Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot

Méjean, Pauline; Pinti, Daniele L.; Kagoshima, Takanori; Roulleau, Emilie; Demarets, Laura; Poirier, André; Takahata, Naoto; Sano, Yuji et Larocque, Marie (2020). « Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot ». Earth and Planetary Science Letters, 545, p. 116352.

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Résumé

The Monteregian Hills are an alignment of magmatic intrusions of Cretaceous age located in the St. Lawrence Lowlands, Quebec, Canada. Their origin is controversial and numerous studies have failed to decipher between a hotspot trail or sub-continental magmatism related to the opening of the North Atlantic Ocean. Here, we show that % of the helium of the modern to Holocene-aged groundwater from the regional aquifer is of mantle origin, with a 3He/4He (R) of up to 1.42 times the atmospheric ratio (Ra). It suggests that a fossil Monteregian Hills magmatic signal, diluted by local radiogenic helium and preserved in the Monteregian Hills intrusions, is leached locally by flowing modern or sub-modern groundwater. Helium isotopic measurements by pyrolysis in Monteregian Hills bulk rocks and clinopyroxene separates show R/Ra values of up to 4.96, suggesting that fossil mantle helium has been partially preserved in these rocks and their mineral phases. Monte Carlo simulations of a magma aging model shows that the initial 3He/4He ratio in these Cretaceous intrusions could have been between Ra and Ra (2σ), favoring the hypothesis that the Monteregian Hills are the product of the passage of the North American plate over the New England hotspot. This study raises the prospect of using modern groundwater as an archive of mantle He over a hundreds of millions of years timescale.

Type:	Article de revue scientifique
Mots-clés ou Sujets:	Gaz rares, hélium, eau souterraine, Montérégiennes, New England hotspot.
Unité d'appartenance:	Centres institutionnels > Centre de recherche en géochimie et géodynamique (GEOTOP) Faculté des sciences > Département des sciences de la Terre et de l'atmosphère
Déposé par:	Marie Larocque
Date de dépôt:	08 sept. 2020 08:53
Dernière modification:	02 sept. 2022 23:10
Adresse URL :	http://archipel.uqam.ca/id/eprint/13504

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