for National Geographic News
After millions of years of slowly being squeezed, warped, and folded higher, the central Andes suddenly shot toward the stars in a geological blink of the eye, according to a new study.
The growth spurt came after chunks of dense, deep rock that anchored the South American mountain range suddenly plopped deeper into the mantle, freeing the buoyant crust to pop up like a cork unleashed from a lead weight.
"This will cause the rapid elevation change that we see over the short period of time," said study co-author Gregory Hoke, a geologist at the University of Rochester in New York.
In a span of as little as a million years, the central Andes grew at least 5,000 feet (1,500 meters)—more than a third of their average height—Hoke and colleagues report in tomorrow's issue of the journal Science.
The spurt occurred between ten and six million years ago, concludes the team, which was led by Carmala Garzione, a geologist at the University of Rochester.
Scientists generally think most mountains rise in a relatively steady, lockstep manner as pieces of Earth's crust crumple and buckle together in the process of plate tectonics.
Garzione and her colleagues used a newly developed technique that interprets chemical signatures from isotopes of oxygen, carbon, and other elements in ancient soils to determine the history and rate of elevation rise.
The ratio of isotopes varies depending on what elevation ancient precipitation fell onto the mountains. Other data allow the researchers to determine when the rain or snow fell.
This so-called paleo-elevation record suggests the mountains rose slowly for tens of millions of years and then suddenly lifted at a rate that is "faster than the commonly accepted tectonic process," Hoke said.
The best explanation for the rapid rise, he added, is delamination—the loss of dense rock at the base of the crust.
The rapid uplift, he noted, helps reconcile the timing of a major reorganization of the landscape on both sides of the Andes.
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