STATISTICAL CHARACTERIZATION OF THE ALASKAN-ALEUTIAN CONVERGENCE ARC

It is a worthy scientific goal to determine how Earth's crust affects convergence arc magmas. Thin mafic oceanic crust or thick felsic continental crust each imprints chemical characteristics on the magmas that originated by hydrous melting of the mantle wedge above a subduction zone [e.g., Kimura et al. 2009]. It is widely accepted that arcs built on thickened continental crust (e.g. the Andes) have more felsic and calc-alkaline magmas than those built on oceanic crust [Winter, 2010]. However, it is not trivial to untangle the processes responsible for the differing lines of descent taken by the mantle magma (primary melt) as it ascends through the mantle and crust to its final eruption or emplacement. This study uses statistical treatments of large geochemical datasets of subduction systems and show that they can reveal broad structures in arc system and thereby allow for new geochemical perspectives in convergent margin magmagenesis. We concentrate on the Alaskan-Aleutian arc system with its two its two crustal type, oceanic in the west and continental in the east, over a subducting slab. We characterize its geochemistry and compare it with two end-members subduction arcs: the oceanic-oceanic system of Izu-Bonin-Mariana, and the oceanic-continental system of the Andes. Result shows that the Alaskan-Aleutian system is a complex hybrid system with convoluted oceanic and continental affinity that is distinct from a simple combinatory of the two end-member types.