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Project Summary
Personnel: Taylor Schildgen (Ph.D.) Katrina Cornell (M.S.)
Kip
Hodges (Ph.D.)
MIT researchers are studying the uplift
history of the Cordillera Occidental of southern Peru, which marks the
western boundary of the Altiplano plateau in the central Andes. Their
approach is to study the spatial and temporal history of incision of
two major river systems (the Colca and Cotahuasi river systems) that
transect the range through what are regarded as the two deepest canyons
in the Western Hemisphere, each with a total relief in excess of 3200m.
Although river incision is an imperfect proxy for rock uplift, the
behavior of major river systems during tectonic activity is a sensitive
indicator of surface uplift relative to sea level. This is true
regardless of whether or not steady-state conditions have been met. The
geology and geography of these drainages provide four independent ways
to estimate the history and pattern of river incision. This
circumstance provides an extraordinary opportunity to develop a
detailed image of the incision history of the Colca and Cotahuasi river
systems, which the MIT researchers are using to deduce the uplift
evolution of the western edge of the Altiplano, and to test the
implicit assumptions in standard applications of each of the four
methods. The MIT researchers are using a combination of the following
four methods to decipher the history and pattern of river incision: 1)
thermochronologic studies of incised granitic plutons; 2)
reconstructions of ancient land surfaces based on preserved remnants of
volcanic flows; 3) measurements of the time-integrated rate of river
incision using bedrock strath terraces; and 4) reconstructions of the
history of valley aggradation and subsequent re-excavation recorded in
alluvial fill terraces and remnants of volcanic infills. The
information being gleaned from these studies about the incision
histories of the Colca and Cotahuasi river systems is essential for
evaluating current models of the growth and uplift of the Andes, and
for better informing future models.
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