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Effects of the Compositional Viscosity Ratio on the Long‐Term Evolution of Thermochemical Reservoirs in the Deep Mantle
Author(s) -
Li Yang,
Deschamps Frédéric,
Yang Jianfeng,
Chen Lin,
Zhao Liang,
Tackley Paul J.
Publication year - 2019
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 - 10.1029/2019gl083668
Subject(s) - mantle (geology) , buoyancy , mantle convection , radiogenic nuclide , geophysics , convection , geology , thermal , thermodynamics , mineralogy , physics , tectonics , subduction , paleontology
Numerical experiments of thermochemical mantle convection in 2‐D spherical annulus geometry are performed to investigate the effects of compositional viscosity ratio (Δ η C ) on the long‐term evolution of reservoirs of dense, primordial material in the lowermost mantle of the Earth. The internal heating rate in the primordial material is larger than in the ambient mantle by a factor of 10, accounting for the fact that this material may be enriched in radiogenic elements. We find that if the chemical density contrast is large (128 kg/m 3 ), Δ η C plays only a second‐order role on the long‐term stability of these reservoirs. As the chemical density contrast decreases to smaller values (90 kg/m 3 ), Δ η C plays a more significant role. More specifically, when Δ η C is large, around 10 or larger, convection within the reservoirs of primordial material is less vigorous, which increases the temperature and thermal buoyancy of these structures. This, in turn, can eventually lead them to become unstable, with the majority of the primordial material being advected into the large‐scale mantle circulation.