The Architecture, Chemistry, and Evolution of Continental Magmatic Arcs

Continental magmatic arcs form above subduction zones where the upper plate is continental lithosphere and/or accreted transitional lithosphere. The best-studied examples are found along the western margin of the Americas. They are Earth’s largest sites of intermediate magmatism. They are long lived (tens to hundreds of millions of years) and spatially complex; their location migrates laterally due to a host of tectonic causes. Episodes of crustal and lithospheric thickening alternating with periods of root foundering produce cyclic vertical changes in arcs. The average plutonic and volcanic rocks in these arcs straddle the compositional boundary between an andesite and a dacite, very similar to that of continental crust; about half of that comes from newly addedmaficmaterial from themantle. Arc products of the upper crust differentiated from deep crustal (>40 km) residual materials, which are unstable in the lithosphere. Continental arcs evolve into stable continental masses over time; trace elemental budgets, however, present challenges to the concept that Phanerozoic arcs are themain factories of continental crust. 10.1 Review in Advance first posted online on February 27, 2015. (Changes may still occur before final publication online and in print.) Changes may still occur before final publication online and in print A nn u. R ev . E ar th P la ne t. Sc i. 20 15 .4 3. D ow nl oa de d fr om w w w .a nn ua lr ev ie w s. or g A cc es s pr ov id ed b y R ic e U ni ve rs ity o n 04 /1 2/ 15 . F or p er so na l u se o nl y. EA43CH10-Ducea ARI 19 February 2015 13:14