Controls on Growth of the Puna Plateau, Northwestern Argentina

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Both the mechanisms of growth of orogenic plateaus and the processes that control or limit their growth remain controversial. Within currently active orogens, only two large-scale orogenic plateaus (in Tibet and the Andes) have developed during Cenozoic times. At the broadest scale, their growth has been driven by sustained plate convergence. If such convergence continues into the future, will these plateaus continue to expand? What controls whether they reach a stable size, continuously expand, or begin to shrink or collapse? This research project explores the factors that limit plateau growth and the interplay between tectonic forcing and erosion that modulates changes in topography along plateau margins with particular focus on one mode of plateau growth: synchronous growth of thrust-related ranges with filling of high, ponded intermontane basins during times of relative aridity. The enhanced crustal loads represented by the basin-range couplet are proposed to drive outward propagation of deformation. This project will be focused along the northeastern margin of the Puna Plateau and the adjacent Eastern Cordillera of northwestern Argentina, a region that lies astride an abrupt climatic boundary and boasts multiple generations of late Cenozoic thrusting and episodes of basin filling and emptying. Successive faults overthrust conglomerates and fluvial-lacustrine strata and are then buried by younger gravels. Radiometric dating of the numerous volcanic ashes that are preserved within the basin fills, as well as within conglomerates will permit tight time control on the growth and decay of the plateau margin and will underpin a detailed reconstruction of the interplay of range growth, an evolving fluvial network, and multiple cycles of basin filling and emptying.Orogenic plateaus represent extensive topographic regions characterized by high elevation, but low topographic relief. The two largest plateaus on earth today have resulted from tectonic plate convergence in the Himalaya and the Andes. The margins of such plateaus are the sites of great earthquakes (such as the devastating ones in Sichuan and Kashmir). Being immense areas of high topography, such plateaus impact global climate by diverting the jet stream, modulating the strength and path of the monsoon, and influencing patterns of rainfall. These plateaus also provide the water that supports over 2 billion people. An improved understanding of how plateaus grow, what controls where faulting occurs, and whether topographic thresholds exist that control climatic change is of significant scientific and societal value. This project focuses on the eastern flank of the Puna Plateau in Argentina, where excellent exposures and a rich diversity of datable volcanic ashes permit reconstruction of the history of plateau growth in a detailed temporal framework. The results of this study will assist the ongoing effort to understand the interactions among climate and tectonics in large, actively deforming mountain ranges.