195-5 Deformation of the ~1100 Ma Duluth Gabbro Complex, Northeastern Minnesota, USA

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism (Posters)

Poster Booth No.: 191

Presenting Author:

Nicte Rivadeneyra-Braswell

Authors:

Rivadeneyra-Braswell, Nicte P¹, Fowler, Kara M², Craddock, John P.³, Malone, David H.⁴, Bowles, Julie A.⁵

(1) Illinois State University, Normal, IL, USA, (2) Illinois State University, Normal, IL, USA, (3) Illinois State University, Normal, IL, USA, (4) Illinois State University, Normal, IL, USA, (5) University of Wisconsin - Milwaukee, Milwaukee, WI, USA,

Abstract:

The ~1100 Ma Duluth Gabbro is a Mesoproterozoic layered mafic intrusion located in the northern Lake Superior region; it is part of the failed midcontinent Keweenaw Rift system. The Duluth Gabbro intrudes Animike Group metasediments (1900-1850 Ma) including the Gunflint banded iron formation. The lower boundary of the Duluth Gabbro is traditionally viewed as intrusive as it is concordant and rests above the Animike Group. Recent field observations and strain analysis reveal that this contact is deformed through shearing, which implies that the lower contact is better interpreted as a thrust fault. To investigate the deformational history of the Duluth Gabbro, alternating field (AF) demagnetization was performed on 8 samples of Duluth Gabbro to isolate characteristic remnant magnetization directions and calculate paleopole orientations. Additionally, anisotropy of magnetic susceptibility (AMS) was performed on 8 samples to determine flow directions. Our results indicate that paleopoles and AMS fabrics have variable orientations, suggesting that the Gabbro experienced extensive and variable regional deformation. The paleopole patterns found in this study suggest that deformation has occurred as a far-field result of the Grenville Orogeny. The Grenville orogen (1300-980 Ma) initiated the Keweenaw rift from 1141–1085 Ma, which was coeval with rift magmatism and Gabbro intrusion. It is also admissible that this deformation occurred after the Grenville orogeny, perhaps as the result of Paleozoic far-field strain that was transmitted to the Laurentian craton during the assembly of Pangea.

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

doi: 10.1130/abs/2025AM-9598

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