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Overview

Midcontinent Region magnetic anomaly study areas.
Regional aeromagnetic anomalies over part of the Midcontinent Rift region. White dots show locations of known Midcontinent Rift-related Ni-Cu-PGE deposits. Grayed pattern is extent of Phanerozoic sedimentary cover. The potential scope of Task 3 includes the entire region shown. Image by USGS.

The Midcontinent Rift system and surrounding Precambrian rocks are known to host highly significant mineral resources. However, more than 90% of the Midcontinent Rift system is covered by Phanerozoic sedimentary rocks and sediments, and many regions lack drilling, meaning that much of the region’s geology and mineral potential is poorly constrained and that geophysical methods are critical.

Our objectives are the following:

  • To map the lithology and structure of concealed and poorly understood Precambrian rocks. This part of the rift is almost completely unknown, and work here will help provide a basis for expanding the understanding of the extent and nature of the entire Midcontinent Rift system.
  • To develop an integrated 3D geology model of the midcontinent rift in the western Lake Superior region from legacy geophysical data, new EarthScope and magnetotelluric data, borehole information, and geologic mapping.
  • To acquire high-resolution ground and/or airborne electromagnetic data in several target regions and to interpret these data together with geophysical, geochemical, and borehole data to define their structural framework.

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Project Activities

3D resistivity model graphic
Depth slices at 10 km through the 3D resistivity model. From Bedrosian, 2016, doi:10.1016/j.precamres.2016.03.009.

We will be conducting the following activities to help characterize and increase understanding of the mineral resource potential of the region:

Task 1 - Geologic Characterization of the Northeast Iowa Intrusive Complex

Contact: Ben Drenth, bdrenth@usgs.gov

Objective: to map the lithology and structure of concealed and poorly understood Precambrian rocks through the collection of aeromagnetic data, ground gravity data and borehole data.

Task 2 - 3D Modeling in the Western Lake Superior Region

Contact: Tien Grauch, tien@usgs.gov

Objective: to develop an integrated 3D geology model of the mid-continent rift in the western Lake Superior region from legacy geophysical data, new EarthScope and magnetotelluric data, borehole information, and geologic mapping.

Task 3 - Regional and Local Electromagnetic Modeling

Contact: Paul Bedrosian, pbedrosian@usgs.gov

Objective: to acquire high-resolution ground and/or airborne electromagnetic data in several target regions and to interpret these data together with geophysical, geochemical, and borehole data to define their structural framework.

Task 4 - Mapping Concealed Precambrian Geology, Central Upper Peninsula, Michigan

Contact: Ben Drenth, bdrenth@usgs.gov

Objective: to map the lithology and structure of concealed and poorly understood Precambrian rocks by securing aeromagnetic data along with ground gravity data.

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Products

Journal Articles

Bedrosian, P.E., 2016, Making it and breaking it in the Midwest: Continental assembly and rifting from modeling of EarthScope magnetotelluric data: Precambrian Research, 278, p. 337-361, doi:10.1016/j.precamres.2016.03.009.

Data

Drenth, B.J., and Brown, P.J., 2016, Airborne Magnetic Total-Field Survey, Manchester Region, Iowa, USA: U.S. Geological Survey data release, https://doi.org/10.5066/F7416V52.

Abstracts for Presentations or Posters

Anderson, E., Grauch, V.J.S., and Powers, M., 2016, Reprocessed seismic data image geology and structure near the Douglas fault on the Bayfield Peninsula, Wisconsin: Institute of Lake Superior Geology Proceedings Volume 62, p. 2. View ILSG 2016 Proceedings. [PDF file 13.8 MB]

Bedrosian, P., 2016, Making it and breaking it in the upper Midwest: Constraints on continental assembly and rifting from EarthScope2: Institute of Lake Superior Geology Proceedings Volume 62, p. 12. View ILSG 2016 Proceedings. [PDF file 13.8 MB]

Bedrosian, P.A., 2016, Making it and breaking it in the upper Midwest: Constraints on continental assemply and rifting from EarthScope: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-285914.

Bedrosian, P., 2015, From Archean to Present – Structure and Evolution of the North American Mid-Continent through the Lens of EarthScope Magnetotelluric Data: American Geophysical Union Annual Meeting, View Bedrosian 2015 AGU abstract.

Drenth, B.J., 2016, The northeast Iowa Instrusive Complex: A major unwritten chapter in the story of the Midcontinent Rift System?: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-281276.

Drenth, B., and Ailes, C., 2016, Re-digitized public aeromagnetic data for parts of the west-central Upper Peninsula, Michigan: Institute of Lake Superior Geology Proceedings Volume 62, p. 37. View ILSG 2016 Proceedings. [PDF file 13.8 MB]

Drenth, B., Anderson, R., Schulz, K., Feinberg, J., Chandler, V., and Cannon, W., 2016, Progress on Geophysical Mapping of the Northeast Iowa Intrusive Complex: Institute of Lake Superior Geology Proceedings Volume 62, p. 36. View ILSG 2016 Proceedings. [PDF file 13.8 MB]

Grauch, V.J.S., Powers, M.H., and Anderson, E.D., 2016, Progress on 3D modeling of the Midcontinent Rift System in the western Lake Superior region and an isopach map of the Oronto Group: Institute of Lake Superior Geology Proceedings Volume 62, p. 54. View ILSG 2016 Proceedings. [PDF file 13.8 MB]

Grauch, V.J.S., Powers, M.H., Heller, S., and Anderson, E.D., 2016, Preliminary 3D model of the Midcontinent Rift System in the western Lake Superior region, Wisconsin, Minnesota, and Michigan: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-283519.

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