Collaborative Research: A new appraisal of tectonic mobility in the northern Cordillera using connections between the Coast Mountains batholith and Alberta foreland basin

University Of Arizona, Tucson AZ

Investigators

Abstract

Western North America is made up of a collage of exotic terranes – blocks of crust that originated in other locations and were later accreted to the continental margin. Myriad studies have been performed to reconstruct the geologic and geographic histories of these blocks and to develop a chronology of how western North America was assembled. One of the enduring controversies is how far-travelled are some of these terranes. In particular, researchers debate the distance that one exotic block – the Insular superterrane – has been translated. Some argue that it has migrated >1500 kilometers northward – and perhaps eastward – along the North American margin, while others believe it has always remained near its present-day latitude. We propose to evaluate these end-member hypotheses by looking for connections between zircons crystallizing in the Coast Mountains batholith (part of the Insular superterrane) and those that have been recycled into sedimentary rocks of interior Canada. The presence or absence of the distinctive Coast Mountains batholith zircon fingerprint in rocks at similar latitudes will either refute or support the idea that the Coast Mountains were far away at the time of deposition of the targeted sedimentary strata. The proposed research will support students at the undergraduate and graduate levels, as well as a postdoctoral scholar. It will broaden and diversify the STEM workforce through promotion of early career female scientists and the inclusion of underrepresented minority students from Hispanic-serving institutions. One of the most critical unresolved questions in the tectonics of the North American Cordillera concerns the degree of tectonic mobility of terranes during Late Jurassic and Cretaceous time. End-member hypotheses posit that terranes presently located in British Columbia and southeast Alaska were either: 1) translated from the latitude of (Baja) California, and perhaps outboard of the Mezcalera Ocean basin, or 2) have remained near their present position and along the continental margin. The debate between the two forms the basis for the enduring “Baja-BC” controversy, which has been reinvigorated by discussion in recently published syntheses. We will test these end-member hypotheses by determining whether detrital zircons in foreland basin strata of Alberta, Canada (part of stable North America) were derived from the Coast Mountains batholith (CMB; part of the purportedly mobile terrane). This test is enabled by the recent recognition that zircons from igneous rocks of the CMB are isotopically and geochemically distinct from other coeval arcs along the margin (e.g. the Sierra Nevada and Idaho batholiths). Our study will: (1) define zircon age, Hf isotopic composition and trace element trends in plutons of the CMB, (2) generate similar data for plutons of the Omineca belt (a second suite of Cretaceous plutons in British Columbia), and (3) compare these igneous records with new studies of zircons in Cretaceous-Paleogene strata of the foreland basin in the northern Cordillera. Establishing connections between the CMB and inland foreland basin strata would provide strong support for models that invoke limited tectonic mobility, whereas the lack of such connections would support models that involve large-scale north-south and/or east-west displacements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.