Publication Date:
2013-02-05
Description:
[1] Island arcs are proposed to be essential building blocks for the crustal growth of continents, however island arcs and continents are fundamentally different in bulk composition: mafic and felsic respectively. The substrate upon which arcs are built (oceanic crust vs. large igneous province) may have a strong influence on crustal genesis. We present results from an across-arc wide-angle seismic survey of the Costa Rican volcanic front, which test the hypothesis that juvenile continental crust is actively forming at this location. Travel-time tomography constrains velocities in the upper arc to a depth of ~15 km where average velocities are 〈6.5 km/s. The upper 5 km of crust is constrained by velocities between 4.0–5.5 km/s, which likely represent sediments, volcaniclastics, flows, and small intrusions. Between 5–15 km depth velocities increase slowly from 5.5–6.5 km/s. Crustal thickness and lower crustal velocities are roughly constrained by reflections from an inferred crust-mantle transition zone. Crustal thickness beneath the volcanic front in Costa Rica is ~40 km with best-fit average lower-crustal velocities between 6.8–7.1 km/s. Overall, velocities across the arc in central Costa Rica are at the high-velocity extreme of bulk continental crust velocities and are lower than modern island arc velocities, suggesting that continental compositions are created at this location. These data suggest that pre-existing thick crust of the Caribbean Large Igneous Province has a measurable effect on bulk composition. This thickened arc crust may be a density filter for mafic material and thereby support differentiation toward continental compositions.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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