Equilibrium boron isotope fractionation during serpentinization and applications in understanding subduction zone processes
Equilibrium boron isotope fractionation during serpentinization and applications in understanding subduction zone processes
Serpentinites entering subduction zones show selective enrichment in trace elements and are the most important carriers of B in this setting. The evolving B isotopic composition (δ
11B) of serpentinite is used in studying water-mediated interactions between mantle and crust in subduction zones, but we lack a full understanding of the processes controlling B isotope fractionation during serpentinization that would allow this tracer to be better utilized. Boron isotope fractionation between lizardite/forsterite/diopside and aqueous fluids is investigated using quantum mechanics (density functional theory, DFT) and the first-principles molecular dynamics simulation (FPMD) here. The
11B enrichment sequence in minerals follows the order of forsterite > clinopyroxene (diopside) > white mica > phlogopite > lizardite. On the basis of boron configurations in aqueous fluid acquired from FPMD simulations based on DFT, the reduced isotopic partition function ratio (β-factor) of aqueous B(OH)
3 and B(OH)
4
− are 1000lnβ
B(OH)3 = −20.1 + 37.07(1000/T) + 8.2(1000/T)
2 and 1000lnβ
B(OH)4- = −13.94 + 24.43(1000/T) + 9.12(1000/T)
2 at the P-T range of 0–500 MPa and 298–1000 K. This theoretical approach gives an equilibrium B isotope fractionation of Δ
11B
lizardite-fluid = 15.89–22.88(1000/T) - 0.19(1000/T)
2 between lizardite and neutral serpentinization fluid in the temperature range from 298 to 673 K. By contrast, the boron isotope fractionation between minerals formed as the slab descends (e.g., forsterite, diopside) and fluid released from subducted crustal lithologies is limited, indicating that secondary olivine minerals may inherit the δ
11B signatures of the dehydrated serpentinites. This study provides new insights into how B isotopes can constrain boron sources and pathways in subduction zones, and trace phases recycled into the deep mantle and their later recycling in ocean island basalts.
Boron isotope, Density functional theory, Equilibrium isotope fractionation, Serpentinization, Subduction zone processes
Li, Yin-chuan
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Wei, Hai-zhen
60e6342b-b6d2-4ac6-a4d5-a1dec963b1a7
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Ma, Jing
3495e3ca-6f13-42ae-8b6a-7d8d4e3166fe
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Chen, Yi-xiang
4e4ef040-bf74-482f-87fc-e8c40a90ac5b
Lu, Jian-jun
a5102598-bc25-4892-b6c4-7ac803412055
Liu, Xi
9589a507-97cc-4672-845c-134499274338
20 October 2022
Li, Yin-chuan
5f9307cf-80a5-4ac8-a6bb-bd678b5206fe
Wei, Hai-zhen
60e6342b-b6d2-4ac6-a4d5-a1dec963b1a7
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Ma, Jing
3495e3ca-6f13-42ae-8b6a-7d8d4e3166fe
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Chen, Yi-xiang
4e4ef040-bf74-482f-87fc-e8c40a90ac5b
Lu, Jian-jun
a5102598-bc25-4892-b6c4-7ac803412055
Liu, Xi
9589a507-97cc-4672-845c-134499274338
Li, Yin-chuan, Wei, Hai-zhen, Palmer, Martin R., Ma, Jing, Jiang, Shao-yong, Chen, Yi-xiang, Lu, Jian-jun and Liu, Xi
(2022)
Equilibrium boron isotope fractionation during serpentinization and applications in understanding subduction zone processes.
Chemical Geology, 609, [121047].
(doi:10.1016/j.chemgeo.2022.121047).
