Regional metamorphism of the Appalachian Humber zone of Gaspé Peninsula: 40Ar/39Ar evidence for crustal thickening during the Taconian orogeny

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.