Why tectonic plates move abruptly

A Yale University-led study may have solved one of the biggest mysteries in geology - why do tectonic plates beneath the Earth's surface sometimes move abruptly.

Traditionally, scientists believed that all tectonic plates are pulled by subducting slabs which result from the colder, top boundary layer of the Earth's rocky surface becoming heavy and sinking slowly into the deeper mantle.

Yet that process does not account for sudden plate shifts.

Such abrupt movement requires that slabs detach from their plates but doing this quickly is difficult since the slabs should be too cold and stiff to detach.

According to the Yale study, there are additional factors at work.

Thick crust from continents or oceanic plateaux is swept into the subduction zone, plugging it up and prompting the slab to break off.

The detachment process is then accelerated when mineral grains in the necking slab start to shrink, causing the slab to weaken rapidly.

The result is tectonic plates that abruptly shift horizontally or continents suddenly bobbing up.

"Understanding this helps us understand how the tectonic plates change through the Earth's history. It adds to our knowledge of the evolution of our planet, including its climate and biosphere," said Yale geophysicist David Bercovici.

The study was published in the journal Proceedings of the National Academy of Sciences.