An olivine fabric database: an overview of upper mantle fabrics and seismic anisotropy

Ismaı̈l, Walid Ben; Mainprice, David

doi:10.1016/s0040-1951(98)00141-3

Cited by 540 publications

(319 citation statements)

References 21 publications

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“…1). Nominally melt-free samples have [100] dominantly parallel to the shear direction and [010] dominantly normal to the shear plane, consistent with previous investigations of experimentally (21,22,24,25) and naturally (26,27) deformed olivine (Fig. 1A).…”

Section: Laboratory Constraints On Upper-mantle Anisotropysupporting

confidence: 86%

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

Hansen

Warren

2016

Proc. Natl. Acad. Sci. U.S.A.

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Tectonic plates are a key feature of Earth's structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.seismic anisotropy | lithosphere−asthenosphere boundary | upper mantle | geodynamics | crystallographic texture A lthough plate tectonics is the unifying paradigm in the Earth sciences, important questions remain regarding the physical nature of a tectonic plate. A cornerstone of plate tectonic theory states that plates translate across Earth's surface in a relatively rigid and coherent fashion, with deformation largely concentrated at plate boundaries. Restated, the plates are taken to have a high viscosity with a relatively sharp transition to the less viscous convecting mantle beneath. Referring to plates as the lithosphere and to the underlying rock as the asthenosphere [terminology which predates plate tectonic theory (1)] is now common. Partial decoupling of the asthenosphere from the lithosphere appears essential to plate-tectonic-like behavior (2), but whether a change in material properties at the base of the lithosphere arises from increasing temperature (3) or from transitions in melt (4-7) or water content (8, 9) remains unclear, even in the tectonically simple ocean basins.Recent seismological investigations of oceanic upper mantle indicate a change in composition at depths often associated with the lithosphere−asthenosphere boundary (LAB). Receiver-function studies and underside reflections of SS precursors detect a sharp velocity discontinuity (the Gutenberg discontinuity) at a depth of 40 to 150 km (4, 6, 10-12). The sharpness of this discontinuity may indicate the presence of a small amount of melt (4), and the lack of a strong dependence of the discontinuity depth on plate age (6, 10, 13) is roughl...

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Section: Laboratory Constraints On Upper-mantle Anisotropysupporting

confidence: 86%

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

Hansen

Warren

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Natural occurrences of each of the olivine fabric types recognized in the laboratory have been identified, notably B-type fabric from convergent boundaries (e.g., Mizukami et al 2004;Skemer et al 2006) and C-type fabric from deep mantle samples (see, e.g., Katayama and Karato 2006). However, global databases of fabric types for natural peridotite samples (Ben Ismail and Mainprice 1998) show that B-, C-, and E-type fabrics make up very small percentages of the global population (approximately 7, 7, and 2%, respectively; Mainprice 2007), and most samples are A-or D-type. Of course, there is potentially a sampling bias in the geological record (since samples come from unusual locales such as kimberlite pipes and ophiolites), so this may not accurately reflect the statistical distribution of fabric types in the mantle.…”

Section: The Upper Mantlementioning

confidence: 99%

Shear Wave Splitting and Mantle Anisotropy: Measurements, Interpretations, and New Directions

2009

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Measurements of the splitting or birefringence of seismic shear waves that have passed through the Earth's mantle yield constraints on the strength and geometry of elastic anisotropy in various regions, including the upper mantle, the transition zone, and the D 00 layer. In turn, information about the occurrence and character of seismic anisotropy allows us to make inferences about the style and geometry of mantle flow because anisotropy is a direct consequence of deformational processes. While shear wave splitting is an unambiguous indicator of anisotropy, the fact that it is typically a near-vertical path-integrated measurement means that splitting measurements generally lack depth resolution. Because shear wave splitting yields some of the most direct constraints we have on mantle flow, however, understanding how to make and interpret splitting measurements correctly and how to relate them properly to mantle flow is of paramount importance to the study of mantle dynamics. In this paper, we review the state of the art and recent developments in the measurement and interpretation of shear wave splitting-including new measurement methodologies and forward and inverse modeling techniques,-provide an overview of data sets from different tectonic settings, show how they help us relate mantle flow to surface tectonics, and discuss new directions that should help to advance the shear wave splitting field.

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“…Mantle seismic anisotropy is most probably related to the latticepreferred orientation of anisotropic minerals (especially olivine) through deformation [Nicolas and Christensen, 1987;Mainprice and Silver, 1993; Ben Ismall and Mainprice, 1998]. In oceanic regions it is probably related to the mantle flow and therefore to the plate motion [Tommasi et al, 1996].…”

mentioning

confidence: 99%

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

Hatzfeld¹,

Karagianni²,

Kassaras³

et al. 2001

J. Geophys. Res.

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Abstract. Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, does not show a homogeneous pattern. It is not restricted to the North Anatolian Fault but is distributed over a region several hundreds kilometers wide. Little anisotropy is observed in continental Greece or along the Hellenic arc; however, significant anisotropy is observed in the north Aegean Sea. Large values of delay times suggest that anisotropy is due to a long path within the upper mantle and to strong intrinsic anisotropy. Our results, both in fast polarization directions and in values of delay time, do not support the idea that anisotropy is associated with inherited tectonic fabric nor are they consistent with the present-day Aegean motion relative to an absolute frame. In contrast, the direction of fast polarization and the magnitude of delay times correlate well with the present-day strain rate observed at the surface deduced from both geodetic measurements and seismicity. This anisotropy is not horizontally restricted to major surface faults but is spread over a wide region.

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An olivine fabric database: an overview of upper mantle fabrics and seismic anisotropy

Cited by 540 publications

References 21 publications

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

Shear Wave Splitting and Mantle Anisotropy: Measurements, Interpretations, and New Directions

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

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