Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy
Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy
Date
2010-05-13
Authors
Conrad, Clinton P.
Behn, Mark D.
Behn, Mark D.
Linked Authors
Alternative Title
Citable URI
As Published
Date Created
Location
DOI
10.1029/2009GC002970
Related Materials
Replaces
Replaced By
Keywords
Net rotation
Lithsopheric drift
Seismic anisotropy
Asthenospheric shear
Plate motions
Global mantle flow
Lithsopheric drift
Seismic anisotropy
Asthenospheric shear
Plate motions
Global mantle flow
Abstract
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.
Description
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.
Embargo Date
Citation
Geochemistry Geophysics Geosystems 11 (2010): Q05W05