PROVENANCE OF THE NEWFOUNDLAND APPALACHIAN FORELAND BASINS: IMPLICATIONS FOR TECTONICS OF THE LAURENTIAN MARGIN

Neoproterozoic to Cambrian break-up of Rodinia opened the Iapetus Ocean and formed an irregular Laurentian margin, defined by NE-striking rift zones offset by NW-striking transfer faults. Contrasts in detrital zircon populations from W Newfoundland indicate two distinct provenance domains in rift-to-drift rocks. A proximal western succession dominated by Mesoproterozoic detritus, with strong peaks at 1.1 Ga, indicates derivation from local basement and the Grenville Province to the west. A distal succession to the east displays similarities with the Laurentian margin in Greenland and Scotland, with prominent 1.85 Ga peaks and many (~2.7 Ga) Archean grains. These contrasts may have resulted from a major NW-striking transfer fault, blocking sediment transport, between the Newfoundland Promontory and Québec Embayment.

Ordovician through Devonian closure of the Iapetus Ocean resulted in multiple orogenic episodes and development of foreland basins above the rift-drift succession. Ages of detrital zircon within the foreland successions are consistent with Laurentian sources, but the details of the distributions indicate provenance changes associated with shifting loads and sources within the orogen. Previous results from the oldest, M. Ordovician, foreland succession (Goose Tickle Gp.) show ages similar to the Humber Arm Allochthon, including a prominent peak at 1.85 Ga. Younger foreland successions (U. Ordovician Long Point Gp. and Silurian – Devonian Clam Bank Fm.) are dominated by ages between 0.95 and 1.3 Ga, with largest peaks between 1.0 and 1.1 Ga, typical of the Grenville Orogen. The abundance of Mesoproterozoic grains and conspicuous lack of 1.85 Ga zircon indicates a major provenance switch. Continental margin units in Québec/New England demonstrate similar signatures, suggesting derivation of the Long Point Group from the SW. Within the mid-Paleozoic Clam Bank - Red Island Road succession, the absence of Gondwanan ages and abundance of 1.0 Ga grains is consistent with underthrusting of Gondwanan microcontinents, Ganderia and Avalonia, during Salinian and Acadian orogenesis. Zircon found in the E. Devonian Red Island Road Formation is consistent with sources in Grenville massifs in W. Newfoundland or Cape Breton Island which were uplifted during Acadian inversion.