Large (1000 to 4000 km) northward movements of tectonic domains in the northern Cordillera, 83 to 45 Ma

Abstract

Using paleomagnetically derived estimates of latitudinal displacement, within the northern Cordillera we identify two major tectonic domains that were active during Late Cretaceous through Eocene time (roughly 83 to 45 Ma). At 100 to 90 Ma, the Interior Domain (comprising much of interior British Columbia, central Yukon, and eastern and central Alaska) was situated in the latitudes of Oregon and northern California, and the Coast Domain (southeastern Alaska, much of the Coast Ranges and islands of British Columbia, and the Cascade Mountains of Washington) was in latitudes similar to those of northern Mexico. Subsequently, both domains moved northward, reaching their present positions before 45 Ma. Within each domain, displacement estimates from northern locations are greater than those from southern locations, as if the domains had been elongated in an orogen‐parallel sense. Evidently, during the latest Cretaceous through Eocene, the Cordillera was a huge dextral shear system, which (83 to 65 Ma) carried the Coast Domain about 2000 km northward until it combined with the Interior Domain and then (65 to 45 Ma) drove the combined domains an additional 1000 to 2000 km north northwestward, spreading them out along the continental margin. Following previous workers, we ascribe these motions to the rapid oblique subduction of the oceanic Kula Plate beneath the continental western margin of the North American Plate, and derive a model based, in part, on comparisons with the oblique subduction of the Nazca Plate beneath the central Andes. Between the Interior Domain and the craton, geologic evidence in the north has been interpreted as indicating displacements comparable in magnitude to paleomagnetic estimates; in the south, the record has been obscured by Eocene extension. Between the Interior and Coast Domains, geological relationships are complex, and most current geologically based interpretations propose that post‐mid‐Cretaceous relative motions between them did not exceed a few hundred kilometers, whereas paleomagnetic evidence indicates 2000 km. Our reading of the geologic evidence is that it neither requires nor precludes the very large displacements inferred from paleomagnetic observations. Hence we argue that although the paleomagnetically derived displacements far exceed those proposed by geologic interpretations, they are not inconsistent with the geologic evidence itself.

East-derived strata in the Methow basin record rapid mid-Cretaceous uplift of the southern Coast Mountains batholith

“…In this model, the Insular superterrane would have accreted to North America as far south as present-day Baja California in western Mexico at ca. 100 Ma, and then translated north to join with the Intermontane superterrane after 70 Ma, and then both would have continued north to their present positions in British Columbia (e.g., Irving et al 1996;Haggart et al 2006).…”

“…The extent of Cretaceous to early Paleogene displacement on the Pasayten fault is more controversial (e.g., Lawrence 1978;Butler et al 1989;Hurlow 1993;Wynne et al 1995;Wyld et al 2006). The Pasayten fault has been proposed as the locus for large-scale dextral translation; values of displacement on the Pasayten fault range from <1000 km (e.g., Butler et al 1989;Kodama and Ward 2001) to >3000 km of displacement (e.g., Wynne et al 1995;Irving et al 1996;Ward et al 1997).…”

The big flush: paleomagnetic signature of a 70 Ma regional hydrothermal event in displaced rocks of the northern Canadian Cordillera

“…The Cordillera features many large strike-slip faults roughly parallel to the orogen with Late Cretaceous to early Cenozoic dextral motion, indicating northward displacement with respect to North America. Paleomagnetic studies since the early 1970s (summarized by Irving et al 1996) indicate that these northward motions were large and differed in places ranging from 1000 to 4000 km. This interpretation has proven controversial, since geological estimates of displacement fall far short of the paleomagnetic estimates.…”

Biography of Edward Irving

“…''The post-war period of generous funding was closing, and as a consequence a leanly manned, two-person, automated facility designed for visitors and direct collaborations with other institutions was developed,'' he says. Some of his work during this time addressed the movements of Vancouver Island and other parts of the Cordillera that have moved sideways and rotated relative to the Precambrian Canadian shield (13)(14)(15).…”