¹Anna Barbaro,^2,3Fabrizio Nestola,⁴Lidia Pittarello,⁴Ludovic Ferrière,⁵Mara Murri,⁶Konstantin D. Litasov,²Oliver Christ,¹Matteo Alvaro,¹M. Chiara Domeneghetti
American Mineralogist 107, 377-384 Link to Article [DOI: https://doi.org/10.2138/am-2021-7856]
¹Department of Earth and Environmental Sciences, University of Pavia, Via A. Ferrata 1, I-27100 Pavia, Italy
²Department of Geosciences, University of Padova, Via Gradenigo 6, 35131 Padova, Italy
³Geoscience Institute, Goethe-University Frankfurt, Altenhöferallee 1, 60323 Frankfurt, Germany
⁴Department of Mineralogy and Petrography, Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁵Department of Earth and Environmental Sciences, University of Milano-Bicocca, I-20126 Milano, Italy
⁶Vereshchagin Institute for High Pressure Physics RAS, Troitsk, Moscow, 108840 Russia
Copyright: The Mineralogical Society of America

The formation and shock history of ureilite meteorites, a relatively abundant type of primitive
achondrites, has been debated for decades. For this purpose, the characterization of carbon phases
can provide further information on diamond and graphite formation in ureilites, shedding light on the
origin and history of this meteorite group. In this work, we present X‑ray diffraction and micro‑Raman
spectroscopy analyses performed on diamond and graphite occurring in the ureilite Yamato 74123
(Y-74123). The results show that nano- and microdiamonds coexist with nanographite aggregates.
This, together with the shock-deformation features observed in olivine, such as mosaicism and planar
fractures, suggest that diamond grains formed by a shock event (≥15 GPa) on the ureilitic parent
body (UPB). Our results on Y-74123 are consistent with those obtained on the NWA 7983 ureilite and
further support the hypothesis that the simultaneous formation of nano- and microdiamonds with the
assistance of a Fe-Ni melt catalysis may be related to the heterogeneous propagation and local scat –
tering of the shock wave. Graphite geothermometry revealed an average recorded temperature (Tmax)
of 1314 °C (±120 °C) in agreement with previously estimated crystallization temperatures reported
for graphite in Almahata Sitta ureilite.

^1,2,4Tomohiro Usui,^2,4Kevin Righter,^3,4Charles K. Shearer,⁴John H. Jones
American Mineralogist 107, 357–368 Link to Article [DOI: https://doi.org/10.2138/am-2021-7743]
¹Institute of Space and Astronautical Sciences, Japan Aerospace Exploration Agency, Kanagawa, 252-5210, Japan
²NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, Texas 77058, U.S.A.
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.
⁴Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
Copyright: The Mineralogical Society of America

Ni and Co variations in primary martian magmas exhibit anomalous incompatible behavior, which
has remained an unexplained conundrum. Because martian magmas are S-rich, and some trace metals
are reported to have enhanced solubility in S-bearing magmas, we have carried out a series of experi–
ments to evaluate the effect of high-S melts on the olivine/melt partitioning of Ni, Co, Mn, V, and Cr.
Near-liquidus experiments on a synthetic primary martian mantle melt (Yamato-980459 [Y98]) were
completed in a piston-cylinder apparatus at 0.75GPa. Previous studies in S-free systems illustrate that
the partition coefficients for these elements are dependent chiefly on DMg(Ol/melt) (the partition coefficient
defined as wt% Mg in olivine/wt% Mg in melt, a proxy for temperature), and were used to calibrate a
predictive expression that includes the effects of temperature [i.e., DMg(Ol/melt)], melt composition, and
oxygen fugacity. These predictive expressions are then used to isolate any effect in DM olivine/melt
due to dissolved sulfur. The results show that S might have a small effect for Co, but not enough to
change Co partitioning from compatible to incompatible in our experiments. The addition of a sulfur
term to the DCo predictive expressions shows that nearly 8000 ppm of sulfur would be required in the
melt (at liquidus temperature of Y98) for DCo to become <1. These S contents are two times higher
than those of a sulfide-saturated melt at the P–T conditions of a martian mantle source region. Therefore,
the anomalous incompatible behavior observed in these primary magma suites must be due to another
mechanism. High temperature, oxygen fugacity, and diffusion are not viable mechanisms, but magma
mixing, assimilation, or kinetic crystallization effects remain possibilities.