|Title||Inverse modeling of annealing of fission tracks in apatite 2: application to the thermal history of the Peace River Arch region, Western Canada Sedimentary Basin|
|Author||Willett, S D; Issler, D R; Beaumont, C; Donelick, R A; Grist, A M|
|Source||American Journal of Science vol. 297, 1997 p. 970-1011, https://doi.org/10.2475/ajs.297.10.970|
|Alt Series||Geological Survey of Canada, Contribution Series 1997134|
|Publisher||American Journal of Science (AJS)|
|Media||paper; on-line; digital|
|Subjects||geochronology; mathematical and computational geology; fission tracks; apatite; modelling; thermal history; paleotemperatures; Peace River Arch; Laramide Orogeny; Western Canada Sedimentary Basin;
|Illustrations||cross-sections; tables; histograms; graphs|
|Abstract||Results of apatite fission track (AIT) analysis for 47 drillcore samples, ranging from Precambrian to Cretaceous in age, are presented for a 700 km transect along the Peace River (PR) Arch which extends
across north-central Alberta and northeast British Columbia. Samples were obtained from depths of 130 to 3560 m, corresponding to present temperatures of 10° to ll5°C (present total annealing temperature). AFT ages and etchable mean track lengths for
all stratigraphic and basement units decrease systematically from east to west, consistent with the westward thickening of the sedimentary wedge toward the disturbed belt. These observations indicate that burial and heating during the late stages of
the Laramide Orogenv (Late Cretaceous-early Cenozoic) left a strong thermal overprint on AFT parameters. The controlled random search (CRS) algorithm (Willett, this issue) was used to extract time-temperature information from measured AFT parameters.
AFT samples are divided into 3 groups based on their observed characteristics and the model results: [l) fully annealed samples, (2) volcanic-type Cretaceous samples, and, (3) basement-type samples with multiple periods of heating and cooling.
Samples that are interpreted as fully annealed are used to determine an age of 60 Ma for the maximum post-Laramide temperature, and, by implication, maximum depth of burial in the basin. With this timing constraint, partially annealed samples were
interpreted through the CRS algorithm to determine the degree of Cenozoic reheating. The temperature at maximum burial (60 Ma) is best resolved, and the suite of samples yield a coherent paJeotemperature field that is regionally self-consistent.
Maximum AFT temperatures at 60 Ma are combined with stratigraphic reconstructions derived using coal moisture data to estimate paleogeothennal gradients. Reconstructed paleogeothermal gradients are similar to present average geothermal gradients
along central portions of the transect but are scantly higher than present values in the deep basin to the west (35 -40°C/km) and in the oil sands region to the east (35°-60°C/km). Although errors in both modeling and burial reconstructions may
account for some of this discrepancy, we interpret the paleotemperatures as indicating thermal disturbances caused by regional paleofluid flow across the basin near the end of the Laramide Orogeny. |