CRETACEOUS TO MIOCENE EXHUMATION AND BURIAL HISTORY OF THE SOUTHERN KLAMATH MOUNTAINS PROVINCE

The Klamath Mountains Province (KMP) is located in northwestern California and southwestern Oregon and consists of Paleozoic-Mesozoic accreted terranes intruded by Jurassic and Cretaceous plutons. In this study, we, an undergraduate research cohort of six students and three faculty members, focus within the southern KMP. We use thermochronology to investigate the thermal histories of the Shasta Bally batholith and Ironside Mountain batholith to interpret Cretaceous to Miocene burial and exhumation.

In this study, we will present new combined apatite (U-Th)/He (AHe, closure temp (Tc) ~60°C), apatite fission track (AFT, Tc ~110°C) and zircon (U-Th)/He (ZHe, Tc ~180°C) thermochronometry from the same hand samples, acquired in Spring 2024. Our sampling rationale was to target plutonic bedrock in contact with, or proximal to, locally preserved Cretaceous sedimentary rocks. The Cretaceous cover has been interpreted to represent regional scale Early-mid Cretaceous marine transgression across the KMP. The Shasta Bally batholith was emplaced at 136 Ma, exhumed between 133-125 Ma based on the onlapping Great Valley Sequence and subsequently reburied to at least 100°C by approximately 64 Ma based on published AFT data. Ironside Mountain batholith was emplaced at 170 Ma, exhumed close to the surface by 135 Ma, subsequently reburied to at least 90°C and recently published AHe data suggests Miocene cooling likely caused by basin exhumation and erosion.

The thickness, spatial variability, and lateral continuity of Cretaceous deposition in this region is not well understood. Applying the ZHe chronometer system will allow us to better constrain the burial temperature and therefore the thickness of Early-mid Cretaceous sedimentary cover in the southern KMP, prior to rock exhumation and uplift. We will apply thermal modeling from the combined AHe-AFT-ZHe data with mapped geologic constraints to explore a range of Cretaceous-Miocene exhumation, burial, and uplift histories of the southern KMP.