ALONG-ARC GEOCHEMICAL TRENDS ON THE ALASKA PENINSULA: USING ARCHIVED U.S. GEOLOGICAL SURVEY SAMPLES FOR A SYNOPTIC GEOPRISMS STUDY

The Alaska Peninsula consists of the continental portion of the Aleutian arc and contains Late Cretaceous through Quaternary igneous rocks. Reanalysis of samples collected during legacy U.S. Geological Survey field campaigns, plus data archived in the Alaska Geochemical Database, are used to evaluate geochemical trends of the Aleutian arc on the Alaska Peninsula. This NSF GeoPRISMS study is the first of its kind for advancing synoptic studies capitalizing on availability of archived U.S. Geological Survey Alaskan samples and geochemical databases. New analytical data includes major and trace element geochemistry on about 200 archive samples in the Alaska Peninsula, ranging from mid-Eocene to Quaternary in age. The samples are subalkaline and metaluminous and are predominantly intermediate in composition, but range from basalt to dacite. La/Yb ratios generally show mild LREE enrichment, consistent with other Aleutian arc rocks, with the exception of one new analysis of a basalt sample that has a MORB-like (LREE-depleted) pattern. Among all of the samples, the ratios of Th/La (proxy for sediment recycling) and Cs/La and Ba/La (proxies for slab fluid) show crude correlation with sediment flux along the trench; these ratios are generally lower where there is lower sediment flux and increase where sediment flux is greater. The preliminary data show the influence of slab flux along strike from the oceanic (SW) to the continental (NE) portion of the Aleutian arc. Ongoing work will include the collection of additional geochemical, isotope (Hf-Nd-Sr), and age (U/Pb and Ar/Ar) data to comprehensively evaluate these trends. This study demonstrates the value in reanalysis of existing U.S. Geological Survey sample collections to yield substantial high-resolution regional datasets in a highly time-efficient and cost-effective manner.