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

This session explores the evolution of orogenesis on Earth, encompassing applications of sedimentology, petrology, geochemistry, paleomagnetism, geochronology, and structural geology. We encourage studies combining field observations with laboratory and modeling techniques to unravel tectonic processes.

Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Deformation of the ~2691 Ma Saganaga Tonalite, Western Superior Province USA and Canada

Paper number: 195-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Saganaga Tonalite (2691 Ma) is a prominent Archean batholith located in the Wawa Terrane of the Superior Province that has been regarded previously as weakly deformed. It intrudes the coeval Ely Greenstone and is unconformably overlain by strata of the deformed Knife Lake Group (<2550 Ma). Alternating field (AF) demagnetization was performed on 12 widely distributed Saganaga Tonalite samples to isolate characteristic remnant magnetization directions and calculate paleopole orientations. Analysis was completed at the University of Wisconsin-Milwaukee paleomagnetic laboratory. The paleopoles are distributed across three quadrants of the equal-area projection, with 11 declinations ranging from 29.2° to 250.7° and inclinations from 2° to 69.8°, and include one reverse polarity. The variation in paleopole orientations indicates that the tonalite experienced regional deformation and tilting after its emplacement. Supporting this, Marathon mafic dikes (~2100 Ma) cross-cut the tonalite and are locally offset by faulting and pseudotachylite is observed in many locations which provides evidence that deformation post-dates dike emplacement. Younger, undated dikes are also offset. Additionally, Ar-Ar dates from mylonitic shear zones on the northern and southern boundaries, each 1 km wide and vertical, of the Saganaga Tonalite indicate deformational events at ~2627 Ma on the northern shear zone and 1110 Ma on the southern margin. This age disparity suggests multiple stages of active tectonism have affected the area and adds to evidence of far field deformation related to either the Grenville Orogeny (~1280–980 Ma) and the assembly of Rodinia, or the Paleozoic assembly of Pangea.

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

doi: 10.1130/abs/2025AM-413687

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