Abstract

The Queen Charlotte basin and adjacent Coast Mountains are paired belts of synchronous subsidence and uplift that formed inboard of the Queen Charlotte fault in Neogene time, accompanied by regional basaltic volcanism. We propose that a combination of pure and simple shear on a lithosphere-scale, low-angle normal fault could have been responsible for the observed vertical motions. Extensive crustal thinning in the basin decreases toward the Coast Mountains and has resulted in net subsidence of as much as 6 km since 20 Ma. East of the basin, in the Coast Mountains, more than 3.5 km of surface uplift has taken place since 14 Ma, probably because the upper mantle lithosphere has been locally thinned and replaced with less-dense asthenosphere. Magmatic activity in the basin and mountain belt could have been caused by decompression melting in the deformed lithosphere and upwelling mantle.

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