FRAGMENT OF AMAZONIA(?) IN THE HUDSON HIGHLANDS, NY: PROVENANCE OF GRANULITE METASANDSTONES USING SHRIMP

SHRIMP analyses of detrital zircon cores from two juxtaposed granulite facies metasandstones in the western Hudson Highlands, New York, show distinct provenances and suggests a cryptic plate suture zone. Because of the degree of deformation and metamorphism of these rocks, it is only through SHRIMP analysis that this distinction could be made. Zircon cores from metasandstones associated with the metavolcaniclastic lithofacies show rhythmic zonation and yield a relatively tight cluster of ages from 1230 to 1160 Ma. These metavolcaniclastic rocks and contained detrital zircons, are interpreted to have been derived from the interlayered metavolcanic lithofacies, which has been geochemically shown to be volcanic arc-generated. They are interpreted to have formed aprons of sediment around the arc at the time of deposition. In contrast, zircon cores from adjacent metasandstones in a package of metasedimentary rocks (metapelites, metapsammites, calcsilicates and minor marble) show complex zonations and range in age from 1184 to 2800 Ma. Such a spread of ages over 1.6 Ga is interpreted to reflect derivation from a deeply incised passive margin with exposure of multiple orogenic belts of variable ages. These contrasting margins were juxtaposed, deformed and metamorphosed to granulite facies conditions during the middle Proterozoic Grenville orogeny. The best fit model for the age distribution of the detrital zircons from the metasedimentary lithofacies is derivation from Amazonia, a consistent interpretation with the paleogeography for the final assembly of Rodinia. The metasedimentary rocks might therefore be an exotic fragment of Amazonia left behind in the Hudson Highlands during the break-up of Rodinia in the late Proterozoic. These metasandstones might also have provided the source for Appalachian Paleozoic sedimentary rocks whose distribution of ages from zircon cores have until now been explained using complex sedimentary models.