¹Larry R. Nittler,²Rhonda M. STROUD, ¹Conel M. O’D. ALEXANDER, ^1,3Kaitlin HOWELL
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13397]
¹Department of Terrestrial Magnetism, Carnegie lnstitution of Washington, Washington,District of Columbia 20015, USA
²U.S. Naval Research Laboralory, Codle 6366, 4555 Overlook Ave. SW, Washington, District of Columbia 20375, USA
³Present address: School of Engineering, Ecole Polytechnique Federale de Lausanne, Lausanne CH-1015, Switzerland
Published by arrangement with John Wiley & Sons

We report a correlated NanoSIMS-transmission electron microscopy study of theungrouped carbonaceous chondrite Northwest Africa (NWA) 5958. We identified 10presolar SiC grains, 2 likely presolar graphite grains, and 20 presolar silicate and/or oxidegrains in NWA 5958. We suggest a slight modification of the commonly used classificationsystem for presolar oxides and silicates that better reflects the grains’ likely stellar origins.The matrix-normalized presolar SiC abundance in NWA 5958 is 18þ1510ppm (2r) similar tothat seen in many classes of unmetamorphosed chondrites. In contrast, the matrix-normalized abundance of presolar O-rich phases (silicates and oxides) is 30:9þ17:813:1ppm (2r),much lower than seen in interplanetary dust particles and the least-altered CR, CO, andungrouped C chondrites, but close to that reported for CM chondrites. NanoSIMS mappingalso revealed an unusual13C-enriched (d13C100–200&) carbonaceous rim surrounding a1.4lm diameter phyllosilicate grain. Transmission electron microscopy (TEM) analysis oftwo presolar grains with a likely origin in asymptotic giant branch stars identified one asenstatite and one as Al-Mg spinel with minor Cr. The enstatite grain amorphized rapidlyunder the electron beam, suggesting partial hydration. TEM data of NWA 5958 matrixconfirm that it has experienced aqueous alteration and support the suggestion of Jacquetet al. (2016) that this meteorite has affinities to CM2 chondrites.

¹D. Ray,¹S. Ghosh,²H. Chennaoui Aoudjehane,³S. Das
Meteoritics & Planetary Science (in Prss) Link to Article [doi: 10.1111/maps.13399]
¹Physical Research Laboralory, Ahrnedabad, Gujaral 380 009, lndia
²Facully of Sciences, GAIA Laboralory, Hassan 11 University Casablanca, llP 5366 Maarif, 20000, Casablanca, Morooco
³Department of Metallurgical and Materials Engineering, Indian lnsli_Lulc ofTcchnology’. Kharagpur 721302, lndia
Published by arrangement with John Wiley & Sons

The Agoudal IIAB iron meteorite exhibits only kamacite grains (~6 mm across)without any taenite. The kamacite is homogeneously enriched with numerous rhabditeinclusions of different size, shape, and composition. In some kamacite domains, this appearsfrosty due to micron-scale rhabdite inclusions (~5 to 100lm) of moderate to high Nicontent (~26 to 40 wt%). In addition, all the kamacite grains in matrix are marked with aprominent linear crack formed during an atmospheric break-up event and subsequentlyoxidized. This feature, also defined by trails of lowest Ni-bearing (mean Ni: 23 wt%) mm-scale rhabdite plates (fractured and oxidized) could be a trace of a pre-existingc–ainterface. Agoudal experienced a very slow rate of primary cooling~4°CMa1estimatedfrom the binary plots of true rhabdite width against corresponding Ni wt% and thecomputed cooling rate curves after Randich and Goldstein (1978). Chemically, Agoudaliron (Ga: 54 ppm; Ge: 140 ppm; Ir: 0.03 ppm) resembles the Ainsworth iron, the coarsestoctahedrite of the IIAB group. Agoudal contains multiple sets of Neumann bands that areformed in space and time at different scales and densities due to multiple impacts withshock magnitude up to 130 kb. Signatures of recrystallization due to postshock lowtemperature mild reheating at about 400°C are also locally present.