Mantle viscosity

Peltier, W. R. (1987). Glacial isostasy, mantle viscosity and Pleistocene climatic change. In North America and Adjacent Oceans during the last deglaciation. "The Geology of North America," Vol. K-3 (W. F. Ruddiman and H. E. Wright, Jr, eds), pp. 155-182. Geological Society of America, Boulder, CO. 

The mantle viscosity which controls much of the dynamics of mantle plumes is not well known (Watson and Mackenzie 1991 Hauri et al. 1994). There are also additional effects such as when the mantle contains even small amounts of volatiles, as these volatiles will significantly lower the viscosity of the mantle (Hirth and Kolhstedt 1996). Once the volatiles are extracted, the increased viscosity will slow down the upwelling mantle (Ito et al. 1999). 

The strain-rate estimates suggest that the microstructures were formed by flow in the mantle related to large-scale tectonic processes. In the case of the Voltri peridotites, Drury et al. (1990) have related this deformation to extension and rifting of a continental lithospheric plate. The high-temperature deformation occurred under asthenospheric conditions, whereas the low-temperature deformation occurred within the lithosphere. The estimates of upper mantle viscosity obtained from the study of microstructures are lower than those for average viscosity obtained independently from other methods, such as analysis of glacial rebound of land surfaces (Nakada and Lambeck 1987), which are also based on a number of assumptions. All the samples studied are derived from the uppermost part of the mantle, so the viscosity estimates obtained from the microstructural study are consistent with the presence of a low viscosity zone between the... 

Nevertheless, this hypothesis has been unpopular since the 1980s, because geodynamic models, incorporating either constant mantle viscosity or a rigid upper plate of prescribed thickness, predicted that solidus temperatures could not be reached in basalt or sediment at the top of the subducting plate, except under unusual circumstances (see reviews in Kelemen et al., 2003a Peacock, 1996, 2003 Peacock et al., 1994). For example (Filer et al., 2000, p. 247), discounted their successful model involving H20-rich silicate melt because [the] successful melt-fluxed [model]. .. require[ s]... temperatures... that are... not obviously compatible with...thermal models... (Peacock, 1996). ... 

Second, whilst there is no agreement on the detail, it is evident that much of the Archaean mantle was hotter than the modern mantle. This has implications for mantle viscosity. The viscosity of the Earth s mantle shows a strong dependence on temperature to the extent that an upper mantle 250°C hotter than the present day mantle would be 60 times less viscous (Davies, 2006). A lower viscosity will influence patterns of mantle convection and the nature of Archaean tectonics, and would have influenced the size plates in the precursor to modern plate tectonics. 

Steinberger B, O Connell RJ (1998) Adveetion of plumes in mantle flow implieations for hotspot motion, mantle viscosity and plume distribution. Geophys J Inti 132 412-434 Stolper EM, Holloway JR (1988) Experimental determination of the solubihty of earbon dioxide in molten basalt at low pressme. Earth Planet Sei Lett 87 397-408 Stuart FM, Ellam RM, J. HP, Fitton JG, Bell BR (2000) Constraints on mantle plumes from the helium isotope composition of basalts from the British Tertiary Igneous Provinee. Earth Planet Sei Lett 177 273-285... 

It has also been suggested that the relatively high lower mantle viscosity may further promote the preservation of geochemically distinct domains. Mantle viscosity has been extensively studied using a variety of techniques. Viscosity models have been obtained from plate reconstructions and geoid inversions (Ricard and Wuming 1991 Ivins et al. 

Ivins ER, Sammis CG, Yoder CF (1993) Deep mantle viscosity structure with prior estimate and satelhte constraint. J Geophys Res 98 4579-4609... 

Kido M, Yuen DA, Cadek O, Nakakuki T (1998) Mantle viscosity derived by genetic algorithm using oceanic geoid and seismic tomography for whole-mantle versus blocked-flow situations. Phys Earth Planet Inti 107 107-326... 

Lambeck, K., Smither, C and Johnston, P. 1998. Sea-level change, glacial rebound and mantle viscosity for northern Europe. Geophysical Journal International, 125, pp. 340-354. 

Fig. 3 (Upper) Map of the UMISM model of the Weichselian ice sheet at the last glacial maximiun (LGM) 18,400 years BP (Schmidt et al. 2014). Endglacial faults indicated with red lines. (Lower) Modelled glacially induced maximum horizontal stress at LGM (Lund and Schmidt 2011). The model has elastic lithospheric thickness 120 km, upper mantle viscosity 5 10 Pa s and lower mantle viscosity 3 10 ...

K) were investigated. From an equation of state for iron the densities at these temperatures could be predicted to enable the simulations to be performed. A periodic system containing 64 atoms was used and the simulation run for 2 ps after equilibration. The calculated pressure agreed within 10% with the experimental values (330 GPa at the inner core boundary and 135GPa at the core-mantle boundary). Additional parameters could also be calculated, including the viscosity, the values for which were at the low end of previous suggestions. 

Bercovici D, Lin J (1996) A gravity current model of cooling mantle plume heads with temperature dependent buoyancy and viscosity. J Geophys Res 101 3291-3309 Blundy J, Wood B (1994) Prediction of crystal-melt partition coefficients from elastic moduh. Nature 372 452-454... 

Rabinowicz M, Ceuleneer G, Monnereau M, Rosemberg C (1990) Three-dimensional models of mantle flow across a low-viscosity zone implications for hotspot dynamics. Earth Planet Sci Lett 99 170-184 Reid MR(1995) Processes of mantle enrichment and magmatic differentiation in the eastern Snake River Plain Th isotope evidence. Earth Planet Sci Lett, 131 239-254 Reid MR, Ramos FC (1996) Chemical dynamics of enriched mantle in the southwestern United States Thorium isotope evidence. Earth Planet Sci Lett, 138 67-81. 

Figure 4-20 Falling velocity of a mantle xenolith (density 3200 kg/ m ) in a basaltic melt (density 2700km/m ) for viscosity of IPa-s and 100 Pa s. The calculation does not continue to greater sizes because the applicability of the formulation is limited to Re <3 X 10 . At small radius, the velocity is proportional to the square of the radius (Stokes law). For larger radius, the velocity does not increase so rapidly with radius, and roughly increases with square root of radius.

Beauchesne, S., Poirier, J. P. (1989). Creep of barium titanate perovskite a contribution to a systematic approach to the viscosity of the lower mantle. Physics of the Earth and Planetary Interiors, 55, 187-99. 

---