Crustal Formation and Assembly in the NW Pacific: Aleutians and Kamchatka

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9406195 Kay Throughout Tertiary time, Kamchatka has collected fragments of continental crust (terranes) that formed as oceanic island arcs and plateaus in the Bering Sea and the Pacific Ocean. Accretion of the fragments has resulted in a subcontinental mass. The process is thought by many to be the main mechanism of present day continental growth. Kamchatka is a particularly good site to study this type of continental growth due to its youth, due to the availability of information on similar but as yet unaccreted oceanic fragments (especially, the Aleutian islands) and due to widespread post-accretion magmatism that records conditions at depth. This investigation focuses on alkaline basaltic magmas that originate in mantle that lies under the Kamchatka terranes. Existing trace element data on these magmas lack typical signatures (e.g. high Ba/La, La/Ta ratios), and support delamination models that call fro wholesale replacement of mantle lithosphere by underlying Oceanic Island Basalt (OIB)-like asthenosphere. Isotope analyses (Pb, Sr, Nd) as well as additional trace element analyses will permit identification of mas reservoirs and quantification of mas fluxes related to fundamental processes of crustal growth and consolidation.