^1,2Brendt C. Hyde,¹Kimberly T. Tait,²Desmond E. Moser,³Douglas Rumble III,^1,4Michelle S. Thompson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13416]
¹Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada, M5S 2C6
²Department of Earth Sciences, University of Western Ontario, London, ON, Canada, N6A 5B7
³Carnegie Institution of Washington, Washington, DC, 20015 USA
⁴Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, IN, 47907 USA
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 869 is the largest sample of chondritic regolith breccia, making it an ideal source for research on accretionary processes and primordial chemical mixing. One such process can be seen in detail through the first identification of a eucrite impactor clast in an L chondrite breccia. The ~7 mm diameter clast has oxygen isotope compositions (Δ¹⁷O = −0.240, −0.258‰) and pigeonite and augite compositions typical for eucrites, but with high areal abundance of silica (9.5%) and ilmenite (1.5%). The rim around the clast is a mixture of breccia and igneous phases, the latter due to either impactor‐triggered melting or later metamorphism. The rim has an oxygen isotope composition falling on a mixing line between known eucrite and L chondrite compositions (Δ¹⁷O = 0.326‰) and, coincidentally, on the Mars fractionation line. Pyroxene grains from the melt component in the rim have compositions that fall on a mixing line between the average eucrite pyroxene composition and equilibrated L chondrite composition. The margins of chondritic olivine crystal clasts in the rim are enriched in Fe as a result of diffusion from the Fe‐rich melt and suggest cooling on the scale of hours. The textures and chemical mixing observed provide evidence for an unconsolidated L chondrite target material, differing from the current state of NWA 869 material. The heterogeneity of oxygen isotope and chemical signatures at this small length scale serve as a cautionary note when extrapolating from small volumes of materials to deduce planetesimal source characteristics.

^1,2Giovanni Pratesi,³Stefano Caporali,⁴Richard C. Greenwood,⁵Vanni Moggi Cecchi,¹Ian A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13409]
¹Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira, 4, 50121 Firenze, Italy
²INAF‐IAPS, Via Fosso del Cavaliere 100, 00133 Rome, Italy
³Dipartimento di Ingegneria Industriale, Università degli Studi di Firenze, Via Santa Marta 3, 50139 Firenze, Italy
⁴Planetary and Space Sciences, The Open University, Milton Keynes, MK7 6AA UK
⁵Museo di Storia Naturale, Università degli Studi di Firenze, Via Giorgio La Pira, 4, 50121 Firenze, Italy
Published by arrangement with John Wiley & Sons

Among the many ungrouped meteorites, Acfer 370, NWA 7135, and El Médano 301—probably along with the chondritic inclusion in Cumberland Falls and ALHA 78113—represent a homogeneous grouplet of strongly reduced forsterite‐rich chondrites characterized by common textural, chemical, mineralogical, and isotopic features. All of these meteorites are much more reduced than OCs, with a low iron content in olivine and low‐Ca pyroxene. In particular, Acfer 370 is a type 4 chondrite that has olivine and low‐Ca pyroxene compositional ranges of Fa 5.2–5.8 and Fs 9.4–33.4, respectively. The dominant phase is low‐Ca pyroxene (36.3 vol%), followed by Fe‐Ni metal (16.3 vol%) and olivine (15.5 vol%); nevertheless, considering the Fe‐oxyhydroxide (due to terrestrial weathering), the original metal content was around 29.6 vol%. Finally, the mean oxygen isotopic composition Δ¹⁷O = +0.68‰ along with the occurrence of a silica phase, troilite, Ni‐rich phosphides, chromite, and oldhamite confirms that these ungrouped meteorites have been affected by strong reduction and are different from any other group recognized so far.