Collaborative Research: Nazca- South America Convergence and Continental Growth in the Central Andes via Global Positioning System (GPS) Measurements

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Dixon EAR-0003621SteinEAR-0004031The origin of large mountain belts like the Andes at ocean-continent convergent margins remains enigmatic despite centuries of study beginning with Darwin. Various hypotheses have been advanced to explain the Andes, but by themselves none seem capable of explaining the formation of this vast region of elevated, thickened crust. For example, the investigator's preliminary GPS data suggest that the Andes are growing today at roughly their long term average rate despite significant slowing of subduction since the Miocene, problematic for models that call on fast subduction alone to form the Andes. This collaborative team from the University of Miami and Northwestern University proposes a series of GPS measurements that exploit a network first occupied in 1994, coupled with related seismic studies, aimed at understanding the processes forming Andean mountain belts. They will focus on the Central Andes of Peru and Bolivia, where the high, wide Altiplano plateau is best developed, and where an active fold and thrust belt accommodates rapid crustal shortening. To enhance their ability to discriminate models and to conserve resources, the measurements will be densified in two transects that cross the entire plate boundary zone, in regions of flat and normal subduction. The new measurements will span a total of four years to obtain velocity accuracy at the new sites adequate to distinguish among several competing hypotheses.