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An oxygen isotope test for the origin of Archean mantle roots

M.E. Regier1,

1Canadian Centre for Isotopic Microanalysis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada

A. Mišković2,3,

2NWT Geological Survey, Yellowknife, NT, Canada
3GeoTarget Solutions Inc., Burnaby, BC, Canada

R.B. Ickert1,4,

1Canadian Centre for Isotopic Microanalysis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada
4Scottish Universities Environmental Research Centre, East Kilbride, Scotland

D.G. Pearson1,

1Canadian Centre for Isotopic Microanalysis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada

T. Stachel1,

1Canadian Centre for Isotopic Microanalysis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada

R.A. Stern1,

1Canadian Centre for Isotopic Microanalysis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton AB, Canada

M. Kopylova5

5Department of Earth, Ocean, and Atmospheric Sciences, Vancouver, BC, Canada

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Regier, M.E., Mišković, A., Ickert, R.B., Pearson, D.G., Stachel, T., Stern, R.A., Kopylova, M. (2018) An oxygen isotope test for the origin of Archean mantle roots. Geochem. Persp. Let. 9, 6–10.

Northwest Territories Geological Survey

Geochemical Perspectives Letters v9  |  doi: 10.7185/geochemlet.1830
Received 30 July 2018  |  Accepted 6 November 2018  |  Published 7 December 2018
Copyright © The Authors

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




Figure 1 Popular models of cratonic mantle formation. (a) Imbrication of MOR sequences to form a thick lithosphere. An estimated oxygen isotope profile through Neoarchean oceanic lithosphere is inset. (b) Depleted cratonic mantle protoliths produced at MOR and in sub-arc environments are compressed via pure shear into a thick lithospheric root.
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Figure 2 (a) Mg# histogram of olivines in this study. Mg#s are both more and less depleted than the worldwide average for olivine in cratonic peridotite, denoted by the dotted line (Pearson and Wittig, 2008

Pearson, D.G., Wittig, N. (2008) Formation of Archaean continental lithosphere and its diamonds: the root of the problem. Journal of the Geological Society 165, 895–914.

). (b) ΔMg/Si histogram of samples compared to a vertically unscaled probability density function for worldwide cratonic mantle xenoliths from Canil and Lee (2009)

Canil, D., Lee, C.-T.A. (2009) Were deep cratonic mantle roots hydrated in Archean oceans? Geology 37, 667–670.

. Negative ΔMg/Si designates Si-enriched lithologies.
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Figure 3 (a) Box-whisker plot of the oxygen isotopic composition of cratonic peridotites, calculated from olivine δ18O, compared to eclogitic xenoliths, serpentinised oceanic lithospheric mantle (OLM), and MORB glass (Supplementary Information). (b) A box-whisker plot of peridotite δ18O, divided into statistically insignificant chemical discriminators – Ca-rich (lherzolitic), Ca-poor (harzburgitic/dunitic) and Si-enriched (-ΔMg/Si) and depleted lithologies (+ΔMg/Si), demonstrates that there is no variation in the distribution of oxygen isotopes with bulk rock chemistry. (c) Scatter plot of olivine δ18O and Mg#. The lack of correlation in the cratonic mantle suite contrasts to the trendline of The Thumb xenoliths (r2 = 0.86).
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Figure 4 pMELTS modelling of slab melts (δ18O of +8 ‰) reacting with 900 ℃ (blue) and 1500 °C (red) harzburgite, as well as a water-fluxed harzburgitic (harz) melt (δ18O of +5.6 ‰) reacting with 1300 ℃ harzburgite (black). The major element and isotopic evolution of crystallising Opx (a) and olivine (c) is indicated by smoothed curves. Numbers indicate the slab melt/assimilated peridotite ratio. Typical cratonic mantle Opx and olivine (Ol) is outlined in gray fields. Relative Kernel estimations of the probability density function (pdf) for Opx (b) and olivine (d) δ18O are included.
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