ZIRCON GEOCHEMISTRY AND GEOCHRONOLOGY OF THE SEVEN DEVILS MOUNTAINS, WESTERN IDAHO: TESTING PROPOSED TIES TO THE WRANGALIA TERRANE

The North American Cordillera provides an excellent location to study terrane translations in an accretionary orogeny. Some previous studies have proposed the Baja B.C. hypothesis of northward terrane transport in the Cordillera. This has been supported by paleomagnetic data and detrital zircon age distributions characteristic of displacements from 1100 to 3000 km in Washington and British Columbia. The Seven Devils Mountains are located in the Wallowa-Whitman National Forest in western Idaho. This geologically complex and variably metamorphosed terrane preserves a Permo-Triassic volcanic arc accreted against the Cordilleran margin. Previous trace element analysis suggests that the volcanic rocks are transitional, calc-alkaline rocks typical of subduction zone volcanic arcs. Whole-rock geochemical analyses from the 1970’s and 1980’s led authors to propose that the Seven Devils terrane was part of the Wrangellia terrane, a volcanic arc terrane located further north in the Cordillera. Despite their physical similarities, the distance between the terranes and significant geochemical differences make correlation uncertain. Zircon trace element geochemistry and geochronology generated by this study will be used to test models for northward displacement of the arc by allowing for robust comparisons with extant data from Wrangellia. If the Seven Devils is indeed part of Wrangellia, then collected data will provide additional evidence for significant long range transport along the Cordilleran margin. If not, then the Seven Devils may represent an independent tectonic element of the Cordillera that may not require long-distance orogenic displacement. This new zircon trace element geochemistry and U-Pb geochronology will bring valuable insight on the formation of the Seven Devils, how volcanic arcs evolve over time, and importantly, how western North American has evolved due to terrane transport.