HR: 09:00h
AN: V41F-05    [Abstracts]
TI: Patterns in Long-Lived Continental Magmatism; Crustal Modulation of Mantle-Derived Input
AU: * Grunder, A R
EM: grundera@geo.oregonstate.edu
AF: Oregon State University, Department of Geosciences, Corvallis, OR 97331, United States
AU: de Silva, S L
EM: desilvas@geo.oregonstate.edu
AF: Oregon State University, Department of Geosciences, Corvallis, OR 97331, United States
AB: Patterns in volumetric eruption rate of continental intermediate to silicic magmatic systems have implications for how heat is delivered and processed in the crust, and reveal the evolution of crustal scale magmatic systems. Drawing on the Neogene volcanic rocks of the Altiplano Puna Volcanic Complex (APVC) and the Aucanquilcha Volcanic Cluster (AVC) of the Central Andes, we compare their histories to other long-lived crustal magmatic complexes. Erupted volumes of such systems vary from a few tens of km³ to tens of thousands of km³ of magma with associated plutonic volumes several times that. Despite differences in volume, these complexes share a general family resemblance. They have lifespans of about 10 million years. Where resolution allows, the record of activity may reveal distinct pulses, lasting a few hundred thousand to ~1 to 2 m.y., demonstrating the composite nature of the magmatic systems. These complexes bear isotopic and compositional evidence of crustal and mantle involvement in the origin of the magmas and mineralogic evidence for subsequent equilibration at shallow crustal levels. Many, but not all, have abundant ignimbrites. Most strikingly they all have a three stage evolutionary history that is scale independent. An early waxing stage characterized by low volume, low flux volcanism that is compositionally diverse and may be dispersed; a climactic stage of dramatically higher flux, that is compositionally more focused and may be spatially more focused; and a final waning stage of small eruptions. We interpret these patterns to be the result of long-lived thermal pulses delivered from the mantle in the form of basaltic magma. A fundamental question is to what extent does the surface pattern reflect the mantle input. We suggest that the thermal signal is modulated by interaction and thermal incubation in the crust that leads to development of a large crustal magma reservoir that in turn modulates the composition of erupted magma. The interplay between mantle power input, heat advection, thermal and mechanical state of the crust, silicic magma production and intrusion rates among other factors need to be explored to resolve the nature and time scales of modulation.
DE: 3640 Igneous petrology
DE: 8140 Ophiolites (3042)
DE: 8185 Volcanic arcs
DE: 9360 South America
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting