The tertiary magmatic sweep, Nevada, and early proterozoic tholeiitic/alkaline/peralkaline plutonism, Northwest Territories

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The goals of this project are to a) better understand the sources of igneous rocks emplaced during the last 40 million years in the western United States, and b) investigate igneous activity associated with breakup of an old supercontinent in the southern Northwest Territories of Canada. The past 40 million years has been a time of intense volcanic activity in the southwestern United States, particularly Nevada, accompanied by stretching and faulting of the crust. Volcanism swept methodically from northeast to southwest across Nevada, presumably a result of the subduction of the Farallon Plate beneath North America. We understand very little of how volcanism was linked to the subducting plate or crustal stretching, what the sources for the volcanic rocks were, and to what degree this igneous activity was responsible for contemporaneous gold mineralization in Nevada. We seek to identify the sources of magmas, either in the mantle or in the crust (or both), and better describe the timing of the sweep of volcanism across northern and western Nevada. In the Northwest Territories, an igneous intrusive complex was emplaced along the East Arm of Great Slave Lake around 2 billion years ago, carrying with it rocks rich in Nb, Ta, and rare earth elements, all important to industry. The intrusions mark a new period in the history of the region, where, after a long period of geological quiescence, an old continental landmass was split into fragments that allowed these intrusions to rise to the surface. Understanding the geochemistry and origin of the intrusions and the relationships between them will improve models for the origin of the economically important rare earth minerals and add to the exploration effort for more mineralization in the area.