¹I. Weber, ¹A. Morlok, ¹A. Bischoff,¹H. Hiesinger1 ¹D. Ward, ²K. H. Joy, ²S. A. Crowther, ²N. D. Jastrzebski, ²J. D. Gilmour, ²P. L. Clay, ²R. A. Wogelius, ³R. C. Greenwood, ³I. A. Franchi,⁴C. Münker
¹Institut für Planetologie, Münster, Germany
²School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester, UK
³Planetary and Space Sciences, The Open University, Milton Keynes, UK
⁴Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany

This work is part of a project to build an infrared database in order to link IR data of planetary materials (and therefore possible Mercury material) with remote sensing observations of Mercury, which will probably be obtained by the MERTIS instrument on the forthcoming BepiColombo mission.
The unique achondrite Northwest Africa (NWA) 7325, which has previously been suggested to represent the first sample from Mercury, was investigated by optical and electron microscopy, and infrared and Raman spectroscopy. In addition, the oxygen, strontium, xenon, and argon isotopes were measured and the abundance of selected trace elements determined. The meteorite is a cumulate rock with subchondritic abundances of HFSE and REE and elevated Sr contents, which underwent a second heating and partial remelting process. Oxygen isotope measurements show that NWA 7325 plots in the ureilite field, close to the ALM-A trachyandesitic fragment found in the unique Almahata Sitta meteorite breccia. On the other hand, mineralogical investigations of the pyroxenes in NWA 7325 provide evidence for similarities to the lodranites and acapulcoites. Furthermore, the rock is weakly shocked and argon isotope data record ancient (~4.5 Ga) plateau ages that have not been reset. The sample records a cosmogenic exposure age of ~19 Ma. Systematics of Rb-Sr indicate an extreme early volatile depletion of the precursor material, similar to many other achondrite groups. However, despite its compositional similarities to other meteorite groups, our results suggest that this meteorite is unique and unrelated to any other known achondrite group. An origin for NWA 7325 as a sample from the planet Mercury is not supported by the results of our investigation. In particular, the evidence from infrared spectroscopy indicates that a direct relationship between NWA 7325 and the planet Mercury can be ruled out: no acceptable spectral match between laboratory analyses and remote sensing observations from Mercury has been obtained. However, we demonstrate that infrared spectroscopy is a rapid and nondestructive method to characterize mineral phases and thus an excellent tool for planetary surface characterization in space missions.

Reference
Weber I, Morlok A, Bischoff A, Hiesinger H, Ward D, Joy KH, Crowther SA, Jastrzebski ND, Gilmour JD, Clay PL, Wogelius RA, Greenwood RC, Franchi IA, Münker C (2015) Cosmochemical and spectroscopic properties of Northwest Africa 7325—A consortium study. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12586]
Published by arrangement with John Wiley & Sons

¹Ashley J. King,¹Jake R. Solomon, ¹Paul F. Schofield, ¹Sara S. Russell
¹Department of Earth Sciences, Natural History Museum

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
King AJ, Solomon JR, Schofield PF, Russell SS (2015) Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy. Earth, Planets and Space 67, 198
Link to Article [DOI: 10.1186/s40623-015-0370-4]

^1,2Arya Udry, ¹Harry Y. McSween Jr., ³Richard L. Hervig,¹Lawrence A. Taylor
¹Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

Degassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry (SIMS). All three light lithophile elements (LLE) are incompatible: Li and B are soluble in H2O-rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous-fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6Li in the vapor phase compared to 7Li during degassing. The Li isotope profiles, with increasing δ7Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.

Reference
Udry A, McSween Jr. HY, Hervig RL, Taylor LA (2015) Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12582]

Published by arrangement with John Wiley & Sons