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Olivine diversity in the Leslie kimberlite, NT, Canada : implications for transport and emplacement processes Landoni, Katherine
Abstract
Olivine crystals are ubiquitous in kimberlites and record petrologic events through all stages of ascent and eruption. Well-preserved olivine from the Leslie kimberlite, NT, Canada elucidates the sequence of events attending kimberlite emplacement. The Leslie kimberlite mainly hosts a single phase of extrusive coherent kimberlite. We used spatially distributed samples (n = 76) from drill core to develop a 3D representation of the Leslie kimberlite. Petrographic investigation defined four distinct olivine populations: phenocrysts, macrocrysts, dunite “nodules”, and mantle xenolith-hosted olivine. SEM imagery, and major and trace element geochemistry were used to characterize and quantify chemical zonation including xenocrystic cores, mid-zones, magmatically crystallized rims, high-Mg rinds, and/or monticellite coronas. Core compositions (Fo85.7 to Fo93.8, NiO ~0.36 wt%) and other textural evidence show that cores are mantle-derived olivine xenocrysts. Mid-zones developed on cores show a sharp decrease in Fo content (~Fo90.9) across irregular, convoluted, and embayed contacts indicating disequilibrium and partial dissolution of the olivine xenocrysts combined with diffusion-driven replacement. Magmatically crystallized olivine rims can jacket xenocrystic cores and mid-zones. Rims have uniform and distinctive chemical compositions of ~Fo91.8 ± 0.7 (2σ) and NiO concentrations that decrease (~0.4 wt% to ~0.1 wt%) outward. Rinds, thin outer fringes, have a convoluted inner contact and a sawtooth contact with the groundmass. Rind compositions have high ~Fo97.1, low NiO, and elevated Mn and Ca. Rind textural relationships and compositions suggest a non-magmatic, post-emplacement origin. The four olivine populations and chemical zonation (only cores, mid-zones, and rims) are uniformly and consistently distributed throughout the Leslie kimberlite. Thus, olivine within a single phase of kimberlite predominantly records pre-emplacement processes and illustrates that magma batches become well mixed during ascent and emplacement. In contrast, both late-stage high-Mg rinds and monticellite coronas are non-uniformly distributed throughout the pipe. Utilizing olivine geochemistry, coupled with petrographic observations, we reconstruct a sequence of events of the Leslie kimberlite ascent and eruption. Our results indicate olivine entrainment and ascent (within a single kimberlite phase) may be sufficiently characterized by a few samples. Conversely, syn- and post-emplacement processes recorded by olivine require systematic sampling to capture all potential heterogeneities within a given kimberlite phase.
Item Metadata
Title |
Olivine diversity in the Leslie kimberlite, NT, Canada : implications for transport and emplacement processes
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Creator | |
Supervisor | |
Publisher |
University of British Columbia
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Date Issued |
2022
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Description |
Olivine crystals are ubiquitous in kimberlites and record petrologic events through all stages of ascent and eruption. Well-preserved olivine from the Leslie kimberlite, NT, Canada elucidates the sequence of events attending kimberlite emplacement. The Leslie kimberlite mainly hosts a single phase of extrusive coherent kimberlite. We used spatially distributed samples (n = 76) from drill core to develop a 3D representation of the Leslie kimberlite. Petrographic investigation defined four distinct olivine populations: phenocrysts, macrocrysts, dunite “nodules”, and mantle xenolith-hosted olivine. SEM imagery, and major and trace element geochemistry were used to characterize and quantify chemical zonation including xenocrystic cores, mid-zones, magmatically crystallized rims, high-Mg rinds, and/or monticellite coronas. Core compositions (Fo85.7 to Fo93.8, NiO ~0.36 wt%) and other textural evidence show that cores are mantle-derived olivine xenocrysts. Mid-zones developed on cores show a sharp decrease in Fo content (~Fo90.9) across irregular, convoluted, and embayed contacts indicating disequilibrium and partial dissolution of the olivine xenocrysts combined with diffusion-driven replacement. Magmatically crystallized olivine rims can jacket xenocrystic cores and mid-zones. Rims have uniform and distinctive chemical compositions of ~Fo91.8 ± 0.7 (2σ) and NiO concentrations that decrease (~0.4 wt% to ~0.1 wt%) outward. Rinds, thin outer fringes, have a convoluted inner contact and a sawtooth contact with the groundmass. Rind compositions have high ~Fo97.1, low NiO, and elevated Mn and Ca. Rind textural relationships and compositions suggest a non-magmatic, post-emplacement origin.
The four olivine populations and chemical zonation (only cores, mid-zones, and rims) are uniformly and consistently distributed throughout the Leslie kimberlite. Thus, olivine within a single phase of kimberlite predominantly records pre-emplacement processes and illustrates that magma batches become well mixed during ascent and emplacement. In contrast, both late-stage high-Mg rinds and monticellite coronas are non-uniformly distributed throughout the pipe. Utilizing olivine geochemistry, coupled with petrographic observations, we reconstruct a sequence of events of the Leslie kimberlite ascent and eruption. Our results indicate olivine entrainment and ascent (within a single kimberlite phase) may be sufficiently characterized by a few samples. Conversely, syn- and post-emplacement processes recorded by olivine require systematic sampling to capture all potential heterogeneities within a given kimberlite phase.
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Genre | |
Type | |
Language |
eng
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Date Available |
2022-04-14
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0412869
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2022-05
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Attribution-NonCommercial-NoDerivatives 4.0 International