The Relationship Between Oceanic and Continental Arc Magmas: A Signal-Processing Treatment on Geochemical Data of the Alaska-Aleutian Arc

Abstract:

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. Here we examine the Alaska-Aleutian arc from Piip seamount to Spurr volcano using statistical technique. We use published data (from the Earthchem database) to characterize geochemistry along the arc, then using similar methods to extract geochemical signals (trends and structures) from the dataset. We show the geochemistry differences between the oceanic affiliated Aleutian and the continental affiliated Alaskan magma and the transition from one lava to the other along the arc. We replicated previously identified geochemical signatures associated with the arc, such as its variations due to the Amlia Fracture Zone, and sediment flux / convergence velocity. We model these features of the arc so that they can be subtracted from the overall trend. We propose that the remainder signals are attributed to the different processes of the two crustal types.