40Ar/39Ar eruption ages and geochemical characteristics of Late Tertiary to Quaternary intraplate and arc-related lavas in interior Alaska

Late Tertiary to Quaternary basaltic rocks from three locations in interior Alaska - Fort Hamlin Hills, Prindle Volcano, and Buzzard Creek - have been characterized geochemically using major and trace element concentrations and radiogenic isotopic ratios. The rocks from Fort Hamlin Hills and Prindle Volcano have well-constrained 40Ar/39Ar eruption ages ranging from 32.83 ± 0.16 Ma for the Fort Hamlin Hills basalts, to 0.20 ± 0.06 Ma for the Prindle Volcano basanites. Ages for the Buzzard Creek basalts have large errors because of the low K2O concentration and young ages of the lavas, which we estimate to be < 0.01 Ma. On the basis of Sr-Nd-Pb-Hf isotope and rare earth element data, we have determined that the primary melts for the Fort Hamlin Hills and Buzzard Creek basalts were produced in the lithospheric mantle at spinel facies depths. The Prindle Volcano basanites were produced in asthenospheric mantle in garnet facies conditions. Although involvement in the source components of small volumes of enriched materials related to Late Jurassic to Early Cretaceous flat-slab subduction is not ruled out for the Fort Hamlin Hills basalts and Prindle Volcano basanites. These lavas do not exhibit the arc signature typified by depletion in high-field-strength elements. We conclude that the volcanism at the Fort Hamlin Hills and Prindle Volcano localities in interior Alaska represents intraplate activity due to lithospheric extension accompanied by decompression melting and additional heating. Buzzard Creek basalts, on the other hand, exhibit an arc signature characterized by troughs at Ta-Nb, and peaks at Pb and Sr on element distribution diagrams. These basalts occur in a 400 km volcano gap between the Aleutian arc system and Wrangell Volcanic Province. © 2009 Elsevier B.V. All rights reserved.