Paper No. 65-12
Presentation Time: 11:15 AM
U-PB ZIRCON AND APATITE CHRONOMETRY OF INTRUSIONS IN AN ACCRETIONARY METAMORPHIC BELT IN WESTERN IDAHO, USA
The Salmon River suture zone (SRSZ) in west central Idaho, USA contains metamorphic rocks of island arc affinity that were accreted to North America during the earliest phases of construction of the Rocky Mountains. To investigate the timing of metamorphism and exhumation, we present U-Pb zircon and apatite ages from pre-, syn- and post- kinematic igneous rocks to bracket deformation and provide estimates for exhumation from the mid-crust. Cretaceous, high U/Th zircon rims are inferred to reflect metamorphic zircon growth and used as estimates for the age of peak metamorphism. Low U/Th zircon populations are interpreted as igneous and resulting U-Pb ages are used in the context of cross cutting relationships and fabrics. U-Pb apatite ages recording mid temperatures (closure temperature=375-600°C) are presented to estimate cooling of rocks that reached 600° C. We present these coupled U-Pb ages and field contextual information in addition to estimates for metamorphism and exhumation that provides a pathway to construct a timeline for the full pressure-temperature path that tracks the movements of the mid-crustal rocks. These data provide insight into the mechanics required for burial and exhumation during Cordilleran-style orogenesis.