HR: 14:25h
AN: V43G-04 INVITED    [Abstracts]
TI: The Pulse of Cordilleran Batholith Formation Revealed in the Spatiotemporal Evolution of Large Silicic Volcanic Fields
AU: * de Silva, S L
EM: desilvas@geo.oregonstate.edu
AF: Oregon State University, Department of Geosciences, Corvallis, OR 97331-5056, United States
AU: Lipman, P W
EM: plipman@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94028, United States
AB: While the linkage between Cordilleran plutonism and volcanism remains debated, data for large silicic volcanic fields (LSVF) document informative space-time-composition parallels. The comparable dimensions and spacing of centers and similar petrological and geochemical characteristics support the view that, like Cordilleran batholiths, LSVF are composed of multiple periodically constructed magmatic systems. The spatiotemporal record of volcanism at two well-studied LSVF that are geometrically, compositionally, and temporally comparable, the 10 to 1 Ma Altiplano-Puna Volcanic Complex (APVC) of the Central Andes and the 37 to 26 Ma Southern Rocky Mountain volcanic field (SRMVF) of Colorado, provide windows into the construction of the uppermost parts of Cordilleran batholiths. Both the APVC and SRMVF involved eruption of numerous dacite to rhyolite ignimbrites with volumes >100 km³; several with volumes >1000 km³. Some calderas in both regions were polycyclic, with the largest caldera sources 60 km or more across. Area covered in both regions is on the order of 70,000 to 100,000 km², during eruptive activity of ~10 m.y. Cumulative magmatic volume of ignimbrites is about 10,000 km³ for the APVC and 15,000 km³ for the SRMVF, and estimated peak magma- production rates are as high as 12,000 to 8,000 km³/m.y respectively. Calderas in both areas are associated with pre-and post-caldera andesitic to dacitic lava eruptions. The calderas and other magmatic centers of both areas lie within regional gravity lows that suggest the subvolcanic growth of upper-crustal composite batholiths associated with the silicic volcanism. Both the APVC and the SRMVF lie along the east margins of broad long-lived Cordilleran magmato-tectonic zones, involving plate convergence and low-angle subduction. The APVC is associated with a regional seismic anomaly interpreted as indicating the presence of partial melt in the middle crust; no comparable feature(s) are present beneath the SRMVF, plausibly because of its greater age. The spatiotemporal records from these fields suggest that the combined volcano-plutonic system records a magmatic flare-up that was at least an order of magnitude more intense than the steady-state rates that characterize the long-term evolution of destructive plate margins. The flare-up initiated suddenly, at rates slightly above steady state, escalated to a climactic stage, and declined rapidly. This pattern, and the organization of activity into distinct pulses of increasing intensity and spatial definition with time at LSVF should produce a plutonic record. While Cordilleran batholiths such as the Sierra Nevada Batholith in California contain evidence of comparable flare-ups, resolution of the plutonic record does not distinguish individual pulses. Issues in need of future study include refining the volume-time and spatiotemporal patterns, determining the trigger for magmatic flare-ups and controls on episodic magmatism—both volcanic and plutonic , and resolving the disparate records in the two realms.
DE: 1020 Composition of the continental crust
DE: 8035 Pluton emplacement
DE: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting