According to new research published in the journal Geophysical Research Letters, the Andes have been a mountain chain for much longer than previously thought.
Torres del Paine, southern Andes, Chile. Image credit: Miguel Vieira.
The Andes are the longest continental mountain range in the world and have huge effect on the regional climate.
This mountain chain is over 4,500 miles (7,250 km) long, about 120 to 430 miles (190 – 690 km) wide. The chain consists of a series of complex ranges which parallel the north coast of Venezuela and the entire west side of South America.
The prevailing view is that the Andes became a mountain range 6 to 10 million years ago when a large of the deep crust detached in response to thickening of the crust.
When this large portion of material was removed, the remaining portion of the crust underwent rapid uplift.
Knowing when mountain belts form major topographic features is essential for understanding how they form and when the start to impact global atmospheric circulation and ultimately climate.
To investigate the timing of Andean uplift, researchers from the University of Bristol, Scottish Universities Environmental Research Center and the University of Aberdeen used a novel method based on cosmic rays that create a rare form of helium – cosmogenic helium-3 – in minerals at the Earth’s surface.
The abundance of cosmogenic helium-3 depends on the altitude of the surface and thus can be used to understand the altitude history of a rock surface.
The team analyzed boulders from 1.2 miles (2 km) high in the arid western margin of the Andes.
The scientists have shown that the region was already near the present elevation 15 million years ago.
“It seems highly likely that the Andes have gone up slowly over at least the last 30 million years, and are the result of gradual thickening of the crust,” said lead author Dr Laura Evenstar, of the University of Bristol.
“This means that the uplift of the Andes probable effected large scale atmospheric circulation patterns at least 4 million years before previously thought.”
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Evenstar, L.A. et al. 2015. Slow Cenozoic uplift of the western Andean Cordillera indicated by cosmogenic 3He in alluvial boulders from the Pacific Planation Surface. Geophysical Research Letter 42, 8448-8455; doi: 10.1002/2015GL065959
