Seismic anisotropy in the uppermost mantle, back‐arc region of the northeast Japan arc: Petrophysical analyses of Ichinomegata peridotite xenoliths

Michibayashi, K.; Abe, Natsue; Okamoto, Atsushi; Satsukawa, Takako; Michikura, Kenta

doi:10.1029/2006gl025812

Cited by 28 publications

(18 citation statements)

References 18 publications

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“…Olivine crystals have a shape-preferred orientation oblique to the main foliation by 0-30°. Such an oblique foliation is typical of shear deformation and has been reported from rocks of the uppermost mantle of the back-arc region (Ichinomegata peridotite xenoliths, northeast Japan) [Michibayashi et al, 2006]. Hence, from the 16 xenoliths data with each one containing more than 200 measurements, we calculated the average sample (4325 measurements, the sum of all the measurements with respect to the same sense of shear based on each oblique foliation), giving the same weight to each measurement, independently of the number of measurements in each xenolith (Figure 2a).…”

Section: Samples and Methodssupporting

confidence: 54%

Rock seismic anisotropy of the low‐velocity zone beneath the volcanic front in the mantle wedge

Michibayashi¹,

Oohara²,

Satsukawa³

et al. 2009

Geophysical Research Letters

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Peridotite xenoliths derived from the low velocity zone beneath the Avacha frontal volcano, Kamchatka, preserve a‐axis slip fabrics, comparable with those in xenoliths from the back‐arc region of the NE Japan. Although low‐velocity zones are commonly attributed to zones of partially melted mantle, migration of the melt does not erase the existing olivine fabrics and related seismic anisotropies. These anisotropies may counteract the anisotropies associated with c‐axis slip fabrics, if they exist, along the slab or in the high‐pressure zone.

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Section: Samples and Methodssupporting

confidence: 54%

Rock seismic anisotropy of the low‐velocity zone beneath the volcanic front in the mantle wedge

Michibayashi¹,

Oohara²,

Satsukawa³

et al. 2009

Geophysical Research Letters

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“…Although olivine and opx are intrinsically orthorhombic, several studies have demonstrated that crystal aggregates display hexagonal symmetry, rather than purely orthorhombic symmetry [ Mainprice and Silver , 1993; Bystricky et al , 2000; Mehl et al , 2003; Michibayashi et al , 2006]. For example, Bystricky et al [2000] and Michibayashi et al [2006] observe LPO in which olivine a axes are aligned ∼parallel with the shear direction and the b and c axes form a “girdle” perpendicular to the shear direction (i.e., D‐type slip, {0 kl }[100]). In order to simulate hexagonal symmetry using the orthorhombic single‐crystal elastic constants of olivine and opx, the coefficients corresponding to the b and c axes must be combined.…”

Section: Shear Wave Splitting Tomographymentioning

confidence: 99%

Shear wave anisotropy beneath Nicaragua and Costa Rica: Implications for flow in the mantle wedge

Abt

Fischer

Abers

et al. 2009

Geochem Geophys Geosyst

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[1] We present new shear wave splitting data from local events in Costa Rica and Nicaragua recorded by the temporary (July 2004 to March 2006 48-station TUCAN broadband seismic array. Observed fast polarization directions in the fore arc, arc, and back arc range from arc-parallel to arc-normal over very short distances (<5 km when plotted at raypath midpoints) making the direct interpretation of individual splitting measurements in terms of flow tenuous, even when considering variations in the relationship between lattice-preferred orientation and deformation (e.g., B-type dislocation creep in olivine). Therefore, we tomographically invert the splitting measurements to find a three-dimensional model of crystallographic orientation in the wedge. We assume the elastic constants of olivine and orthopyroxene with hexagonal symmetry and use a damped, iterative least squares approach to account for the nonlinear behavior of splitting when considering three-dimensional ray propagation and distributions of anisotropy. The best fitting model contains roughly horizontal, arc-parallel olivine [100] axes in the mantle wedge down to at least 125 km beneath the back arc and arc, which we interpret to indicate along-arc flow in the mantle wedge. Pb and Nd isotopic ratios in arc lavas provide additional evidence for arc-parallel flow and also constrain the direction (northwest, from Costa Rica to Nicaragua) and minimum flow rate (63-190 mm/a). With only slightly oblique subduction at 85 mm/a of the relatively planar Cocos Plate, the most likely mechanism for driving along-arc transport is toroidal flow around the edge of the slab in southern Costa Rica, generated by greater slab rollback in Nicaragua. Two important implications of this arc-parallel flow are the progressive depletion of the mantle source for arc lavas from Costa Rica to Nicaragua and the possible need for significant decoupling between the wedge and downgoing plate.Components: 15,269 words, 15 figures.

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“…Our analysis of subgrain boundaries in olivine indicates that the dominant slip system differed between the granular and sheared peridotites, whereas the equilibrium P-T conditions and present water concentrations are nearly identical between the two types. The olivine [100](010) slip system found to be active in the granular peridotite is commonly reported as being active in naturally deformed peridotites from ophiolite complexes (Nicolas and Christensen, 1987) and mantle xenoliths (Avé Lallemant, 1975;Michibayashi et al, 2006), and in laboratory experiments performed at high temperatures under dry conditions (Carter and Avé Lallemant, 1970;Zhang and Karato, 1995). We suggest, therefore, that deformation of the granular peridotites occurred in a hot and dry region in the cratonic root.…”

Section: Differences In Water Contents Estimated Based On Ir and Defomentioning

confidence: 76%

Water content of the mantle xenoliths from Kimberley and implications for explaining textural variations in cratonic roots

et al. 2011

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Water contents estimates based on infrared spectroscopy and deformation microstructures are used to constrain the origin of textural variations observed in mantle xenoliths from Kimberley, South Africa. Infrared spectra indicate water contents of 10–370 ppm (H2O by weight) in olivine, 20–370 ppm in orthopyroxene, up to 340 ppm in garnet and 30–550 ppm in clinopyroxene, although no systematic differences are detected among texturally distinct xenoliths (i.e. granular and sheared peridotites). In contrast, active slip systems in olivine, as inferred from tilt boundaries, are different between the granular and sheared peridotites; the former deformed via the [100](010) slip system, which is commonly active under hot, dry conditions, whereas the latter deformed via the [001](100) slip system, which is commonly activated in water‐rich environments. The discrepancy in water contents estimates based on infrared spectroscopy and deformation microstructures may reflect different stages of the evolution of water content: the present water contents, as analysed by infrared spectroscopy, may have been modified by the most recent events (e.g. eruption by kimberlite magma), whereas the water contents inferred from tilt boundaries may have resulted from the various deformation processes in the deep cratonic mantle. Accordingly, we suggest that the observed heterogeneity in water content within cratonic roots facilitates local deformation, and gives rise to the range of textures seen in cratonic mantle xenoliths. Copyright © 2010 John Wiley & Sons, Ltd.

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Seismic anisotropy in the uppermost mantle, back‐arc region of the northeast Japan arc: Petrophysical analyses of Ichinomegata peridotite xenoliths

Cited by 28 publications

References 18 publications

Rock seismic anisotropy of the low‐velocity zone beneath the volcanic front in the mantle wedge

Rock seismic anisotropy of the low‐velocity zone beneath the volcanic front in the mantle wedge

Shear wave anisotropy beneath Nicaragua and Costa Rica: Implications for flow in the mantle wedge

Water content of the mantle xenoliths from Kimberley and implications for explaining textural variations in cratonic roots

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