¹Jeremy J. Kent,²Alan D. Brandon,³Katherine H. Joy,⁴Anne H. Peslier,²Thomas J. Lapen,⁵Anthony J. Irving,⁶Daniel M. Coleff
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12898]
¹GeoControl Systems, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
²University of Houston, Department of Earth and Atmospheric Sciences, Houston, Texas, USA
³School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
⁴Jacobs, NASA-Johnson Space Center, Houston, Texas, USA
⁵University of Washington, Department of Earth and Space Sciences, Seattle, Washington, USA
⁶HX5, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
Published by arrangement with john Wiley & Sons

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first-discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg-suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact-related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact-induced shock.

¹Alex M. Ruzicka,¹Melinda Hutson,^2,3Jon M. Friedrich,⁴Mark L. Rivers,^3,5Michael K. Weisberg,³Denton S. Ebel,⁶Karen Ziegler,⁷Douglas Rumble III,^2,8Alyssa A. Dolan
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12901]
¹Cascadia Meteorite Laboratory, Department of Geology, Portland State University, Portland, Oregon, USA
²Department of Chemistry, Fordham University, Bronx, New York, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York City, New York, USA
⁴Consortium for Advanced Radiation Sources, University of Chicago, Argonne, Illinois, USA
⁵Department of Physical Sciences, Kingsborough College and Graduate School of the City University of New York, Brooklyn, New York, USA
⁶Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁷Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C., USA
⁸Georgetown Law Center, Washington, D.C., USA
Published by arrangement with John Wiley & Sons

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine-grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone-like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain-free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to ~15–19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back-reaction of high-pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration.