NORTHWEST AFRICA 15468

A large number of dark brown, weathered fragments lacking fusion crust, having a combined weight of ~30 kg, were found in Mali at an undisclosed location. The meteorite fragments were distributed by various dealers to several collectors over a period of time (see MetBull 112 for further details). About 5 kg of material was acquired by Shun-Chung Yang, who kindly contributed the specimen above to the DWeir collection. Multiple samples were submitted to a number of research institutions, including the University of Washington in Seattle (A. Irving), Washington University in St. Louis (P. Carpenter), Brown University in Providence, Rhode Island (J. Boesenberg, D. Ibarra [oxygen isotopes]), and the Museum für Naturkunde in Berlin, Germany (A. Greshake). After completion of analyses, NWA 15468 was classified as an OC4-melt breccia.

Northwest Africa 15468 contains both melted and unmelted portions, the latter exhibiting chondrules measuring up to 760 µm in size and composed of forsteritic olivine (Fa8.5 [±0.4]), enstatite, pigeonite, diopside, and devitrified feldspathic glass. The mesostasis contains a high abundance of FeNi-metal blebs along with chromite, troilite, and chlorapatite. Thin metallic rims have formed around chondritic domains where partial melting has occurred.

Results of an oxygen isotopic analysis conducted on the freshest material plot slightly above the TFL near the unequlibrated ungrouped OC3 JaH 846 and along a trend line populated by a small number of anomalous, ungrouped, non-carbonaceous chondrites including HaH 180, NWA 960, NWA 2335, and NWA 2336, along with the members of the F chondrite group. Taken together with the NWA-series meteorites 2040 [LL], 2041 [L], 3114 [L], 3127 [LL], 3157 [L], 4294 [LL], 4298 [LL], 4486 [L], 4531 [LL], 5717 [dual lith], NWA 7835 [acho-ung; Irving et al., 2014, #5332; photo courtesy of Stefan Ralew], and NWA 10769 [acho-ung; Moggi Cecchi et al., 2017, #2696], these O-isotopic values infer a possible "supra-TFL" genetic grouping which defines a slope distinct from the ordinary chondrites. As demonstrated in the diagrams below, these meteorites plot far away from the trend lines for the H, L, and LL ordinary chondrite groups and probably represent several previously unrecognized parent asteroids (e.g., Irving et al., 2014 #5332; Irving et al., 2023 #2309).

NWA 15468 fragments have undergone low to heavy terrestrial weathering (W1/W3) with shock features consistent with stage S2. It has a relatively high magnetic susceptibility mean value of 5.60. The specimen of NWA 15468 shown above is a 12.2 g cut fragment. Shown below are public domain photos of representative unmelted and partially melted sections, courtesy of Dr. Anthony Irving.