A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides

Kosuke T. Goto; Yasuhito Sekine; Gen Shimoda; James R. Hein; Shogo Aoki; Akira Ishikawa; Katsuhiko Suzuki; Gwyneth W. Gordon; Ariel D. Anbar

doi:10.1016/j.gca.2020.04.017

A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides

Kosuke T. Goto, Yasuhito Sekine, Gen Shimoda, James R. Hein, Shogo Aoki, Akira Ishikawa, Katsuhiko Suzuki, Gwyneth W. Gordon, Ariel D. Anbar

Earth and Space Exploration, School of (SESE)

Research output: Contribution to journal › Article › peer-review

14 Scopus citations

Abstract

Molybdenum isotopic compositions (δ^98/95Mo) of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks have been used to investigate local accumulations of O₂ in an O₂-lean ocean. Previous studies interpret that these δ^98/95Mo values would be a representation of the global minimum for δ^98/95Mo of contemporaneous seawater and would, therefore, link to global paleoredox conditions. Here, we present new δ^98/95Mo data on modern marine hydrothermal Fe-Mn oxides, for a wide range of Fe/Mn ratios, from five hydrothermal systems. Samples composed mainly of Fe oxides (Fe/Mn > 10) show positive values (δ^98/95Mo ∼ +0.7‰), whereas those containing substantial amounts of Mn oxides (Fe/Mn < 10⁻¹) generally exhibit negative values (δ^98/95Mo ∼ −0.8 ‰). These δ^98/95Mo values are consistent with isotopic fractionations due to the adsorption of seawater Mo onto Fe and Mn oxides, respectively. The aforementioned positive and negative values are connected by a positive correlation between δ^98/95Mo values and the Fe/Mn ratios of samples with Fe/Mn ∼ 10⁻¹–10¹. The positive correlation can be explained by the mixing of δ^98/95Mo in Fe and Mn oxides. Based on these data, we propose that the measured δ^98/95Mo trends for the modern hydrothermal Fe-Mn oxides can be reproduced using a simple mass-balance calculation with both modern seawater δ^98/95Mo and Mo isotopic fractionations due to the adsorption of Mo onto Fe and Mn oxides. By applying this mass-balance calculation to published Fe/Mn and δ^98/95Mo data on ancient Fe- and Mn-rich sedimentary rocks, we estimate Archean and Paleoproterozoic seawater δ^98/95Mo and their deviations (Δ^98/95Mo) from modern seawater δ^98/95Mo. The long-term evolution of seawater δ^98/95Mo inferred as a result suggests extensive deposition of Fe and Mn oxides at ∼2.3–2.2 Ga and an expansion of euxinic conditions at ∼1.9 Ga, which are broadly consistent with the proposed redox evolution of the ocean–atmosphere system during the Archean and Paleoproterozoic.

Original language	English (US)
Pages (from-to)	221-236
Number of pages	16
Journal	Geochimica et Cosmochimica Acta
Volume	280
DOIs	https://doi.org/10.1016/j.gca.2020.04.017
State	Published - Jul 1 2020

Keywords

Archean
Modern hydrothermal iron and manganese oxides
Molybdenum isotope
Ocean paleoredox
Paleoproterozoic

ASJC Scopus subject areas

Geochemistry and Petrology

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10.1016/j.gca.2020.04.017

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Goto, K. T., Sekine, Y., Shimoda, G., Hein, J. R., Aoki, S., Ishikawa, A., Suzuki, K., Gordon, G. W., & Anbar, A. D. (2020). A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides. Geochimica et Cosmochimica Acta, 280, 221-236. https://doi.org/10.1016/j.gca.2020.04.017

Goto, KT, Sekine, Y, Shimoda, G, Hein, JR, Aoki, S, Ishikawa, A, Suzuki, K, Gordon, GW & Anbar, AD 2020, 'A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides', Geochimica et Cosmochimica Acta, vol. 280, pp. 221-236. https://doi.org/10.1016/j.gca.2020.04.017