Abstract
Serpentinites entering subduction zones show selective enrichment in trace elements and are the most important carriers of B in this setting. The evolving B isotopic composition (δ
11B) of serpentinite is used in studying water-mediated interactions between mantle and crust in subduction zones, but we lack a full understanding of the processes controlling B isotope fractionation during serpentinization that would allow this tracer to be better utilized. Boron isotope fractionation between lizardite/forsterite/diopside and aqueous fluids is investigated using quantum mechanics (density functional theory, DFT) and the first-principles molecular dynamics simulation (FPMD) here. The
11B enrichment sequence in minerals follows the order of forsterite > clinopyroxene (diopside) > white mica > phlogopite > lizardite. On the basis of boron configurations in aqueous fluid acquired from FPMD simulations based on DFT, the reduced isotopic partition function ratio (β-factor) of aqueous B(OH)
3 and B(OH)
4
− are 1000lnβ
B(OH)3 = −20.1 + 37.07(1000/T) + 8.2(1000/T)
2 and 1000lnβ
B(OH)4- = −13.94 + 24.43(1000/T) + 9.12(1000/T)
2 at the P-T range of 0–500 MPa and 298–1000 K. This theoretical approach gives an equilibrium B isotope fractionation of Δ
11B
lizardite-fluid = 15.89–22.88(1000/T) - 0.19(1000/T)
2 between lizardite and neutral serpentinization fluid in the temperature range from 298 to 673 K. By contrast, the boron isotope fractionation between minerals formed as the slab descends (e.g., forsterite, diopside) and fluid released from subducted crustal lithologies is limited, indicating that secondary olivine minerals may inherit the δ
11B signatures of the dehydrated serpentinites. This study provides new insights into how B isotopes can constrain boron sources and pathways in subduction zones, and trace phases recycled into the deep mantle and their later recycling in ocean island basalts.
Text
Equilibrium boron isotope fractionation during serpentinization and applications in understanding subduction zone processes
More information
Accepted/In Press date: 2 August 2022
e-pub ahead of print date: 8 August 2022
Published date: 20 October 2022
Additional Information:
Funding Information:
This research was supported by the National Natural Science Foundations of China (Grant No. 41973005), the Research Funds for the Frontiers Science Center for Critical Earth Material Cycling, Nanjing University (Grant No. 2022300193). We are grateful to the High Performance Computing Center (HPCC) of Nanjing University for processing the numerical calculations in this paper using its blade cluster system. The authors thank Dr. Li Yonghui from National Supercomputing Center in Chengdu, China, and Dr. Gao Caihong from Institute of Geochemistry, Chinese Academy of Sciences for helpful comments on the manuscript. The authors are grateful to Marc Blanchard and two anonymous reviewers for their constructive and insightful comments that have improved the manuscript significantly. The careful editorial handling by Prof. Donald Porcelli is greatly appreciated.
Funding Information:
This research was supported by the National Natural Science Foundations of China (Grant No. 41973005), the Research Funds for the Frontiers Science Center for Critical Earth Material Cycling, Nanjing University (Grant No. 2022300193). We are grateful to the High Performance Computing Center (HPCC) of Nanjing University for processing the numerical calculations in this paper using its blade cluster system. The authors thank Dr. Li Yonghui from National Supercomputing Center in Chengdu, China, and Dr. Gao Caihong from Institute of Geochemistry, Chinese Academy of Sciences for helpful comments on the manuscript. The authors are grateful to Marc Blanchard and two anonymous reviewers for their constructive and insightful comments that have improved the manuscript significantly. The careful editorial handling by Prof. Donald Porcelli is greatly appreciated.
Publisher Copyright:
© 2022 Elsevier B.V.
Keywords:
Boron isotope, Density functional theory, Equilibrium isotope fractionation, Serpentinization, Subduction zone processes
Identifiers
Local EPrints ID: 470284
URI: http://eprints.soton.ac.uk/id/eprint/470284
ISSN: 0009-2541
PURE UUID: 804b8875-b894-440c-a076-3dab791060b2
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Date deposited: 05 Oct 2022 16:49
Last modified: 08 Aug 2024 04:01
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Contributors
Author:
Yin-chuan Li
Author:
Hai-zhen Wei
Author:
Jing Ma
Author:
Shao-yong Jiang
Author:
Yi-xiang Chen
Author:
Jian-jun Lu
Author:
Xi Liu
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