¹Laurence E. Nyquist, ²Chi-Yu Shih, ^1,3Francis M. McCubbin, ^3,4Alison R. Santos, ^3,4Charles K. Shearer, ²Zhan X. Peng, ^3,4Paul V. Burger,³Carl B. Agee
¹NASA Johnson Space Center, Mailcode XI, Houston, Texas, USA
²Jacobs, NASA Johnson Space Center, Houston, Texas, USA
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA

The bulk matrix domain of the Martian breccia NWA 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia. Both 147Sm-143Nd and 146Sm-142Nd age results for mineral separates from the bulk matrix portion of breccia NWA 7034 suggest that various lithological components in the breccia probably formed contemporaneously ~4.44 Ga ago. This old age is in excellent agreement with the upper intersection ages (4.35–4.45 Ga) for U-Pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous-textured clasts. Consequently, we confirm an ancient age for the igneous components that make up the NWA 7034 breccia. Substantial disturbance in the Rb-Sr system was detected, and no age significance could be gleaned from our Rb-Sr data. The disturbance to the Rb-Sr system may be due to a thermal event recorded by bulk-rock K-Ar ages of 1.56 Ga and U-Pb ages of phosphates at about 1.35–1.5 Ga, which suggest partial resetting from an unknown thermal event(s), possibly accompanying breccia formation. The NWA 7034 bulk rock is LREE enriched and similar to KREEP-rich lunar rocks, which indicates that the earliest Martian crust was geochemically enriched. This enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on Mars that have been detected in studies of other Martian meteorites.

Reference
Nyquist E, Shih C-Y,McCubbin, FM,Santos AR, Shearer CK, Peng ZX, Burger PV, Agee CB (2016) Rb-Sr and Sm-Nd isotopic and REE studies of igneous components in the bulk matrix domain of Martian breccia Northwest Africa 7034. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12606]
Published by arrangement wit John Wiley & Sons

^1,2Kathryn A. Dyl et al.(>10*)
¹Department of Applied Geology, Curtin University, Perth, WA, Australia
²CSIRO Earth Sciences and Resource Engineering, Perth, WA, Australia
*Find the extensive, full author and affiliation list on the publishers website

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS-XRD, element mapping via energy dispersive spectroscopy [EDS], and X-ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67−0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α-quartz and a rim of both low- and high-Ca pyroxene. The mineralogy allows the calculation of the temperatures and ƒ(O2) characterizing thermal metamorphism on the parent body using both the two-pyroxene and the olivine-chromite geo-oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ƒ(O2) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.

Reference
Dyl KA et al. (2016) Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12605]
Published by arrangement with John Wiley & Sons