Ophiolites, the Sierra Nevada, “Cordilleria,” and Orogeny along the Pacific and Caribbean Margins of North and South America

Abstract

Ophiolites are major expressions of orogeny; they are dominantly oceanic crust and mantle emplaced by collision of a mantle-rooted thrust (subduction zone) with a continental margin or island arc. Ophiolite nappes thus represent remnants of lithospheric plates; their basal thrusts (fossil subduction zones) intrinsically cannot be balanced; their displacements are unknown but very large. Two major belts of Mesozoic ophiolites and related island-arc complexes extend along the western and Caribbean margins of the Americas from Alaska to Ecuador. An eastern belt (e.g., Stikinia-Intermontane superterranes, Canada, United States; rocks of western Baja Californa and the Guerrero terrane, Mexico; ophioliticand related rocks of Guatemala, Cuba, Hispaniola, Puerto Rico, and La Desirade; Cordillera de la Costa, Venezuela; and the Cordillera Central, Colombia) was an active island-arc complex in the Early to Middle Jurassic and was emplaced in Middle Jurassic-Cretaceous time. A western belt (e.g., the Wrangellia/Insular superterrane of Canada and United States; Choco-Chortis blocks of Central America; Cordillera Occidental (Pinon) of Colombia and Ecuador) experienced activity during the Jurassic-Cretaceous and was emplaced during Late Cretaceous-Tertiary time. These relations inspire an outrageous hypothesis that in Middle to Late Mesozoic time, a separate intra-oceanic plate similar to the present Philippine plate, herein named “Cordilleria,” was separated by active island-arc complexes from the American and Farallon/Kula plates to the east and west, respectively. Basement rocks of the Colombian, Venezuelan, and Yucatan basins may represent remnants of “Cordilleria.” Convergence and collision of “Cordilleria” and its island-arc margins with the American continents were major factors in western American and Caribbean orogenic development. The Mesozoic tectonic history of the North American Cordillera, with its conflicting sinistral and dextal motions at varying locations and times, suggests a model involving a rigid-plastic continuum approximation using slip-line field theory, as successfully applied to the Indian-Eurasian collision. Complex evolution of the northern Sierra Nevada and its surroundings may reflect such tectonics. Direct contact between the Kula/Farallon plates and North America may not have occurred until Late Cretaceous time.