Isotope evolution in the HIMU reservoir beneath St. Helena: Implications for the mantle recycling of U and Th

Takeshi Hanyu, Hiroshi Kawabata, Yoshiyuki Tatsumi, Jun Ichi Kimura, Hironobu Hyodo, Keiko Sato, Takashi Miyazaki, Qing Chang, Yuka Hirahara, Toshiro Takahashi, Ryoko Senda, Shun'ichi Nakai

研究成果: ジャーナルへの寄稿記事

24 引用 (Scopus)

抄録

HIMU (high-μ 238U/204Pb) is a mantle reservoir that has been thought to form by subduction and subsequent storage of ancient oceanic crust and lithosphere in the mantle. In order to constrain the processes that acted on subducted materials over several billion years, we present precise Pb-Sr-Nd-Hf-He isotopic data together with 40Ar/39Ar and K/Ar ages of HIMU lavas from St. Helena in the Atlantic. Clinopyroxene separates were analyzed together with whole-rock samples to better describe the geochemical characteristics of the HIMU component. Although isotopic variations are small in the St. Helena lavas (20.6-21.0 for 206Pb/204Pb) between 12 and 8Ma, the younger lavas have more HIMU-like isotopic compositions than the older lavas. The mixing arrays defined by these lavas are remarkably similar to those observed in HIMU lavas from Austral Islands in the Pacific, suggesting that the two HIMU reservoirs located in different mantle domains are characterized by similar isotopic compositions with radiogenic 206Pb/204Pb and 208Pb/204Pb, enriched Nd and Hf isotopes, depleted Sr isotopes, and radiogenic 3He/4He. However, there is a significant difference between the St. Helena and Austral Islands lavas in 207Pb/204Pb. The St. Helena lavas show systematically higher 207Pb/204Pb for a given 206Pb/204Pb. Lead isotope evolution models suggest that both HIMU reservoirs formed around 2Ga; however, the HIMU reservoir for St. Helena is about 0.3Ga older than that for Austral Islands. The relation between 206Pb/204Pb and 208Pb/204Pb could reflect the time-integrated κ (232Th/238U) in the components. The HIMU components for St. Helena and Austral Islands have κ values between 3.3 and 3.7, which are intermediate between the present-day fresh mid-ocean ridge basalts (MORB; 2.6-3.2) and the chondritic silicate Earth (~4). This is consistent with the model that the HIMU precursor is subducted oceanic crust created around 2Ga from depleted upper mantle, in which κ monotonously decreased from the chondritic to the present-day values since late Archean or early Proterozoic, because of enhanced U recycling from the Earth's surface back to the mantle in response to the increasing oxygen levels in the hydrosphere. Moreover, the fact that the HIMU components have much higher κ than the present-day hydrothermally altered MORB (0.2-2) suggests that either the HIMU precursor was an unaltered ancient oceanic crust, or more likely, an altered oceanic crust with minimal U enrichment by hydrothermal fluids in the less oxic marine environment of the late Archean or early Proterozoic. The unradiogenic 87Sr/86Sr of the HIMU components also suggests formation of ancient oceanic crust altered with hydrothermal fluids having much lower 87Sr/86Sr in that eon than at present, followed by removal of Rb from it by subduction dehydration.

元の言語英語
ページ(範囲)232-252
ページ数21
ジャーナルGeochimica et Cosmochimica Acta
143
DOI
出版物ステータス出版済み - 10 5 2014
外部発表Yes

Fingerprint

Isotopes
oceanic crust
Recycling
recycling
isotope
mantle
mid-ocean ridge basalt
Hydrosphere
Earth (planet)
Silicates
hydrothermal fluid
Fluids
Archean
Proterozoic
Chemical analysis
Dehydration
isotopic composition
subduction
Rocks
hydrosphere

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

これを引用

Isotope evolution in the HIMU reservoir beneath St. Helena : Implications for the mantle recycling of U and Th. / Hanyu, Takeshi; Kawabata, Hiroshi; Tatsumi, Yoshiyuki; Kimura, Jun Ichi; Hyodo, Hironobu; Sato, Keiko; Miyazaki, Takashi; Chang, Qing; Hirahara, Yuka; Takahashi, Toshiro; Senda, Ryoko; Nakai, Shun'ichi.

:: Geochimica et Cosmochimica Acta, 巻 143, 05.10.2014, p. 232-252.

