Geochemical and oxygen isotope perspective of a new R chondrite Dhofar 1671: Affinity with ordinary chondrites

1,2Arshad Ali,1Sobhi J. Nasir,2Iffat Jabeen,3Ahmed Al Rawas,2Neil R. Banerjee,
2,4Gordon R. Osinski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12903]
1Earth Sciences Research Centre, Sultan Qaboos University, Muscat 123, Sultanate of Oman
2Department of Earth Sciences & Centre for Planetary Science and Exploration, Western University, London, Ontario, Canada
3Department of Physics, College of Science, Sultan Qaboos University, Muscat 123, Sultanate of Oman
4Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the Rumuruti chondrite class. Major and REE compositions are generally in agreement with average values of the R chondrites (RCs). Moderately volatile elements such as Se and Zn abundances are lower than the R chondrite values that are similar to those in ordinary chondrites (OCs). Porphyritic olivine pyroxene (POP), radial pyroxene (RP), and barred olivine (BO) chondrules are embedded in a proportionately equal volume of matrix, one of the characteristic features of RCs. Microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing Fa-poor interior and Fa-rich outer zones. Precise oxygen isotope data for chondrules and matrix obtained by laser-assisted fluorination show a genetic isotopic relationship between OCs and RCs. On the basis of our data, we propose a strong affinity between these groups and suggest that OC chondrule precursors could have interacted with a 17O-rich matrix to form RC chondrules (i.e., ∆17O shifts from ~1‰ to ~3‰). These interactions could have occurred at the same time as “exotic” clasts in brecciated samples formed such as NWA 10214 (LL3–6), Parnallee (LL3), PCA91241 (R3.8–6), and Dhofar 1671 (R3.6). We also infer that the source of the oxidation and 17O enrichment is the matrix, which may have been enriched in 17O-rich water. The abundance of matrix in RCs relative to OCs, ensured that these rocks would be apparently more oxidized and appreciably 17O-enriched. In situ analysis of Dhofar 1671 is recommended to further strengthen the link between OCs and RCs.

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