The Arrival of Wrangellia and the Nevadan Orogeny: Late Triassic to Late Jurassic: Ca. 240–145 Ma

Abstract

The accretion of the Antler and Sonoma terranes in the Cordillera during the Paleozoic and Early Triassic was merely a prelude to the number of terranes and the scale of activity that would occur during the Mesozoic. Pangaea achieved its greatest extent around 250 Ma but not all of Earth’s continental crust was attached to it. Perhaps up to 15 % of the planet’s continental make-up existed as detached microcontinents, lying in the warm tropical waters of the Paleotethys Sea or Panthalassa Ocean. Some of these microcontinents would ultimately make their way to North America, arriving as terranes that resulted in large orogenic events. The fragmentation of Pangaea, ultimately yielding the various continental fragments that are familiar shapes on a globe today, signals a worldwide plate reorganization that brought on these changes. Included in this reorganization is the birth of the Atlantic Ocean as Africa and Europe drifted eastward, and the opening of Gulf of Mexico when South America drifted south (Table 7.1 and Fig. 7.1).