HR: 08:00h
AN: V41A-01 INVITED     [PDF]
TI: Expressions and controls on intra-crustal recycling
AU: * Bergantz, G W
EM: bergantz@u.washington.edu
AF: Univ. of Washington, Box 351310, Seattle, WA 98195 United States
AU: Bachmann, O
EM: bachmann@ess.washington.edu
AF: Univ. of Washington, Box 351310, Seattle, WA 98195 United States
AU: Dufek, J
EM: dufek@u.washington.edu
AF: Univ. of Washington, Box 351310, Seattle, WA 98195 United States
AB: Heat and mass transfer associated with arc magmatism can play a significant role in crustal differentiation. However, the timescales and controls are diverse and poorly understood. To assess the expression of crustal recycling, we will review and compare three examples: the Sierra Nevada, Cascade, and Costa Rica arcs. Coupled basaltic inputs and crustal melting or reaction provides the template for crustal recycling. This process can be dominated by heat and/or fluid transport, and the relative contributions can be difficult to decipher from anhydrous, residual xenoliths and arc magmas. If the crust is young, thin, and mafic (south Cascade arc), low-K compositions dominate. The compositional diversity in the mafic rocks is nearly as great as in the silicic rocks. Wet melting by mantle input is possible, but radiogenic Os signatures limit the addition of primitive basalts and high Mg andesites as mass sources for erupted magmas. If the crust is old, thick, and silicic (Sierra Nevada), crustal recycling is expressed as a sequence of amphibolite-tonalite-granodiorite with amphibolite and granulite facies roots. High-K compositions result from a multi-stage process of "igneous distillation" but the relative roles of true melting and reaction-assimilation has not been resolved. High-K concentration can also be generated in continental arcs where thin, mafic, refractory oceanic crust constitutes most of the crustal column (Costa Rica). We suggest that the presence of high-K silicic magmas in this setting can be reconciled with repeated melting of a young, mafic lower crust, effectively by-passing the existing crustal framework.
DE: 3640 Igneous petrology
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting