3-billion-year-old crystals hint at lost continent’s fate

Relics of a long-lost continent may lurk beneath the Indian Ocean.

Tiny zircon crystals coughed up by volcanic eruptions on the island of Mauritius are around 2.5 billion to 3 billion years old. That’s billions of years older than the island itself, researchers report January 31 in Nature Communications. The zircons, the researchers propose, are remnants of an ancient continent called Mauritia that formed part of the nexus of Madagascar and India before the two landmasses split apart around 84 million years ago (SN: 1/21/17, p. 18).

Comparing the crystals’ ages with those of nearby landmasses, petrologist Lewis Ashwal of the University of the Witwatersrand, Johannesburg and colleagues retraced Mauritia’s fate. Volcanic eruptions and shifting tectonic plates fragmented Mauritia, the researchers say, and the land was eventually buried under thick layers of lava. Some of that land, including the zircon crystals, was recycled into the rising plume of magma that fueled the eruptions that eventually built Mauritius.

A handful of zircons dating back nearly 2 billion years had already been uncovered in the island’s sands. Some scientists raised concerns that those crystals were brought to the island from elsewhere as part of ship ballast or construction material. Ashwal and colleagues pried the newfound crystals from rocky outcrops on the island, erasing any doubts of the zircons’ origins.