Insights into the Tectonic Development of the Klamath Mountains Province from Thermal Data and Modeling

The Klamath Mountains Province (KMP) of northern California and southern Oregon straddles a fundamental transition in the North America plate boundary, and as such its Neogene to recent tectonic history provides a window into the evolution of the plate boundary as it undergoes the transition from subduction to translation. The Klamath province hosts some of the highest topography along the convergent boundary, but when this topography developed is not clear, and thus whether its development is linked to modern plate boundary processes is unknown. This poorly understood uplift history is accompanied by extensional faulting—consisting of both a system of low-angle faults that makes up a regional detachment, and steeper graben-bounding faults—that overprints the eastern part of the KMP at a high angle to the accretionary fabric of the region. These faults appear to have played a significant role in the tectonic development of the KMP, and some constraints on their timing exist, but the specific relationship between this extension and the development of high topography is unknown. We are using new and existing low-temperature thermochronologic data, as well as thermal maturation indicators from organic-rich sediments to unravel the timing and contributions of tectonic and erosional exhumation in the eastern KMP. Existing apatite fission track and (U-Th)/He ages have been interpreted to record two distinct exhumation events, one middle/Late Cretaceous and one Late Eocene/Early Miocene. However, the spatial coverage and resolution of sampling is such that alternative histories are not ruled out; such histories include periods of slow (but measurable) exhumation throughout the Tertiary, as well as recent exhumation events that are not directly recorded by any thermochronologic ages. The existing data provide some information on the relative contributions of tectonic and erosional exhumation to the total exhumation experienced by the lower plate of the detachment. Our work builds on this aspect of the analysis by increasing the spatial resolution of sampling within the focused detachment footwall area, by expanding sampling coverage to areas in the upper plate and in parts of the KMP that are distal from the detachment, and by using vitrinite reflectance data from Cretaceous and Tertiary sediments preserved in small grabens to further constrain the magnitude of exhumation in the eastern Klamaths. By incorporating these sets of new, additional data and detailed forward thermal modeling that assesses a diverse range of exhumation scenarios, we are further constraining the Cenozoic extensional and uplift history of the KMP in order to determine how this key region fits into the larger picture of the plate boundary.