The western Churchill Province of Canada preserves an extraordinary geologic record of processes active during the growth, evolution, exhumation, and stabilization of early continental crust. The East Athabasca area in particular exposes a huge tract (1000's of km2) of rocks that were heated to temperatures of nearly 1000 deg C at depths of more than 20 km. In fact some of the rocks were formed at the highest pressures ever recognized in North America. The region can be divided into a number of small domains that preserve distinct rock types and geological histories. Each of the individual domains record, with impressive clarity, key stages in the tectonic evolution of the Canadian shield. Together, they provide a map view of the complexity that may characterize the deep crust in general. Since the deep crust is generally not accessible for study this area provides a unique view of what happens deep in the earth's crust. Most of the rocks in this study are about 2.6 billion years old. Field and laboratory research in the East Athabasca area documents the effects of a much younger event (1.9 billion years ago) that has transformed these rocks leading to the hypothesis that the area represents a map view of domains assembled in the deep crust 1.9 billion years ago immediately prior to being uplifted and exposed. As such, the region may provide a direct view of the rock types, structures, and heterogeneity at several km wavelengths that are seismically imaged or inferred to exist in other areas where the deep crust is not exposed. Crucial to strengthening this hypothesis is a better understanding of the internal structure of individual domains and their boundaries. Goals of this project are to understand (1) the assembly of heterogeneous deep crustal domains; (2) the significance and cause of metamorphism 1.9 billion years ago; (3) the role of adding melts from deep within the earth to the deep crust (4) how an enormous area of deep crustal rocks can be exhumed; and (5) the setting of these rocks within the broader context of western North America. This integrated approach is placing important first-order constraints on the character, behavior, and evolution of lower crust during crustal assembly, stabilization, and exhumation.
