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The Continually Stable Subduction, Iron‐Spin Transition, and the Formation of LLSVPs From Subducted Oceanic Crust
Author(s) -
Huang Chuan,
Leng Wei,
Wu Zhongqing
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb018262
Subject(s) - geology , subduction , oceanic crust , crust , mantle (geology) , plate tectonics , geophysics , convergent boundary , geochemistry , tectonics , petrology , paleontology
Large low shear velocity provinces (LLSVPs) in the lower mantle beneath Africa and the Pacific Ocean have been widely accepted as compositionally distinct zones characterized by their large spatial scale, distinctive geometry (high topography and steep side boundaries), and long‐term stability. One possible explanation for the chemical origin of the LLSVPs is that they formed from subducted oceanic crust. However, some previous geodynamic models suggest that it is difficult for a sufficient quantity of recycled crust to accumulate in the deep mantle and form chemical structures matching those of LLSVPs. Here we show that the continually stable subduction can significantly enhance the gathering of recycled oceanic crust above the core‐mantle boundary. The resulting chemical structures in our model show high elevations and steep sides similar to those of the seismically observed LLSVPs when the effects of iron‐spin transition in ferropericlase are incorporated. These LLSVP‐like structures usually emerge 1–1.5 billion years (Gyr) after the model starts and remain recognizable at 3 Gyr. The total volume of these structures first increases to approximately double the current LLSVPs' volume and then gradually decreases over time. With a subduction pattern corresponding to extroversion supercontinent cycles, two antipodal chemical structures form similar to the current LLSVPs and survive longer than 1 Gyr.