60-29 Geology of the Kekekabic Traverse, Boundary Waters Canoe Area Wilderness, Minnesota, USA

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

Poster Booth No.: 29

Presenting Author:

Preston Kietzman

Authors:

Kietzman, Preston¹, Malone, David H.², Craddock, John P.³, Rivadeneyra-Braswell, Nicte⁴, Fowler, Kara⁵, Bruckner, Lucy⁶

Abstract:

The Kekekabic traverse, located in the Boundary Waters Canoe Area Wilderness (BWCAW) of northeastern Minnesota, contains a complex host of geologic oddities across a NNW to SSE traverse near the east end of the Kekekabic trail in Cook county. The Archean Saganaga Tonalite, part of the Wawa Terrane (2691 Ma), intrudes the Ely Greenstone (2691 Ma). The southern margin of the Saganaga tonalite includes a 1 km wide, vertical mylonitic shear zone. Ar-Ar radiometric age dating reveals the age of this mylonite to be 1.11 Ga. Deposited unconformably above the Saganaga Tonalite and Ely Greenstone shear zone is the Proterozoic Gunflint Formation, a banded iron formation (BIF). Gunflint Formation bedding along the traverse transitions from horizontal to vertical, indicating a local syncline that trends (N80°E). The SE limb of the syncline is in thrust contact with overturned Ely Greenstone best exposed atop Lookout Mountain. Farther SE, the overturned Ely Greenstone is unconformably overlain by the undeformed Gunflint Fm. which dips ~80° S. The tectonized Gunflint formation is ~100 m thick, the foliation dips steeply to the south with boudins and porphyroclasts as kinematic indicators, preserving E-W extension with top-to-the-north thrusting. Geochronological analyses using U-Pb zircon, U-Pb apatite, and Ar-Ar radiometric dating indicate that the tectonized Gunflint Formation is 1.11 Ga. The final unit exposed along the traverse is the Duluth Gabbro (1099 Ma), which dips to the south and has no fabric; it is younger than the tonalite-greenstone shear zone and the Gunflint Formation tectonite mylonites. The gabbro includes BIF xenoliths of various sizes as well as Fe-rich injectites. Therefore, a deformational event prior to the intrusion of the Duluth Gabbro occurred at 1110 Ma, a far-field shortening and metamorphic of the Grenville orogen 800 km to the east.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8281

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