U-Pb zircon age of metafelsite from the Pinney Hollow Formation: implications for the development of the Vermont Appalachians

The Pinney Hollow Formation of central Vermont is part of a rift-elastic to drift-stage sequence of cover rocks deposited on the Laurentian margin dur ing the development of the Iapetan passive margin in Late Proterozoic to Ca mbrian time. Conventional U-Pb zircon data indicate an age of 571 +/- 5 Ma for a metafelsite from the Pinney Hollow Formation. Geochemical data indica te that the protolith for the metafelsite, now a quartz-albite gneiss or gr anofels, was rhyolite from a source that was transitional between a within- plate granite and ocean-ridge granite setting and probably came through par tially distended continental crust. The transitional setting is consistent with previous data from metabasalts in the Pinney Hollow Formation and supp orts the idea that the source magma came through continental crust on the r ifted margin of the Laurentian craton. The 571 +/- 5 Ma age Provides the fi rst geochronologic age from the rift-elastic cover sequence New England and establishes a Late Proterozoic age for the Pinney Hollow Formation. The La te Proterozoic age of the Pinney Hollow; confirms the presence of a signifi cant mapped thrust fault between the autochthonous and para-autochthonous r ocks of the cover sequence. These findings support the interpretation that the Taconic root zone is located in the hinterland of the Vermont Appalachi ans on the eastern side of the Green Mountain massif.