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.