Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p11b1340g&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P11B-1340
Physics
[8145] Tectonophysics / Physics Of Magma And Magma Bodies, [8159] Tectonophysics / Rheology: Crust And Lithosphere, [8440] Volcanology / Calderas
Scientific paper
It is increasingly being recognized that caldera models assuming elastic rheologies are inadequate to describe the collapse of the largest calderas. In these supervolcanic systems, where host rocks are heated well above the brittle-ductile transition (450°C) the thermal evolution of the crust and resultant inelastic rheological properties will influence both the threshold and mechanism of caldera collapse. Furthermore, volcanological observations implicate mechanical roof failure during overpressured conditions rather than the classically accepted underpressured condition. To investigate these effects, we are developing a 2D time-dependent finite-element model that utilizes a temperature- and strain rate-dependent viscoelastic rheology. Specifically, we employ an axisymmetric model with an elliptical magma chamber in a homogeneous viscoelastic half-space with a generalized Maxwell rheology. The background thermal field is assumed to be quasi steady-state with periodic magmatic influx to maintain the thermal input from the magma chamber. Coupling Mohr-Coulomb failure criteria with Andersonian fault theory we are investigating the characteristics of failure in the brittle portions of the host rock in response to under/overpressurization of the magma chamber as well as variations in chamber size and geometry. Initial results illustrate the importance of incorporating temperature dependence and the background crustal thermal evolution when predicting the maximum magma chamber growth size and predicting the zones of failure in the roof rock. We are comparing our results to elastic predictions of roof failure and caldera formation and exploring the implications for the formation of large silicic calderas in the Central Volcanic Zone of the Andes.
de Silva Shanaka L.
Gregg Patricia M.
Grosfils Eric B.
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