ANATOMY AND GLOBAL SETTING OF THE NORTH AMERICAN CORDILLERA

The Cordillera of western North America forms the central 5000 km of the Circum-Pacific orogenic belt extending for 25,000 km along a great circle path from the Antarctic Peninsula to Taiwan, but is anomalous because transform faults have supplanted subduction zones along much of the adjacent continental margin since mid-Cenozoic time. Mesozoic-Cenozoic Arctic and Mesoamerican transforms also delimit the North American Cordillera to the north and south. The Cordilleran margin of Laurentia was formed initially by rift breakup of Rodinia leading to development of the Neoproterozoic-Paleozoic Cordilleran miogeocline, but was modified in California and Mexico by Permian-Triassic transform truncation of Paleozoic tectonic trends. Paleozoic-Mesozoic accretion of oceanic island arcs and associated subduction complexes expanded the width of the Cordilleran orogen along its full length both before and after mid-Triassic initiation of ancestral Circum-Pacific subduction beneath the Laurentian margin. Mesozoic-Cenozoic extensions and counterparts of Cordilleran accreted terranes extend southward into the Caribbean Antilles and northern South America, and assembly of subduction complexes continued into Cenozoic time all along the Cordilleran continental margin. Strike slip along the Pacific flank of the Cordilleran orogen has displaced segments of the orogen laterally, but inferred translation of suspect terranes over distances undocumented by offsets of geologic features are based on underinterpretation of paleomagnetic vectors affected by pluton tilt and compaction shallowing which foster invalid overestimates of latitudinal transport. Successive forearc and retroforeland basins record the progress of Cordilleran orogenesis, and coeval Mesozoic-Cenozoic batholith belts reflect continuing plate consumption at subduction zones along the continental margin. In the USA and Mexico, Paleogene Laramide breakup of the Cordilleran foreland during shallow slab subduction expanded the net width of the orogen, and extensional structures of the Neogene Basin and Range taphrogen were superimposed on older orogenic trends.