Abstract

The Early Proterozoic Ungava orogen contains evidence for the development of a longlived (>80 m.y.) and presumably wide ocean that was subsequently destroyed during plate convergence leading to arc-continent collision. A magmatic arc was built on 2.00 Ga oceanic crust above a north-dipping subduction zone between about 1.90 and 1.86 Ga. Development of a south-verging continental thrust belt containing units associated with prior rifting of the Archean Superior province basement probably records impingement of the upper plate against the underthrust continental margin at ca. 1.87 Ga. Subduction of the Superior province continental crust is inferred to have led to a reversal in subduction polarity. A younger, south-dipping subduction zone is suggested by a suite of 1.85-1.83 Ga quartz diorite to granite plutons that intrude the upper- plate oceanic crust and the older arc. The arc-continent collision resulted in a minimum of 65 km of tectonic overlap of the composite arc's plutonic core on the autochthonous footwall basement.

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