GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 291-4
Presentation Time: 2:20 PM


MACDONALD, Francis A., Department of Earth Science, UCSB, 2111 Webb Hall, Santa Barbara, CA 93109, HODGIN, Eben Blake, Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, CROWLEY, Jim L., Department of Geosciences, Boise State University, Boise, ID 83725 and KARABINOS, Paul, Department of Geosciences, Williams College, 947 Main St., Williamstown, MA 01267

A detailed synthesis of the Ordovician Taconic orogeny in the northern Appalachians has been hindered by along strike variations in Laurentian, Gondwanan-derived, and arc-generated tectonic elements. In particular, it is not clear which variations reflect primary differences in plate tectonic geometry, differential erosion, or post-Taconic strike-slip faulting. Here we present new geochronologic data from the Corner Brook Lake block (CBLB) and the Dashwood terrane of Newfoundland and compare them with data from New England. New Grenvillian magmatic and metamorphic dates from the CBLB constitute piercing points with the Indian Head Range across the Humber River Fault. Metasediments on the Dashwoods terrane, previously correlated with the Fleur de Lys Supergroup (FDLS) on the Laurentian margin, are bracketed in age by Early to Middle Ordovician detrital zircon and Middle Ordovician intrusions and metamorphism. These data demonstrate that the CBLB is not far travelled and that the Lush’s Bight and Dashwoods metasediments were deposited in a syncollisional basin postdating the deposition of the FDLS. The Middle to Late Cambrian (?) Twillingate Granite and Little Port Trondhjemite are the only pre-Ordovician basement present in the Dashwoods terrane. We have found neither Laurentian basement nor Gondwanan-derived Moretown terrane equivalent underlying Dashwoods. Dashwoods may be an Early Paleozoic juvenile arc terrane or an intra-arc basin and potentially equivalent to the Hawley Formation in New England.