Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot
Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot
复制标题
魁北克南部地下水中的地幔氦：新英格兰热点的可能化石记录
DOI：
10.1016/j.epsl.2020.116352
复制
发表时间：
2020
影响因子：
5.3
通讯作者：
Larocque Marie
中科院分区：
文献类型：
--
作者：
Mejean Pauline;Pinti Daniele L.;Kagoshima Takanori;Roulleau Emilie;Demarets Laura;Poirier Andre;Takahata Naoto;Sano Yuji;Larocque Marie
蒙特雷吉山是位于加拿大魁北克省圣劳伦斯低地的白垩纪岩浆侵入序列。它们的起源是有争议的，许多研究都未能破译热点轨迹或与北大西洋开放有关的次大陆岩浆活动。结果表明，该地区现代至全新世地下水氦（17.7±9.6%）来自地幔，3 He/4 He (R)高达大气氦（Ra）的1.42倍。这表明化石蒙特利亚山岩浆信号，被当地的放射性氦稀释并保存在蒙特利亚山侵入物中，被流动的现代或亚现代地下水淋滤。蒙特雷gian Hills块状岩石和斜辉石分离物的氦同位素测量结果显示，R/Ra值高达4.96，表明化石地幔氦在这些岩石及其矿物相中有部分保存。岩浆老化模型的Monte Carlo模拟表明，这些白垩纪侵入岩的初始3 He/4 He比值可能介于21±10 Ra和33±28 Ra （2σ）之间，这有利于蒙特雷亚山是北美板块经过新英格兰热点的产物的假设。这项研究提出了利用现代地下水作为数亿年时间尺度上地幔He档案的前景。
Abstract 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±10 Ra and 33±28 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.