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Published 1990 | public
Book Section - Chapter

Tectonic development of Cordilleran mid-Paleozoic volcano-plutonic complexes; Evidence for convergent margin tectonism


Devonian and Lower Mississippian volcano-plutonic complexes and related basinal strata that extend from California to British Columbia lie outboard of coeval North American shelf rocks. Remarkable similarities between these complexes indicate that they form the remnants of a mid-Paleozoic east Pacific fringing arc system. Arc basement was composite. It is characterized in part by high initial Sr ratios, radiogenic Pb, and −ɛ_(Nd) values, and in part by low initial Sr ratios, various initial Pb ratios, and +ɛ_(Nd) values. These distinctive isotopic signatures, together with the presence of Proterozoic average ages for detrital zircon in ultimately continent-derived sedimentary rocks and Proterozoic upper-intercept (inheritance) ages on zircon from arc- and rift-related magmatic rocks, imply that basement was composed of both continental crust and transitional or oceanic crust overlain by continent-derived sedimentary rocks. These data suggest that the arc system formed adjacent to a continental landmass. The initial geometry of the arc has been highly modified by subsequent crustal thickening, extension, associated uplift, and transport along strike-slip faults.

Additional Information

© 1990 Geological Society of America. Accepted 27 March 1990. We thank Cynthia Dusel-Bacon, Dave Klepacki, Bill McClelland, Elizabeth Miller, Jason Saleeby, and Jim Wright for helpful discussions regarding mid-Paleozoic Cordilleran stratigraphy and tectonics, and Jim Mortensen and JoAnne Nelson for thorough and careful reviews of the manuscript. Some of these ideas were refined by discussions in the field with Jim Monger, JoAnne Nelson, Andy Okulitch, and Mike Orchard.

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August 19, 2023
January 13, 2024