QUANTIFYING TRIBUTARY RESPONSE TO CANYON INCISION IN THE CENTRAL ANDES, SOUTHERN PERU

The rivers of southern Peru have carved some of the deepest canyons on earth and are essential to quantifying and constraining the timing of surface uplift in the Central Andes. Tributary basins within these larger watersheds contain a break in slope that separates high relief, adjusted canyons from low relief, relict surfaces that remain untouched by recent transience. The erosional history of these tributary basins can be used to constrain the style, rate and timing of uplift in this region. We will present erosion rates derived from ¹⁰Be cosmogenic radionuclide concentrations from five tributary basins in both the adjusted and relict reaches of these channels. The study basins are located along a transect extending from the dry (<1 mm yr^-1), low elevation coast up to the high, wetter (700 mm yr^-1) Central Andean plateau. Erosion rates range from 0.003 – 0.35 mm yr^-1, and are consistent with longer-term estimates of exhumation from thermochronology. Relict and adjusted erosion rates both increase by more than an order of magnitude between low (dry) and high (wetter) elevation sites. We present these trends in erosion rates along with comparisons between a number of metrics including mean annual precipitation, channel steepness, knickpoint distribution, and incision depth. The patterns among these metrics will clarify the relative influence of climate and tectonics in this region as well establish a foundation for understanding the history of uplift in the Central Andes. Specifically, by focusing on tributaries, we can account for the control of climate on the transient response of the landscape and provide robust reconstructions of the spatiotemporal pattern of canyon incision.