TRANSTENSION AND TRANSPRESSION AMONG LARGE-SCALE STRIKE-SLIP FAULT SYSTEMS IN WESTERN NORTH AMERICA
A very long, sinistral, fault (1000’s of km) with large displacement (ca. 1000 km) formed following cessation of Middle Jurassic subduction between ca. 165 and 148 Ma. During relative movement of the North America plate with respect to the proto-Pacific plate, large basins (e.g. Bedford Canyon - Great Valley, Kahiltna - Nutzotin) and suites of basins (Bisbee – Huachuca – McCoy Mtns., Methow-Tyaughton, Gambier, Gravina) formed at releasing steps. Late Jurassic contractional structures in Blue Mountains of Oregon and Angayucham domain of Alaska and coeval magmatic rocks probably record transpression followed by collision and partial melting. Early oceanic crust in the Gulf of Mexico, central Atlantic Basin, and Mediterranean Sea probably formed in the floors of left-releasing steps along the sinistral fault. Late Jurassic contractional deformation and coeval magmatism that are characteristic of parts of the Yanshan and more northerly Mongolo-Okhotsk collisional zone may record co-genetic regional transpression.