Constraining continental deformation with the apatite (uranium-thorium)/helium thermochronometer

During the past decade, apatite (U-Th)/He thermochronology has become a useful and reliable tool for understanding low-temperature deformational events in the upper crust. The Stanford (U-Th)/He lab became fully operational in 2004, and can now regularly measure single grain apatite (U-Th)/He ages. The two study areas addressed in this thesis experienced very different Cenozoic cooling histories, and show that apatite (U-Th)/He thermochronology can provide critical constraints in a wide variety of geologic settings.; The Deep Creek Range is a west-tilted, normal fault bounded mountain range in western Utah. Apatite (U-Th)/He and fission-track data indicate that the Deep Creek Range experienced two separate and distinct Miocene exhumational events at ∼15 Ma and ∼11.4 Ma. Both events involved slip along north-south trending normal faults on the east side of the range. Isotherms reconstructed from the He age data indicate that the second event was accommodated on a younger, unexposed high-angle fault on the east side of the range. Combined apatite (U-Th)/He and fission-track data can constrain both the timing and magnitude of exhumation in tilted fault blocks, and can also offer insight into the evolution of normal fault systems that cannot be constrained by field evidence or fission-track data alone.; In contrast to the Deep Creek Range, the Dabie Shan [mountains] in eastern China experienced very slow cooling and exhumation. Cooling rates determined from apatite fission-track and (U-Th)/He age pairs show that the eastern Dabie Shan cooled at an average rate of ∼1.3 °C/My during the Cenozoic. Apatite (U-Th)/He ages decrease towards the eastern margin of the range, which is defined by the Tan-Lu fault, indicating that the Tan-Lu fault was active in the uplift and cooling of the range. He ages from nearby the Tan-Lu fault (< 10 km) are consistent, and indicate that the eastern Dabie Shan cooled through ∼60 °C in the Oligocene, coincident with a widespread regional unconformity. This suggests that the Cenozoic exhumation of the Dabie Shan was in response to a regional uplift event.