Abstract
A thermal record of growth and destruction across the thin- to thick-skinned Idaho-Montana fold-thrust belt
Abstracts with programs - Geological Society of America, Vol.54(5)
Geological Society of America, 2022 annual meeting; GSA connects 2022
10/2022
DOI: 10.1130/abs/2022AM-379527
Abstract
Growing fold-thrust belts propagate toward their forelands, promoting erosion of early, wedge-top strata. Although wedge-top deposits may be stripped, burial heating during sedimentation and cooling-related exhumation of these strata leave a thermal record archiving the competition between growth and destruction of fold-thrust belts. In the Idaho-Montana fold-thrust belt, the thin-skinned Sevier belt and thick-skinned Laramide belt overlap in space and time, suggesting that the transition in structural style may have resulted from fold-thrust belt propagation into a thin section of passive margin strata. Using Raman spectroscopy of carbonaceous material, we quantify maximum temperatures across the Idaho-Montana fold-thrust belt to constrain the dimensions of the early orogenic wedge and test the hypothesis that thin strata over the Lemhi arch caused a shift from thin- to thick-skinned thrusting. Sampling the low-relief unconformity that hosted the early decollement reveals a cold (<100 degrees C) foreland in fault contact with a uniformly hot ( nearly equal 250 degrees C) wedge interior. Most of the internal fold-thrust belt reveals comparable maximum temperatures, suggesting that the early decollement was everywhere buried to at least nearly equal 6.5 km depth, requiring an exceptionally low taper for the early orogenic wedge. Estimated maximum burial depths are nearly equal 1.5-5.0 km deeper than can be explained by observed pre-Cretaceous stratigraphic thicknesses, suggesting that the low-relief wedge was achieved by widespread wedge-top deposition and thin-skinned shortening above the Lemhi arch. In contrast, cumulative exhumation is irregular, varying by up to 5 km over large ( nearly equal 75 km) wavelength folds that involve mechanical basement. Our results support a tectonic inheritance model, where the maximum possible thickness of the thin-skin wedge was limited by thin strata over the low-relief Lemhi arch. Subsequent thickening required activation of a much deeper decollement, and a switch to a thick-skinned structural style. Sedimentation and burial heating in low-relief orogenic wedges may facilitate the transition from thin- to thick-skinned thrusting by bringing the plastic middle crust, which hosts the late decollement, closer to the early decollement near the basement/cover contact.
Details
- Title: Subtitle
- A thermal record of growth and destruction across the thin- to thick-skinned Idaho-Montana fold-thrust belt
- Creators
- Stuart Parker - Montana Bureau of Mines and Geology Butte, MT USA United StatesDavid M. Pearson - Idaho State UniversityEmily Finzel - University of Iowa
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.54(5)
- Conference
- Geological Society of America, 2022 annual meeting; GSA connects 2022
- Publisher
- Geological Society of America (GSA)
- DOI
- 10.1130/abs/2022AM-379527
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2022 annual meeting; GSA connects 2022
- Language
- English
- Date published
- 10/2022
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984442227602771
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