Ricci Keller Symone Stinson Amber Colter

Sediment is subducted with oceanic crust to produce arc- andesitic magma Sediment from eroded continents has high Sr/Pb ratios Evidence for some involvement of sediment: Major Elements Trace Elements Isotopic Characteristics

10 Be Formed in the atmosphere Transferred to Earth by rain Absorbed by sediment and soil Has a half life of 1.5my Is a tracer of sediment moving into a subduction zone and back to the surface via magma transport Can only be recycled once Samples from several arcs show elevated levels of 10 Be Evidence for participation of sediment in magma genesis potsdam.de/portal/gfz/Struktur/Departments/Department+3/se c34/Bilder/Meteoric+10Be?binary=true&status=300&language=e n

No compelling case of large scale sediment anatexis Sediment melting is indistinguishable from crustal contamination Sediment melting is most likely part of a more complex model involving andesite genesis Be isotope data suggests a less than 4% sediment component

Mafic Oceanic Crust converts to eclogite during subduction and is melted to yield a primary andesitic magma The product of this process is Adakite magma

Eclogite Formed via metamorphism during the subduction process and is the direct parent of adakite Adakite Silica Rich Volcanic or plutonic rock derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs Ecolgite Adakite

Experimental data found does not match andesite data found in the field ie: REE patterns “…most thermal models of subduction zones do not predict temperatures high enough to melt subducted crustal rocks at sites near the top of the plate below the arc.” Model 3 opposes fractional crystallization and magma mixing Fractional Crystallization is a major component of andesite formation The model does not explain why basalts and andesites commonly occur together in volcanic arc settings Equillibrium crystallization models suggest that high alumina- andesites are not likely to be primary melts. Experimental Melts Theoretical Calculations Major/Trace Element Data

Except for Adakites, it is unlikely that anatexis of a mafic, oceanic crust during subduction, will produce magma with andesitic composition.