Panoptic View of Mantle Flow Beneath Trans‐Continental Northeast Asia: Distinct Variation Detected From ∼2,000 km Shear Wave Splitting Profile

• Published in: Geophysical research letters 2022-04, Vol.49 (7), p.n/a
• Main Authors: Yang, Fan, Guo, Guangrui, Li, Juan, Chen, Qi‐Fu, Chen, Yun, Chen, Sidan
• Format: Article
• Language: English
• Subjects: Anisotropy; Arrays; Asthenosphere; Deflection; Deformation; Delay time; Direction; Earth mantle; Flow; Fossils; Gravity; Lava; Lithosphere; mantle flow; Northeast China; north‐south gravity lineament; P-waves; Rotation; S waves; Seismic activity; seismic anisotropy; Seismic arrays; Seismic velocities; Seismic wave velocities; Seismic waves; Shear; shear wave splitting; Splitting; Stagnation; Subduction (geology); subduction zone; Tectonics; Thickness; Variation; Wave velocity; Waveforms; Wedges
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097116

We obtained a panoptic view of the pattern of mantle flow in the “Big Mantle Wedge” associated with the stagnation of the subducting Pacific slab. We applied a simultaneous inversion of multiple waveforms method to measure SKS‐wave splitting parameters for a dense seismic array in trans‐continental Northeast Asia. We identify distinct patterns separated by the North‐South Gravity Lineament (NSGL): to the west, the ENE fast axis orientation with small δt reflects limited frozen anisotropy in the stable lithosphere; while to the east, local variation of anisotropy is superimposed on the NNW‐dominated fast direction, suggesting contribution of other mechanisms rather than the only asthenospheric flow. Within a distance of 200 km crossing the NSGL, we reveal a gradual clockwise rotation in the fast direction, and the keel‐deflected flow caused by the 60–80 km reduction in the lithosphere thickness across the NSGL might contribute to the variation of anisotropy. Plain Language Summary Seismic anisotropy, which is used to describe the directional dependence of seismic wave velocity, can illuminate preferred orientations or fabrics in the Earth aligned by mantle deformation. The tectonic evolution of Northeast China is largely affected by the “Big Mantle Wedge”, which is formed by the stagnation of the subducting Northwest Pacific slab. Based on the SKS shear‐wave splitting measurements of a dense seismic array, we identified a contrast in anisotropy characteristics on both sides of the North‐South Gravity Lineament (NSGL) region. Westward of the NSGL, the fast axis direction is generally consistent with small delay times, indicating a limited fossil deformation pattern that originated in the stable lithosphere; eastward of the NSGL, the anisotropy pattern is more complicated with a NNW‐dominated fast axis direction, implying contributions from other regional tectonic mechanisms other than solely asthenospheric flow model. More interestingly, we reveal a clockwise rotation in the fast axis direction within a narrow width of 200 km across the NSGL. We argue that the sharp change in the thickness of the lithosphere across the NSGL caused a deflection in flow around the edge of a thick continental lithosphere keel, leading to the observed rotation in the fast axis direction. Key Points SKS splitting parameters are measured along a ∼2,000 km dense seismic profile orthogonal to the subducting Pacific slab Distinct anisotropy patterns are found across North‐South Gravi