Timing, Rates, and Styles of Cenozoic Tectonism in the Basin and Range and Lesser Caucasus: Linking Observations of Intracontinental Deformation to Geodynamic Processes

Abstract

Continental lithosphere exhibits complex deformation across broad regions, challenging simplistic tectonic models of how plate boundaries behave. As geologists develop models to explain observed patterns of deformation, they have proposed a wide array of geodynamic mechanisms and material properties that may control the rates, styles, and magnitudes of continental deformation. In most study areas, we now have an excess of hypothesized controls and a dearth of data with which to test competing models of deformation. This dissertation presents three field studies of continental deformation that apply a diverse set of investigative approaches to characterize deformation, then link that deformation to the most likely geodynamic causes.

Two studies are from the Basin and Range extensional province, addressing debates around the relative role of plate boundary stresses and internal gravitational potential energy gradients in driving extensional tectonism over the Cenozoic. In Chapter 2, I use field mapping, stratigraphy, detrital zircon geochronology, and structural observations to build a basin history for the Titus Canyon Formation, one of the earliest syn-extensional deposits in the central Basin and Range. Our results from the Titus Canyon Formation suggest that it records extension related to a ~40 Ma slowdown in plate convergence along western North America. In Chapter 3, I apply multiple low-temperature thermochronometers to a suite of Jurassic plutons in the northern Basin and Range to decipher their exhumational histories. My data support a major phase of extension in the Miocene, and also reveal changes in Cretaceous-Paleogene exhumation that may be related to contractional tectonism of the Sevier orogeny and construction of the Nevadaplano. Chapter 4 examines the recent tectonic history of the down-going plate in the Caucasus collisional orogen. I apply low-temperature thermochronology to measure the tectonic response to the initiation of collision at 5 Ma with the goal of understanding the partitioning of strain between the two colliding plates. The results indicate that the collision is highly asymmetric, with the majority of shortening in the down-going plate being accommodated by strike-slip faulting, in contrast with deformation in the overriding plate which is accommodated primarily by reverse faulting and folding. Together these studies illustrate the rich complexity of continental deformation and the wide variety of geodynamic mechanisms that must be considered when building models of how deformation evolves in old continental lithosphere.