STRUCTURES AND STRAIN HISTORIES ACROSS THE SUTURE: IMPLICATIONS FOR THE KINEMATICS OF THE COLLISION OF THE WRANGELLIA COMPOSITE TERRANE WITH THE MARGIN OF NORTH AMERICA

Structural mapping and strain analysis in marine rocks along the collisional suture between the Wrangellia composite terrane (WCT) and the Mesozoic margin of North America suggest an oblique collision with a significant component of right-lateral shearing. The location of the collision and therefore the plate kinematics remain controversial. In central Alaska, the broadly-defined suture zone consists of the Kahiltna assemblage, a Jurassic-Cretaceous submarine fan complex that has been subdivided into two basins: the Talkeetna Range basin and the Alaska Range basin with affinities to North America and the WCT, respectively. In south-central Alaska, the basins are separated by Broad Pass and the Reindeer Hills. We have completed structural analysis along two transects across the Kahiltna assemblage: a northern transect across the Reindeer Hills and northern Talkeetna Mountains, and a southern transect across the Alaska Range. At the northern end of Broad Pass, the depositional and deformational history of three tectonostratigraphic units enables determination of the tectonic evolution of the suture zone. The Reindeer Hills exposes mélange units that include oceanic lithologies and represent a remnant of an accretionary complex that formed during subduction prior to the collision of the WCT. Structures and strain histories within the Kahiltna assemblage in the Talkeetna Mountains indicate oblique northwest-directed thrusting and right-lateral shear during the collision of the WCT. The Jack River conglomerate, a fluvial clast-supported conglomerate, unconformably overlies the Reindeers Hills mélange and indicates uplift and erosion of the accretionary complex, followed by fluvial deposition late in the collision. On the other side of Broad Pass, in the southern Alaska Range, horizontal stretching lineations and steeply-dipping foliation indicate that deformation occurred during transpression as a result of highly oblique convergence. Strain analysis of pressure shadows indicates a counterclockwise rotation of the extension direction in map view and thus, right-lateral shearing during the collision. These results are consistent with the hypothesis that the WCT was carried on the Kula or Resurrection plate and experienced moderate northward transport.