THE NORTH AMERICAN CORDILLERAN ANATECTIC BELT AND LARAMIDE-AGE CRUSTAL MELTING IN THE SOUTHWEST US

A fundamental component of the North American Cordillera is a belt of peraluminous granite that stretches from southern British Columbia, Canada to northern Sonora, Mexico and is located landward of the Mesozoic Cordilleran coastal batholiths. These rocks are colloquially called the belt of two-mica granites, display a wide range of ages (Jurassic to Neogene), and were produced by diverse processes including hydrothermal alteration and fractional crystallization. However, a large subset were emplaced during Laramide time and are demonstrably related to crustal melting – a subset we refer to as the North American Cordilleran Anatectic Belt. In terms of size, the Cordilleran Anatectic Belt (~3,000 km along-strike length) rivals or exceeds other major collision-related anatectic belts including the Himalayan leucogranite belt (~2,000 km along-strike), making it one of the largest anatectic provinces in the world. There is a close spatial and temporal relationship between crustal melting and metamorphic core complexes in most of the Cordillera, suggesting a potential petrogenetic link. However, this relationship is more complex in the southwestern U.S. where anatectic melting generally occurs 20-50 Myr prior to exhumation and cooling. New and compiled geochronological and geochemical data is utilized to assess melting mechanisms in the southern Cordillera including melting associated with decompression, fluid-flux, crustal thickening, and the addition of heat from the mantle.