Rocking the Arctic

Winter 2010

Don Francis with his dog, Shake, and student Jeff Larocque in background at Porpoise Cove, Ungava, Quebec, the site of the world's oldest crustal rocks.

Two years ago, Earth and Planetary Science professor Don Francis made headlines when his team of McGill researchers discovered the world’s oldest known rocks in northern Quebec. Now, Francis is part of a team that has discovered a new window into the Earth’s violent past, through geochemical evidence from volcanic rocks collected on Baffin Island in the Canadian Arctic.

The rocks suggest that beneath Baffin Island lies a region of the Earth’s mantle that has largely escaped the billions of years of melting and geological churning that has affected the rest of the planet. Francis believes the discovery offers clues to the early chemical evolution of the Earth.

The newly identified mantle reservoir, as it is called, dates from just a few tens of millions years after the Earth was first assembled from the collisions of smaller bodies. This reservoir likely represents the composition of the mantle shortly after formation of the core, but before the 4.5 billion years of crust formation and recycling modified the composition of most of the rest of Earth’s interior.

The study, published this past August in Nature, was co-authored by Richard Carlson of the Carnegie Institution’s Department of Terrestrial Magnetism, and lead author Matthew Jackson of Boston University. The findings suggest there is far less uranium and thorium inside the Earth than expected.

The rocks were originally collected by Francis more than a decade ago in the Canadian Arctic. Francis often shares his rock finds with other researchers.

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