LANDSCAPE RESPONSE TO SUBDUCTION OF THE COCOS RIDGE: TALAMANCAS RANGE, COSTA RICA

The Talamancas Range, the extinct volcanic arc associated with the Central American convergent margin, is the highest mountain range in Central America, with peak elevations reaching as high as ~3800 m. Uplift, denudation and cessation of volcanism within this range is attributed to low-angle (<10°) subduction of the Cocos Ridge, an aseismic feature generated during passage of the Cocos Plate over the Galapagos hot spot. The thick (~20 km), buoyant crust associated with the Cocos Ridge first collided with the Middle America Trench at ~2-3 Ma. Here, we utilize topographic and longitudinal profile analyses to place constraints on the pattern and magnitude of differential rock uplift within the Talamancas due to Cocos Ridge subduction. Analysis of digital topographic data reveals a low-relief surface perched within the northeastern slopes of the range. The preserved edge of this surface coincides with the location of ~34 convex-up knickpoints occurring at a mean elevation of 2140 +/- 40 m. Each knickpoint identified separates a low-gradient (mean k_sn = ~100) upstream channel segment from a steeper (mean k_sn = ~250) downstream reach. The knickpoints cluster around a constant elevation, do not coincide with major lithologic boundaries, and occur well below the ice extent from the last glacial maximum. Our analysis suggests that the topography in the Talamancas Range is in a transient state of adjustment due to an increase in rock uplift initiated by Cocos Ridge subduction. By reconstructing the paleo-tributary networks of the low-relief surface, we estimate the total amount of differential rock uplift across the Talamancas Range since the onset of Cocos Ridge subduction to be ~1700-1800 m, and place constraints on the incision and uplift rates associated with subduction of this feature.