In order to optimize current and future deployment of EarthScope (ES) resources in the northern Rocky Mountains/Great Plains, a group of earth scientists from the University of Florida, Montana State University, and the U.S. Geological Survey are conducting research directed toward development of an integrated temporal and spatial (i.e., 4-D) framework for crustal evolution in this region. In particular, this region contains one of the most enigmatic segments of continental crust in North America, the Great Falls tectonic zone (GFTZ). This long-lived crustal structure has the most temporally extensive rock record in North America (ages to 4 billion years) and has had a major impact on the geologic history of this region, including younger episodes of faulting and seismicity, distribution of magmatism and ore deposits, and the creation of resource-rich sedimentary basins. For example, the intersection of the GFTZ and Trans-Hudson orogen, which developed ~ 1.8 billion years ago, is now the site of a major petroleum resource province, the Williston basin. Similarly, Phanerozoic structural reactivation, magmatism, seismicity, and mineralization in the northern Rocky Mountains is concentrated in the GFTZ, which leads to additional possibilities of how ancient structures and events may control modern earth processes and the distribution of resources.
The research group is applying modern geochronologic (ion probe U-Pb), thermochronologic (multi-and single grain 40Ar-39Ar), and geochemical (major and trace elements) techniques to samples from outcrops, deep test wells, and xenoliths (pieces of the mantle and lower crust brought to the surface via volcanic eruptions). These results will be critical for both optimizing the deployment of ES resources and ultimately developing an integrated 4-D framework for the northern Rocky Mountain/northern Great Plains portion of North America. This 4-D framework is essential to: 1) unraveling one of the most intriguing episodes of continent formation in the geologic record, the formation of Laurentian North America; 2) understanding how the amalgamating collisional events were recorded in the crust and mantle; and 3) to what extent these ancient events affected subsequent crustal and lithospheric evolution in the northern Rocky Mountains/Great Plains. The research team is utilizing facilities from all three organizations (University of Florida, Montana State University, and the U.S. Geological Survey). Student participation at the graduate and undergraduate level is providing critical workforce training in geologic and analytical skills. The results of this research will be integrated into the evolving Montana GIS/DEM geologic map base being developed at Montana State University. All of the geochemical and geochronologic data will be numerically and spatially displayed in an interactive web format and accessible to geoscientists, educators, and the general public. Results will also be disseminated via meeting presentations and peer reviewed journals.
