@article{5191d9edfacc4c48a50fd556165e5d7b,
title = "Secular mantle oxidation across the Archean-Proterozoic boundary: Evidence from V partitioning in komatiites and picrites",
abstract = "The oxygen fugacities of nine mantle-derived komatiitic and picritic systems ranging in age from 3.55 Ga to modern day were determined using the redox-sensitive partitioning of V between liquidus olivine and komatiitic/picritic melt. The combined set of the oxygen fugacity data for seven systems from this study and the six komatiite systems studied by Nicklas et al. (2018), all of which likely represent large regions of the mantle, defines a well-constrained trend indicating an increase in oxygen fugacity of the lavas of ∼1.3 ΔFMQ log units from 3.48 to 1.87 Ga, and a nearly constant oxygen fugacity from 1.87 Ga to the present. The oxygen fugacity data for the 3.55 Ga Schapenburg komatiite system, the mantle source region of which was previously argued to have been isolated from mantle convection within the first 30 Ma of the Solar System history, plot well above the trend and were not included in the regression. These komatiite's anomalously high oxygen fugacity data likely reflect preservation of early-formed magma ocean redox heterogeneities until at least the Paleoarchean. The observed increase in the oxygen fugacity of the studied komatiite and picrite systems of ∼1.3 ΔFMQ log units is shown to be a feature of their mantle source regions and is interpreted to indicate secular oxidation of the mantle between 3.48 and 1.87 Ga. Three mechanisms are considered to account for the observed change in the redox state of the mantle: (1) recycling of altered oceanic crust, (2) venting of oxygen from the core due to inner core crystallization, and (3) convection-driven homogenization of an initially redox-heterogeneous primordial mantle. It is demonstrated that none of the three mechanisms alone can fully explain the observed trend, although mechanism (3) is best supported by the available geochemical data. These new data provide further evidence for mantle involvement in the dramatic increase in the oxygen concentration of the atmosphere leading up to the Great Oxidation Event at ∼2.4 Ga.",
keywords = "Mantle redox",
author = "Nicklas, {Robert W.} and Puchtel, {Igor S.} and Ash, {Richard D.} and Piccoli, {Philip M.} and Eero Hanski and Nisbet, {Euan G.} and Pedro Waterton and Pearson, {D. Graham} and Ariel Anbar",
note = "Funding Information: This study was supported by NSF FESD Type I Grant # 1338810 “The Dynamics of Earth System Oxygenation” (lead PI is A.D. Anbar, I.S. Puchtel is a co-PI). This source of support is gratefully acknowledged. Eero Hanski acknowledges support from Academy of Finland Grant # 281859 . The authors wish to thank Nadezhda Tolstykh and Andrey Vishnevsky for providing the Song Da samples VS 5-1, VS 6-1 and VS 6-2, and Alan Brandon for providing the Icelandic samples ICE4A, ICE4B, and ICE5. We thank Valentina Puchtel for help with sample preparation. We also thank Mark Fornace (undergraduate assistant), Valentina Puchtel, and William F. McDonough for their assistance in the initial development of the standard addition technique, which was supported by NSF grant EAR-0739006 (to W.F.M.). The support of the Maryland NanoCenter and its AIMLab is gratefully acknowledged. Finally, thorough reviews by Dr. Sonja Aulbach and Dr. Guilherme Mallmann, as well as comments by Associate Editor Dr. Munir Humayun, greatly improved the initial version of this manuscript. Funding Information: This study was supported by NSF FESD Type I Grant #1338810 “The Dynamics of Earth System Oxygenation” (lead PI is A.D. Anbar, I.S. Puchtel is a co-PI). This source of support is gratefully acknowledged. Eero Hanski acknowledges support from Academy of Finland Grant #281859. The authors wish to thank Nadezhda Tolstykh and Andrey Vishnevsky for providing the Song Da samples VS 5-1, VS 6-1 and VS 6-2, and Alan Brandon for providing the Icelandic samples ICE4A, ICE4B, and ICE5. We thank Valentina Puchtel for help with sample preparation. We also thank Mark Fornace (undergraduate assistant), Valentina Puchtel, and William F. McDonough for their assistance in the initial development of the standard addition technique, which was supported by NSF grant EAR-0739006 (to W.F.M.). The support of the Maryland NanoCenter and its AIMLab is gratefully acknowledged. Finally, thorough reviews by Dr. Sonja Aulbach and Dr. Guilherme Mallmann, as well as comments by Associate Editor Dr. Munir Humayun, greatly improved the initial version of this manuscript. Publisher Copyright: {\textcopyright} 2019 Elsevier Ltd",
year = "2019",
month = apr,
day = "1",
doi = "10.1016/j.gca.2019.01.037",
language = "English (US)",
volume = "250",
pages = "49--75",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
}