Age, origin, and thermal evolution of the ultra-fresh ~1.9Ga Winnipegosis Komatiites, Manitoba, Canada
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Age, origin, and thermal evolution of the ultra-fresh ~1.9Ga Winnipegosis Komatiites, Manitoba, Canada. / Waterton, Pedro; Pearson, D. Graham; Kjarsgaard, Bruce; Hulbert, Larry; Locock, Andrew; Parman, Stephen; Davis, Bill.
I: Lithos, Bind 268-271, 2017, s. 114 - 130.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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T1 - Age, origin, and thermal evolution of the ultra-fresh ~1.9Ga Winnipegosis Komatiites, Manitoba, Canada
AU - Waterton, Pedro
AU - Pearson, D. Graham
AU - Kjarsgaard, Bruce
AU - Hulbert, Larry
AU - Locock, Andrew
AU - Parman, Stephen
AU - Davis, Bill
PY - 2017
Y1 - 2017
N2 - The Proterozoic spans the longest portion of earth's history, yet in contrast to the Archaean, the record of komatiites and related high MgO igneous rocks from this Eon is sparse. This paper describes the pristine Palaeoproterozoic Winnipegosis Komatiites, from Manitoba, Canada, which form part of the Circum-Superior Belt large igneous province. We present a comprehensive petrographical investigation, mineral and bulk rock geochemistry, and Al-in-olivine thermometry for the Winnipegosis Komatiites, along with new U-Pb SHRIMP dating of zircons from a mafic unit, which yield an age of 1870.3±7.1Ma for the Winnipegosis Komatiite Belt. The komatiites are Al-undepleted and dominated by massive olivine porphyritic flows with a median thickness of 6m. Differentiated flows containing layers of olivine spinifex are present, but rare. Trace element data indicate the komatiites were derived from depleted mantle, and subsequently contaminated with 2–3% continental crust. Temperatures from Al-in-olivine thermometry are consistent with a nominally dry melt, and combined with olivine-melt Mg–Fe partitioning, suggest a parental melt with ~24wt% MgO and a liquidus (olivine) temperature of ~1501°C, approximately 100°C cooler than their hottest Archaean counterparts. At ~1424°C chromite joined olivine as a crystallising phase. Olivine and chromite phenocrysts were re-mixed with residual melt shortly before or during komatiite eruption, which occurred by the time the magma had cooled to ~1321°C. Combined geochemical and geological evidence requires that the Winnipegosis Komatiites erupted onto rifting continental crust. Their high liquidus temperatures require anomalously hot mantle. Considering the Winnipegosis Komatiites in the context of the broader Circum-Superior Belt, we suggest that these magmas formed from a mantle plume that was deflected towards the margins of the Superior craton by strong gradients in lithospheric thickness. This interpretation of the mode of formation of the Circum-Superior Belt casts doubt on ambient mantle potential temperatures as high as 1600°C during the Proterozoic.
AB - The Proterozoic spans the longest portion of earth's history, yet in contrast to the Archaean, the record of komatiites and related high MgO igneous rocks from this Eon is sparse. This paper describes the pristine Palaeoproterozoic Winnipegosis Komatiites, from Manitoba, Canada, which form part of the Circum-Superior Belt large igneous province. We present a comprehensive petrographical investigation, mineral and bulk rock geochemistry, and Al-in-olivine thermometry for the Winnipegosis Komatiites, along with new U-Pb SHRIMP dating of zircons from a mafic unit, which yield an age of 1870.3±7.1Ma for the Winnipegosis Komatiite Belt. The komatiites are Al-undepleted and dominated by massive olivine porphyritic flows with a median thickness of 6m. Differentiated flows containing layers of olivine spinifex are present, but rare. Trace element data indicate the komatiites were derived from depleted mantle, and subsequently contaminated with 2–3% continental crust. Temperatures from Al-in-olivine thermometry are consistent with a nominally dry melt, and combined with olivine-melt Mg–Fe partitioning, suggest a parental melt with ~24wt% MgO and a liquidus (olivine) temperature of ~1501°C, approximately 100°C cooler than their hottest Archaean counterparts. At ~1424°C chromite joined olivine as a crystallising phase. Olivine and chromite phenocrysts were re-mixed with residual melt shortly before or during komatiite eruption, which occurred by the time the magma had cooled to ~1321°C. Combined geochemical and geological evidence requires that the Winnipegosis Komatiites erupted onto rifting continental crust. Their high liquidus temperatures require anomalously hot mantle. Considering the Winnipegosis Komatiites in the context of the broader Circum-Superior Belt, we suggest that these magmas formed from a mantle plume that was deflected towards the margins of the Superior craton by strong gradients in lithospheric thickness. This interpretation of the mode of formation of the Circum-Superior Belt casts doubt on ambient mantle potential temperatures as high as 1600°C during the Proterozoic.
KW - Faculty of Science
KW - Proterozoic
KW - Komatiite
KW - Circum-Superior Belt
KW - Trans-Hudson Orogeny
KW - Al-in-olivine thermometer
KW - Mantle potential temperature
U2 - 10.1016/j.lithos.2016.10.033
DO - 10.1016/j.lithos.2016.10.033
M3 - Journal article
VL - 268-271
SP - 114
EP - 130
JO - Lithos
JF - Lithos
SN - 0024-4937
ER -
ID: 211990087