HR: 1340h
AN: V13A-1457    [Abstracts]
TI: Along Strike Hf-Nd Isotopic Composition of Aleutian Arc Lavas
AU: * Gerseny, M G
EM: gersula@wsu.edu
AF: Washington State University, Department of Geology PO Box 642812, Pullman, Wa 99164 United States
AU: Vervoort, J D
EM: vervoort@wsu.edu
AF: Washington State University, Department of Geology PO Box 642812, Pullman, Wa 99164 United States
AU: Yogodozinski, G M
EM: gene@sc.edu
AF: University of South Carolina, Department of Geological Sciences 701 Sumter St, Columbia, SC 29208 United States
AB: The Aleutian Arc provides an ideal tectonic setting to study Hf-Nd systematics due to its along-strike tectonic and geochemical variation. Sediment load and subduction rate decrease westward along the arc with an increasingly oblique subduction angle, causing a progressive decrease westward in the flux of sediment into the subduction zone. A suite of samples collected across the length of the arc were analyzed for Hf and Nd isotopic composition. A coupled decrease in both Hf and Nd isotopic composition was observed from east to west along the arc. Piip seamount samples at 193\deg W have the highest $\epsilon$$_{Hf}$20.3 and $\epsilon$$_{Nd}$10.4. Lavas from Great Sitkin (176\deg W) and Korovin (174\deg W) have intermediate compositions of 7.4-7.9 $\epsilon$$_{Nd}$and 13.6-14.4 $\epsilon$$_{Hf}$. The lowest $\epsilon$$_{Hf}$ values obtained (12.2-13.0) were from the Cold Bay Volcanic Complex (163\deg W). Various ashes of the DSDP site 178 of the Alaskan abyssal plain have approximately the same Hf and Nd isotopic composition as Cold Bay. Clay and turbidite sequences from site 178 have lower $\epsilon$$_{Hf}$0.8-7.8 and $\epsilon$$_{Nd}$2.8-0.82 values. The change in Hf and Nd isotopic composition along the arc is consistent with a decrease in sediment flux westward. A sediment melt component in the east could mobilize Hf and Nd into the mantle wedge. Fluxing of the subducting sediment could also incorporate Nd into the melting mantle. Both these processes would lower the radiogenic signature of the source region.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting