¹Earl O’Bannon III, ¹Quentin Williams
Physics and Chemistry of Minerals 43, 181–208   Link to Article [doi:10.1007/s00269-015-0786-1]
¹Department of Earth and Planetary Sciences University of California Santa Cruz USA

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^1,2Youmo Zhou,¹Tetsuo Irifune,¹Hiroaki Ohfuji,¹Toru Shinmei,^1,2Wei Du
Physics and Chemistry of Minerals (in Press) Link to Article [DOI: 10.1007/s00269-016-0834-5]
¹Geodynamics Research Center Ehime University Matsuyama Japan
²Earth-Life Science Institute Tokyo Institute of Technology Tokyo Japan

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¹A. Rodríguez, ¹M.J. van Bergen
Netherlands Journal of Geosciences 95, 153-169 Link to Article [DOI: http://dx.doi.org/10.1017/njg.2015.12]
¹Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3508 TA, Utrecht, the Netherlands

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¹Shuai Li, ¹Ralph E. Milliken
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005035]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
Published by arrangement with John Wiley & Sons

Radiance measured by the Moon Mineralogy Mapper (M3) at wavelengths beyond ~2 µm commonly includes both solar reflected and thermally emitted contributions from the lunar surface. Insufficient correction (removal) of the thermal contribution can modify and even mask absorptions at these wavelengths in derived surface reflectance spectra, an effect that precludes accurate identification and analysis of OH and/or H2O absorptions. This study characterized thermal effects in M3 data by evaluating surface temperatures measured independently by the Lunar Reconnaissance Orbiter Diviner radiometer, and results confirm that M3 data (Level 2) currently available in the Planetary Data System (PDS) often contain significant thermal contributions. It is impractical to use independent Diviner measurements to correct all M3 images for the Moon because not every M3 pixel has a corresponding Diviner measurement acquired at the same local time of lunar day. Therefore, a new empirical model, constrained by Diviner data, has been developed based on the correlation of reflectance at 1.55 µm and at 2.54 µm observed in laboratory reflectance spectra of Apollo and Luna soil and glass-rich samples. Reflectance values at these wavelengths follow a clear power law, inline image, for a wide range of lunar sample compositions and maturity. A nearly identical power law is observed in M3 reflectance data that have been independently corrected using Diviner-based temperatures, confirming this is a general reflectance property of materials that typify the lunar surface. These results demonstrate that reflectance at a thermally-affected wavelength (2.54 µm) can be predicted within 2% (absolute) based on reflectance values at shorter wavelengths where thermal contributions are negligible and reflectance is dominant. Radiance at 2.54 µm that is in excess of the expected amount is assumed to be due to thermal emission and is removed during conversion of at-sensor radiance to reflectance or I/F. Removal of this thermal contribution using this empirically-based model provides a more accurate view of surface reflectance properties at wavelengths >2 µm, with the benefit that it does not require independent measurements or modeling of surface temperatures at the same local time as M3 data were acquired. It is demonstrated that this model is appropriate for common lunar surface compositions (e.g., mare and highlands soils, pyroclastic deposits), but surface compositions with reflectance properties that deviate strongly from these cases (e.g., pyroxene-, olivine-, or spinel-rich locations with minimal space weathering) may require the use of more sophisticated thermal correction models or overlapping Diviner temperature estimates.

¹Kyoungwon Min, ¹Annette Farah, ²Seung Ryeol Lee, ³Jong Ik Lee
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.09.009]
¹Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA
²Korea Institute of Geosciences and Mineral Resources, Daejeon, Korea
³Korea Polar Research Institute, Incheon, Korea
Copyright Elsevier

Shock conditions of martian meteorites provide crucial information about ejection dynamics and original features of the martian rocks. To better constrain equilibrium shock temperatures (Tequi-shock) of martian meteorites, we investigated (U-Th)/He systematics of moderately-shocked (Zagami) and intensively shocked (ALHA77005) martian meteorites. Multiple phosphate aggregates from Zagami and ALHA77005 yielded overall (U-Th)/He ages 92.2 ± 4.4 Ma (2σ) and 8.4 ± 1.2 Ma, respectively. These ages correspond to fractional losses of 0.49 ± 0.03 (Zagami) and 0.97 ± 0.01 (ALHA77005), assuming that the ejection-related shock event at ∼3 Ma is solely responsible for diffusive helium loss since crystallization. For He diffusion modeling, the diffusion domain radius is estimated based on detailed examination of fracture patterns in phosphates using a scanning electron microscope. For Zagami, the diffusion domain radius is estimated to be ∼2-9 μm, which is generally consistent with calculations from isothermal heating experiments (1-4 μm). For ALHA77005, the diffusion domain radius of ∼4-20 μm is estimated.

Using the newly constrained (U-Th)/He data, diffusion domain radii, and other previously estimated parameters, the conductive cooling models yield Tequi-shock estimates of 360-410 °C and 460-560 °C for Zagami and ALHA77005, respectively. According to the sensitivity test, the estimated Tequi-shock values are relatively robust to input parameters. The Tequi-shock estimates for Zagami are more robust than those for ALHA77005, primarily because Zagami yielded intermediate fHe value (0.49) compared to ALHA77005 (0.97). For less intensively shocked Zagami, the He diffusion-based Tequi-shock estimates (this study) are significantly higher than expected from previously reported Tpost-shock values. For intensively shocked ALHA77005, the two independent approaches yielded generally consistent results. Using two other examples of previously studied martian meteorites (ALHA84001 and Los Angeles), we compared Tequi-shock and Tpost-shock estimates. For intensively shocked meteorites (ALHA77005, Los Angeles), the He diffusion-based approach yield slightly higher or consistent Tequi-shock with estimations from Tpost-shock, and the discrepancy between the two methods increases as the intensity of shock increases. The reason for the discrepancy between the two methods, particularly for less-intensively shocked meteorites (Zagami, ALHA84001), remains to be resolved, but we prefer the He diffusion-based approach because its Tequi-shock estimates are relatively robust to input parameters.