¹Stefanie Brachfeld, ¹Deepa Shah, ²Emily First, ²Julia Hammer, ³Julie Bowles
¹Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey, USA
²Department of Geology and Geophysics, University of Hawai‘i, Honolulu, Hawai‘i, USA
³Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA

We evaluate the relationship between the intensity of remanent magnetization and fO2 in natural and synthetic Mars meteorites. The olivine-phyric shergottite meteorite Yamato 980459 (Y-980459) and a sulfur-free synthetic analog (Y-98*) of identical major element composition were analyzed to explore the rock magnetic and remanence properties of a basalt crystallized from a primitive melt, and to explore the role of magmatic and alteration environment fO2 on Mars crustal anomalies. The reducing conditions under which Y-980459 is estimated to have formed (QFM-2.5; Shearer et al. 2006) were replicated during the synthesis of Y-98*. Y-980459 contains pyrrhotite and chromite. Chromite is the only magnetic phase in Y-98*. The remanence-carrying capacity of Y-980459 is comparable to other shergottites that formed in the fO2 range of QFM-3 to QFM-1. The remanence-carrying capacity of these low fO2 basalts is 1–2 orders of magnitude too weak to account for the intense crustal anomalies observed in Mars’s southern cratered highlands. Moderately oxidizing conditions of >QFM-1, which are more commonly observed in nakhlites and Noachian breccias, are key to generating either a primary igneous assemblage or secondary alteration assemblage capable of acquiring an intense remanent magnetization, regardless of the basalt character or thermal history. This suggests that if igneous rocks are responsible for the intensely magnetized crust, these oxidizing conditions must have existed in the magmatic plumbing systems of early Mars or must have existed in the crust during secondary processes that led to acquisition of a chemical remanent magnetization.

Reference
Brachfeld S, Shah D, First E, Hammer J, Bowles J (2015) Influence of redox conditions on the intensity of Mars crustal magnetic anomalies. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12505]
Published by arrangement with John Wiley & Sons

¹Mehmet Yesiltas, ¹Robert E. Peale, ²Miriam Unger, ³Julia Sedlmair,²Carol J. Hirschmugl
¹Department of Physics, University of Central Florida, Orlando, Florida, USA
²Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
³Forest Products Laboratory, US Department of Agriculture Forest Service, Madison, Wisconsin, USA

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C-H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH2 and CH3 band strengths (CH2/CH3 = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.

Reference
Yesiltas M, Peale RE, Unger M, Sedlmair J, Hirschmugl CJ (2015) Organic and inorganic correlations for Northwest Africa 852 by synchrotron-based Fourier transform infrared microspectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12498]
Published by arrangement with John Wiley & Sons

¹R. Terik Daly, ¹Peter H. Schultz 
¹Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St., Box 1846, Providence, RI 02912, United States

Dark material on Vesta may consist of carbonaceous chondrite-like material delivered by impact events. This study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis. Experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds. Hence, dark material can plausibly be delivered to Vesta by impacts, with the projectile component accumulating in the regolith with time. Projectile retention is sensitive to impact angle, ranging from 7% for 30° impacts (measured from horizontal) to 72% for vertical impacts. Averaged over the probability distribution of impact angles, 17% of the projectile’s mass remains in or near the crater. Projectile-contaminated breccias largely remain inside the crater for vertical impacts. In oblique impacts, projectile-contaminated pieces concentrate downrange beyond the crater rim. Based on experiments, projectile delivery is expected for typical vestan impact conditions, not only for extraordinary events such as low-probability and very low-speed (e.g. <2 km s⁻¹) impacts. These experiments indicate that other (non-dark) impactors contaminate the vestan regolith. Regolith-laden bodies in environments with similar impact speeds also may accrete significant amounts of foreign debris.

Reference
Daly RT, Schultz PH (2015) Delivering a projectile component to the vestan regolith. Icarus 264, 9–19
Link to Article [doi:10.1016/j.icarus.2015.08.034]
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