Abstract Low-temperature thermochronometers can be used to measure the timing and the rate at which rocks cool. Generally, rocks cool as they move towards Earth’s surface by erosion or normal faulting (tectonic exhumation of the footwall), or warm as they are buried by sediments and/or thrust sheets, or when they are intruded by magma and association hydrothermal fluids. Changes in heat flow or fluid flow can also cause heating or cooling. Apatite fision-track and apatite (U-Th)/He dating have low closure temperatures of ~120° C and ~70° C respectively, and are used to date cooling in the upper ~3–4 km (~1.8–2.4 mi) of Earth’s crust. Age-elevation relationships from samples collected from different elevations along vertical transects or from wellbores are used to calculate exhumation rates and the time of onset of rapid exhumation. The spatial distribution of cooling ages can be used to map faults in basement or intrusive rocks where faults can be difficult to recognize. Cooling ages from detrital minerals in sedimentary rocks can be used to constrain provenance. If sedimentary samples reached temperatures high enough to reset the thermochronometers, then ages may provide information on the cooling history of the basin. Forward thermal modeling can be used to test proposed thermal history models and predict thermochronometer ages. Inverse thermal modeling finds a best-fit thermal history that provides a good statistical match to measured thermochronometer ages. Both types of thermal modeling may help contrain maximum temperature of the sample and time spent at that temperature. Thermochronometer ages can be used as constraints in basin modeling. Maturation of kerogen to petroleum in a sedimentary basin is controlled by the maximum temperature reached by the kerogen and the amount of time it spends at or near that temperature (i.e., the thermal history of the basin). The timing of tectonics and the formation of structures in a region influence the generation, migration, entrapmet, and preservation of petroleum. Techniques such as low-temperature thermochronology that illuminate the relationship between time and tempearture during basin evolution can be valuable in understanding petroleum systems. These techniques are especially powerful when multiple dating techniques (such as apatite fission-track, zircon fission-track, and apatite (U-Th)/He dating) are applied to the same sample and when they are combined wiht other thermal indicators such as vitrinite reflectance data.

Abstract A synthesis of low-temperature thermochronologic results throughout the Laramide foreland illustrates that samples from wellbores in Laramide basins record either (1) detrital Laramide or older cooling ages in the upper ~1 km (0.62 mi) of the wellbore, with younger ages at greater depths as temperatures increase; or (2) Neogene cooling ages. Surface samples from Laramide ranges typically record either Laramide or older cooling ages. It is apparent that for any particular area the complexity of the cooling history, and hence the tectonic history interpreted from the cooling history, increases as the number of studies or the area covered by a study increases. Most Laramide ranges probably experienced a complex tectono-thermal evolution. Deriving a regional timing sequence for the evolution of the Laramide basins and ranges is still elusive, although a compilation of low-temperature thermochronology data from ranges in the Laramide foreland suggests a younging of the ranges to the south and southwest. Studies of subsurface samples from Laramide basins have, in some cases, been integrated with and used to constrain results from basin burial-history modeling. Current exploration for unconventional shale-oil or shale-gas plays in the Rocky Mountains has renewed interest in thermal and burial history modeling as an aid in evaluating thermal maturity and understanding petroleum systems.This paper suggests that low-temperature thermochronometers are underutilized tools that can provide additional constraints to burial-history modeling and source rock evaluation in the Rocky Mountain region.

Abstract Detachment folds basinward of Laramide Rocky Mountain arches are relatively poorly known, partially due to coverage by synorogenic strata that may conceal undiscovered anticlinal fields. This study documents the geometry and kinematics of the Beaver Creek Detachment system (BCD), which is located west of a series of NW-trending thrust faults and folds defining the Beaver Creek reentrant on the western edge of the Bighorn Arch. Possible origins for this proposed detachment include syn-Laramide detachment rooted in mountain-front faulting, syn-Laramide gravity slinding during mountain-front folding, and post-Laramide gravity sliding.