DETRITAL ZIRCON CONSTRAINTS ON SEDIMENT DISPERSAL PATTERNS IN WESTERN NORTH AMERICA

Detrital zircon provenance studies during the past 10 years have greatly improved our understanding of sediment dispersal patterns in western North America. These studies have been conducted by several different research groups utilizing ID-TIMS, ion probe, and, most recently, laser-ICPMS techniques.

First-order patterns are as follows: (1) In southwestern North America, a large volume of sediment was generated during 1.25 Ga volcanism. This detritus is now preserved primarily in restricted basins on the craton (e.g., Apache Group). (2) Grenville-age tectonism produced a huge volume of detritus that was carried in large river systems north and west across Laurentia, apparently blanketing much of the continent. (3) Neoproterozoic-early Paleozoic emergence stripped most of this Grenville blanket from the craton, with much of the detritus accumulating in lower units of the Cordilleran miogeocline. (4) Paleozoic and Triassic miogeoclinal strata include sediments shed from local basement, from the Peace River arch (during Middle Ordovician time), and from the Innuitian orogen (and perhaps Caledonian orogen) in the northern Cordillera. Appalachian-derived sediment reached the southern Cordilleran margin during Permian and Jurassic time, providing much of the detritus in Colorado Plateau eolianites. (5) Pericratonic assemblages in the Cordillera consist largely of detritus shed from the Peace River arch region, with subordinate input from Grenville basement to the south. (6) Most clastic detritus in arc-type terranes in the Cordillera was generated during contemporaneous or slightly older magmatism. Most sequences also include detritus derived from mid-Paleozoic arc magmatism and from cratonal rocks. With the exception of the Alexander terrane, there is little evidence for exotic or far-travelled components in the Cordillera.

Given the reconnaissance nature of most studies, and the small proportion of sedimentary sequences that have been analyzed, much remains to be learned about the origin and transport history of clastic detritus in western North America.