While diamonds might look pretty perched atop a ring, the rocks they hail from venture to Earth’s surface in a journey that’s anything but glamorous. Millions of years ago, some of our planet’s strangest and most violent volcanic outbursts dredged from deep underground most of the diamonds mined today in the form of blue-tinged rocks called kimberlites.
Unlike the volcanoes that more commonly pop up near the thinner edges of continents, the eruptions that produced most kimberlites came through the thick, stable continental cores known as cratons. Kimberlite eruptions start near the cratonic roots, at least 75 miles underground, and race upward at tens of feet per second — a fiery fury driven by an abundance of carbon dioxide and water.
“It’s like rocket fuel,” said Thomas Gernon, a geologist at the University of Southampton in England who has long studied kimberlites. The turbulent flow punches a carrot-shaped pipe through the ground, ripping out chunks of deep subsurface rock, including some that are studded with diamonds.
But existing research still has a giant diamond-shaped hole: Why do kimberlites form?
A new study led by Dr. Gernon and published Wednesday in the journal Nature points to the ancient roots of these eruptions. He and his colleagues report that the breakup of ancient supercontinents like Pangaea and Rodinia caused deep disruptions in the flow of the mantle beneath Earth’s crust, setting off the blasts.