Sahara 03505 sulfide‐rich iron meteorite: Evidence for efficient segregation of sulfide‐rich metallic melt during high‐degree impact melting of an ordinary chondrite

Abstract

Abstract-The Sahara 03505 meteorite is a 65 g sulfide-rich iron found in an undisclosed locality of the Sahara. It consists of roughly equal volumetric proportion of polycrystalline troilite (crystal size 1.5-7.5 mm) enclosing cellular/dendritic metallic Fe-Ni (width of the dendrite arms, ~100 µm). The mineral assemblage is completed by sparse skeletal crystals of chromite, abundant droplets, 5-100 µm in size, of anhydrous Fe-, Fe-Na-, and Fe-Mn-Mg-Ca-Na-K-phosphates, tiny crystals of schreibersite, and particles of metallic Cu. The medium-to fine-grained quench texture, and cooling modeling suggest that Sahara 03505 formed through crystallization of a sulfur-rich metallic melt under rapid cooling conditions (1-4°C s −1 ). The low troilite/metallic Fe-Ni ratio (~0.6 by weight) shows that this liquid was generated at much higher temperatures (>1300 °C) with respect to the FeS-Fe,Ni cotectic liquids. Based on bulk chemistry and oxygen isotope composition of chromite, we propose that Sahara 03505 formed by extensive impact melting of an ordinary chondrite lithology, followed by the efficient segregation of the immiscible silicate and metallic liquids. The sulfur-rich metallic liquid rapidly cooled either by radiation into space as a small lump, or by conduction to a chondrite country rock as a vein intruded into the walls of an impact crater.Sahara 03505 belongs to a small group of sulfide-rich iron meteorites which are characterized by medium-to fine-grained quench textures and by bulk chemistry that is different from the other iron meteorite groups. We propose here to use the descriptive term "sulfide-irons" for this meteorite group, by analogy with the stony-irons.

Sulfide‐rich metallic impact melts from chondritic parent bodies

“…7). They also show similar enrichment and depletion patterns among some elements to that of Sahara 03505, which D’Orazio et al. (2009) suggests originated from impact melting of an ordinary chondrite.…”

“…Average values over IIIABs from Willis (1980), Portales Valley metal data by INAA from Ruzicka et al. (2005), and Sahara 03505 data from D’Orazio et al. (2009) are plotted for reference.…”

“…A few sulfur‐rich ungrouped iron meteorites have been discovered which are likely related to the ordinary chondrites (Schrader et al. 2008; D’Orazio et al. 2009).…”

“…Sahara 03505 is a sulfide‐rich iron meteorite (65 g), consisting of approximately equal amounts of troilite surrounding cellular and dendritic Fe,Ni metal. Its composition and petrology suggest it formed during the impact melting of a chondritic precursor (D’Orazio et al. 2009).…”

“…2009). Due to similarities with Sahara 03505, D’Orazio et al. (2009) also suggested that the paired meteorites Roberts Massif (RBT) 04162 (52.3 g) and RBT 04299 (55.2 g) may share a similar origin.…”