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Abstract Low‐temperature thermochronometric data can reveal the long‐term evolution of erosion, uplift, and thrusting in fold‐thrust belts. We present results from central Idaho and southwestern Montana, where the close spatial overlap of the Sevier fold‐thrust belt and Laramide style, basement‐involved foreland uplifts signify a complex region with an unresolved, long‐term tectono‐thermal history. Inverse QTQt thermal history modeling of new zircon (U‐Th)/He (ZHe,n = 106), and apatite (U‐Th)/He dates (AHe,n = 43) collected from hanging walls of major thrusts systems along a central Idaho to southwestern Montana transect, and apatite fission track results from 6 basement samples, reveal regional thermal and spatial trends related to Sevier and Laramide orogenesis. Inverse modeling of foreland basement uplift samples suggest Phanerozoic exhumation initiated as early as ∼80 Ma and continued through the early Paleogene. Inverse modeling of interior Idaho fold‐thrust belt ZHe samples documents Early Cretaceous cooling at ∼125 Ma in the Lost River Range (western transect), and a younger cooling episode in the Lemhi Arch region (mid‐transect) at ∼90–80 Ma through the late Paleogene. This cooling in the Lemhi Arch temporally overlaps with cooling in southwestern Montana's basement‐cored uplifts, which we interpret as roughly synchronous exhumation related to contractional tectonics and post‐orogenic collapse. These data and models, integrated with independent timing constraints from foreland basin strata and previously published thermochronometric results, suggests that middle Cretaceous deformation of southwestern Montana's basement‐cored uplifts was low magnitude and preceded tectonism along the classic Arizona‐Wyoming Laramide “corridor.” In contrast, Late Cretaceous and Paleogene thrust‐related exhumation was more significant and largely complete by the Eocene. The basement‐involved deformation was contemporaneous with and younger than along‐strike Sevier belt thrusting in central Idaho.
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Thermal history of the northern Great Valley forearc basin, California
The Great Valley Forearc basin of California preserves >15 km of strata deposited during latest Jurassic-earliest Cretaceous to Eocene sedimentation. Along the western margin of the central-northern Great Valley forearc, the oldest basin strata are preserved as an eastward dipping homoclinal belt. Previous work on the thermal history of the western outcrop belt has constrained sub-normal geothermal gradients (<20C/km) during middle Cretaceous to Eocene time related to subduction refrigeration. However, the timing of maximum burial and subsequent exhumation is restricted to a few local studies. This study applies apatite and zircon (U-Th)/He and apatite fission track thermochronology to quantify maximum burial temperatures and the timing and rate of cooling of latest Jurassic-middle Cretaceous strata of the western homocline and neighboring subsurface along 350 km of the basin margin. Zircon (U-Th)/He dates range from ~167 to 85 Ma, which are either older or bracket corresponding depositional ages. Apatite fission track dates range from ~162 to 90 Ma, with the majority of grains between ~110-90 Ma. All apatite (U-Th)/He dates are less than 50 Ma, with most grains yielding dates between ~40-20 Ma. Preliminary integration of these data into thermal history models indicate that maximum burial temperatures did not exceed 120-180 C. The timing of basin cooling ranges based on locality, with the western outcrop yielding rapid exhumation starting between ~100-65 Ma and subsurface cooling at ~50 Ma. Final cooling to modern temperatures, as constrained by apatite (U-Th)/He dates, generally coincides with the transition to a transform margin after ~30 Ma.
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- Award ID(s):
- 1942460
- PAR ID:
- 10495834
- Publisher / Repository:
- Geological Society of America
- Date Published:
- Journal Name:
- Geological Society of America Penrose
- Format(s):
- Medium: X
- Location:
- McCall, Idaho
- Sponsoring Org:
- National Science Foundation
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