High Shear Strain of Olivine Aggregates: Rheological and Seismic Consequences

Bystricky, Misha; Kunze, Karsten; Burlini, L.; Burg, Jean‐Pierre

doi:10.1126/science.290.5496.1564

Cited by 263 publications

(305 citation statements)

References 26 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: 78%

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: 78%

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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“…The small 3 m wide dunite exhibits an LPO with girdles in (010) and (001) about the (100) direction (figure 5a) similar to, although less girdled than, the harzburgite (figure 4a). The LPO in these rocks is also similar to that observed in the experiments of Bystricky et al (2000). In contrast, the large 50 m wide dunite has a distinct (010) and (001) pole figures, the orientation of the (100) maximum in all dunite samples is the same as in the harzburgites.…”

Section: Defonnation Microstructuressupporting

confidence: 68%

“…The J-index reflects the strength of the LPO by quantifying the homogeneity in the distribution of crystallographic orientations (Mainprice and Silver, 1993). Both the and Bystricky et al (2000) experiments demonstrate that the J-index increases with increasing strain. However, in the naturally Observations of both -(Okll(100) and (010)(100) lattice preferred orientations are common among naturally deformed harzburgites.…”

Section: Magnitude and Orientation Of Shearmentioning

confidence: 99%

Petrologic and microstructural constraints on focused melt transport in dunites and the rheology of the shallow mantle

Braun¹

2004

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“…In numerous experimental studies, such as high strain torsion and split-cylinder experiments, on quartz (Schmocker et al, 2003), olivine (Bystricky et al, 2000), feldspar (Rybacki et al, 2008), marble and limestone (Barnhoorn et al, 2004;Rybacki et al, 2003), it was found that single-phase rocks generally show minor localization, independent of the dominant deformation mechanism. Localization, however, appears to be more easily initiated at constant stress rather than at constant creep rate (Hansen et al, 2012a;Paterson, 2007).…”

Section: Introductionmentioning

confidence: 99%

Strain localization during high temperature creep of marble: The effect of inclusions

et al. 2014

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The deformation of rocks in the Earth's middle and lower crust is often localized in ductile shear zones. To better understand the initiation and propagation of high-temperature shear zones induced by the presence of structural and material heterogeneities, we performed deformation experiments in the dislocation creep regime on Carrara marble samples containing weak (limestone) or strong (novaculite) second phase inclusions. The samples were mostly deformed in torsion at a bulk shear strain rate of ≈ 1.9x10 -4 s -1 to bulk shear strains γ between 0.02 and 2.9 using a Paterson-type gas deformation apparatus at 900°C temperature and 400 MPa confining pressure. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at γ > 0.1 -0.2.Peak shear stress at the imposed conditions is about 20 MPa, which is ≈8% lower than the strength of intact samples. Strain progressively localized within the matrix with increasing bulk strain, but decayed rapidly with increasing distance from the inclusion tip.Microstructural analysis shows twinning and recrystallization within this process zone, with a strong crystallographic preferred orientation, dominated by {r} and (c) slip in .Recrystallization-induced weakening starts at local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. In contrast, torsion of a sample containing strong inclusions deformed at similar stress as inclusion-free samples but do not show localization. The experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips. Recrystallizationinduced grain size reduction may only locally promote grain boundary diffusion creep. Accordingly, the bulk strength of the twisted aggregate is close to or slightly below the lower (isostress) strength bound, determined from the flow strength and volume fraction of matrix and inclusions.

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High Shear Strain of Olivine Aggregates: Rheological and Seismic Consequences

Cited by 263 publications

References 26 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

Petrologic and microstructural constraints on focused melt transport in dunites and the rheology of the shallow mantle

Strain localization during high temperature creep of marble: The effect of inclusions

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