研究成果: ジャーナルへの寄稿記事

Hanyu, T, Kawabata, H, Tatsumi, Y, Kimura, JI, Hyodo, H, Sato, K, Miyazaki, T, Chang, Q, Hirahara, Y, Takahashi, T, Senda, R & Nakai, S 2014, 'Isotope evolution in the HIMU reservoir beneath St. Helena: Implications for the mantle recycling of U and Th', Geochimica et Cosmochimica Acta, 巻. 143, pp. 232-252. https://doi.org/10.1016/j.gca.2014.03.016
Hanyu, Takeshi ; Kawabata, Hiroshi ; Tatsumi, Yoshiyuki ; Kimura, Jun Ichi ; Hyodo, Hironobu ; Sato, Keiko ; Miyazaki, Takashi ; Chang, Qing ; Hirahara, Yuka ; Takahashi, Toshiro ; Senda, Ryoko ; Nakai, Shun'ichi. / Isotope evolution in the HIMU reservoir beneath St. Helena : Implications for the mantle recycling of U and Th. :: Geochimica et Cosmochimica Acta. 2014 ; 巻 143. pp. 232-252.
@article{1c84465bbbd64bf49006f542249e0727,
title = "Isotope evolution in the HIMU reservoir beneath St. Helena: Implications for the mantle recycling of U and Th",
abstract = "HIMU (high-μ 238U/204Pb) is a mantle reservoir that has been thought to form by subduction and subsequent storage of ancient oceanic crust and lithosphere in the mantle. In order to constrain the processes that acted on subducted materials over several billion years, we present precise Pb-Sr-Nd-Hf-He isotopic data together with 40Ar/39Ar and K/Ar ages of HIMU lavas from St. Helena in the Atlantic. Clinopyroxene separates were analyzed together with whole-rock samples to better describe the geochemical characteristics of the HIMU component. Although isotopic variations are small in the St. Helena lavas (20.6-21.0 for 206Pb/204Pb) between 12 and 8Ma, the younger lavas have more HIMU-like isotopic compositions than the older lavas. The mixing arrays defined by these lavas are remarkably similar to those observed in HIMU lavas from Austral Islands in the Pacific, suggesting that the two HIMU reservoirs located in different mantle domains are characterized by similar isotopic compositions with radiogenic 206Pb/204Pb and 208Pb/204Pb, enriched Nd and Hf isotopes, depleted Sr isotopes, and radiogenic 3He/4He. However, there is a significant difference between the St. Helena and Austral Islands lavas in 207Pb/204Pb. The St. Helena lavas show systematically higher 207Pb/204Pb for a given 206Pb/204Pb. Lead isotope evolution models suggest that both HIMU reservoirs formed around 2Ga; however, the HIMU reservoir for St. Helena is about 0.3Ga older than that for Austral Islands. The relation between 206Pb/204Pb and 208Pb/204Pb could reflect the time-integrated κ (232Th/238U) in the components. The HIMU components for St. Helena and Austral Islands have κ values between 3.3 and 3.7, which are intermediate between the present-day fresh mid-ocean ridge basalts (MORB; 2.6-3.2) and the chondritic silicate Earth (~4). This is consistent with the model that the HIMU precursor is subducted oceanic crust created around 2Ga from depleted upper mantle, in which κ monotonously decreased from the chondritic to the present-day values since late Archean or early Proterozoic, because of enhanced U recycling from the Earth's surface back to the mantle in response to the increasing oxygen levels in the hydrosphere. Moreover, the fact that the HIMU components have much higher κ than the present-day hydrothermally altered MORB (0.2-2) suggests that either the HIMU precursor was an unaltered ancient oceanic crust, or more likely, an altered oceanic crust with minimal U enrichment by hydrothermal fluids in the less oxic marine environment of the late Archean or early Proterozoic. The unradiogenic 87Sr/86Sr of the HIMU components also suggests formation of ancient oceanic crust altered with hydrothermal fluids having much lower 87Sr/86Sr in that eon than at present, followed by removal of Rb from it by subduction dehydration.",
author = "Takeshi Hanyu and Hiroshi Kawabata and Yoshiyuki Tatsumi and Kimura, {Jun Ichi} and Hironobu Hyodo and Keiko Sato and Takashi Miyazaki and Qing Chang and Yuka Hirahara and Toshiro Takahashi and Ryoko Senda and Shun'ichi Nakai",
year = "2014",
month = "10",
day = "5",
doi = "10.1016/j.gca.2014.03.016",
language = "English",
volume = "143",
pages = "232--252",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",

