On the origin of fluorine-poor apatite in chondrite parent bodiesOPEN ACCESS 

Francis M. McCubbin, Jonathan A. Lewis, Jessica J. Barnes, Jeremy W. Boyce, Juliane Gross, Molly C. McCanta, Poorna Srinivasan, Brendan A. Anzures, Nicole G. Lunning, Stephen M. Elardo, Lindsay P. Keller, Tabb C. Prissel, and Carl B. Agee

American Mineralogist
peer-reviewed author’s accepted manuscript (AAM)


“We conducted a petrologic study of apatite within one LL chondrite, six R chondrites, and six CK chondrites. These data were combined with previously published apatite data from a broader range of chondritic meteorites to determine that chondrites host either chlorapatite or hydroxylapatite with ≤ 33 mol% F in the apatite X-site (unless affected by partial melting by impacts, which can cause F-enrichment of residual apatite). These data indicate that either fluorapatite was not a primary condensate from the solar nebula or it did not survive lower temperature nebular processes and/or parent body processes. Bulk rock Cl and F data from chondrites were used to determine that the solar system has a Cl/F ratio of 10.5 ± 1.0 (3σ). The Cl/F ratios of apatite from chondrites are broadly reflective of the solar system Cl/F value, indicating that apatite in chondrites are fluorine poor because the solar system has about an order of magnitude more Cl than F. The Cl/F ratio of the solar system was combined with known apatite-melt partitioning relationships for F and Cl to predict the range of apatite compositions that would form from a melt with a chondritic Cl/F ratio. This range of apatite compositions allowed for the development of a crude model to use apatite X-site compositions from achondrites (and chondrite melt rocks) to determine whether they derive from a volatile-depleted and/or differentiated source, albeit with important caveats that are detailed in the manuscript. This study further highlights the utility of apatite as a mineralogical tool to understand the origin of volatiles (including H2O) and the diversity of their associated geological processes throughout the history of our solar system, including at its nascent stage.”