This project is designed to use the central Aleutian arc as a natural experiment to examine the influence that melts of terrigenous turbidites has upon the abundances of high field strength elements (HFSE) and Hf isotopic compositions in arc lavas. The Amlia Fracture Zone (AFZ) contains sediment in greater volume than elsewhere in the Aleutian trench and delivers anomalous quantities of sediment and water directly to the mantle. Oblique subduction of the Pacific plate has moved the AFZ westward along the arc front, sequentially subducting a pulse of sediment and fluid beneath the islands of Chuginadak, Yunaska and Seguam circa 5, 2.5 and 1 million years ago, respectively. Lavas from Atka Island, which has not yet received the sediment and fluid spike from the AFZ provides control compositions. This section of the Aleutians was selected because Sr and Pb isotopic compositions are markedly more radiogenic at Seguam and Yunaska volcanoes than at Atka. This study proposes to examine the variation of HFSE and Hf isotopic compositions in fifteen lavas from these islands to test whether a pulse of sediment in the magma source, delivered by a subducted fracture zone, affected these lavas. Because this sediment addition occurred as a spatially and temporally discrete spike, temporal variation in the hafnium characteristics of the lavas constrains the duration of HFSE transfer to arc magmas.
Because the ages and petrogenesis of several of the volcanic complexes in the Aleutians has never been investigated, this project will contribute significantly to the understanding of this active arc. This project will establish the research program of the PI at KSU, where the PI provides a role model for women students. The project will support the graduate training of Ms. Katrina Pekar and partially support that of Mr. David Bridges. The project will foster national and international collaborations between the KSU geology department and other institutions. An important aspect of these collaborations includes training graduate students in the use of analytical techniques not currently available at KSU (ICP-MS) or in the state of Kansas (40Ar/39Ar geochronology, isotope analysis by MC-ICPMS and TIMS). The results of the study will be shared with the geologic community through national meetings, manuscript publication and archive on the Aleutian Arc Data System.
