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Formation of Horizontally Deflected Slabs in the Mantle Transition Zone Caused by Spinel‐to‐Post‐Spinel Phase Transition, Its Associated Grainsize Reduction Effects, and Trench Retreat
Author(s) -
Mao Wei,
Zhong Shijie
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl093679
Subject(s) - transition zone , slab , mantle (geology) , geology , spinel , subduction , mantle wedge , mantle convection , geophysics , trench , petrology , phase transition , seismology , materials science , condensed matter physics , tectonics , composite material , physics , layer (electronics) , paleontology
Seismic observations indicate accumulation of subducted slabs in the mantle transition zone in many subduction zones. By systematically conducting 2‐D numerical experiments, we demonstrate that a weak layer or zone beneath the spinel‐to‐post‐spinel phase transition leads to horizontally deflected (stagnant) slab structures in the mantle transition zone, which is consistent with recent studies of 3‐D global mantle convection models. Trench retreat velocity, Clapeyron slope and the viscosity contrast between the lower mantle and mantle transition zone also affect horizontally deflected slab formation. By considering grain size dependent viscosity and grainsize evolution for slabs going through the phase change in the lower mantle, our models with a dynamically generated weak zone beneath the phase boundary indicate that the geometry and viscosity reduction of the weak zone is strongly affected by grain growth rate. A smaller grain growth rate results in a thicker and wider weak zone that promotes deflected slab formation.