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The contribution of locally tangential CMB-mantle flow and cold-source subducting plates to ULVZ's formation and morphology
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  • Jie Xin,
  • Huai Zhang,
  • Yaolin Shi,
  • Felipe Orellana-Rovirosa,
  • Zhen Zhang,
  • Yimin Jin
Jie Xin
University of Chinese Academy of Sciences
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Huai Zhang
University of Chinese Academy of Sciences

Corresponding Author:[email protected]

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Yaolin Shi
University of Chinese Academy of Science
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Felipe Orellana-Rovirosa
Southern University of Science and Technology
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Zhen Zhang
Institute of Geology, China Earthquake Administration
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Yimin Jin
Institute of Geophysics, China Earthquake Administration
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Ultra-low velocity zones (ULVZs) above the Core-Mantle Boundary (CMB) are significant structures probably connecting the lowermost mantle and the outer core. As “thin patches” of dramatically low seismic-wave velocity, they are occasionally found near the base of mantle plumes and in-or-near high seismic-wave speed regions above CMB. The causes of their morphology-distribution and geodynamics remain unclear, and simulation results of high-density melt diverge from seismic-observations speculation (~+10%). We introduce a 2D time-dependent Stokes’ two-phase-flow (with melt-migration) numerical model to investigate the formation and morphological characteristics of ULVZs caused by CMB-mantle tangential flows and a neighboring cold source (subducted plate). We discover that (a) the participation of cold sources with temperature differences between ~4000 °K at the plume central regions to <~3900 °K at the plume-cooling mantle region, separated by horizontal distances of about 100 (±<50) km are necessary for the stable existence of dense melts with mass-density difference >+1-2% (even +10%) with respect to the surrounding mantle; and additionally (b) an enhanced tangential flow coincident with the internal reverse circulation within the broad plume base (with speeds >3 times the lowermost-mantle characteristic flow speed); are necessary for higher aspect-ratio-morphology lenses compatible with seismic observations. Our findings suggest that the CMB-mantle tangential flow and/or outer-core interacting with CMB-topography, may be implicated in generating mega-ULVZs, especially if they appear along the edges of LLVSPs and especially when in/near high seismic-speed “cold” zones. We infer a strong link between ULVZs morphology and the dynamical environment of the lowermost mantle and uppermost outer core.
19 Oct 2023Submitted to ESS Open Archive
27 Oct 2023Published in ESS Open Archive