The Proterozoic Slab Volcanics of northern Yukon, Canada: Megaclasts of a volcanic succession in Proterozoic Wernecke Breccia, and implications for the evolution of northwestern Laurentia.

摘要

During the Proterozoic, northwestern Laurentia underwent episodes of sedimentation, intrusion, deformation, volcanism, and hydrothermal activity. In Yukon, the oldest sedimentary succession, the Wernecke Supergroup, was deposited in a marine basin after cratonisation (ca. 1840 Ma) and before 1710 Ma. The earliest orogenic event to disturb these pericratonic strata was the Racklan orogeny. An unconformity and deformational structures record at least three events of contraction associated with the Racklan orogeny. These features and those of the correlative Forward orogeny are recognized throughout much of northwestern Canada. Related metamorphism reached peak temperatures of 450--550°C. Zones of Wernecke Breccia (hydrothermal breccias previously dated at 1595 Ma) were emplaced into the Wernecke Supergroup after Racklan deformation, metamorphism, exhumation of at least 8 km from the core of a major anticline, and eruption of the Slab Volcanics. Vent facies of Wernecke Breccia are characterized by grey, sodic breccias whereas breccias from greater depths tend to be red and more potassic. Fragments of the Slab Volcanic succession occur as clasts within Wernecke Breccia and their preservation at three localities is the only record of this stratigraphic unit. (Abstract shortened by UMI.)