120-5 Using High-resolution Aeromagnetic Data to Refine the Precambrian Tectonic Evolution of the Southern Lake Superior Region USA

Abstract:

The southern Lake Superior region is an area with sparse bedrock exposure that has had an extraordinarily complex 2.5-billion-year history of multiple superimposed orogenies. A high-resolution (150 m line spacing, 100 m nominal terrain clearance) aeromagnetic survey conducted by the USGS Earth MRI program in 2025, combined with high-resolution data acquired by the USGS in 2016 and 2018 with the same specifications, provides Rank 1 coverage for nearly all of the western Upper Peninsula of Michigan and parts of northern Wisconsin. The new data provide a wealth of information on the complex Precambrian geology of this region greatly improving accuracy in defining boundaries of the myriad tectonic terranes of the region and mapping features internal to those terranes that were not evident from older, more generalized, geophysical data. Highlights include: 1) improved resolution of the trace of the Niagara fault[CS1] , a terrane boundary between the southern margin of the Archean Superior craton and Paleoproterozoic arc volcanics obducted onto it, 2) an increase in the mappable extent of the Paleoproterozoic Bush Lake fault revealing that it is also an important tectonic boundary between areas of contrasting structural and metamorphic history, 3) detailed resolution of the flood basalt sequences of the Midcontinent Rift, including previously unresolved structural complexities within the thick basalt flow sequence, 4) refinement of the location and extent of domes of uplifted Archean gneisses and surrounding iron-rich Paleoproterozoic sequences in a region in northern Wisconsin and adjacent northern Michigan that is nearly devoid of outcrops, 5) revelation of several distinct sets of diabase dikes, probably ranging in age from Archean to circa 1.1 Ga, 6) extension of exposed Precambrian geologic features eastward for nearly 100 kilometers beneath thin Paleozoic sedimentary cover.

The improved spatial resolution of geologic units provided by the new high-resolution aeromagnetic data, combined with a wealth of recent geochronologic constraints on igneous, metamorphic, and tectonic events, is spurring a vastly improved understanding of the prolonged and complex geologic and regional metallogenic framework of this region where multiple orogenies that were superimposed through 2.5 billion years have left behind an extraordinarily complex odyssey of geologic history.

 [CS1]Faults and similar features are typically not upper case but there are a few exceptions like the San Andreas Fault. I will defer to your expertise.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-18822

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