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Contribution of locally tangential CMB-mantle flow and cold-source subducting plates to ULVZ 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 that connect the lowermost mantle and 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 the CMB. The causes of their morphological distribution and geodynamics remain unclear, and simulation results of high-density melts diverge from seismic observations. We introduced a two-dimensional 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 discovered 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 approximately 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; 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. The CMB-mantle tangential flow and/or outer-core interacting with CMB-topography may help generate mega-ULVZs, particularly if they appear along the edges of large low-shear-wave-velocity provinces (LLSVPs) and in/near high seismic-speed “cold” zones. Thus, we infer that a strong link exists between ULVZ morphology and the dynamic environment of the lowermost mantle and uppermost outer core.
15 Nov 2023Submitted to ESS Open Archive
22 Nov 2023Published in ESS Open Archive