Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy
MetadataShow full item record
KeywordNet rotation; Lithsopheric drift; Seismic anisotropy; Asthenospheric shear; Plate motions; Global mantle flow
Although an average westward rotation of the Earth's lithosphere is indicated by global analyses of surface features tied to the deep mantle (e.g., hot spot tracks), the rate of lithospheric drift is uncertain despite its importance to global geodynamics. We use a global viscous flow model to predict asthenospheric anisotropy computed from linear combinations of mantle flow fields driven by relative plate motions, mantle density heterogeneity, and westward lithosphere rotation. By comparing predictions of lattice preferred orientation to asthenospheric anisotropy in oceanic regions inferred from SKS splitting observations and surface wave tomography, we constrain absolute upper mantle viscosity (to 0.5–1.0 × 1021 Pa s, consistent with other constraints) simultaneously with net rotation rate and the decrease in the viscosity of the asthenosphere relative to that of the upper mantle. For an asthenosphere 10 times less viscous than the upper mantle, we find that global net rotation must be <0.26°/Myr (<60% of net rotation in the HS3 (Pacific hot spot) reference frame); larger viscosity drops amplify asthenospheric shear associated with net rotation and thus require slower net rotation to fit observed anisotropy. The magnitude of westward net rotation is consistent with lithospheric drift relative to Indo-Atlantic hot spots but is slower than drift in the Pacific hot spot frame (HS3 ≈ 0.44°/Myr). The latter may instead express net rotation relative to the deep mantle beneath the Pacific plate, which is moving rapidly eastward in our models.
Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q05W05, doi:10.1029/2009GC002970.
Showing items related by title, author, creator and subject.
Global mantle flow and the development of seismic anisotropy : differences between the oceanic and continental upper mantle Conrad, Clinton P.; Behn, Mark D.; Silver, Paul G. (American Geophysical Union, 2007-07-26)Viscous shear in the asthenosphere accommodates relative motion between Earth's surface plates and underlying mantle, generating lattice-preferred orientation (LPO) in olivine aggregates and a seismically anisotropic fabric. ...
Behn, Mark D.; Hirth, Greg; Elsenbeck, James R. (2009-03-04)We construct a 1-D steady-state channel flow model for grain size evolution in the oceanic upper mantle using a composite diffusion-dislocation creep rheology. Grain size evolution is calculated assuming that grain size ...
Finite-frequency wave propagation through outer rise fault zones and seismic measurements of upper mantle hydration Miller, Nathaniel C.; Lizarralde, Daniel (John Wiley & Sons, 2016-08-14)Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, ...