Tectonic implications of syn- and post-emplacement deformation of the Mount Stuart batholith for mid-Cretaceous orogenesis in the North Cascades

The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting and folding, and west-northwest stretching. Contraction ended shortly after emplacement, as indicated by high-temperature recrystallization in thrust-related mylonites of the pluton and by geochronological data, whereas west-northwest stretching continued for an unknown period of time. This is the best documented mid-Cretaceous contractional belt in the main part of the crystalline core. The shortening direction and timing are identical to that of southwest-vergent thrusts in the offset continuation of the core in British Columbia. The contractional belt provides a link between thrusting in the Northwest Cascades thrust system and deformation in the crystalline core.