Abstract

Geochronological studies on the timing of deformation and metamorphism along the Laurentian margin have shown that the ages of metamorphic events change along-strike within the Newfoundland – southern Quebec segment of the Canadian Appalachians. The Gaspé Peninsula is located at mid-point of the two extremities of this segment. New single-grain laser 40Ar/39Ar plateau ages solely reflect latest Middle–Late Ordovician metamorphism. Samples taken within the internal Humber zone in the Shickshock Group rocks yield 40Ar/39Ar muscovite and hornblende ages ranging from 457 to 454 Ma. Samples from the Amphibolite du Diable, the metamorphic sole of the Mont Albert ophiolite, yield 40Ar/39Ar muscovite and hornblende ages ranging from 459 to 457 Ma. Ordovician ages of the internal Humber zone are consistent with 40Ar/39Ar ages from southern Quebec and are interpreted as the result of the emplacement onto the margin of both the ophiolite and its metamorphic sole.

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