}

TY - JOUR

T1 - Isotope evolution in the HIMU reservoir beneath St. Helena

T2 - Implications for the mantle recycling of U and Th

AU - Hanyu, Takeshi

AU - Kawabata, Hiroshi

AU - Tatsumi, Yoshiyuki

AU - Kimura, Jun Ichi

AU - Hyodo, Hironobu

AU - Sato, Keiko

AU - Miyazaki, Takashi

AU - Chang, Qing

AU - Hirahara, Yuka

AU - Takahashi, Toshiro

AU - Senda, Ryoko

AU - Nakai, Shun'ichi

PY - 2014/10/5

Y1 - 2014/10/5

N2 - HIMU (high-μ 238U/204Pb) is a mantle reservoir that has been thought to form by subduction and subsequent storage of ancient oceanic crust and lithosphere in the mantle. In order to constrain the processes that acted on subducted materials over several billion years, we present precise Pb-Sr-Nd-Hf-He isotopic data together with 40Ar/39Ar and K/Ar ages of HIMU lavas from St. Helena in the Atlantic. Clinopyroxene separates were analyzed together with whole-rock samples to better describe the geochemical characteristics of the HIMU component. Although isotopic variations are small in the St. Helena lavas (20.6-21.0 for 206Pb/204Pb) between 12 and 8Ma, the younger lavas have more HIMU-like isotopic compositions than the older lavas. The mixing arrays defined by these lavas are remarkably similar to those observed in HIMU lavas from Austral Islands in the Pacific, suggesting that the two HIMU reservoirs located in different mantle domains are characterized by similar isotopic compositions with radiogenic 206Pb/204Pb and 208Pb/204Pb, enriched Nd and Hf isotopes, depleted Sr isotopes, and radiogenic 3He/4He. However, there is a significant difference between the St. Helena and Austral Islands lavas in 207Pb/204Pb. The St. Helena lavas show systematically higher 207Pb/204Pb for a given 206Pb/204Pb. Lead isotope evolution models suggest that both HIMU reservoirs formed around 2Ga; however, the HIMU reservoir for St. Helena is about 0.3Ga older than that for Austral Islands. The relation between 206Pb/204Pb and 208Pb/204Pb could reflect the time-integrated κ (232Th/238U) in the components. The HIMU components for St. Helena and Austral Islands have κ values between 3.3 and 3.7, which are intermediate between the present-day fresh mid-ocean ridge basalts (MORB; 2.6-3.2) and the chondritic silicate Earth (~4). This is consistent with the model that the HIMU precursor is subducted oceanic crust created around 2Ga from depleted upper mantle, in which κ monotonously decreased from the chondritic to the present-day values since late Archean or early Proterozoic, because of enhanced U recycling from the Earth's surface back to the mantle in response to the increasing oxygen levels in the hydrosphere. Moreover, the fact that the HIMU components have much higher κ than the present-day hydrothermally altered MORB (0.2-2) suggests that either the HIMU precursor was an unaltered ancient oceanic crust, or more likely, an altered oceanic crust with minimal U enrichment by hydrothermal fluids in the less oxic marine environment of the late Archean or early Proterozoic. The unradiogenic 87Sr/86Sr of the HIMU components also suggests formation of ancient oceanic crust altered with hydrothermal fluids having much lower 87Sr/86Sr in that eon than at present, followed by removal of Rb from it by subduction dehydration.

AB - HIMU (high-μ 238U/204Pb) is a mantle reservoir that has been thought to form by subduction and subsequent storage of ancient oceanic crust and lithosphere in the mantle. In order to constrain the processes that acted on subducted materials over several billion years, we present precise Pb-Sr-Nd-Hf-He isotopic data together with 40Ar/39Ar and K/Ar ages of HIMU lavas from St. Helena in the Atlantic. Clinopyroxene separates were analyzed together with whole-rock samples to better describe the geochemical characteristics of the HIMU component. Although isotopic variations are small in the St. Helena lavas (20.6-21.0 for 206Pb/204Pb) between 12 and 8Ma, the younger lavas have more HIMU-like isotopic compositions than the older lavas. The mixing arrays defined by these lavas are remarkably similar to those observed in HIMU lavas from Austral Islands in the Pacific, suggesting that the two HIMU reservoirs located in different mantle domains are characterized by similar isotopic compositions with radiogenic 206Pb/204Pb and 208Pb/204Pb, enriched Nd and Hf isotopes, depleted Sr isotopes, and radiogenic 3He/4He. However, there is a significant difference between the St. Helena and Austral Islands lavas in 207Pb/204Pb. The St. Helena lavas show systematically higher 207Pb/204Pb for a given 206Pb/204Pb. Lead isotope evolution models suggest that both HIMU reservoirs formed around 2Ga; however, the HIMU reservoir for St. Helena is about 0.3Ga older than that for Austral Islands. The relation between 206Pb/204Pb and 208Pb/204Pb could reflect the time-integrated κ (232Th/238U) in the components. The HIMU components for St. Helena and Austral Islands have κ values between 3.3 and 3.7, which are intermediate between the present-day fresh mid-ocean ridge basalts (MORB; 2.6-3.2) and the chondritic silicate Earth (~4). This is consistent with the model that the HIMU precursor is subducted oceanic crust created around 2Ga from depleted upper mantle, in which κ monotonously decreased from the chondritic to the present-day values since late Archean or early Proterozoic, because of enhanced U recycling from the Earth's surface back to the mantle in response to the increasing oxygen levels in the hydrosphere. Moreover, the fact that the HIMU components have much higher κ than the present-day hydrothermally altered MORB (0.2-2) suggests that either the HIMU precursor was an unaltered ancient oceanic crust, or more likely, an altered oceanic crust with minimal U enrichment by hydrothermal fluids in the less oxic marine environment of the late Archean or early Proterozoic. The unradiogenic 87Sr/86Sr of the HIMU components also suggests formation of ancient oceanic crust altered with hydrothermal fluids having much lower 87Sr/86Sr in that eon than at present, followed by removal of Rb from it by subduction dehydration.

UR - http://www.scopus.com/inward/record.url?scp=84908461211&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84908461211&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2014.03.016

DO - 10.1016/j.gca.2014.03.016

M3 - Article

AN - SCOPUS:84908461211

VL - 143

SP - 232

EP - 252

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

ER -