Dk. Mcdaniel et al., GRENVILLIAN PROVENANCE FOR THE AMPHIBOLITE-GRADE TRAP-FALLS FORMATION- IMPLICATIONS FOR EARLY PALEOZOIC TECTONIC HISTORY OF NEW-ENGLAND, Canadian journal of earth sciences, 34(9), 1997, pp. 1286-1294
The Trap Falls Formation is a sequence of interlayered quartzites and
schists that crops out in the Appalachian belt in southern Connecticut
, and was deformed and metamorphosed to middle amphibolite grade durin
g Acadian orogenesis. Schists have high Al2O3 and low CaO, Na2O, and K
2O (chemical index of alteration CIA = 68-70), consistent with a signi
ficant weathering history in the sediment source. Rare earth element (
REE) patterns for both schists and quartzites parallel post-Archean av
erage Australian Shale, with light REE enrichment and well-developed E
u anomalies, suggesting an average upper crustal source. Whole-rock Nd
and Pb isotopic analyses indicate old sources, with depleted mantle m
odel ages (T-DM) from 1880 to 1660 Ma, Pb-207/Pb-204 from 15.62 to 15.
87, and Pb-206/Pb-204 from 19.11 to 22.08. U-Pb ages for single-grain
and multigrain populations of detrital zircons range between 1113 and
992 Ma, the youngest of which defines a maximum depositional age for t
he Trap Falls Formation. U-Pb zircon ages indicate a late Grenvillian
source for the zircons, Nd and Pb isotopic compositions are consistent
with a source that is dominated by Grenville-age rocks with some comp
onent of older crust. Combining ail of the data, we interpret that the
protolith of the Trap Falls Formation was comprised of aluminous muds
interbedded with clean quartz arenites, and suggest that they were de
posited on the stable, trailing-edge margin of North America sometime
during the Late Proterozoic to the Early Cambrian, The sediments were
derived from a weathered source with an upper continental crust compos
ition. Isotopic data and zircon ages indicate that this source was dom
inated by Grenville-age rocks.