Print Email Facebook Twitter Grain size-sensitive viscoelastic relaxation and seismic properties of polycrystalline MgO Title Grain size-sensitive viscoelastic relaxation and seismic properties of polycrystalline MgO Author Barnhoorn, A. (TU Delft Applied Geophysics and Petrophysics; Research School of Earth Sciences; Australian National University) Jackson, I. (Australian National University) Fitz Gerald, J. D. (Australian National University) Kishimoto, A. (Okayama University) Itatani, K. (Sophia University) Date 2016-07-01 Abstract Torsional forced-oscillation experiments on a suite of synthetic MgO polycrystals, of high-purity and average grain sizes of 1–100 µm, reveal strongly viscoelastic behavior at temperatures of 800–1300°C and periods between 1 and 1000 s. The measured shear modulus and associated strain energy dissipation both display monotonic variations with oscillation period, temperature, and grain size. The data for the specimens of intermediate grain size have been fitted to a generalized Burgers creep function model that is also broadly consistent with the results for the most coarse-grained specimen. The mild grain size sensitivity for the relaxation time τL, defining the lower end of the anelastic absorption band, is consistent with the onset of elastically accommodated grain boundary sliding. The upper end of the anelastic absorption band, evident in the highest-temperature data for one specimen only, is associated with the Maxwell relaxation time τM marking the transition toward viscous behavior, conventionally ascribed a stronger grain size sensitivity. Similarly pronounced viscoelastic behavior was observed in complementary torsional microcreep tests, which confirm that the nonelastic strains are mainly recoverable, i.e., anelastic. With an estimated activation volume for the viscoelastic relaxation, the experimentally constrained Burgers model has been extrapolated to the conditions of pressure and temperature prevailing in the Earth's uppermost lower mantle. For a plausible grain size of 10 mm, the predicted dissipation Q−1 ranges from ~10−3 to ~10−2 for periods of 3–3000 s. Broad consistency with seismological observations suggests that the lower mantle ferropericlase phase might account for much of its observed attenuation. Subject anelasticitylower mantlemagnesium oxideseismic wave attenuation To reference this document use: http://resolver.tudelft.nl/uuid:05e13e96-a053-4885-8ecc-74240e14114d DOI https://doi.org/10.1002/2016JB013126 Embargo date 2018-08-01 ISSN 2169-9313 Source JGR Solid Earth, 121 (7), 4955-4976 Part of collection Institutional Repository Document type journal article Rights © 2016 A. Barnhoorn, I. Jackson, J. D. Fitz Gerald, A. Kishimoto, K. Itatani Files PDF Barnhoorn_et_al_2016_Jour ... _Earth.pdf 3.63 MB Close viewer /islandora/object/uuid:05e13e96-a053-4885-8ecc-74240e14114d/datastream/OBJ/view