Abstract Title: Reactivation history of continental lithosphere of the Great 
Basin RegionÑProterozoic to Present

Abstract Author(s): Karlstrom, Karl E. (University of New Mexico)  

Abstract: The lithospheric structure of the western U.S. represents an 
interaction of structures that formed during the Proterozoic (assembly to 
Rodinia breakup), and structures that formed or were modified during Cenozoic 
tectonism. This interaction of old structures and young driving forces, at 
lithospheric scale, provides a set of ongoing natural ÒexperimentsÓ that can be 
used to understand geodynamics of continents. This research involves 
collaborative investigations involving teleseismic studies, geologic studies 
that add ground truth and the time dimension, and geodynamic models that test 
realistic physical models. One of the most fundamental questions concerns the 
extent to which mantle velocity variations at 10-100 km scale are old and 
influenced by ancient lithospheric structure of North America, as opposed to 
young upwellings of asthenosphere and displacement of lithosphere due to small 
scale mantle convection. In the Great Basin region, mantle velocity variations 
coincide with both old structures (and Cenozoic tectonic provinces), such as: 
the Cordilleran miogeoclinal hingeline (Colorado Plateau edge), Great Falls 
tectonic zone (Snake River Plain), Proterozoic shear zones (Virgin Mountains), 
and Mojave-Yavapai province boundary (St. George lineament. Hence, a working 
hypothesis is that mantle velocity variations can represent original 
differences in bulk composition, thickness, and state of hydration of the 
Proterozoic lithosphere and that these compositional variations have been 
accentuated by different fertility and partial melt content of different mantle 
provinces due to asthenospheric upwelling in the Cenozoic. If so, present 
lithospheric structure cannot be understood without understanding both 
neotectonics and cumulative lithospheric evolution.