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Overview

Midcontinent Rift location map
Generalized geologic map of the Midcontinent Rift System. Modified from Dean Peterson, Duluth Metals. View full size map.

The Midcontinent region is the focus of active mineral exploration, including for mineral deposit types previously unrecognized there. This is an opportune time to re-evaluate models for the development of the tectonic, magmatic, and metallogenic evolution of the Midcontinent Rift System. Using the USGS's new geographic information system (GIS) compilation for the entire Lake Superior region (including the Canadian side) and new tools for analyzing large amounts of spatial data, we can now integrate and evaluate data in a larger regional and 3-D context. This new regional data compilation (as yet unpublished) will help determine:

  1. How the crust and lithosphere responded to the upwelling of the proposed mantle plume and their subsequent interactions from about 1120 Ma to 1085 Ma, and
  2. How the architecture of the rift (evolving from plateau basalts to the formation of central grabens, with subsequent development of sedimentary basins and horsts) influenced formation and distribution of a wide variety of mineral deposit types.

The goals of this project are:

  1. To develop a comprehensive synthesis of the tectonic, magmatic, and mineral deposit evolution of the Midcontinent Rift System by integrating geophysical, magmatic, and geochemical data
  2. To illustrate the results with a series of conceptual 3-D models of the rift over its ~35 Ma evolution.

Project Activities

Architecture of the Midcontinent Rift System

Contact: Laurel Woodruff, woodruff@usgs.gov

We'll collaborate with geophysicists working on the Midcontinent Rift System to develop a series of conceptual 3-D models of the magmatic evolution of the rift event. These results will provide details of the upper crustal structure and stratigraphy of buried parts of the rift, and deeper structures within the lower crust and lithosphere, to evaluate the potential for undiscovered mineralization in unexposed rift segments.

Magmatic Evolution and Metallogeny of the Midcontinent Rift System

Contact: Klaus Schulz, kschulz@usgs.gov

We will use the rift-wide GIS compilation of geochemical, isotopic, and age data for volcanic and intrusive rocks to synthesize the magmatic evolution of the rift. New geochemical and isotopic analyses, along with limited additional age dating, will be done to fill in key gaps. This task will also use the GIS compilation, as well as new deposit model information and outcomes of recent assessments for conduit- and contact-type nickel-copper-platinum group elements (Ni-Cu-PGE) mineralization in the Lake Superior region, to update the metallogeny of the Midcontinent Rift System (Nicholson and others, 1992).

Dynamic GIS Archive of Midcontinent Rift System Data

Contact: Connie Dicken, cdicken@usgs.gov

Having compiled the initial GIS for the Midcontinent Rift System, we will continue to update the GIS, adding new datasets where appropriate, updating existing geochemical and isotopic datasets as time and funding allow, and responding to other uses for these data.

2013 ILSG field trip
2013 Institute on Lake Superior Geology field trip. Photo by W. Cannon, USGS.

Products

Abstracts

Schulz, Klaus J. and Nicholson, Suzanne W., 2016, The geochemistry of the Siemens Creek Formation and the nature of early Midcontinent rift magmatism: Institute on Lake Superior Geology Proceedings – Part 1, p. 88-89.

Lake of the Clouds
Panoramic view of Lake of the Clouds, Porcupine Mountains Wilderness State park (from Woodruff and others, 2013). Photograph by Bill Cannon, USGS.

References

Miller, James and Nicholson, S.W., 2013, Geology and mineral deposits of the 1.1 Ga Midcontinent Rift in the Lake Superior region–an overview. In (Miller, J., ed.) Field guide to the copper-nickel-platinum group element deposits of the Lake Superior Region: Precambrian Research Center Guidebook, 13-01, p. 1-49. View PRC Guidebook 13-01. [PDF file, 78 MB]

Nicholson, S.W., Cannon, W.F., and Schulz, K.J., 1992, Metallogeny of the Midcontinent Rift System of North America: Precambrian Research, 58(1-4), p. 355-386, doi:10.1016/0301-9268(92)90125-8.

Woodruff, L.G., Cannon, W.F., Nicholson, S.W., Schulz, K.J., and Wild, Robert, 2013, Geology of the Keweenawan Supergroup, Porcupine Mountains, Ontonagon and Gogebic Counties, Michigan: Institute on Lake Superior Geology Proceedings - Part 2, p. 69-96. View 2013 ILSG Proceedings - Part 2. [PDF file, 16.2 MB]

Project Contacts

Laurel Woodruff
Phone: 763-783-3291
Email: woodruff@usgs.gov
Eastern Mineral and Environmental Resources Science Center

Mineral Resources Program Science Priority

scientists at anorthosite quarry
USGS scientists Laurel Woodruff and Suzanne Nicholson at anorthosite quarry, Duluth Complex, MN. Photo by K. Schulz, USGS.

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