From: Robin Blackstone, ENN
Published April 22, 2014 03:10 PM

The Andes' pulsating rise

New research by Carmala Garzione, Earth and Environmental Sciences professor from the University of Rochester suggests that the Antiplano plateau in the central Andes Mountains along with the entire mountain range likely arose in a series of periodic rapid pulses instead of a more continuous gradual surface uplift. According to Garzione, "In geologic terms, rapid means rising one kilometer or more over several millions of years, which is very impressive."

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Researchers have known that as the Nazca oceanic plate slid under the South American continental plate, the Andes mountain range has risen. This process has made the Earth's crust fold and fault thus shortening and thickening it. Scientists were left wondering about the process and its speed.

Beginning in 2006, Garzione and her team estimated mountain uplift speed by measuring the ancient surface temperatures and rainfall compositions preserved in the soils of the Altiplano plateau in Bolivia and Peru. The plateau sits about 12,000 feet above sea level. Garzione concluded that portions of the dense lower crust and upper mantle act as the crust’s anchor, periodically detaching and sinking through the mantle as the thickened continental plate heats up. Detachment allows the lower-density upper crust to rebound and rise more quickly.

More recently, Garzione and Andrew Leier, assistant professor of Earth and Ocean Sciences at the University of South Carolina, used a relatively new temperature-recording technique in two separate studies in different regions of the Andes to determine whether pulses of rapid surface uplift are the norm, or the exception, for mountain formation of mountain.

Garzione and Leier each independently focused on the bonding behavior of carbon and oxygen isotopes in the mineral calcite precipitated from rainwater; their results were similar.

Garzione worked in the southern Altiplano, collecting climate records preserved in ancient soils from low elevations where temperatures remained warm, and at high elevations where temperatures should have cooled as the mountains rose. The calcite found in the soil contains both the lighter isotopes of carbon and oxygen—12C and 16O—as well as the rare heavier isotopes—13C and 18O. Paleo-temperature estimates from calcite rely on the fact that heavy isotopes form stronger bonds. At lower temperatures, where atoms vibrate more slowly, the heavy isotope 13C-18O bonds would be more difficult to break, resulting in a higher concentration of 13C-18O bonds in calcite, compared to warmer temperatures. By measuring the abundance of heavy isotope bonds in both low and high elevation (warm) sites over time, Garzione used the difference to estimate the elevation of various layers of ancient soils at specific points in time.

Read more at the University of Rochester.

Altiplano plateau in Bolivia image via Shutterstock.

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