Gj. Walsh et Jn. Aleinikoff, U-Pb zircon age of metafelsite from the Pinney Hollow Formation: implications for the development of the Vermont Appalachians, AM J SCI, 299(2), 1999, pp. 157-170
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.