@article{84b776f6fdaa46c683e2d5654aae7fbc,

title = "A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides",

abstract = "Molybdenum isotopic compositions (δ98/95Mo) of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks have been used to investigate local accumulations of O2 in an O2-lean ocean. Previous studies interpret that these δ98/95Mo values would be a representation of the global minimum for δ98/95Mo of contemporaneous seawater and would, therefore, link to global paleoredox conditions. Here, we present new δ98/95Mo data on modern marine hydrothermal Fe-Mn oxides, for a wide range of Fe/Mn ratios, from five hydrothermal systems. Samples composed mainly of Fe oxides (Fe/Mn > 10) show positive values (δ98/95Mo ∼ +0.7‰), whereas those containing substantial amounts of Mn oxides (Fe/Mn < 10−1) generally exhibit negative values (δ98/95Mo ∼ −0.8 ‰). These δ98/95Mo values are consistent with isotopic fractionations due to the adsorption of seawater Mo onto Fe and Mn oxides, respectively. The aforementioned positive and negative values are connected by a positive correlation between δ98/95Mo values and the Fe/Mn ratios of samples with Fe/Mn ∼ 10−1–101. The positive correlation can be explained by the mixing of δ98/95Mo in Fe and Mn oxides. Based on these data, we propose that the measured δ98/95Mo trends for the modern hydrothermal Fe-Mn oxides can be reproduced using a simple mass-balance calculation with both modern seawater δ98/95Mo and Mo isotopic fractionations due to the adsorption of Mo onto Fe and Mn oxides. By applying this mass-balance calculation to published Fe/Mn and δ98/95Mo data on ancient Fe- and Mn-rich sedimentary rocks, we estimate Archean and Paleoproterozoic seawater δ98/95Mo and their deviations (Δ98/95Mo) from modern seawater δ98/95Mo. The long-term evolution of seawater δ98/95Mo inferred as a result suggests extensive deposition of Fe and Mn oxides at ∼2.3–2.2 Ga and an expansion of euxinic conditions at ∼1.9 Ga, which are broadly consistent with the proposed redox evolution of the ocean–atmosphere system during the Archean and Paleoproterozoic.",

keywords = "Archean, Modern hydrothermal iron and manganese oxides, Molybdenum isotope, Ocean paleoredox, Paleoproterozoic",

author = "Goto, {Kosuke T.} and Yasuhito Sekine and Gen Shimoda and Hein, {James R.} and Shogo Aoki and Akira Ishikawa and Katsuhiko Suzuki and Gordon, {Gwyneth W.} and Anbar, {Ariel D.}",

note = "Funding Information: We thank Yoshio Takahashi, Ryuji Tada, Eiichi Tajika, and Yusuke Yokoyama for their valuable feedback during the preparation of this manuscript, Margaret Sulanowska, Meg Tivey, and Susan Humphris for providing TAG samples, and three anonymous reviewers and associate editor Timothy W. Lyons for very helpful comments during the review process. This study was a part of the “Scientific research on genesis of marine resources” project for the Next-Generation Technology for Ocean Resources Exploration in the Cross-Ministerial Strategic Innovation Promotion Program (SIP). It was also supported by JSPS KAKENHI grant numbers JP15H02142 and JP19K14832 and MEXT KAKENHI grant number JP17H06456. Funding Information: We thank Yoshio Takahashi, Ryuji Tada, Eiichi Tajika, and Yusuke Yokoyama for their valuable feedback during the preparation of this manuscript, Margaret Sulanowska, Meg Tivey, and Susan Humphris for providing TAG samples, and three anonymous reviewers and associate editor Timothy W. Lyons for very helpful comments during the review process. This study was a part of the “Scientific research on genesis of marine resources” project for the Next-Generation Technology for Ocean Resources Exploration in the Cross-Ministerial Strategic Innovation Promotion Program (SIP). It was also supported by JSPS KAKENHI grant numbers JP15H02142 and JP19K14832 and MEXT KAKENHI grant number JP17H06456 . Publisher Copyright: {\textcopyright} 2020 Elsevier Ltd",

year = "2020",

month = jul,

day = "1",

doi = "10.1016/j.gca.2020.04.017",

language = "English (US)",

volume = "280",

pages = "221--236",

journal = "Geochimica et Cosmochimica Acta",

issn = "0016-7037",

publisher = "Elsevier Limited",

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TY - JOUR

T1 - A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks

T2 - Insights from modern marine hydrothermal Fe-Mn oxides

AU - Goto, Kosuke T.

AU - Sekine, Yasuhito

AU - Shimoda, Gen

AU - Hein, James R.

AU - Aoki, Shogo

AU - Ishikawa, Akira

AU - Suzuki, Katsuhiko

AU - Gordon, Gwyneth W.

AU - Anbar, Ariel D.

N1 - Funding Information: We thank Yoshio Takahashi, Ryuji Tada, Eiichi Tajika, and Yusuke Yokoyama for their valuable feedback during the preparation of this manuscript, Margaret Sulanowska, Meg Tivey, and Susan Humphris for providing TAG samples, and three anonymous reviewers and associate editor Timothy W. Lyons for very helpful comments during the review process. This study was a part of the “Scientific research on genesis of marine resources” project for the Next-Generation Technology for Ocean Resources Exploration in the Cross-Ministerial Strategic Innovation Promotion Program (SIP). It was also supported by JSPS KAKENHI grant numbers JP15H02142 and JP19K14832 and MEXT KAKENHI grant number JP17H06456. Funding Information: We thank Yoshio Takahashi, Ryuji Tada, Eiichi Tajika, and Yusuke Yokoyama for their valuable feedback during the preparation of this manuscript, Margaret Sulanowska, Meg Tivey, and Susan Humphris for providing TAG samples, and three anonymous reviewers and associate editor Timothy W. Lyons for very helpful comments during the review process. This study was a part of the “Scientific research on genesis of marine resources” project for the Next-Generation Technology for Ocean Resources Exploration in the Cross-Ministerial Strategic Innovation Promotion Program (SIP). It was also supported by JSPS KAKENHI grant numbers JP15H02142 and JP19K14832 and MEXT KAKENHI grant number JP17H06456 . Publisher Copyright: © 2020 Elsevier Ltd

