TY - JOUR
T1 - The abundances of F, Cl, and H2O in eucrites
T2 - Implications for the origin of volatile depletion in the asteroid 4 Vesta
AU - McCubbin, Francis M.
AU - Lewis, Jonathan A.
AU - Barnes, Jessica J.
AU - Elardo, Stephen M.
AU - Boyce, Jeremy W.
N1 - Funding Information: We are grateful to the Meteorite Working Group, now the Antarctic Meteorite Review Panel of the Astromaterials Allocation Review Board, for carefully evaluating our sample requests, and we thank the curatorial staff at NASA Johnson Space Center for allocation of the Antarctic eucrites used in this study. The US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center, respectively. We also thank Carl Agee of the Institute of Meteoritics at the University of New Mexico in Albuquerque, NM, USA for the allocation of Berthoud, and we thank Ludovic Ferrière of the Naturhistorisches (Natural History) Museum in Vienna, Austria for the allocation of Stannern. Finally, we wish to thank Daniel Kent Ross for his help with using the electron microprobe at NASA JSC and working closely with F.M.M., J.A.L., J.J.B., and J.W.B. to implement our apatite analytical routines. Kent will be dearly missed, and we dedicate this work to his memory. We are grateful to Wim van Westrenen for the editorial handling of this manuscript and to Thomas Barrett and an anonymous reviewer that provided constructive and helpful comments that improved the overall quality of this work. F.M.M. and J.W.B. were supported by NASA’s Planetary Science Research Program during this work. J.A.L. was supported by the NASA Postdoctoral Program during this work. J.J.B was supported by start-up funds from the University of Arizona. S.M.E. acknowledges support from NASA Solar System Workings grant 80NSSC19K0752. Funding Information: We are grateful to the Meteorite Working Group, now the Antarctic Meteorite Review Panel of the Astromaterials Allocation Review Board, for carefully evaluating our sample requests, and we thank the curatorial staff at NASA Johnson Space Center for allocation of the Antarctic eucrites used in this study. The US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center, respectively. We also thank Carl Agee of the Institute of Meteoritics at the University of New Mexico in Albuquerque, NM, USA for the allocation of Berthoud, and we thank Ludovic Ferri?re of the Naturhistorisches (Natural History) Museum in Vienna, Austria for the allocation of Stannern. Finally, we wish to thank Daniel Kent Ross for his help with using the electron microprobe at NASA JSC and working closely with F.M.M. J.A.L. J.J.B. and J.W.B. to implement our apatite analytical routines. Kent will be dearly missed, and we dedicate this work to his memory. We are grateful to Wim van Westrenen for the editorial handling of this manuscript and to Thomas Barrett and an anonymous reviewer that provided constructive and helpful comments that improved the overall quality of this work. F.M.M. and J.W.B. were supported by NASA's Planetary Science Research Program during this work. J.A.L. was supported by the NASA Postdoctoral Program during this work. J.J.B was supported by start-up funds from the University of Arizona. S.M.E. acknowledges support from NASA Solar System Workings grant 80NSSC19K0752. Publisher Copyright: © 2021
PY - 2021/12/1
Y1 - 2021/12/1
N2 - We conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. These data were combined with previously published data to quantify the abundances of F, Cl, and H2O in the bulk silicate portion of asteroid 4 Vesta (BSV). Using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that BSV has 3.0–7.2 ppm F, 0.39–1.8 ppm Cl, and 3.6–22 ppm H2O. The abundances of F and H2O are depleted in BSV relative to CI chondrites to a similar degree as F and H2O in the bulk silicate portion of the Moon. This degree of volatile depletion in BSV is similar to what has been determined previously for many moderately volatile elements in 4 Vesta (e.g., Na, K, Zn, Rb, Cs, and Pb). In contrast, Cl is depleted in 4 Vesta by a greater degree than what is recorded in samples from Earth or the Moon. Based on the Cl-isotopic compositions of eucrites and the bulk rock Cl/F ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37Cl and Cl/F, not as extracts from a partially crystallized global magma ocean. Furthermore, the volatile depletion and Cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 Vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. Although our results can be reconciled with the past presence of wide-scale melting on 4 Vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to Cl/F ratios and Cl isotopes.
AB - We conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. These data were combined with previously published data to quantify the abundances of F, Cl, and H2O in the bulk silicate portion of asteroid 4 Vesta (BSV). Using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that BSV has 3.0–7.2 ppm F, 0.39–1.8 ppm Cl, and 3.6–22 ppm H2O. The abundances of F and H2O are depleted in BSV relative to CI chondrites to a similar degree as F and H2O in the bulk silicate portion of the Moon. This degree of volatile depletion in BSV is similar to what has been determined previously for many moderately volatile elements in 4 Vesta (e.g., Na, K, Zn, Rb, Cs, and Pb). In contrast, Cl is depleted in 4 Vesta by a greater degree than what is recorded in samples from Earth or the Moon. Based on the Cl-isotopic compositions of eucrites and the bulk rock Cl/F ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37Cl and Cl/F, not as extracts from a partially crystallized global magma ocean. Furthermore, the volatile depletion and Cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 Vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. Although our results can be reconciled with the past presence of wide-scale melting on 4 Vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to Cl/F ratios and Cl isotopes.
KW - Achondrites
KW - Apatite
KW - Chlorine isotopes
KW - Magma ocean
KW - Meteorites
KW - Water
UR - http://www.scopus.com/inward/record.url?scp=85116219333&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85116219333&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2021.08.021
DO - 10.1016/j.gca.2021.08.021
M3 - Article
SN - 0016-7037
VL - 314
SP - 270
EP - 293
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -