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Permanent link (DOI): https://doi.org/10.7939/R3C06J

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The origin and evolution of eclogite xenoliths and associated diamonds from the Jericho kimberlite, northern Slave craton, Canada: an integrated petrological, geochemical and isotopic study Open Access

Descriptions

Other title
Subject/Keyword
diamond
geochemistry
mantle petrology
eclogite xenolith
Slave craton
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Smart, Kathleen A
Supervisor and department
Chacko, Thomas (Earth and Atmospheric Sciences)
Examining committee member and department
Muehlenbachs, Karlis (Earth and Atmospheric Sciences)
Gu, Jeff (Physics)
Jacob, Dorrit (Mainz, Petrologie)
Stachel, Thomas (Earth and Atmospheric Sciences)
Pearson, Graham (Earth and Atmospheric Sciences)
Department
Department of Earth and Atmospheric Sciences
Specialization

Date accepted
2011-10-05T18:46:26Z
Graduation date
2011-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Diamond-bearing eclogite xenoliths are relatively rare but provide insight into the composition and evolution of the cratonic lithospheric mantle and also insight into the diamond formation process. The major-, trace-element and Sr-Pb-O-isotope compositions of both high- and low-MgO diamond eclogites from the Jericho kimberlite, Nunavut, Canada, indicate that each group had different geneses. Both eclogite groups formed as parts of ancient oceanic lithosphere; positive Sr anomalies and δ18O values of 6.5-6.6‰ of the low MgO eclogites indicate seawater-altered gabbroic protoliths, while the high Mg and Cr, fractionated HREEs, and δ18O values of 5.3-5.5‰ of the high-MgO eclogites indicate a mantle origin. High-MgO eclogite crystallization probably occurred at 2-3 GPa where mantle-derived melts are generally basaltic, as melts in the diamond stability field are far too Mg-rich. As such, eclogite crystallization likely occurred as pyroxenite veins at the underside of thick Archean oceanic lithosphere. Although there are no age constraints for the diamond eclogites, both groups could have been imbricated into the cratonic mantle by subduction stacking of lithosphere during putative Neoarchean or Paleoproterozoic subduction events in the Slave craton. The petrogenesis of the high-MgO eclogites is further complicated by diamond inclusions with lower Cr2O3 and Mg-numbers but higher CaO, Na2O and Al2O3; element exchange with surrounding peridotite after diamond formation altered the eclogite composition. Diamonds from each eclogite group have widely different carbon isotope compositions and nitrogen contents and thus the diamond forming fluids/melts were derived from disparate sources. Diamonds from the high-MgO eclogites have extremely low δ13C values of -40‰ which require derivation from subducted organic carbon; diamonds from the low-MgO eclogites have δ13C values from -4.75 to -3.5 and could have been sourced from either fractionated mantle-derived carbon or subducted carbonate sediments. The reducing nature of the deep CLM favors the latter carbon source. Detailed SIMS investigations of both diamond groups revealed coupled increases in δ13C and decreases in N in growth zones towards diamond rims. The coupled δ13C-N changes indicate diamond growth occurred from oxidized fluids or melts, where nitrogen behaved compatibly in diamond compared to the source fluid/melt.
Language
English
DOI
doi:10.7939/R3C06J
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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