HR: 1330h
AN: V12B-0589    [PDF]
TI: Late Mesozoic-Cenozoic Evolution of the North American Cordillera: Lithospheric Response to Plume-Slab Interaction
AU: * Ihinger, P D
EM: ihinger@uwec.edu
AF: University of Wisconsin-Eau Claire, Dept. Geology, 105 Garfield Ave., Eau Claire, WI 54701 United States
AU: Watkins, J M
AF: University of Wisconsin-Eau Claire, Dept. Geology, 105 Garfield Ave., Eau Claire, WI 54701 United States
AU: Bernhardt, J E
AF: University of Wisconsin-Eau Claire, Dept. Geology, 105 Garfield Ave., Eau Claire, WI 54701 United States
AU: Johnson, B R
AF: University of Wisconsin-Eau Claire, Dept. Geology, 105 Garfield Ave., Eau Claire, WI 54701 United States
AB: Throughout the late Mesozoic and Cenozoic eras, western North America experienced widespread deformation and volcanism. The nature and extent of this activity does not fit conveniently into the plate tectonic framework for crustal evolution. To date, there is no satisfying explanation that integrates the Laramide Orogeny, Basin and Range extensional activity, and the rise of the Colorado Plateau with the voluminous Tertiary volcanism including Eocene high-K magmatism, the mid-Tertiary ignimbrite `flare-up' in and around the Great Basin, and the more recent out-pouring of the Columbia River flood basalts (CRB). In fact, the unusual spatial and temporal relationship between the CRB and the on-going time-progressive basaltic and rhyolitic volcanism associated with the Yellowstone hot-spot track has led some researchers to question whether upwelling plumes do, indeed, exist. We note that magmas produced in western North America throughout the Cenozoic were derived from two compositionally distinct source regions: the sub-continental lithosphere (representing $>$95% of the magmatism) and the OIB source region ($<$5%). The two magma types occur at the same place and time throughout the province. We propose that the impingement of the positively buoyant plume head of the Yellowstone hot spot with the underside of the negatively buoyant, subducting Farallon plate at 80 My is responsible for the widespread Tertiary deformation and magmatic activity in the North American Cordillera. The dynamics of mantle flow required to accommodate the mutual passing of the two bodies led to a crisis in the normal mantle flow regime. Upwelling of the plume head was accommodated by shallowing both the Farallon slab and the overlying mantle wedge. This activity drove the subsequent tectonics of the over-riding continental lithosphere for nearly 80 My. We argue that this model is consistent with existing geological, geochemical and geophysical observations of the Cordillera; it provides a new framework in which to view several present-day features of the Cordilleran province, including the observed broad regional uplift, high heat flow, and the anomalous slow propagation of P and S waves through the underlying upper mantle.
DE: 1040 Isotopic composition/chemistry
DE: 3640 Igneous petrology
DE: 8109 Continental tectonics--extensional (0905)
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting