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Incision into the Eastern Andean Plateau During Pliocene Cooling

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Science  16 Aug 2013:
Vol. 341, Issue 6147, pp. 774-776
DOI: 10.1126/science.1239132

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Bringing Down the Andes

Mountain ranges, like the Andes in South America, have a number of forces acting on them that control their elevation. High rates of precipitation can induce rapid incision of canyons, but tectonic forces from deep within the mountain range may balance or even exceed the rate of erosion. Lease and Ehlers (p. 774) examined the exhumation histories of the northeastern Andean Plateau. The erosion of sediments older than ∼10 million years was controlled largely by tectonic processes. However, more recent sediments suggest that a shift to cooler temperatures increased precipitation 3 to 4 million years ago.

Abstract

Canyon incision into mountain topography is commonly used as a proxy for surface uplift driven by tectonic or geodynamic processes, but climatic changes can also instigate incision. The ~1250-kilometer (km)–long eastern margin of the Andean Plateau hosts a series of 1.5- to 2.5-km-deep canyons that cross major deformation zones. Using (U-Th)/He thermochronology, we document a transition from Miocene faulting to Pliocene canyon incision across the northeastern plateau margin. Regionally, widespread Pliocene incision into the eastern plateau margin is concurrent with a shift in global climate from early Pliocene warmth to late Pliocene cooling. Enhanced moisture transport onto the Andean Plateau driven by sea surface temperature changes during cooling is the likely pacemaker for canyon incision.

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