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The effect of depth‐dependent viscosity on convective mixing in the mantle and the possible survival of primitive mantle
Author(s) -
Gurnis Michael,
Davies Geoffrey F.
Publication year - 1986
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/gl013i006p00541
Subject(s) - mantle (geology) , mantle convection , geology , convection , earth's internal heat budget , geophysics , hotspot (geology) , transition zone , planetary differentiation , lithosphere , thermodynamics , physics , paleontology , tectonics
The effect depth‐dependent viscosity has on convective mixing and sampling (or degassing) of primitive mantle beneath ridges is explored in two‐dimensional models. Higher relative viscosities in the deep mantle decrease convection velocities and strain rates and prolong the residence time of material in the deep mantle. If the average viscosity of the lower mantle is at least 100 times the viscosity of the upper mantle, then some mantle material could have survived from very early in the earth's history. If, in addition, the depth of degassing under ridges has been less than 75 km, on average over earth history, then helium isotopic systematics are qualitatively consistent with whole mantle convection.