Recycled Continental Crustal Components in Aleutian arc Magmas: Implications for Crustal Growth and Mantle Heterogeneity

Abstract

Mantle-derived magmatic rocks of the Aleutian island arc are isotopically and geochemically distinct from their counterparts in the ocean basins immediately to the south and north. Aleutian magmas contain crustal components from subducted oceanic sediment, subducted hydrothermally altered mid-oceanic ridge basalt (MORB), and oceanic crust that is imbedded within the Aleutian arc crust. Olivine tholeiite is the commonest magma type that rises from the mantle to the crust-mantle boundary, but it is observed as a lava only infrequently, due to crustal assimilation and fractionation. Aleutian olivine tholeiites originate by partial melting of upwelling peridotite rendered buoyant by addition of excess (XS) elements from the subducting plate. At present, operation of the subduction process (S-process) at arcs like the Aleutians is the main mechanism for both crustal growth and for recycling continental crustal material into the mantle is a second recycling mechanism. Mantle heterogeneities (as sampled by OIB melts) were largely created in the past by the same recycling processes. Lower crustal delamination accompanying accretion of arc terranes at continental margins.