PENROSE MEDAL: ARC AND BACKARC MAGMATISM AND THE EVOLUTION OF THE CONTINENTAL CRUST FROM THE ALEUTIANS TO THE CENTRAL AND SOUTHERN ANDES AND PATAGONIA

Many processes exhibited from the Aleutians to Patagonia have contributed to the evolution of the continental crust including changing crustal thickness, variable slab dip and arc width, frontal arc migration, forearc subduction erosion, delamination of lower crust and lithospheric mantle and subduction of oceanic ridges. Understanding these processes requires integrating petrologic and geochemical signals from magmatic rocks with their structural and tectonic setting, the shape and length of an underlying subduction zone and the geophysical nature and composition of the crust and mantle. Comparisons of magmatic processes in the oceanic Aleutian arc with the continental Andes have enhanced understanding of crustal formation and the evolution of both. In the central Andes, a north to south progression of shallowing and steepening of the subducting Nazca plate correlates with a southward pattern of giant backarc andesitic to dacitic calderas linked to episodes of lower crustal and mantle delamination. The foreland migration of the frontal arc and chemistry of the magmatic rocks support episodes of forearc subduction erosion in parts of both the Central Andes and the Aleutians. Evidence of forearc subduction erosion and delamination suggests that the central Andes is a region of net crustal destruction rather than growth. Advances in deciphering Andean crustal and mantle processes have led to enhanced understanding of the formation of giant Au, Cu, and Ag deposits.