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Zircon halogen geochemistry: Insights into Hadean-Archean fluids

H. Tang1,

1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles CA, 90095 USA

D. Trail1,2,

1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles CA, 90095 USA
2Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, 14618 USA

E.A. Bell1,

1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles CA, 90095 USA

T.M. Harrison1

1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles CA, 90095 USA

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Tang, H., Trail, D., Bell, E.A., Harrison, T.M. (2019) Zircon halogen geochemistry: Insights into Hadean-Archean fluids. Geochem. Persp. Let. 9, 49–53.

Instrumentation and Facilities Program, Division of Earth Sciences, NSF (1339051).

Geochemical Perspectives Letters v9  |  doi: 10.7185/geochemlet.1905
Received 21 September 2018  |  Accepted 20 January 2019  |  Published 19 February 2019
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0




Figure 1 Fluorine concentrations in Jack Hills zircons ([F]average = 2.28 ± 0.19 μg/g) are generally indistinguishable from those in young granitic zircons ([F]average = 1.80 ± 0.11 μg/g). Elevated Cl concentrations observed in eight 3.9–3.8 Ga zircons (black columns) yield distinctly high Cl/F ratios (Cl/F > 0.3) when compared with other Jack Hills zircons.
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Figure 2 High values of (Sm/La)N and LREE-I [(Dy/Nd) + (Dy/Sm)] in Jack Hills sample grains imply that most of samples, especially Cl-rich zircons, are primary. The elevated Cl concentrations in zircons therefore derived from primary sources.
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Figure 3 (a) Chlorine distribution and (b) Cl/F fractionation in Jack Hills zircons are mainly identical to the ranges determined from modern magmatic zircons in this study (red circles: <3.8 Ga zircons; white diamonds: 3.9–3.8 Ga Group I zircons; blue rectangles: >3.9 Ga zircons; grey bar: modern zircon ranges) except Group II zircons crystallised at 3.9–3.8 Ga (black diamonds). A synthetic zircon grown in an aqueous-rich fluid exhibits Cl content and Cl/F ratios (blue bars) that fall within the range of Group II.
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Figure 4 Chlorine-rich Group II zircons are characterised by Ti-in-zircon temperatures below granite solidus. The clearly distinguished cluster of Group II from other magmatic zircons suggests the mechanism of Group II as solid state recrystallisation involving Cl-bearing fluids.
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