^1,3Eve L. Berger, ²Lindsay P. Keller,¹Dante S. Lauretta
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
²NASA Johnson Space Center, Houston, Texas, USA
³GeoControl Systems, Inc. — Jacobs JETS contract — NASA Johnson Space Center, Houston, Texas, 77058, USA

The low-temperature form of CuFe2S3, cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum temperature to 210 °C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time-varying, low-temperature fluids which existed on the CI-chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low-temperature aqueous conditions relevant to the CI-chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 °C, pH approximately 9, and oxygen fugacities corresponding to the iron-magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI-chondrite parent body and Wild 2 when cubanite was forming.

Reference
Berger EL, Keller LP, Lauretta DS (2014) An experimental study of the formation of cubanite (CuFe2S3) in primitive meteorites. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12399]

Published by arrangement with John Wiley&Sons

¹Yangting Lin et al. (>10)*
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
*Find the extensive, full author and affiliation list on the publishers website

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ13C = −12.8 to −33.1‰) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.

Reference
Lin Y et al. (2014) NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic-bearing fluids on Mars. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12389]

Published by arrangement with John Wiley&Sons

¹Jean-Yves Bonnet et al. (>10)*
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France, CNRS, IPAG, F-38000 Grenoble, France
*Find the extensive, full author and affiliation list on the publishers website

Nitrogen-rich refractory organics are scarce phases recovered as a fraction of stratospheric IDPs and constitute the bulk of the organic matter of some ultracarbonaceous Antarctic micrometeorites. They are likely formed under very specific conditions within a nitrogen-rich environment and may provide valuable clues on the origin of the population of interplanetary dusts accreted by Earth. In this study, we produced relevant analogs of such refractory organics characterized in three ultracarbonaceous Antarctic micrometeorites, starting from the carbonization of an HCN polymer and a tholin. Indeed, carbonization is a process that can increase the polyaromatic character toward a structure similar to that observed in these cosmomaterials. Both these precursors were degraded in an Ar atmosphere at 300, 500, 700 and 1000°C over ∼1 hour and characterized by elemental analysis, micro-FTIR and Raman micro-spectroscopy (at 244 and 514 nm excitation wavelengths). Our results show that the precursors evolve along distinct chemical and structural pathways during carbonization and that the influence of the precursor structure is still very strong at 1000°C. Interestingly, these different carbonization routes appear in the spectral characteristics of the G and D bands of their Raman spectra. Several of the residues present chemical and structural similarities with three recently studied ultracarbonaceous micrometeorites [Dobrica et al. (2011)Meteoritics Planet. Sci.46, 1363; Dartois et al. (2013)Icarus224, 243] and with N-rich inclusions in stratospheric IDPs. However the residues do not simultaneously account for the carbon structure (Raman) and the chemical composition (IR, N/C ratio). This indicates that the precursors and/or heating conditions in our experiments are not fully relevant. Despite this lack of full relevancy, the formation of a polyaromatic structure fairly similar to that of UCAMMs and IDPs suggests that the origin of N-rich refractory organics lies in a thermal process in the proto-solar disk, however radiolysis cannot be excluded.

Reference
Bonnet J-Y et al. (2014) Formation of analogs of cometary nitrogen-rich refractory organics from thermal degradation of tholin and hcn polymer. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.006]

Copyright Elsevier

¹Oliver Tschauner, ²Chi Ma, ²John R. Beckett, ³Clemens Prescher, ³Vitali B. Prakapenka, ²George R. Rossman
¹Department of Geoscience and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89134, USA.
²Division of Geology and Planetary Science, California Institute of Technology, Pasadena, CA 91125, USA.
³Center of Advanced Radiation Sources, University of Chicago, Chicago, IL 60632, USA.

Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth’s mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

Reference
Tschauner O, Ma C, Beckett JR, Prescher C, Prakapenka VB, Rossman GR (2014) Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked Meteorite. Science 346, 1100-1102
Link to Article [DOI: 10.1126/science.1259369]

Reprinted with permission from AAAS