255 Broad Applications of Thermochronology to Understanding Geologic Rates and Processes Through the Sedimentary Record

This session showcases the many ways mid-to-low temperature thermochronometers can be used in isolation or with additional chronometers to understand geologic processes preserved in the sedimentary record such as sediment provenance, source exhumation, burial and/or erosion history.

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 304C

Integrated Multi-System Thermochronology Resolves the Deep-Time Evolution of the Great Unconformity Surface in the Upper Midwest, USA

Paper number: 255-0
Program: Technical Sessions
Time: 8:00 AM – 8:15 AM

Authors

Abstract

Deep-time thermochronology enables the reconstruction of thermal histories spanning over a billion years in Precambrian rocks, offering insights into mid- to upper-crustal geological processes occurring at temperatures below 350 °C. This approach has been used to infer the origin of the Great Unconformity surface, which separates lowermost Paleozoic strata from underlying Precambrian basement. Within the US Upper Midwest, exposures of Precambrian basement rocks present an opportunity to unravel the poorly understood Mesoproterozoic–Phanerozoic thermal history of the cratonic interior region. We present medium- to low-temperature thermochronometric datasets from Precambrian basement samples across the Upper Midwest USA, specifically in Wisconsin and the Upper Peninsula of Michigan. Our data include biotite 40Ar/39Ar (n=2), K-feldspar 40Ar/39Ar (n=2), zircon (n=124) and apatite (n=19) (U-Th)/He, and apatite fission track (n=3) samples. Thermal history models from Thermochron.jl inversions integrate data from all available thermochronometric systems for each sample location. In the Precambrian, these models show several late Mesoproterozoic and Neoproterozoic reheating and cooling events that broadly coincide. In the late Mesoproterozoic–early Neoproterozoic, our models suggest cooling pulse(s) (and by inference, exhumation) at ~1.1–1.0 Ga. We infer that this is associated with broad rift-margin uplift during the 1.1 Ga Midcontinent rifting and/or basement-cored uplifts due to continental-interior fault inversion driven by 1.09–0.98 Ga Grenville compression. Models show variable degrees of reheating and cooling in the Neoproterozoic, which we interpret as widespread Grenvillian sedimentation followed by exhumation due to Snowball Earth glacial erosion. Taken together, these late Mesoproterozoic–Neoproterozoic burial and erosional events represent a complex, non-monotonic evolution of the Great Unconformity surface in the US Upper Midwest. In the Phanerozoic, we attribute Paleozoic–Mesozoic reheating and cooling pulses to a combination of sedimentary burial and unroofing, and late Paleozoic basin-scale hot brine migration focused along high-permeability, Great Unconformity-parallel pathways. Overall, our work demonstrates that the US Upper Midwest cratonic interior has experienced late Mesoproterozoic to Phanerozoic burial, erosional, and thermal episodes driven by the localized effects of tectonic events subsequent to cratonization. We also demonstrate that an integrated multi-system thermochronometric approach is essential in resolving the dates and rates of cooling events in deep time.

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

doi: 10.1130/abs/2025AM-412384

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