Proterozoic plate tectonics in Canada with emphasis on evidence for a Late Proterozoic rifting event

Abstract

Several Early Proterozoic fold belts in the Canadian shield have been interpreted in terms of plate tectonic processes. The most impressive evidence comes from those preserved on the margins of Archaean cratons such as the Wopmay orogen and the Penokean fold belt. There are striking similarities in the stratigraphic successions of many widely separated Early Proterozoic fold belts within the Canadian shield. Most of these are currently best interpreted in terms of some modified version of plate tectonics. Post-Grenville rocks contain several independent lines of evidence that support a major episode of continental fragmentation. Stratigraphic and sedimentological evidence from the Cordilleran region records a dramatic change from widespread development of essentially platformal marine sediments (L. Mackenzie Mountains Supergroup) through rift-related evaporites and clastics (U. Mackenzie Mountains Supergroup) to a largely resedimented sequence (Ekwi or Windermere Supergroup) that has been interpreted as a continental margin facies. A closely comparable succession of facies can be documented in other parts of the world but perhaps the closest analogue is found in S.E. Australia. It has been suggested that these two regions may formerly have been juxtaposed and represent the sundered fragments of a Late Proterozoic supercontinent. Relevant to these interpretations are geochemical data such as δ 34S values from Late Proterozoic evaporites and 87Sr/ 86Sr measurements from carbonates, and processes involved in precipitation of glacially-related iron-formations such as those of the Rapitan Group in the N. Cordillera. Preservation of Late Proterozoic ophiolites in North Africa provides additional evidence of plate tectonic processes at that time. These several lines of evidence all suggest a significant period of Late Proterozoic continental breakup which produced many of the continental margins that were and are the loci of subsequent Phanerozoic orogenic activity.