SEARCHING FOR THE SAINT ELIAS PLUTONIC SUITE IN GLACIER BAY NATIONAL PARK AND PRESERVE, ALASKA

The Saint Elias plutonic suite consists of a belt of Early Cretaceous and latest Jurassic plutons in eastern south-central Alaska, and Yukon and British Columbia, Canada. The suite ranges from granite to diorite, but is composed chiefly of quartz monzodiorite. K/Ar and Ar/Ar ages for plutons in the suite in east-central Alaska, Yukon, and British Columbia tend to cluster between approximately 160 and 130 Ma. The few available U/Pb age determinations on rocks of the suite range between about 156 and 150 Ma. In southern east-central Alaska, plutons of the suite intrude rocks of the Wrangellia terrane, whereas in Yukon and British Columbia, they intrude both Wrangellia and Alexander terrane rocks. The plutons of the suite appear to extend southward into Glacier Bay National Park and Preserve (GLBA) where a number of compositionally similar, but undated plutons are exposed. The suite may also continue to northern Chichagof Island east of the Peril Strait Fault (PSF) where it would intrude rocks of the Alexander terrane. The rocks west of the PSF do not include rocks of the Alexander terrane and are correlated with Paleozoic to Mesozoic rocks of Wrangellia on Vancouver Island and Haida Gwaii. The rocks west of the PSF are intruded by plutons that generally have ages (K/Ar, Ar/Ar, and U/Pb) that are about155 Ma and older, including many pluton ages significantly older than any known ages in the Saint Elias suite. Fieldwork in the summer of 2016 will sample some of the plutons in GLBA to evaluate their inclusion in the suite. Our new work in GLBA will help to constrain the tectonic history of different and potentially far-traveled components of the Wrangellia and Alexander terranes. Discrete segments of the Wrangellia terrane host magmatic suites of different ages, which 1) serve as a useful correlation tools, 2) help to identify the paleo-location of terrane segments, and 3) provide insights into the variability of the tectonic history over the Wrangellia terrane’s >2500 km length.