scholarly journals Grain boundary wetness of texturally equilibrated rocks, with implications for seismic properties of the upper mantle

2005 ◽  
Vol 110 (B8) ◽  
Author(s):  
Takashi Yoshino
Keyword(s):  
Grain Boundary ◽  
Upper Mantle ◽  
Seismic Properties

Redox-influenced seismic properties of upper-mantle olivine

Nature ◽  
2018 ◽  
Vol 555 (7696) ◽  
pp. 355-358 ◽  
Author(s):  
C. J. Cline II ◽  
U. H. Faul ◽  
E. C. David ◽  
A. J. Berry ◽  
I. Jackson
Keyword(s):  
Upper Mantle ◽  
Seismic Properties ◽  
Mantle Olivine

Petrological constraints on seismic properties of the Slave upper mantle (Northern Canada)☆

Lithos ◽  
2004 ◽  
Vol 77 (1-4) ◽  
pp. 493-510 ◽  
Author(s):  
M.G. Kopylova ◽  
J. Lo ◽  
N.I. Christensen
Keyword(s):  
Upper Mantle ◽  
Northern Canada ◽  
Seismic Properties

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

2006 ◽  
Vol 428 (1-4) ◽  
pp. 65-85 ◽  
Author(s):  
Pierre Vonlanthen ◽  
Karsten Kunze ◽  
Luigi Burlini ◽  
Bernard Grobety
Keyword(s):  
Canary Islands ◽  
Upper Mantle ◽  
Seismic Properties ◽  
Model Predictions

Effects of melt-percolation, refertilization, and deformation on upper mantle seismic anisotropy: constraints from peridotite xenoliths, Marie Byrd Land, West Antarctica

2021 ◽  
pp. M56-2020-16
Author(s):  
V. Chatzaras ◽  
S. C. Kruckenberg
Keyword(s):  
Upper Mantle ◽  
Mantle Xenoliths ◽  
P Wave ◽  
West Antarctica ◽  
Seismic Properties ◽  
West Antarctic ◽  
Peridotite Xenoliths ◽  
Melt Percolation ◽  
Supplementary Material ◽  
Reactive Melt

AbstractWe report on the petrology, microstructure, and seismic properties of 44 peridotite xenoliths extracted from the upper mantle beneath Marie Byrd Land (MBL), West Antarctica. The aim of this work is to understand how melt-rock reaction, refertilization, and deformation affected the seismic properties (velocities, anisotropy) of the West Antarctic upper mantle, in the context of MBL tectonic evolution and West Antarctic Rift System formation. Modal compositions, mineral major element compositions, microstructures, and crystallographic preferred orientations (CPOs) provide evidence for diachronous reactive melt percolation and refertilization. Olivine shows three main CPO patterns, the A-type, axial-[010], and axial-[100] texture types. Average seismic properties of the MBL mantle lithosphere are mainly controlled by the strength of olivine crystallographic texture. Reactive melt percolation and refertilization likely modified seismic velocities and anisotropy, as is suggested by a systematic decrease in maximum P-wave and S-wave anisotropies with increasing modal abundance of pyroxene. At larger spatial scales, the seismic properties of the MBL mantle xenoliths are dominated by the anisotropy resulting from the A-type olivine CPO. Variations between individual volcanic centers, however, attest to spatial variations in the mantle structure, potentially related to 3-D deformation and the prolonged tectonic history of MBL.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5315261

Origin and significance of seismic discontinuities in the continental upper mantle: An interdisciplinary study

2021 ◽  
Author(s):  
Shun-ichiro Karato ◽  
Lidong Dai ◽  
Gary Egbert ◽  
Jennifer Girard ◽  
Benjamin Murphy ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Grain Boundary ◽  
Pressure Dependence ◽  
Upper Mantle ◽  
Grain Boundary Sliding ◽  
Seismic Attenuation ◽  
Depth Range ◽  
Seismic Discontinuities ◽  
Boundary Sliding ◽  
Interdisciplinary Study

