Metamorphosed gabbroic dikes related to opening of Iapetus Ocean at the St. Lawrence promontory: Blair River inlier, Nova Scotia, Canada
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Metamorphosed mafic dikes in the Laurentian Blair River inlier of northern Cape Breton Island, Nova Scotia, are related to the opening of the Iapetus Ocean during the breakup of the supercontinent Rodinia. The dikes were metamorphosed during a Paleozoic (likely Silurian) thermal event related to Appalachian orogenesis but were not deformed significantly. Two dikes yielded U-Pb zircon ages of 581 6 and 576 6 Ma, have the chemical characteristics of subalkaline basalt generated at rift environments, and have initial Nd values of + 4.9. Metagabbro dikes of the Blair River inlier are contemporaneous with and geochemically similar to other Iapetus rift-related, mafic rocks in eastern North America. A block of Laurentia "missing" from the Quebec embayment should also contain rift-related dikes of this age and basement of similar character to the Blair River inlier. If this block could be identified, much as the Argentine Precordillera has been identified as a block derived from southern Laurentia, then these new data will aid in Neoproterozoic paleogeographic reconstructions of Rodinia. 2004 by The University of Chicago. All rights reserved.
