HR: 16:30h
AN: T14B-03    [Abstracts]
TI: Coast Mountains Batholith: The Anatomy Of A Cordilleran Arc
AU: * Ducea, M
EM: ducea@email.arizona.edu
AF: University of Arizona, 1040 E Fourth Street, Tucson, AZ 85721, United States
AU: Andronicos, C
EM: ca98@cornell.edu
AF: Cornell University, Department of Earth & Atmospheric Sciences, Snee Hall, Ithaca, NY 14853, United States
AB: The Coast Mountains Batholith is one of the largest individual segments of any continental (Andean) magmatic arcs on the planet. Here we focus on a segment located between latitudes 52 and 54 N, and on the Cretaceous and younger plutons, since some of the earlier intrusives may have originated elsewhere before docking to the North American continent as out-of-place terranes. The batholith is the sum of numerous individual plutons and volcanic equivalents that were emplaced on the continental margin during the prolonged subduction of various segments of the Pacific realm under North America between the Jurassic and Eocene. The tempo of the batholith was uneven, with several 10 m.y. long high-flux episodes separated by magmatic lulls. The western (Cretaceous) arc was emplaced successively as sheets of calc-alkaline tonalites during times of convective overturn of the mid- to lower crust. Its postulated surface equivalent would have been similar to the modern chain of andesitic volcanoes of the Andean Western Cordillera (the volcanic front). As a result of crustal thickening prior to the last and most voluminous high-flux event (Paleocene-Eocene), the arc migrated inland. This event produced mostly granodiorites and related rocks that were emplaced as sills in the mid-crust and had more irregular shapes as hypabyssal plutons. The wide spatial distribution of this event suggest that it was a result of primarily crustal melting of thick crust, similar to the Miocene to modern magmatic flare-up of the Altiplano-Puna plateau, within the orogenic core of the Andes. Extensional collapse during and immediately after the Eocene flare-up rapidly brought up the ductile mid-crust of the orogenic core, the Central Gneiss Complex, closer to the surface. A subsequent, more cryptic event, during the early Miocene (20 Ma) led to the changes in isotopic characteristics of the underlying mantle, as indicated by isotopic tracers on post batholith mafic dikes. We interpret this to reflect to loss of the arc root via foundering. Overall, we suggest the batholith is the equivalent of a collapsed equivalent to the central Andes, which now exposes the mid-crust of the former arc (average of 25 km).
UR: http://www.geo.arizona.edu/tectonics/Ducea/Batholiths/index.html
DE: 8032 Rheology: general (8160)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8108 Continental tectonics: compressional
DE: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting