Initial Results from the Sixth Community Achieving, Affording, and Sustaining Human Exploration of Mars Workshop (AM VI)

A critical assessment by approximately 70 community representatives from NASA, academia, industry, research institutions, and international organizations of candidate activities on the lunar surface and its vicinity that may feed forward to support affordable and sustainable human missions to the surface of Mars in 2030s

Prediction of silicate melt viscosity from electrical conductivity : a model and its geophysical implications

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 1685–1692, doi:10.1002/ggge.20103.Our knowledge of magma dynamics would be improved if geophysical data could be used to infer rheological constraints in melt-bearing zones. Geophysical images of the Earth's interior provide frozen snapshots of a dynamical system. However, knowledge of a rheological parameter such as viscosity would constrain the time-dependent dynamics of melt bearing zones. We propose a model that relates melt viscosity to electrical conductivity for naturally occurring melt compositions (including H2O) and temperature. Based on laboratory measurements of melt conductivity and viscosity, our model provides a rheological dimension to the interpretation of electromagnetic anomalies caused by melt and partially molten rocks (melt fraction ~ >0.7).We acknowledge partial support under NASA USRA subaward 02153–04, NSF EAR 0739050, and the ASU School of Earth and Space Exploration (SESE) Exploration Postdoctoral Fellowship Program.2013-12-1

Single-crystal elasticity and sound velocities of (Mg_(0.94)Fe_(0.06))O ferropericlase to 20 GPa

The single-crystal elastic properties of high-spin (Mg_(0.94)Fe_(0.06))O ferropericlase were measured by Brillouin spectroscopy on a sample compressed to 20 GPa with diamond anvil cells using methanol-ethanol-water as a pressure-transmitting medium. At room pressure, the adiabatic bulk (K_0S) and shear (μ_0S) moduli are K_0S = 163 ± 3 GPa and μ_0S = 121 ± 2 GPa, in excellent agreement with ultrasonic results from the same bulk sample (Jacobsen et al., 2002). A fit to all our high-pressure Brillouin data using a third-order finite-strain equation of state yields the following pressure derivatives of the adiabatic bulk and shear moduli: K′_0S = 3.9 ± 0.2 and μ′_0S = 2.1 ± 0.1. Within the uncertainties, we find that K_0S and K′_0S of (Mg_0.94)Fe_(0.06))O are unchanged from MgO. However, μ_0S and μ′_0S of (Mg_(0.94)Fe_(0.06))O are reduced by 8% and 11%, respectively. The aggregate compressional (VP) and shear (VS) wave velocities are reduced by 4% and 6%, respectively, as compared to MgO. The pressure dependence of the single-crystal elastic moduli and aggregate sound velocities is linear within the investigated pressure range. The elastic anisotropy of (Mg_(0.94)Fe_(0.06))O is about 10% greater than that of MgO at ambient conditions. At the highest pressure obtained here, the elastic anisotropy of (Mg_(0.94)Fe_(0.06))O is close to zero. On the basis of our measurements and earlier ultrasonic measurements, we find that the pressure derivatives of shear moduli obtained at room pressure for low iron concentrations (<20 mol% FeO) of high-spin ferropericlase are inconsistent with those inferred from the lower mantle PREM model

Viscous relaxation as a probe of heat flux and crustal plateau composition on Venus

It has recently been suggested that deformed crustal plateaus on Venus may be composed of felsic (silica-rich) rocks, possibly supporting the idea of an ancient ocean there. However, these plateaus have a tendency to collapse owing to flow of the viscous lower crust. Felsic minerals, especially water-bearing ones, are much weaker and thus lead to more rapid collapse, than more mafic minerals. We model plateau topographic evolution using a non-Newtonian viscous relaxation code. Despite uncertainties in the likely crustal thickness and surface heat flux, we find that quartz-dominated rheologies relax too rapidly to be plausible plateau-forming material. For plateaus dominated by a dry anorthite rheology, survival is possible only if the background crustal thickness is less than 29 km, unless the heat flux on Venus is less than the radiogenic lower bound of 34 [Formula: see text]. Future spacecraft determinations of plateau crustal thickness and mineralogy will place firmer constraints on Venus's heat flux

Fe Mg Interdiffusion in (Mg,Fe)O

International audienceWe have performed a series of interdiffusion experiments on magnesiowüstite samples at room pressure, temperatures from 1,320° to 1,400°C, and oxygen fugacities from 10?1.0 Pa to 10?4.3 Pa, using mixed CO/CO2 or H2/CO2 gases. The interdiffusion couples were composed of a single-crystal of MgO lightly pressed against a single-crystal of (Mg1- x Fe x )1-?O with 0.07< x<0.27. The interdiffusion coefficient was calculated using the Boltzmann Matano analysis as a function of iron content, oxygen fugacity, temperature, and water fugacity. For the entire range of conditions tested and for compositions with 0.01< x<0.27, the interdiffusion coefficient varies as tilde D = 2.9×10^{ - 6} f_{{text{O}}_2 }^{0.19} x^{0.73} {text{e}}^{ - (209,000 - 96,000 x)/RT} {text{m}}^{text{2}} {text{s}}^{ -1} These dependencies on oxygen fugacity and composition are reasonably consistent with interdiffusion mediated by unassociated cation vacancies. For the limited range of water activity that could be investigated using mixed gases at room pressure, no effect of water on interdiffusion could be observed. The dependence of the interdiffusion coefficient on iron content decreased with increasing iron concentration at constant oxygen fugacity and temperature. There is a close agreement between our activation energy for interdiffusion extrapolated to zero iron content ( x=0) and that of previous researchers who used electrical conductivity experiments to determine vacancy diffusivities in lightly doped MgO