COLLISIONAL OROGENY ALONG THE PANTHALASSA-CIRCUMPACIFIC MARGIN OF NORTH AMERICA: DEVELOPMENTS SINCE THE PLATE TECTONIC REVOLUTION

Since the advent of the Plate Tectonic Revolution 50 years ago, plate-tectonic interpretation of the Alpine-Himalayan orogens has consistently pointed to continent-continent and island arc-continent collisions with large-scale orogen-parallel horizontal translations, with multiple ophiolite-bearing sutures. Around the Panthalassa-Circumpacific margin, similar tectonic processes have operated since the late Precambrian opening of that ocean by the fragmentation of Rodinia. In the North American Cordillera (NAC), interpretations have focused either on uniform E-ward subduction ("Andean-style") orogeny, or an "archipelago-style" orogeny of periodic collision of offshore island arcs or continental fragments with the North American continental margin.

Recent advances in "tomotectonics" (e.g., Sigloch and Mihalynuk, 2017)--correlation of deep mantle structure with near surface tectonics, have falsified the "Andean" scenario and made clear that an "archipelago-style" or Alpine-style orogeny has prevailed along the NAC portion of the Panthalassa-Circumpacific margin since early Paleozoic time. Collisions of various offshore crustal blocks with each other and the NAC resemble Alpine-Himalayan and Taiwan–Papuan style orogenic events. Subduction zones may have dipped both beneath and away from the NAC margin, and at times in simultaneous modes. As many as nine sutures between the NAC and far travelled island arc systems may be present in the US Cordillera. In the Basin-Range province and its N-ward continuation, a Tibet-like highland with thick orogenic crust, formed by Mesozoic collisional orogeny, became the foci of extensional collapse, bimodal volcanism and metamorphic core complex development in the Neogene. The Nevada highland was the primary source region of early Cenozoic gold-bearing river gravels in California and Nevada. Continental margin-parallel transform fault tectonics has played a major role in long-distance lithospheric scale translation, both dextral and sinistral, of crustal fragments. Present-day collisional–accretionary orogens around the western Pacific margin (Australia-Indonesia, Japan-Kuriles-Kamchatka) and in Melanesia (Papua–New Guinea, Indonesia) provide actualistic models of Paleozoic-Mesozoic orogenic processes in the NAC.