Along strike variations in metamorphism and deformation of the strata of the Kahiltna Basin, south-central Alaska

Late Cretaceous to early Paleocene deformation and metamorphism of strata of the Kahiltna basin varies in depth and style from east to west during the collision of the Wrangellia composite terrane. In the east, the Maclaren Glacier metamorphic belt experienced kyanite-grade regional metamorphic conditions of approximately 650 degrees C at >670 MPa during top-to-the-south thrusting. About 100 km along strike to the west, the Devil Creek area experienced contact metamorphic conditions at approximately 300 MPa forming andalusite, with sillimanite+ or -migmatite near pluton margins. Three plutons from the Devil Creek area yield U-Pb zircon ICP-MS dates of 68.3+ or -2.6 Ma, 66.1+ or -2.6 Ma, and 62.6+ or -2.1 Ma, which we interpret to be the crystallization ages of the plutons. In the Maclaren Glacier metamorphic belt and 74 Ma, 1-kilometer-thick tonalite sill intruded during top-to-the-south thrusting. In the Devil Creek area, pluton emplacement occurred during NW-SE shortening and NE-SW near horizontal stretching. The age dates suggest that deformation and metamorphism in these two areas was diachronous, and the difference in depth of metamorphism of at least approximately 14 km between the Maclaren Glacier metamorphic belt and Devil Creek shows that exhumation of the strata of the Kahiltna basin was greater in the eastern part of the Alaska Range suture zone.