HR: 17:15h
AN: T44C-06    [Abstracts]
TI: Volcanic Segmentation, Nb Depletion, Reactive Flow Path Length and Volcano Size are Linked in Central America
AU: * Carr, M J
EM: carr@rutgers.edu
AF: Rutgers University, Department of Geological Sciences, Wright Laboratory, 610 Taylor Rd., Piscataway, NJ 08854, United States
AU: Bolge, L L
EM: bolge@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, P.O. Box 1000, 61 Route 9W, Palisades, NY 10964, United States
AB: Central America is unusual among the global set of arcs because the volcanic front is segmented by abrupt right steps of up to 40 km. Nb depletion (Zr/Nb) jumps at these steps (Bolge, 2005). Nb depletion is greater (Zr/Nb higher) at the volcano closer to the trench. Between steps, Nb depletion decreases to the SE, creating a saw- tooth pattern. Given the smooth Benioff zone revealed by seismicity and the slight anticlockwise rotation of the linear volcanic segments relative to the isobaths to the seismic zone, the variation in Nb depletion correlates with depth to the seismic zone. Thus, short paths have maximum Nb depletion and long paths have minimum depletion. This suggests a melt/fluid generation with a Nb retaining phase in the residue to create the initial depletion. A reactive flow through the mantle wedge then progressively reduces the initial depletion. The full set of incompatible elements is consistent with simple AFC models of this process. Furthermore, the uneven distribution of volcanic output along the volcanic front appears related to the variation in path length. A short path generates maximum Nb depletion and a small volcano. An intermediate length path generates a large volcano and moderate Nb depletion. A long path generates minimum Nb depletion and, again, a small volcano. This suggests that the magma generating region has an optimal depth or distance from the trench for magma productivity. Finally, although the origin of the volcanic lines is not explained, it must be a facet of upper plate tectonics, rather than a segmented slab.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1037 Magma genesis and partial melting (3619)
DE: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting