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The minimum mantle viscosity of an accreting Earth
Author(s) -
Cooperman Stephen A.
Publication year - 1983
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/gl010i010p00925
Subject(s) - planetesimal , mantle (geology) , planet , solidus , terrestrial planet , viscosity , convection , geology , thermodynamics , accretion (finance) , geophysics , mantle convection , physics , mechanics , materials science , astrophysics , lithosphere , alloy , composite material , paleontology , tectonics
The minimum mantle viscosity in an earth accreting from planetesimals is estimated. A plausible distribution of planetesimal sizes deposits enough energy to melt the outer nine‐tenths of earth's mass; however, vigorous convection keeps temperatures near the solidus. Viscosity is significantly lower than prevails now. The temperature‐dependent viscosity provides self‐regulation so there is a continuing balance between accretional energy input and heat transfer out. This allows calculation of the minimum viscosity necessary to transfer out heat by a Nu/Ra‐number relation. Typical viscosities are 10 −1 to 10 6 m²sec −1 , lowest at mid‐accretion when the mass growth rate is largest. Terrestrial planets are compared, and minimum iron descent times to central lithospheres are calculated.