Scientists Propose Overlooked Step in Tectonic Squeeze

Scientists use tiny minerals called zircons as geologic timekeepers. Often no bigger than a grain of sand, these crystals record chemical signatures of the geological environment where they formed.

In a study published in Geology, the researchers describe zircons from the Andes Mountains of Patagonia with a chemical signature that made them do a double take. Although the zircons formed when tectonic plates were colliding, they have a chemical signature associated with when the plates were moving apart.

The researchers said the zircons’ signature could capture a transitional step in the formation of back-arc basins — an important geological structure that shapes landscapes, geologic records and helps regulate the planet’s climate.

The researchers think that this transitional step could involved oceanic crust entering the magma chamber where the zircons form ahead of continental crust. This in turn changes the zircon signature.

“If you put some oceanic basin below this magma, you have a change in the composition of this magma as it’s incorporated,” said the study’s lead author Fernando Rey, a doctoral student at the Jackson School of Geosciences. “This is something that was not documented before this study.”