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

• Published in: Earth and Planetary Science Letters
• Main Authors: Méjean, Pauline, Pinti, Daniele L., Kagoshima, Takanori, Roulleau, Emilie, Demarets, Laura, Poirier, André, Takahata, Naoto, Sano, Yuji, Larocque, Marie
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: noble gases; helium isotopes; groundwater; magma aging; Monteregian Hills; New England hotspot; [SDU]Sciences of the Universe [physics]; Canada; North Atlantic
• Online Access: https://insu.hal.science/insu-03661438; https://doi.org/10.1016/j.epsl.2020.116352

International audience 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 17.7 ± 9.6% of the helium of the modern to Holocene-aged groundwater from the regional aquifer is of mantle origin, with a 3 He/ 4 He (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 3 He/ 4 He ratio in these Cretaceous intrusions could have been between 21 ± 10Ra and 33 ± 28Ra (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.