NORTHWEST AFRICA 7891

CV3-anom or ung
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Purchased 2012
no coordinates recorded

A single stone weighing 168 g was purchased by A. Habibi in Morocco in 2012. Initial analysis and classification was conducted at University of New Mexico (C. Agee and K. Ziegler, UNM), and NWA 7891 was determined to be an anomalous member of the CV3 chondrite group. The meteorite was subsequently sold to R. Garcia who then sold some specimens to collectors.

This meteorite was classified as anomalous due to its high variability in oxygen isotope values and its low mean Fe/Mn value for olivine. The O-isotopic values plot on the CCAM line along an extension of the CV and CK trends (see diagram below).

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Diagram from Meteoritical Bulletin 102

In an effort to further resolve differences between the CV and CK chondrite groups, Yin and Sanborn (2019) analyzed Cr isotopes in a significant number and broad range of meteorites. Their study included samples from each of the three CV subgroups (oxA, oxB, Red), two anomalous CV3 (NWA 6047 and NWA 7891), a C3-ungrouped (Ningqiang), several CK members, and other potential CV-related meteorites (see top diagram below). It is demonstrated that the CV and CK meteorites are clearly resolved into two distinct isotopic reservoirs. In addition, it is shown in the top diagram below that the ε54Cr value for NWA 6047 puts it in a distinct location compared to other CV group meteorites, and therefore it may represent a separate carbonaceous chondrite parent body. Furthermore, despite the varied classification history of Ningqiang, it can now be assigned to the CK group. A coupled Δ17O vs. ε54Cr diagram plotting all of the meteorites in the study is shown in the bottom diagram below. Notably, anomalous CV3 NWA 7891 (Δ17O = –7.7 [±4.5] ‰) plots far below the range considered in the bottom diagram.

Cr Isotope Weighted Average For CV and CK Chondrites
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click on photo for a magnified view

O–Cr Diagram For CV and CK Chondrites
CK: orange shades; CV: green shades; Achondrites: open
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click on photo for a magnified view

Diagrams credit: Yin and Sanborn et al., 50th LPSC, #3023 (2019)

Further studies are needed to better resolve any genetic relationships that might exist between NWA 7891 and other anomalous and ungrouped meteorites, as well as with the CV parent body. The specimen shown above is a small part slice weighing 0.29 g. The photo below shows the interior surface and weathered exterior of a 3.3 g end section, shown courtesy of R. Garcia.

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Photos courtesy of Ruben Garcia