The research by Wernicke and his group is primarily observational, and is strongly multidisciplinary and collaborative. Current projects include studying large-scale intracontinental extension, mainly in the Basin and Range province of the western United States; studies of high-temperature evolution of the deeper parts of collision zones; and studies of active tectonics of diffuse zones of intracontinental deformation. With field observation and geological mapping as a foundation, students and postdocs in the group address problems using a wide spectrum of methods, including sequence stratigraphy, paleomagnetism, geochronology, petrologic thermobarometry, remote sensing and GPS geodesy.

Large-Scale Intracontinental Extension

The tectonics of horizontal contraction of the earth's continental lithosphere have been well studied for more than a century, in orogens such as the Alps, Caledonides and Appalachians. Equivalent understanding of extension has arisen mainly over the last decade, spurred by geologic field studies in the Basin and Range province of western North America, the earth's best exposed region of large-scale intracontinental extension. Recent work by Wernicke and postdoctoral fellow J.K. Snow in the central Basin and Range (lat 37N) demonstrates about 250 km of west-northwest translation of the Sierra Nevada relative to the Colorado Plateau since 20 Ma, accommodated along both normal and strike-slip fault systems.

Geological reconstructions show the principal zones of extension, now 100-150 km wide, are nearly completely stripped of their upper 12-15 km of crust. The lack of major topographic or gravity anomalies over the extended zones has prompted two major projects, BARGE (Basin and Range Geoscientific Experiment) and the Southern Sierra Nevada Continental Dynamics Project, aimed at understanding how the deep crust responds to extension by imaging the deep structure of the eastern and western boundaries, respectively, of the central Basin and Range. These projects involve explosion seismology, "marine" deep reflection profiling (off barges in Lake Mead), magnetotelluric imaging, xenolith studies, geologic mapping, thermochronology and thermobarometry, and paleomagnetism. One of the main results coming from this work is that the complex patchwork of extended upper crustal blocks are floating on a fluid deep crustal layer, which is appears to have been "pumped" into the region between the separating blocks, completely reconstituting the upper crust. Modeling studies suggest this layer may be as much as four to five orders of magnitude less viscous than the upper mantle.

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