NWA 1465

standby for nwa 1465 photo
Found 2001
no coordinates recorded Many fusion-crusted fragments weighing together 3 kg were found in the Western Sahara desert, and were subsequently acquired by a German meteorite collector in 2002. Analysis and classification was conducted at the Museum für Naturkunde, Institut für Mineralogie, Humboldt-Universität zu Berlin, Germany (Greshake et al., 34th LPSC, #1560 [2003]). The name NWA 1465 was assigned to this meteorite by the Nomenclature Committee of the Meteoritical Society.

This carbonaceous chondrite has a bulk mineralogy and composition similar to the CV3 chondrites, but with O-isotopes that plot nearest to the CR trend line (Greshake et al., 2003). Chondrules measuring up to several mm in size are strongly foliated like those in the Leoville CV3 carbonaceous chondrite. Also exhibiting foliation are an abundance of tens of µm- to cm-sized, melilite-rich CAI fragments, probably derived from compact Type A CAIs (Simon et al. 70th MetSoc, #5071 [2007]). Many refractory assemblages have been identified in NWA 1465. Some of the CAI fragments are hibonite-bearing, while others contain fassaite assemblages having the highest TiO and lowest MgO contents known among CAIs. The unexpected finding of silica-rich glass in contact with melilite is poorly understood.

The fine-grained matrix material is composed primarily of Fe-rich olivine, along with Ca-rich pyroxene, enstatite, forsterite, troilite, magnetite, and FeNi-metal. A variety of shock features are present in olivines, and melt veins and melt pockets occur within chondrules and matrix, features that are consistent with shock stage S4. Terrestrial weathering has progressed to grade W3.

Within the host meteorite are large (>3 cm) dark inclusions that have O-isotope ratios similar to matrix material found in Al Rais (anomalous, CR clan), and close to those of dark inclusions found in Belgica 7904 (petrographically and chemically CM-like, but isotopically CI-like), as well as in Leoville and Vigarano (both CV3-reduced). These dark inclusions have O-isotope ratios and chemical compositions that deviate significantly from the host meteorite and from typical CI/CM-like dark inclusions commonly present in CV3 chondrites. Furthermore, in contrast to the visually distinct boundaries of typical CV3 dark inclusions, the dark inclusions in NWA 1465 exhibit an imperceptible contact with the host meteorite, resolvable only through high magnification. These dark inclusions also exhibit none of the shock effects that are prevalent in the host meteorite, which suggests that they accreted after this shock event occurred. Chondrule-free dark inclusions like the one embedded in NWA 1465 might represent the primitive precursor material of magmatic CC irons, which accreted before the onset of chondrule formation in the region of the protoplanetary disk beyond Jupiter (A. Rubin, 2018).

Other CV3 meteorites have been either officially designated as anomalous members or argue for such a classification based on independent research; examples include ALHA81003, Camel Donga 040, MET 01017, and NWA 1152. Notably, NWA 1465 is chemically reduced. The specimen of NWA 1465 shown above is a 5.1 g partial slice that contains a small portion of a dark inclusion on the right edge. The photo below shows a full slice that has been sectioned through one of these unusual inclusions.

standby for nwa 1465 photo
Photo courtesy of S. Kambach

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