Mapping the 3D extent of the Duluth Layered Mafic Complex from geophysical data

Abstract:

The Mesoproterozoic Duluth Complex in Northeastern Minnesota is one of the major plutonic components of the Midcontinent Rift System and hosts a variety of copper-nickel sulfide and platinum group element deposits. The Duluth Complex is composed of a series of individual mafic and felsic intrusions emplaced 1110-1098 Ma within Paleoproterozoic sedimentary rocks and volcanic flows of the Midcontinent Rift. Extensive prior work has been done to create 2D maps and cross sections of magnetic and density anomalies across the Duluth Complex to aid geologic interpretation, however, very little 3D modeling has been done. Given the complex geology of the area, 3D modeling is necessary to provide a complete picture of the variable densities, susceptibilities, and geometries of intrusive suites throughout the Duluth Complex as well as its extent at depth beneath sedimentary cover. We use aeromagnetic data acquired between 1979-1991, Bouguer gravity data collected over the past ~60 years, and magnetotelluric data collected in 2019 to create new 2D and 3D geophysical models of the Duluth Complex constrained by seismic, geologic, and drill core data. These models delineate the 3D extent of the Duluth Complex, identify internal subdivisions within the complex, provide improved thickness estimates of the layered mafic sequence, and bring us one step closer to determining the evolutionary history of the Duluth Complex.