Anisotropy of the Pacific upper mantle

Raitt, Russell W.; Shor, George G.; Francis, T. J. G.; Morris, G. B.

doi:10.1029/jb074i012p03095

Cited by 408 publications

(207 citation statements)

References 7 publications

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“…Raitt et al, 1969;Forsyth, 1975;Nataf et al, 1984;Tanimoto and Anderson, 1985;Shearer and Orcutt, 1986;Montagner and Tanimoto, 1990;Silver and Chan, 1991) and laboratory experiments (e.g. Carter and Avé Lallemant, 1970;Nicolas et al, 1973;Kunze and Avé Lallemant, 1981;Chopra and Paterson, 1981;Zeuch and Green, 1984;Zhang and Karato, 1995;Tommasi et al, 1999;Zhang et al, 2000;Bystricky et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD

et al. 2006

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We present a petrophysical analysis of upper mantle xenoliths, collected in the Quaternary alkali basalt fields (Series III and IV) from the island of Lanzarote. The samples consist of eight harzburgite and four dunite nodules, 5 to 15 cm in size, and exhibit a typical protogranular to porphyroclastic texture. An anomalous foliation resulting from strong recovery processes is observed in half of the specimens. The lattice preferred orientations (LPO) of olivine, orthopyroxene and clinopyroxene were measured using electron backscatter diffraction (EBSD). In most samples, olivine exhibits LPOs intermediate between the typical single crystal texture and the [100] fiber texture. Occasionally, the [010] fiber texture was also observed. Simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime, probably dominated by a simple shear component under low strain rate and moderate to high temperature. Orthopyroxene and clinopyroxene display a weaker but significant texture. The LPO data were used to calculate the seismic properties of the xenoliths at PT conditions obtained from geothermobarometry, and were compared to field geophysical data reported from the literature. The velocity of P-waves (7.9 km/s) obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation. Our results are consistent with a roughly W-E oriented fastest P-wave propagation direction in the uppermost mantle beneath the Canary Islands, and with the lithosphere structure proposed by previous authors involving a crust-mantle boundary at around 18 km in depth, overlaid by intermediate material between 11 and 18 km.

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Section: Introductionmentioning

confidence: 99%

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD

et al. 2006

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“…Raitt et al (1969) and Morris et al (1969) have shown that the Pacific mantle immediately beneath the Moho is anisotropic.…”

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Anisotropy and the structural evolution of the oceanic upper mantle

Forsyth¹

1973

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The dispersion of Love and Rayleigh waves in the period range 17-167 sec. is used to detect the change in the structure of the upper mantle as the age of the sea-floor increases away from the mid-ocean ridge. Using the single station method, the group and phase velocities of Rayleigh waves were measured for 78 paths in the east Pacific. The focal mechanisms of the source events were determined from P-wave first motion data and the azimuthal variation in Rayleigh wave amplitudes. In order to describe the observed wave data unless SH velocity is higher than SV velocity within the uppermost 125 km of the mantle. Anisotropy deeper than 250 km is suggested, but not required, by the data. Acknowledgements

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“…Upper mantle anisotropy of the Eastern Pacific was first observed by HESS (1964), RAITT et al (1969), andMORRIS et al (1969). They found the direction of maximum seismic velocity is perpendicular to the ridge axis .…”

Section: Seismic Anisotropy Of Upper Mantle and Stress Regime Within mentioning

confidence: 99%

Preferred orientation of olivine in mantle-derived peridotites and stress in the lithosphere.

Toriumi

1984

J,Phys,Earth

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From fabrics of experimentally and naturally deformed olivine polycrystals, it is shown that the a-axis of olivine tends to the maximum extension direction, the b-axis to the maximum shortening, and the c-axis to the intermediate strain direction. The seismic anisotropy suggests that the a-axis of olivine is nearly parallel to the direction of plate motion in the lithospheric upper mantle under the Western Pacific and normal to the trench axis in the island arc mantle beneath the Honshu arc, Combining the preferred mineral orientation of natural and experimental dunites, we obtain the conclusion that stress acting within the lithospheric upper mantle of the Pacific plate is the tensional one along the direction of plate motion. Consequently, it is suggested that the driving force of plate motion is the pull of subducting slabs at trench, and that the induced flow generating extensional stress appears in the upper mantle under the island arc.

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Anisotropy of the Pacific upper mantle

Cited by 408 publications

References 7 publications

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD

Anisotropy and the structural evolution of the oceanic upper mantle

Preferred orientation of olivine in mantle-derived peridotites and stress in the lithosphere.

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