Delamination of the Subcontinental Lithosphere of the Wyoming Craton Related to the Yellowstone Hot Spot

Analysis of the van der Lee and Frederikson NA04 S-wave tomographic model for western North America shows two significant E-trending embayments in the Precambrian lithospheric mantle. The northern embayment is characterized by asthenospheric velocities at shallow levels and lies beneath Archean and Proterozoic crust. It extends from the Rocky Mountain Basin and Range in central and SW Montana southeast to the Bighorn Range, Wyoming, and is centered on the Yellowstone Hot Spot. Within the embayment the subcontinental lithosphere extends only to 70-90 km depth, and is similar to the Basin and Range Province. East of the embayment at 43-45 degrees N latitude S-wave velocities up to 2% slower than typical subcontinental lithosphere occur at depths of 70-110 km across the Wyoming craton to the Black Hills. At depths of about 150 km the S-wave velocities are 2% faster. This suggests that a tongue of mantle with asthenospheric velocity is present at depths 70 and 110 km with lithospheric velocities above and below, beneath the geographic center of the Wyoming craton. At about 42 degrees N latitude the Precambrian lithospheric root is intact to a depth of 150 km in the west and to >200 km in the east. Published data from mantle xenoliths and Cenozoic volcanic rocks indicates that the lithospheric mantle within the anomalous zone at 43-45 degree N was intact during Laramide time. Xenoliths from the Leucite Hills are consistent with intact Archean mantle in the southern Wyoming province at ca. 5 Ma. The seismic velocity anomaly data suggest that lithospheric root of the Wyoming craton is delaminating from west to east due to the encroachment of the Yellowstone hot spot.