Viscosity Jump in Earth’s Mid-Mantle
The viscosity of Earth's deep interior plays a key role in mediating plate tectonics. Rudolph et al. combined several geophysical data sets to model the viscosity of the mantle. Mantle viscosity abruptly increases below 1000 km. The increase could explain the stalling of subducting slabs and the deflections of hot upwelling plumes around this depth. Although the viscosity increase explains some recent unexpected observations, the origin of the jump itself remains a mystery.
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Rudolph, M. L., Lekić, V., & Lithgow-Bertelloni, C. (2015). Viscosity jump in Earth’s mid-mantle. Science, 350(6266), 1349-1352.