UNIVERSITY OF ARIZONA
The Puna Plateau, northwestern Argentina, together with the Altiplano of Bolivia, is the second largest plateau on Earth. One popular model often invoked to explain the present day crustal structure and elevation of the Central Andean Plateau, including the Argentinean Puna and the Bolivian Altiplano, is lithospheric delamination. Full, convective removal of eclogitized lower crust and lithospheric root and subsequent rebound in the Altiplano of Bolivia is proposed to explain paleoaltimetric evidence for high magnitude (greater than 2 kilometers) surface uplift. However, the region of thin crust and lithosphere and of basaltic volcanism originally argued to be the site of lithospheric removal is located to the south in the Puna Plateau of Argentina. Moreover, geochemical data suggest the presence of Ordovician lithosphere beneath the Puna, arguing against complete lithospheric removal. The objective of this research project is to reconcile the geological observations with geophysical data in the area of thin crust and mantle lithosphere in the Puna Plateau. This international effort, lead by researchers at the University of Wyoming and University of Arizona, is a multidisciplinary investigation utilizing structural geology, sedimentology and stratigraphy, geochronology, thermochronology, geochemistry and paleontology, targeting the thinned region in order to constrain: 1) the history of horizontal shortening and extension; 2) basin evolution and incision; 3) magma geochemistry; and 4) paleo-environment in the mid-late Cenozoic. These comprehensive new data are being used as input parameters to a combined numerical-analog model that will test a set of hypotheses to explain the present crustal configuration of the Plateau including: 1) full removal of mantle lithosphere and possibly lower crust through viscous Rayleigh-Taylor type convective instability; 2) partial removal of mantle lithosphere and possibly lower crust plateau-wide, leaving a horizon of uppermost mantle lithosphere intact following viscous convective instability; 3) partial removal of mantle lithosphere and possibly lower crust via small-scale viscous convective instability; 4) full removal of mantle lithosphere through; 5) lithospheric extension in a continental back-arc type environment.
The tectonic explanations for the uplift of large plateaus in orogenic belts, such as the Altiplano in the Andes and the Tibet plateau, are numerous and controversial. The objective of this project is to test these models by using geological observations as constraints on numerical and physical models of the processes. This research will ultimately constrain the connection between mantle processes on deformation, uplift, subsidence and magmatism within the Puna Plateau, a natural laboratory that will serve as an example for other geodynamically similar regions on Earth.