ORIGINS OF THE MORETOWN FORMATION, VERMONT: A DETRITAL ZIRCON STUDY

The tectonic history of the Vermont Appalachians can be refined with the aid of geochronological data. The Moretown Formation of Vermont has been interpreted as sediments deposited in the fore-arc basin of the Cambrian-Ordovician Shelburne Falls arc. This study uses detrital zircons to provide new information on the provenance of the Moretown sediments. Zircons have been separated from ten samples taken from the Moretown Formation of northern Vermont. U-Pb ages were determined on 75 to 100 zircons per sample using the LA-ICP-MS at Rensselaer Polytechnic Institute. Age distributions represent a signature of the range of ages of sources that contributed to the sediment. The age signatures of the Moretown, and some rift-related sediments of Vermont, are compared to age signatures of potential source regions to determine the sedimentary provenance. The Late Proterozoic, rift-related Hazens Notch Formation shows, as expected, a dominant Laurentian (Grenville) signature. Preliminary results from Moretown samples suggest a peri-Gondwanan source component, likely mixed with a Laurentian component. This result indicates more provenance sources than the exclusively Laurentian signature postulated by previous work on the Moretown in southern Vermont and northern Massachusetts. Such a distinction could indicate that the Moretown is not the same along strike and that there is variation in local sources of zircons, or that tectonic models to explain the origin of the Moretown sediments need to be revised. More detrital zircon ages on a larger number of samples will provide further precision in describing the paleogeography of the Moretown depositional basin and associated terranes.