The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada
Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at m...
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Online Access: | https://era.library.ualberta.ca/items/2451c062-108f-4535-9e49-41827c93cd96 https://doi.org/10.7939/R31Z4262T |
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ftunivalberta:oai:era.library.ualberta.ca:2451c062-108f-4535-9e49-41827c93cd96 2023-05-15T17:46:46+02:00 The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada Luth, R. W. Stone, Rebecca Menzies, Andrew Bussweiler, Yannick Pearson, Graham Stachel, Thomas Kjarsgaard, B. A. 2016/07 https://era.library.ualberta.ca/items/2451c062-108f-4535-9e49-41827c93cd96 https://doi.org/10.7939/R31Z4262T English eng https://era.library.ualberta.ca/items/2451c062-108f-4535-9e49-41827c93cd96 doi:10.7939/R31Z4262T © Springer-Verlag Berlin Heidelberg 2016 Kimberlite Polymineralic inclusions Cr-rich megacrysts Kimberlite evolution Decarbonation reaction Melt inclusions Article (Published) 2016 ftunivalberta https://doi.org/10.7939/R31Z4262T 2022-08-22T20:09:39Z Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside → forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of ... Other/Unknown Material Northwest Territories University of Alberta: Era - Education and Research Archive Canada Lac de Gras ENVELOPE(-110.501,-110.501,64.500,64.500) Northwest Territories |
institution |
Open Polar |
collection |
University of Alberta: Era - Education and Research Archive |
op_collection_id |
ftunivalberta |
language |
English |
topic |
Kimberlite Polymineralic inclusions Cr-rich megacrysts Kimberlite evolution Decarbonation reaction Melt inclusions |
spellingShingle |
Kimberlite Polymineralic inclusions Cr-rich megacrysts Kimberlite evolution Decarbonation reaction Melt inclusions Luth, R. W. Stone, Rebecca Menzies, Andrew Bussweiler, Yannick Pearson, Graham Stachel, Thomas Kjarsgaard, B. A. The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
topic_facet |
Kimberlite Polymineralic inclusions Cr-rich megacrysts Kimberlite evolution Decarbonation reaction Melt inclusions |
description |
Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside → forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of ... |
format |
Other/Unknown Material |
author |
Luth, R. W. Stone, Rebecca Menzies, Andrew Bussweiler, Yannick Pearson, Graham Stachel, Thomas Kjarsgaard, B. A. |
author_facet |
Luth, R. W. Stone, Rebecca Menzies, Andrew Bussweiler, Yannick Pearson, Graham Stachel, Thomas Kjarsgaard, B. A. |
author_sort |
Luth, R. W. |
title |
The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
title_short |
The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
title_full |
The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
title_fullStr |
The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
title_full_unstemmed |
The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada |
title_sort |
evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from lac de gras kimberlites, canada |
publishDate |
2016 |
url |
https://era.library.ualberta.ca/items/2451c062-108f-4535-9e49-41827c93cd96 https://doi.org/10.7939/R31Z4262T |
long_lat |
ENVELOPE(-110.501,-110.501,64.500,64.500) |
geographic |
Canada Lac de Gras Northwest Territories |
geographic_facet |
Canada Lac de Gras Northwest Territories |
genre |
Northwest Territories |
genre_facet |
Northwest Territories |
op_relation |
https://era.library.ualberta.ca/items/2451c062-108f-4535-9e49-41827c93cd96 doi:10.7939/R31Z4262T |
op_rights |
© Springer-Verlag Berlin Heidelberg 2016 |
op_doi |
https://doi.org/10.7939/R31Z4262T |
_version_ |
1766150614266413056 |