Changing Tectonics, Cooling Climates and the Dawn of Crustal Extension: Late Eocene to Early Miocene (ca. 35–20 Ma)

Abstract

Subduction of the Farallon plate starting in the Late Triassic (225 Ma) was the single most important factor in shaping the Mesozoic and early Cenozoic landscapes of the Cordillera. Subduction shortened the crust laterally, thickened it vertically, gave rise to the development of a great magmatic arc, and brought numerous exotic terranes to the continent. The outcome of this subduction was that real estate was added to the continent. However, this nearly 200 million-year time interval of terrane accretion and compression started to change beginning around 35 Ma. This is when the East Pacific Rise and the Pacific plate first arrived at the North American margin and initiated a new set of processes that would alter the Cordilleran landscape in completely different ways (Fig. 10.1; Table 10.1).