The thermal structure of a generic subduction zone is investigated to elucidate the source region of subduction zone volcanics. The steady state thermal field is evaluated for a model subduction zone where the plates are prescribed by kinematic boundary conditions, such that the subducting slab induces a flow in the mantle wedge. The resulting model suggests that the oceanic crust of the downgo...

GRA 06128/9: Since their discovery at Graves Nunataks icefield during the 2006/2007 Antarctic Search for Meteorites field season, GRA 06128 and GRA 06129 have received considerable scientific attention. Their elevated modal abundances of oligoclase (>75%), blocky or slab-like character, granoblastic textures and ‘andesitic’ bulk compositions set them apart from all other meteorite classes. It h...

Fifteen andesite-dacite stratovolcanoes on the volcanic front of a single segment of the Andean arc show along-arc changes in isotopic and elemental ratios that demonstrate large crustal contributions to magma genesis. All 15 centers lie 90 km above the Benioff zone and 280 _+ 20 km from the trench axis. Rate and geometry of subduction and composition and age of subducted sediments and seafloor...

Slab breakoff is the buoyancy-driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision. In a recent paper Davies and von Blanckenburg [1994] have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts. Br...

Arc magmas are distinguished from those of other tectonic settings by several first order characteristics; 1) they tend to be realtively differentiated with even the most mafic rocks in a suite typically ≥50% SiO2, 2) they typically contain high H2O contents and 3) they have distinctive trace element signatures. The “standard” model for arc petrogenesis involves melting of a mantle wedge, preco...

Timescales of magma transfer and differentiation processes can be estimated when the mechanism is known. When conventional major trace element analyses fail to distinguish between various differentiation, isotope compositions useful. Lower Th ratios in silicic relative basaltic magmas at a given volcano could result from storage over period several tens thousands years, or if process was fracti...