40 Ar/ 39 Ar, apatite fi ssion-track, and apatite (U-Th)/He thermochronological techniques were used to determine the Neogene exhumation history of the topographically asymmetric eastern Alaska Range. Exhumation cooling ages range from ~33 Ma to ~18 Ma for 40 Ar/ 39 Ar biotite, ~18 Ma to ~6 Ma for K-feldspar minimum closure ages, and ~15 Ma to ~1 Ma for apatite fi ssion-track ages, and apatite (U-Th)/He cooling ages range from ~4 Ma to ~1 Ma. There has been at least ~11 km of exhumation adjacent to the north side of Denali fault during the Neogene inferred from biotite 40 Ar/ 39 Ar thermochronology. Variations in exhumation history along and across the strike of the fault are infl uenced by both far-fi eld effects and local structural irregularities. We infer deformation and rapid exhumation have been occurring in the eastern Alaska Range since at least ~22 Ma most likely related to the continued collision of the Yakutat microplate with the North American plate. The Nenana Mountain region is the late Pleistocene to Holocene (~past 1 Ma) primary locus of tectonically driven exhumation in the eastern Alaska Range, possibly related to variations in fault geometry. During the Pliocene, a marked increase in climatic instability and related global cooling is temporally correlated with an increase in exhumation rates in the eastern Alaska Range north of the Denali fault system.

The Taranaki Basin is an active‐margin basin that has been significantly affected by Miocene subduction tectonics along the Pacific‐Australian plate boundary. We have analyzed its present‐day thermal state using 354 bottom‐hole temperatures (BHTs) from 115 wells distributed throughout the basin. The measured temperatures were corrected using an exact solution to Bullard's equation rather than the Horner approximation, thereby allowing for recovery dependence on well diameter and correction for some BHTs at early time after circulation had ceased. Thermal conductivity measurements were completed on 256 samples from eight wells, and matrix conductivities were determined for six end‐member lithologies by inversion. Formation conductivities are based on the conductivity and relative proportion of each end‐member component. Corrected BHTs, in situ thermal conductivity, and estimates of sediment heat production were combined to compute the present‐day, steady state heat flow. The average heat flow is 60 mW m−2, but important geographic variations are present: heat flow on the Western Platform is remarkably consistent at 53–60 mW m−2, attesting to its relative stability since the Late Cretaceous; heat flow in the southern part of the basin is 65–70 mW m−2 due to as much as 3 km of late Miocene erosion; on the southern onshore and to the south of the peninsula, heat flow is 50 ± 3 mW m−2, possibly due to the heat sink effects of crustal thickening; heat flow is highest at 74 mW m−2 on the northern peninsula adjacent to the Taranaki volcanic zone, suggesting a causal relationship between Quaternary volcanism and high heat flow.

Abstract.The tectonic relations between foreland and hinterland deformation in noncollisional orogens are critical to understanding the overall development of orogens.

The western Chugach Mountains and Prince William Sound are located in a syntaxial bend, which lies above fl at-slab subduction of the Yakutat microplate and inboard of the Yakutat collision zone of southern Alaska. The syntaxis is characterized by arcuate fault systems and steep, high topography, which suggest focused uplift and exhumation of the accretionary prism. We examined the exhumation history with low-temperature thermochronometry of 42 samples collected across the region. These new apatite (U-Th)/He, apatite fi ssion-track, zircon (U-Th)/He, and zircon fi ssion-track ages, combined with ages from surrounding regions, show a bull'seye pattern, with the youngest ages focused on the western Chugach syntaxis. The ages have ranges of ca. 10-4 Ma, ca. 35-11 Ma, ca. 33-25 Ma, and ca. 44-27 Ma, respectively. The youngest ages are located on the south (windward) side of the Chugach Mountains and just north of the Contact fault. Sequentially higher closure temperature systems are nested across Prince William Sound in the south, the Chugach Mountains, and the Talkeetna Mountains to the north. Computed exhumation rates typically are 0.2 mm/yr across Prince William Sound, increase abruptly to ~0.7 mm/yr across and adjacent to the Contact fault system, and decrease to ~0.4 mm/yr north of the core of the Chugach Mountains. The abrupt age and exhumation rate changes centered on the Contact fault system suggest that it may be a critical structural system for facilitating rock uplift. Our data are most consistent with Yakutat fl at-slab subduction starting in the Oligocene, and since then ~11 km of rock uplift north of the Contact fault and ~4-5 km of rock uplift in Prince William Sound to the south. These data are consistent with a deformation model where the western Chugach core has approached long-term exhumational steady state, though exhumation rates have probably increased in the last ~5 m.y. We interpret that rock uplift in the overriding wedge has been driven dominantly by underplating, with long-term vertical displacement concentrated at the southern edge of the Chugach Mountains and centered on the Contact fault system. Though our data do not unequivocally differentiate between Pliocene tectonic-or climate-related causes for increased exhumation in the last ~5 m.y., we interpret the increased rates to be due to increased infl ux of underplated sediments that are derived from erosion in the Saint Elias orogen collision zone.

[1] The Wasatch fault is a $370 km long normal fault in Utah that marks the boundary between the stable Colorado Plateau to the east and the extending Basin and Range to the west. Understanding the thermokinematic evolution of this fault can provide insights into intracontinental extensional tectonics and deformation processes in other rift zones (e.g., East Africa Rift, Transantarctic Mountains). We explore the thermokinematics of footwall exhumation and erosion in the Cottonwood Intrusive Belt of the central Wasatch Mountains. Emphasis is placed on using low-temperature thermochronometers to quantify (1) the spatial and temporal variability of exhumation and erosion rates, (2) the geometry of footwall tilt, (3) the fault dip angle, and (4) the magnitude and duration of exhumation. These processes are investigated using two-dimensional (2-D) thermal-kinematic models coupled with cooling-rate-dependent kinetic models which predict exhumed apatite fission track (AFT) and (U-Th)/He ages. The range of model parameters considered includes footwall exhumation and erosion rates at the fault between 0.2 and 2.0 mm yr À1 , footwall tilt hinge positions between 15 and 40 km distance from the fault, a single planar normal fault with dip angles of 45°and 60°, and exhumation magnitudes of up to 15 km at the fault. Simulations include the formation of a low thermal conductivity sedimentary basin and erosion of heat-producing layers. Erosion maintains a constant topographic profile. The kinematic and exhumation history of the Wasatch Mountains is investigated by comparing model predicted thermochronometer ages to observed AFT, ZFT, and (U-Th)/He ages. Predicted and observed ages are compared using a reduced chi-square analysis to determine a best fit kinematic model for the Wasatch Mountains. The preferred model includes exhumation occurring on either a 45°or 60°dipping fault, a footwall hinge located a minimum of 20-25 km from the fault, and a step decrease (deceleration) in the footwall exhumation rate at the fault from 1.2 to 0.8 mm yr À1 at around 5 Ma. The model also suggests an exhumation duration of $12 Myr ± 2 Myr).