The primary goal of this project was to explore links between helium and other elements in mantle-plume-derived lavas on Baffin Island, Arctic Canada. The measurement of high ³He/⁴He in mantle plumes relative to the upper convecting mantle that produces mid-ocean ridge basalt places fundamental constraints on planetary formation and evolution. By measuring the compositions of lavas on Baffin Island associated with especially high ³He/⁴He, this project assessed the origins and implications of high ³He/⁴He in plumes globally. Our thorough geochemical assessment of these lavas led to some impactful results, including the discovery of higher ³He/⁴He than measured in any terrestrial igneous rocks.

Our comprehensive geochemical assessment of the Baffin Island lavas collected in 2018 constrained the elemental and isotopic compositions of these samples. We measured major element abundances by X-ray fluorescence; whole-rock trace element concentrations by inductively coupled plasma mass spectrometry (ICPMS); whole-rock radiogenic isotopic compositions (⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb) via ICPMS; helium isotopic ratios via crushing and fusion (135 analyses in total); neon, argon, and xenon isotopic ratios via crushing; in situ olivine major and trace element compositions by electron probe microanalyzer (EPMA); in situ trace elements in olivine-hosted melt inclusions by EPMA; hydrogen isotopes by secondary ion mass spectrometry (SIMS); volatile elements in olivine-hosted melt inclusions via SIMS; tungsten isotopic compositions by thermal ionization mass spectrometry; vanadium isotopic compositions by ICPMS; thallium isotopic compositions by ICPMS; iron speciation by X-ray absorption near edge spectroscopy; ⁴⁰Ar-³⁹Ar dates by mass spectrometry; and paleomagnetic poles across multiple stratigraphic sections of lava flows and underlying sediments.

The ³He/⁴He in mantle-derived lavas has traditionally been interpreted as evidence for the survival of primordial noble gases (captured during planetary accretion) in the mantle. Our finding of even higher ³He/⁴He (more than 65 times the atmospheric ratio) than previously measured implies that either (a) a mantle reservoir exists with more pristine primordial gases than previously realized or (b) the high-³He/⁴He helium is derived from elsewhere, such as the core. Based on the radiogenic isotopic compositions, modeling constraints, and the results of prior studies, we argue that the isotopically anomalous helium could derive from the core. This relaxes the constraint that primordial noble gases must have been preserved in the mantle and permits more vigorous outgassing during planetary accretion and subsequent mantle convection.

The helium isotopic anomalies in Baffin Island lavas are linked with solar-like neon isotopes (also presumably of primordial origin) but not other isotopic or elemental abundances that are diagnostic of ancient primordial mantle or the core. One explanation is that helium diffuses faster through mantle material and therefore travels farther from the high-³He/⁴He source (presumably primordial mantle or the core) into the convecting mantle. This seems to be corroborated by our tungsten isotopic results, which imply that little if any bulk core exists in the Baffin Island mantle. Cumulatively, these results may indicate that physical mixing of material, such as oxides exsolved from the outer core, into the lowermost mantle, where helium from the core diffuses into surrounding mantle regions. In these regards, this study has implications for our understanding of planetary formation and brings into focus a dynamic core-mantle boundary region.

Our paleomagnetism, geochronology, and stratigraphic results have implications for our understanding of climate-volcanism feedbacks. Paleomagnetic constraints imply that the lavas erupted rapidly (~67 years per lava flow) at approximately 62 million years ago. This links them to similar lava flows on the West Greenland margin. Coevally, there was a ~2 degrees C global warming event, which might have been caused by these eruptions. Notably, a mass extinction event did not occur then; either the eruption rate was too slow or, more likely, the lava volumes were too small to cause major extinctions, like those associated with more voluminous large igneous provinces. This aspect of the project sheds light on the resilience of biological systems during major volcanic events.

This research led to five peer-reviewed publications and has produced datasets for at least four more. Our Nature paper about the highest reported ³He/⁴He in terrestrial igneous rocks has been featured prominently in the media, including by CNN and Vice. The results of this work have been the subject of ten abstracts and presentations at scientific conferences.

This project supported graduate students at Woods Hole Oceanographic Institution (WHOI) and California Institute of Technology (Caltech), as well as an undergraduate guest student at WHOI. Employment and professional development opportunities were provided to an autistic individual through a local organization in Massachusetts. Also, laboratory fees supported specialized technicians and facilities at WHOI and Caltech, including the Isotope Geochemistry Facility, Plasma Facility, and the Northeastern Ion Microprobe Facility at WHOI. Results have been made publicly available in a data repository (EarthChem) and have been shared with communities on Baffin Island.

Last Modified: 10/31/2023
Modified by: Forrest Horton