs at a deeper portion of the upper mantle (Long andSilver, 2008, 2009;Russo and Silver, 1994;Tian and Zhao, 2012). Proposed mechanisms for the source of this trench-parallel seismic anisotropy include waterinduced B-type LPO of olivine in the mantle wedge (Jung, 2009;Jung and Karato, 2001a;Karato et al, 2008;Katayama and Karato, 2006;Kneller et al, 2008;Mizukami et al, 2004), LPO of serpentine in serpentinite altered from peridotite (Ji et al, 2013;Jung, 2011;Katayama et al, 2009;Soda and Wenk, 2014;Watanabe et al, 2011), trench-parallel mantle flow due to slab roll back (Long andSilver, 2008, 2009;Russo and Silver, 1994), rapid toroidal flow around slab edge (Jadamec and Billen, 2010), pressure-induced B-type LPO of olivine due to slip transition at high pressure greater than P ¼ 3 GPa Ohuchi et al, 2011;Raterron et al, 2011), aligned faults by hydration in subducting oceanic plate (Faccenda et al, 2008) and an effective orthorhombic symmetry for the oceanic asthenosphere, which is translated to the depth beneath the subducting slab (Song and Kawakatsu, 2012). However, the origin of seismic anisotropy remains poorly understood.…”

Section: Introductionmentioning

confidence: 95%

Lattice-preferred orientation of olivine found in diamond-bearing garnet peridotites in Finsch, South Africa and implications for seismic anisotropy

Lee

Jung

2015

Journal of Structural Geology

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a b s t r a c tSeismic anisotropy in the upper mantle provides important constraints on mantle dynamics, continental evolution and global tectonics and is believed to be produced by the flow-induced lattice-preferred orientation (LPO) of olivine. Recent experimental studies at high pressure and temperature have suggested that the LPO of olivine is affected by pressure in addition to water and stress. However, there has been no report yet for the pressure-induced LPO of natural olivine because samples from the deep upper mantle are rare and often unsuitable for study due to ambiguous foliation and lineation. Here we show evidence of the pressure-induced LPO of natural olivine in diamond-bearing garnet peridotites from Finsch, South Africa. We found that the [010] axes of olivine are aligned subnormal to foliation and that the [001] axes are aligned subparallel to lineation, which is known as B-type LPO of olivine. The equilibrium pressure of the samples, as estimated using geobarometer, was greater than 4 GPa, indicating that the samples originated from a depth greater than~120 km. In addition, FTIR spectroscopy of the olivine showed that the samples are dry, with a water content of less than 90 ± 20 ppm H/Si (5.5 ± 1.2 ppm wt. H 2 O). These data suggest that the samples are the first natural examples of olivine displaying B-type LPOs produced due to high pressure under dry condition. Our data indicate that the trench-parallel seismic anisotropy observed in many subduction zones in and below subducting slabs at depths greater than~90 km under dry condition may be attributed to the pressure-induced olivine fabrics (B-type LPO) and may be interpreted as the entrainment of the sub-lithospheric mantle in the direction of subduction rather than anomalous trench-parallel flow.

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Seismic velocities, anisotropy, and shear‐wave splitting of antigorite serpentinites and tectonic implications for subduction zones

Cited by 69 publications

References 105 publications

Low‐Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

Low‐Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole‐rich rocks

Lattice-preferred orientation of olivine found in diamond-bearing garnet peridotites in Finsch, South Africa and implications for seismic anisotropy

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