Bridgmanite Deformation in the Earth’s Mid-Mantle is Likely Responsible for Seismically Defined Discontinuities, According to Study

    The main mineralogical phase in the Earth’s lower mantle is in the form of bridgmanite, which is intrinsically anisotropic and generates seismic anisotropy in actively deforming regions, including subduction zones. Structures observed at mid-mantle depths have unclear origins. According to a recent paper published in Nature Communications, a new model of these discontinuities is emerging:

“By coupling thermo-mechanical subduction models with pressure-dependent fabric calculations, we show that gradual slip transitions in bridgmanite with depth can manifest anisotropic discontinuities near 1000 km, which can deepen depending on the extent of accumulated deformation.”

“These results suggest that mid-mantle reflectors near subduction zones may be strain-induced, providing an additional mechanism that links mantle flow, mineral physics, and seismic observations.”

     Seismic anisotropy from crystallographic preferred orientation (CPO) of intrinsically anisotropic mantle minerals has long been recognized. This also occurs through deformation deep in the mantle. Slabs of rock subducting deep into the mantle are thought to be the source of the deformation and the anisotropic discontinuities.

     The figure below shows an anisotropic discontinuity due to the bridgmanite phase around a subducting slab. The anisotropy is due to the deformation resulting from the subducting slab. The yellow represents isotropic parts of the mantle.

 

References:

 

Mid-mantle discontinuities beneath subduction zones linked to depth-dependent deformation of bridgmanite. John Keith Magali, Sébastien Merkel, Angelo Pisconti, Jeffrey Gay, James Wookey & Christine Thomas. Nature Communications volume 17, Article number: 10494 (October 5, 2026). Mid-mantle discontinuities beneath subduction zones linked to depth-dependent deformation of bridgmanite | Nature Communications