¹Wilfred F.M. Röling, ¹Joost W. Aerts, ¹C.H. Lucas Patty, ²Inge Loes ten Kate, ^3,4Pascale Ehrenfreund, ^1,5Susana O.L. Direito
¹Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands.
²Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands.
³Space Policy Institute, George Washington University, Washington, DC, USA.
⁴Leiden Observatory, University of Leiden, Leiden, the Netherlands.
⁵School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.

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Reference
Röling WFM, Aerts JW, Patty CHL, ten Kate IL, Ehrenfreund P, Direito SOL (2015) The Significance of Microbe-Mineral-Biomarker Interactions in the Detection of Life on Mars and Beyond. Astrobiology 15(6): 492-507.
Link to Article [doi:10.1089/ast.2014.1276]

^1,2A. Pommier,³K. Leinenweber, ⁴M. Tasaka
¹University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA 92093, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
³Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287, USA
⁴Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA

Electrical conductivity measurements were performed during melting experiments of olivine compacts (dry and hydrous Fo77 and Fo90) at 4 and 6 GPa in order to investigate melt transport properties and quantify the effect of partial melting on electrical properties. Experiments were performed in the multi-anvil apparatus and electrical measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Changes in impedance spectra were used to identify the transition from an electrical response controlled by the solid matrix to an electrical response controlled by the melt phase. This transition occurs slightly above the solidus temperature and lasts until View the MathML sourceTsolidus+75°C (±25). At higher temperature, a significant increase in conductivity (corresponding to an increase in conductivity values by a factor ranging from ∼30 to 100) is observed, consistent with the transition from a tube-dominated network to a structure in which melt films and pools become prominent features. This increase in conductivity corresponds to an abrupt jump for all dry samples and to a smoother increase for the hydrous sample. It is followed by a plateau at higher temperature, suggesting that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of partial melting. Electron microprobe analyses on quenched products indicated an increase in Mg# (molar Mg/(Mg+Fe)Mg/(Mg+Fe)) of olivine during experiments (∼77–93 in the quenched samples with an initial Fo77 composition and ∼92–97 in the quenched samples with an initial Fo90 composition) due to the partitioning of iron to the melt phase. Assuming a respective melt fraction of 0.10 and 0.20 before and after the phase of significant increase in conductivity, in agreement with previous electrical and permeability studies, our results can be reproduced satisfactorily by two-phase electrical models (the Hashin and Shtrikman bounds and the modified brick layer model), and provide a melt conductivity value of 78 (±8) S/m for all Fo77 samples and 45 (±5) S/m for the Fo90 sample. Comparison of our results with electromagnetic sounding data of the deep interior of the Moon supports the hypothesis of the presence of interconnected melt at the base of the lunar mantle. Our results underline that electrical conductivity can be used to investigate in situ melt nucleation and migration in the interior of terrestrial planets.

Reference
Pommier A, Leinenweber K, Tasaka M (2015) Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.05.052]

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¹Dwijesh Ray, ¹S. Ghosh, ¹S.V.S. Murty
¹PLANEX, Physical Research Laboratory, Ahmedabad 380009, India

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Ray D, Ghosh D, Murty SVS (2015) Shock-Thermal History of Kavarpura IVA Iron: Evidences from Microtextures and Nickel Profiling. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.05.016]

¹David M.H. Baker, ¹James W. Head
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912

Important to understanding the process of basin formation on planetary bodies are constraints on the mineralogy and depths of origin of interior ring structures. We summarize previous analyses of the mineralogy of basin materials on the Moon and use hyperspectral image-cubes from the Chandrayaan-1’s Moon Mineralogy Mapper (M3) to determine the mineralogy of interior rings in lunar protobasins and peak-ring basins. Nearly all peak rings outside of South Pole-Aitken (SPA) basin have extensive outcrops of pure anorthosite (⩾99% plagioclase) on the order of several square kilometers in areal dimensions. No obvious mantle components were identified. Outcrops spectrally dominated by pyroxene occur within SPA and other areas of thinner crust, such as regions within large ancient impact basins. In addition, many outcrops of candidate shocked plagioclase are observed within the same peak rings containing crystalline plagioclase. These spectral observations strongly support a crustal origin for peak rings on the Moon. Recent analyses of the Orientale basin and other lunar basins show that the inner rings of multi-ring basins are also anorthosite-rich and therefore derived from the lunar crust. To further constrain the depths of origin of materials forming peak rings, we compare the pre-impact crustal thickness for each basin with calculated vertical reference points, including: 1) maximum depth of excavation, which is the deepest point at which the crater will excavate material, 2) maximum depth of melting, which is deeper than the maximum depth of excavation and represents the maximum extent of impact-induced melting beneath the sub-impact point, and 3) maximum depth of the transient cavity, which is deepest part of the growing transient cavity that is formed of both excavated and displaced target material. Taken together with the observed mineralogy, the origin of peak-ring lithologies is constrained to stratigraphic levels near the maximum depth of excavation and likely shallower than this if the lower crust is comprised of noritic materials. The maximum depth of melting for peak-ring basins extends far into the mantle and is therefore not a valid proxy for estimating the depth of origin of materials forming peak rings. We find that our estimates of the depths of origin of peak-ring materials are consistent with current models of peak-ring formation, including predictions by hydrocode simulations and conceptual models emphasizing the role of interior impact melting and centro-symmetric collapse of the walls of the transient cavity. Firmer constraints on the depths of origin of peak rings on the Moon await an improved understanding of the crustal compositional structure, particularly that of the lower crust, and improved model predictions on the sampling depths and shock pressures experienced by uplifted peak-ring materials.

Reference
Baker DMH, Head JW (2015) Constraints on the Depths of Origin of Peak Rings on the Moon from Moon Mineralogy Mapper Data. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.013]

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