Abstract

In the central and southwestern Grenville province in Canada and the northeastern United States, anorthosites and related granitoids were emplaced during two distinct pulses, at ca. 1.16–1.13 Ga and 1.09–1.05 Ga, each following major crustal thickening events. U-Pb age constraints on movement along major ductile shear zones indicate that they were emplaced within extending crust in an overall convergent orogen. We suggest that convective thinning of the lithosphere played a significant role in their emplacement and in the tectonic evolution of the Grenvillian orogeny.

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