Geochronology of ophiolites of the Newfoundland Appalachians

Abstract

Precise U/Pb zircon ages (2σ errors) are reported for four ophiolite complexes from the Newfoundland Appalachians.Zircons from trondhjemite from Blow Me Down Mountain, Bay of Islands Complex, give an age of [Formula: see text] (five points). Those from gabbro from Blow Me Down Brook give a minimum 207Pb/206Pb age of 480 Ma (one point), confirming that this is the age of the main plutonic episode. These data refute previously determined latest Cambrian U/Pb zircon and Sm/Nd (mineral–rock isochron) ages of 504 ± 10 and 505 Ma for the complex.Gabbro from the Betts Cove Complex yielded zircon that gives an age of [Formula: see text] (four points). This refutes the interpretation of an earlier U/Pb (zircon) age of 463 ± 6 Ma for a trondhjemite dyke as the age of the ophiolite. It was inconsistent with the presence of Arenigian graptolites in the overlying Snooks Arm Group.Two zircon ages from a pegmatitic and medium-grained trondhjemite of the Annieopsquotch Complex are [Formula: see text] (five points) and [Formula: see text] (two points). Zircon from trondhjemite of the Pipestone Pond Complex of central Newfoundland gives an age of [Formula: see text] (five points). Analysis of a single zircon fraction from the Coy Pond Complex gives a minimum 207pb/206pb age of 489 MaThe ages are comparable to those of the Lushes Bight Terrane, Newfoundland, the M'Clintock West Massif, Arctic Canada, and the Ballantrae Complex, Scotland, and together span 18 Ma of the Tremadocian and Arenigian stages. This short age range may imply that only young "hot" oceanic crust was emplaced and preserved in the Appalachian–Caledonian mountain belt.