DETRITAL ZIRCON AGES OF THE UMBRELLA HILL AND SHAW MOUNTAIN FORMATIONS, VERMONT

U-Pb ages of detrital zircons have played a major role in our understanding of tectonic models of the Appalachians, including the Vermont part of the belt. Recently, a major suture, formed during closing of the Early Paleozoic Iapetan Ocean, has been postulated to exist within the Rowe-Hawley Belt of central Vermont. The Hawley slices within this belt in Vermont include the Cambro-Ordovician Moretown, Cram Hill and Umbrella Hill formations. Recent work has shown that the provenance of metasediments within the Moretown Formation and Cram Hill is Gondwanan. In a continuation of this work, we focus here on the Umbrella Hill Formation, a distinctive conglomeratic unit within the Rowe Hawley Belt. The stratigraphic relationship of the unit to the Moretown and Cram Hill formations is a subject of continued discussion. The Shaw Mountain Formation, a basal conglomerate of the Connecticut Valley Sequence east of the Rowe-Hawley Belt, is also part of this study. Detrital zircon ages of both units are correlated to known magmatic period signatures of potential source terranes. Through LA-ICP-MS analysis of isolated zircon grains of the Umbrella Hill and Shaw Mountain formations, a series of age peaks have been determined. Preliminary data based on 109 grains from one sample of the Shaw Mountain Formation and 60 grains from the Umbrella Hill Formation show intriguing, albeit tentative, results. Age peaks produced for the Umbrella Hill sample are centered around 460 Ma, 600 Ma, and 1000 Ma, suggesting possible Shelburne Falls Arc, Peri-Gondwanan, and Peri-Laurentian provenances, respectively. A single prominent peak was produced for the Shaw Mountain sample, centered around 445 Ma, suggesting a Bronson Hill Arc provenance. As part of this ongoing study, more samples from both units will be analyzed for detrital zircon ages. These results will be used to shed further light on our understanding of the northeast Appalachian orogenic and tectonic model.