<p>              The mid-lithosphere discontinuity (MLD) and the lithosphere-asthenosphere-boundary (LAB) are two well-known seismic discontinuities in the continental upper mantle. Both MLD and LAB are present in most of the continents but at different depths and with different magnitude of velocity change and sharpness. Understanding the causes for these discontinuities including their regional variations is critical in inferring the evolution of the continents from geophysical observations on these discontinuities.</p><p>              Among various models, we focus on the elastically-accommodated grain-boundary sliding (EAGBS) model that provides plausible and unified explanations for the MLD and the LAB (Karato and Park, 2019). This model has a few testable predictions, and the main purpose of this talk is to review the current status of these tests.</p><ul><li>(i) One assumption of the EAGBS model is that EAGBS is enhanced by water. A recent paper by Cline et al. (2018) challenges this hypothesis by showing that water has no effects on attenuation in Ti-doped hydrated olivine. However, the relevance of the results on highly Ti-doped olivine to Ti-poor real upper mantle is unclear.</li> <li>(ii) A clear and unique prediction of the EAGBS is the presence of a peak in seismic attenuation at/near the MLD. However, inferring an attenuation peak in a narrow depth range is challenging and this hypothesis has not been tested.</li> <li>(iii) Another prediction of the “dry” version of the EAGBS model for the MLD is that although seismic wave velocity drops and there is a peak in attenuation, electrical conductivity does not change.</li> <li>(iv) If the MLD is caused by EAGBS, then materials below are in the “relaxed” state. This would explain the lack of large velocity drop at the LAB. However, the validity of this explanation depends on the pressure dependence of grain-boundary sliding. If pressure dependence of EAGBS is large, then the un-relaxed state will re-establish itself at a relatively shallow depth within the lithosphere. In this case, a deeper thermal transition to the relaxed state should produce stronger LAB than reported.  </li> </ul><p>We have conducted an interdisciplinary study to address these issues including mineral physics and seismology. We found that the addition of Ti modifies the defect-related properties of olivine and complicates the application of Cline et al. (2018) to actual upper-mantle conditions. We determined the pressure dependence of olivine grain-growth, from which we infer that the pressure dependence of grain-boundary sliding is small. Regarding the seismological test of attenuation peak, we forward-modeled surface-wave dispersion in a dispersive medium. Calculations show that the over-tones of Love waves are a key to detecting an attenuation peak near the GBS transition. Combined with a comparison of seismological studies (on velocity and attenuation) and MT estimates of electrical conductivity, we will have better constraints on the validity of the EAGBS model for the origin of the MLD.</p>

Low-frequency seismic properties of olivine-orthopyroxene mixtures

2020 ◽  
Author(s):  
Tongzhang Qu ◽  
Ian Jackson ◽  
Ulrich Faul
Keyword(s):  
Shear Modulus ◽  
Upper Mantle ◽  
Forced Oscillation ◽  
Low Frequency ◽  
Secondary Phase ◽  
Confining Pressure ◽  
Creep Function ◽  
Seismic Properties ◽  
New Findings

<p>Although the seismic properties of polycrystalline olivine have been the subject of systematic and comprehensive study at seismic frequencies, the role of orthopyroxene as the major secondary phase in the shallow parts of the Earth’s upper mantle has so far received little attention. Accordingly, we have newly prepared synthetic melt-free polycrystalline specimens containing different proportions of olivine (Ol, Fo<sub>90</sub>) and orthopyroxene (Opx, En<sub>90</sub>) by the solution-gelation method. The resulting specimens, ranging in composition between Ol<sub>95</sub>Opx<sub>5</sub> and Ol<sub>5</sub>Opx<sub>95</sub> composition, were mechanically tested by torsional forced oscillation at temperatures of 1200 ºC to 400 ºC accessed during staged cooling under a confining pressure of 200 MPa. The microstructures of tested specimens were evaluated by BSE, EBSD and TEM. The forced-oscillation data, i.e. shear modulus and associated strain-energy dissipation at 1-1000 s period, were closely fitted by a model based on an extended Burgers-type creep function. This model was also required to fit data from previous ultrasonic and Brillouin spectroscopic measurements at ns-µs periods. Within the observational window (1-1000 s), the shear modulus and dissipation vary monotonically with period and temperature for each of the tested specimens, which is broadly comparable with that previously reported for olivine-only samples. There is no evidence of the superimposed dissipation peak reported by Sundberg and Cooper (2010) for an Ol<sub>60</sub>Opx<sub>40</sub> specimen prepared from natural precursor materials and containing a melt fraction of 1.5%. The higher orthopyroxene concentrations are associated with systematically somewhat lower levels of dissipation and corresponding weaker modulus dispersion. The new findings suggest that the olivine-based model for high-temperature viscoelasticity in upper-mantle olivine requires only modest modification to accommodate the role of orthopyroxene, including appropriate compositional dependence of the unrelaxed modulus and its temperature derivative.</p>

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