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Elsevier, Geochimica et Cosmochimica Acta, (112), p. 340-373

DOI: 10.1016/j.gca.2012.06.022

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Metallic phases and siderophile elements in main group ureilites: Implications for ureilite petrogenesis

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Abstract

Metallic phases and siderophile elements are critical to understanding the petrogenesis of the enigmatic ureilite meteorites. We obtained petrographic, major and minor element, and the first in situ trace element data for metallic phases (metal, sulfides, phosphide, carbide) in 24 main group ureilites of various petrographic types with Fo ∼75–95. The most abundant type of metal (∼1–3 vol.%) occurs as ∼10–40 μm-wide strips along silicate grain boundaries. Ni contents of this metal range from ∼0 to 7.3 wt.% and are correlated with Co among all samples (Ni/Co = 0.64 × CI). A less abundant type of metal occurs as ∼5–150 μm diameter metallic spherules, consisting of cohenite (Fe3C), metal, phosphide and sulfide, enclosed in silicates (preferentially low-Ca pyroxene). Most samples contain 2 types of sulfide: (1) low-Cr (<0.1 wt.%) troilite, and (2) lamellar intergrowths of daubreelite (FeCr2S4) and troilite.