Along Strike Hf-Nd Isotopic Composition of Aleutian Arc Lavas

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 ɛ _Hf20.3 and ɛ _Nd10.4. Lavas from Great Sitkin (176\deg W) and Korovin (174\deg W) have intermediate compositions of 7.4-7.9 ɛ _Ndand 13.6-14.4 ɛ _Hf. The lowest ɛ _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 ɛ _Hf0.8-7.8 and ɛ _Nd2.8-0.82 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.