Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy

被引:148
作者
Conrad, Clinton P. [1 ]
Behn, Mark D. [2 ]
机构
[1] Univ Hawaii Manoa, Dept Geol & Geophys, Honolulu, HI 96822 USA
[2] Woods Hole Oceanog Inst, Dept Geol & Geophys, Woods Hole, MA 02543 USA
基金
美国国家科学基金会;
关键词
net rotation; lithsopheric drift; seismic anisotropy; asthenospheric shear; plate motions; global mantle flow; CURRENT PLATE VELOCITIES; DEPENDENT VISCOSITY; EMPEROR SEAMOUNTS; ATLANTIC HOTSPOTS; HAWAIIAN HOTSPOT; TRENCH MIGRATION; REFERENCE FRAME; DRIVING FORCES; SURFACE-WAVES; MOTION MODEL;
D O I
10.1029/2009GC002970
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
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 x 10(21) 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 degrees/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 approximate to 0.44 degrees/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.
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页数:19
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