Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada
Abstract In the Lac de Gras (LDG) kimberlite field, Northwest Territories, Canada, coherent kimberlites (CKs) occur as tabular dykes, pipe-shaped diatremes, and irregular bodies without well-defined geometries. Combining the morphology of CK bodies with the occurrence of fragmented olivine microcrys...
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Oxford University Press (OUP)
2022
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Online Access: | http://dx.doi.org/10.1093/petrology/egac028 https://academic.oup.com/petrology/advance-article-pdf/doi/10.1093/petrology/egac028/43026317/egac028.pdf https://academic.oup.com/petrology/article-pdf/63/4/egac028/44057924/egac028.pdf |
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croxfordunivpr:10.1093/petrology/egac028 2023-11-05T03:44:21+01:00 Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada Tovey, Madeline Giuliani, Andrea Phillips, David Nowicki, Tom Pearson, D Graham Fedortchouk, Yana Russell, James K 2022 http://dx.doi.org/10.1093/petrology/egac028 https://academic.oup.com/petrology/advance-article-pdf/doi/10.1093/petrology/egac028/43026317/egac028.pdf https://academic.oup.com/petrology/article-pdf/63/4/egac028/44057924/egac028.pdf en eng Oxford University Press (OUP) http://creativecommons.org/licenses/by/4.0/ Journal of Petrology volume 63, issue 4 ISSN 0022-3530 1460-2415 Geochemistry and Petrology Geophysics journal-article 2022 croxfordunivpr https://doi.org/10.1093/petrology/egac028 2023-10-06T10:37:30Z Abstract In the Lac de Gras (LDG) kimberlite field, Northwest Territories, Canada, coherent kimberlites (CKs) occur as tabular dykes, pipe-shaped diatremes, and irregular bodies without well-defined geometries. Combining the morphology of CK bodies with the occurrence of fragmented olivine microcrysts allows distinction of four CK types at LDG: (1) dykes with no broken olivine; (2) CK without well-defined but probable sheet geometry and no broken olivine; (3) pipe-filling CK (pfCK) with abundant broken olivine and (4) pfCK with no broken olivine. These features suggest an intrusive origin for type 1 and, probably, type 2 CK; a high-energy extrusive emplacement for CK type 3 and a low-energy intrusive or extrusive emplacement for the CK type 4. Here, we compare petrographic and whole-rock, olivine and spinel compositional data for high-energy extrusive pfCK, low-energy pfCK and intrusive CK units to understand the factors controlling their variable emplacement styles. Extrusive CK contain more abundant groundmass phlogopite and monticellite, lower carbonate/silicate mineral abundance ratios and significantly lower dolomite and pleonaste-spinel abundances compared to intrusive CK. This indicates greater CO2 loss and higher H2O/CO2 in the melt phase for the extrusive CK during emplacement. Lower incompatible element concentrations in the extrusive CKs and different chromite Ti# and olivine rim Mg# indicate derivation from distinct primitive melt compositions. The extrusive CK feature higher ɛNdi and marginally higher ɛHfi compositions than the intrusive CK, pointing to derivation from distinct sources. These findings strongly imply that distinct primary melt compositions were largely responsible for the differences in emplacement styles of CK at LDG. Low-energy pfCKs have similar olivine rim Mg#, chromite Ti# and, hence, primitive melt compositions to the high-energy extrusive CK samples. Their marginally different emplacement styles may depend on local factors, such as changing stress regimes, or slightly ... Article in Journal/Newspaper Northwest Territories Oxford University Press (via Crossref) Journal of Petrology 63 4 |
institution |
Open Polar |
collection |
Oxford University Press (via Crossref) |
op_collection_id |
croxfordunivpr |
language |
English |
topic |
Geochemistry and Petrology Geophysics |
spellingShingle |
Geochemistry and Petrology Geophysics Tovey, Madeline Giuliani, Andrea Phillips, David Nowicki, Tom Pearson, D Graham Fedortchouk, Yana Russell, James K Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
topic_facet |
Geochemistry and Petrology Geophysics |
description |
Abstract In the Lac de Gras (LDG) kimberlite field, Northwest Territories, Canada, coherent kimberlites (CKs) occur as tabular dykes, pipe-shaped diatremes, and irregular bodies without well-defined geometries. Combining the morphology of CK bodies with the occurrence of fragmented olivine microcrysts allows distinction of four CK types at LDG: (1) dykes with no broken olivine; (2) CK without well-defined but probable sheet geometry and no broken olivine; (3) pipe-filling CK (pfCK) with abundant broken olivine and (4) pfCK with no broken olivine. These features suggest an intrusive origin for type 1 and, probably, type 2 CK; a high-energy extrusive emplacement for CK type 3 and a low-energy intrusive or extrusive emplacement for the CK type 4. Here, we compare petrographic and whole-rock, olivine and spinel compositional data for high-energy extrusive pfCK, low-energy pfCK and intrusive CK units to understand the factors controlling their variable emplacement styles. Extrusive CK contain more abundant groundmass phlogopite and monticellite, lower carbonate/silicate mineral abundance ratios and significantly lower dolomite and pleonaste-spinel abundances compared to intrusive CK. This indicates greater CO2 loss and higher H2O/CO2 in the melt phase for the extrusive CK during emplacement. Lower incompatible element concentrations in the extrusive CKs and different chromite Ti# and olivine rim Mg# indicate derivation from distinct primitive melt compositions. The extrusive CK feature higher ɛNdi and marginally higher ɛHfi compositions than the intrusive CK, pointing to derivation from distinct sources. These findings strongly imply that distinct primary melt compositions were largely responsible for the differences in emplacement styles of CK at LDG. Low-energy pfCKs have similar olivine rim Mg#, chromite Ti# and, hence, primitive melt compositions to the high-energy extrusive CK samples. Their marginally different emplacement styles may depend on local factors, such as changing stress regimes, or slightly ... |
format |
Article in Journal/Newspaper |
author |
Tovey, Madeline Giuliani, Andrea Phillips, David Nowicki, Tom Pearson, D Graham Fedortchouk, Yana Russell, James K |
author_facet |
Tovey, Madeline Giuliani, Andrea Phillips, David Nowicki, Tom Pearson, D Graham Fedortchouk, Yana Russell, James K |
author_sort |
Tovey, Madeline |
title |
Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
title_short |
Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
title_full |
Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
title_fullStr |
Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
title_full_unstemmed |
Controls on the Emplacement Style of Coherent Kimberlites in the Lac de Gras Field, Canada |
title_sort |
controls on the emplacement style of coherent kimberlites in the lac de gras field, canada |
publisher |
Oxford University Press (OUP) |
publishDate |
2022 |
url |
http://dx.doi.org/10.1093/petrology/egac028 https://academic.oup.com/petrology/advance-article-pdf/doi/10.1093/petrology/egac028/43026317/egac028.pdf https://academic.oup.com/petrology/article-pdf/63/4/egac028/44057924/egac028.pdf |
genre |
Northwest Territories |
genre_facet |
Northwest Territories |
op_source |
Journal of Petrology volume 63, issue 4 ISSN 0022-3530 1460-2415 |
op_rights |
http://creativecommons.org/licenses/by/4.0/ |
op_doi |
https://doi.org/10.1093/petrology/egac028 |
container_title |
Journal of Petrology |
container_volume |
63 |
container_issue |
4 |
_version_ |
1781704029913481216 |