PY - 2020/7/1

Y1 - 2020/7/1

N2 - Molybdenum isotopic compositions (δ98/95Mo) of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks have been used to investigate local accumulations of O2 in an O2-lean ocean. Previous studies interpret that these δ98/95Mo values would be a representation of the global minimum for δ98/95Mo of contemporaneous seawater and would, therefore, link to global paleoredox conditions. Here, we present new δ98/95Mo data on modern marine hydrothermal Fe-Mn oxides, for a wide range of Fe/Mn ratios, from five hydrothermal systems. Samples composed mainly of Fe oxides (Fe/Mn > 10) show positive values (δ98/95Mo ∼ +0.7‰), whereas those containing substantial amounts of Mn oxides (Fe/Mn < 10−1) generally exhibit negative values (δ98/95Mo ∼ −0.8 ‰). These δ98/95Mo values are consistent with isotopic fractionations due to the adsorption of seawater Mo onto Fe and Mn oxides, respectively. The aforementioned positive and negative values are connected by a positive correlation between δ98/95Mo values and the Fe/Mn ratios of samples with Fe/Mn ∼ 10−1–101. The positive correlation can be explained by the mixing of δ98/95Mo in Fe and Mn oxides. Based on these data, we propose that the measured δ98/95Mo trends for the modern hydrothermal Fe-Mn oxides can be reproduced using a simple mass-balance calculation with both modern seawater δ98/95Mo and Mo isotopic fractionations due to the adsorption of Mo onto Fe and Mn oxides. By applying this mass-balance calculation to published Fe/Mn and δ98/95Mo data on ancient Fe- and Mn-rich sedimentary rocks, we estimate Archean and Paleoproterozoic seawater δ98/95Mo and their deviations (Δ98/95Mo) from modern seawater δ98/95Mo. The long-term evolution of seawater δ98/95Mo inferred as a result suggests extensive deposition of Fe and Mn oxides at ∼2.3–2.2 Ga and an expansion of euxinic conditions at ∼1.9 Ga, which are broadly consistent with the proposed redox evolution of the ocean–atmosphere system during the Archean and Paleoproterozoic.

AB - Molybdenum isotopic compositions (δ98/95Mo) of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks have been used to investigate local accumulations of O2 in an O2-lean ocean. Previous studies interpret that these δ98/95Mo values would be a representation of the global minimum for δ98/95Mo of contemporaneous seawater and would, therefore, link to global paleoredox conditions. Here, we present new δ98/95Mo data on modern marine hydrothermal Fe-Mn oxides, for a wide range of Fe/Mn ratios, from five hydrothermal systems. Samples composed mainly of Fe oxides (Fe/Mn > 10) show positive values (δ98/95Mo ∼ +0.7‰), whereas those containing substantial amounts of Mn oxides (Fe/Mn < 10−1) generally exhibit negative values (δ98/95Mo ∼ −0.8 ‰). These δ98/95Mo values are consistent with isotopic fractionations due to the adsorption of seawater Mo onto Fe and Mn oxides, respectively. The aforementioned positive and negative values are connected by a positive correlation between δ98/95Mo values and the Fe/Mn ratios of samples with Fe/Mn ∼ 10−1–101. The positive correlation can be explained by the mixing of δ98/95Mo in Fe and Mn oxides. Based on these data, we propose that the measured δ98/95Mo trends for the modern hydrothermal Fe-Mn oxides can be reproduced using a simple mass-balance calculation with both modern seawater δ98/95Mo and Mo isotopic fractionations due to the adsorption of Mo onto Fe and Mn oxides. By applying this mass-balance calculation to published Fe/Mn and δ98/95Mo data on ancient Fe- and Mn-rich sedimentary rocks, we estimate Archean and Paleoproterozoic seawater δ98/95Mo and their deviations (Δ98/95Mo) from modern seawater δ98/95Mo. The long-term evolution of seawater δ98/95Mo inferred as a result suggests extensive deposition of Fe and Mn oxides at ∼2.3–2.2 Ga and an expansion of euxinic conditions at ∼1.9 Ga, which are broadly consistent with the proposed redox evolution of the ocean–atmosphere system during the Archean and Paleoproterozoic.

KW - Archean

KW - Modern hydrothermal iron and manganese oxides

KW - Molybdenum isotope

KW - Ocean paleoredox

KW - Paleoproterozoic

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JO - Geochimica et Cosmochimica Acta

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A framework for understanding Mo isotope records of Archean and Paleoproterozoic Fe- and Mn-rich sedimentary rocks: Insights from modern marine hydrothermal Fe-Mn oxides

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