¹B. W. Young, ¹M. A. Chan
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005118]
¹University of Utah, Salt Lake City, UT, USA
Published by agreement with John Wiley & Sons

Well-exposed gypsum veins in the Triassic Moenkopi Formation in southern Utah, USA, are similar to veins at Endeavour and Gale craters on Mars. Both Moenkopi and Mars veins are hydrated calcium sulfate, have fibrous textures, and cross-cut other diagenetic features. Moenkopi veins are stratigraphically localized with strontium and sulfur isotope ratios similar to primary Moenkopi sulfate beds, and are thus interpreted to be sourced from within the unit. Endeavour veins seem to be distributed by lithology and may have a local source. Gale veins cut across multiple lithologies and appear to be sourced from another stratigraphic interval. Evaluation of vein network geometries indicate horizontal Moenkopi veins are longer and thicker than vertical veins. Moenkopi veins are also generally oriented with the modern stress field, so are interpreted to have formed in the latest stages of exhumation. Endeavour veins appear to be generally vertical and oriented parallel to the margins of Cape York, and are interpreted to have formed in response to topographic collapse of the crater rim. Gale horizontal veins appear to be slightly more continuous than vertical veins and may have formed during exhumation. Abrupt changes in orientation, complex cross-cutting relationships, and fibrous (antitaxial) texture in Moenkopi and Mars veins suggest emplacement via hydraulic fracture at low temperatures. Moenkopi and Mars veins are interpreted as late-stage diagenetic features that have experienced little alteration since emplacement. Moenkopi veins are useful terrestrial analogs for Mars veins because vein geometry, texture, and chemistry record information about crustal deformation and vein emplacement.

¹Y. Nakamuta,²K. Urata,³Y. Shibata,⁴Y. Kuwahara
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12808]
¹Kyushu University Museum, Kyushu University, Fukuoka, Japan
²Faculty of Science, Kyushu University, Fukuoka, Japan
³Sawara P.O., Japan Post Co., Fukuoka, Japan
⁴Graduate School of Social and Cultural Studies, Kyushu University, Fukuoka, Japan
Published by agreement with John Wiley & Sons

In Lindsley’s thermometry, a revised sequence of calculation of components is proposed for clinopyroxene, in which kosmochlor component is added. Temperatures obtained for the components calculated by the revised method are about 50 °C lower than those obtained for the components calculated by the Lindsley’s original method and agree well with temperatures obtained from orthopyroxenes. Ca-partitioning between clino- and orthopyroxenes is then thought to be equilibrated in types 5 to 7 ordinary chondrites. The temperatures for Tuxtuac (LL5), Dhurmsala (LL6), NWA 2092 (LL6/7), and Dho 011 (LL7) are 767–793°, 818–835°, 872–892°, and 917–936°C, respectively, suggesting that chondrites of higher petrographic types show higher equilibrium temperatures of pyroxenes. The regression equations which relate temperature and Wo and Fs contents in the temperature-contoured pyroxene quadrilateral of 1 atm of Lindsley (1983) are also determined by the least squares method. It is possible to reproduce temperatures with an error less than 20 °C (2SE) using the regression equations.

¹Jeffrey J. Gillis-Davis, ¹Paul G. Lucey, ¹John P. Bradley, ¹Hope A. Ishii, ¹Heather M. Kaluna, ¹¹Anumpam Misra, ²Harold C. Connolly Jr.
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.12.031]
¹University of Hawaii, Hawaii Institute of Geophysics and Planetology, Honolulu, HI 96822 USA
²Department of Geology, School of Earth and the Environment, Rowan University, 201 Mullica Hill Road, Glassboro, NJ 08028, USA.
Copyright Elsevier

We report findings from a series of laser-simulated space weathering experiments on Allende, a CV3 carbonaceous chondrite. The purpose of these experiments is to understand how spectra of anhydrous C-complex asteroids might vary as a function of micrometeorite bombardment. Four 0.5-gram aliquots of powdered, unpacked Allende meteorite were incrementally laser weathered with 30 mJ pulses while under vacuum. Radiative transfer modeling of the spectra and Scanning Transmission Electron Microscope (STEM) analyses of the samples show lunar-like similarities and differences in response to laser-simulated space weathering. For instance, laser weathered Allende exhibited lunar-like spectral changes. The overall spectra from visible to near infrared (Vis-NIR) redden and darken, and characteristic absorption bands weaken as a function of laser exposure. Unlike lunar weathering, however, the continuum slope between 450-550 nm does not vary monotonically with laser irradiation. Initially, spectra in this region redden with laser irradiation; then, the visible continua become less red and eventually spectrally bluer. STEM analyses of less mature samples confirm submicroscopic iron metal (SMFe) and micron sized sulfides. More mature samples reveal increased dispersal of Fe-Ni sulfides by the laser, which we infer to be the cause for the non-lunar-like changes in spectral behavior. Spectra of laser weathered Allende are a reasonable match to T- or possibly K-type asteroids; though the spectral match with a parent body is not exact. The key take away is, laser weathered Allende looks spectrally different (i.e., darker, and redder or bluer depending on the wavelength region) than its unweathered spectrum. Consequently, connecting meteorites to asteroids using unweathered spectra of meteorites would result in a different parent body than one matched on the basis of weathered spectra. Further, spectra for these laser weathering experiments may provide an explanation for inconsistencies observed in both laboratory (e.g., Hiroi et al., 2003 & Hiroi et al., 2001, Lazzarin et al., 2006 and Moroz et al., 2004 & Moroz et al., 1996 and Shingareva et al., 2004) and telescopic data (Lazzarin et al., 2006, Marchi et al., 2006 and Nesvorný et al., 2005).