ONSET OF EOCENE-OLIGOCENE EXTENSION RECORDED BY DETRITAL ZIRCON PROVENANCE IN THE TITUS CANYON FORMATION, DEATH VALLEY, CA

Understanding the geodynamic evolution of the Basin and Range province relies on the unraveling of multiple phases of extension that vary in spatial extent, timing, and style. Within the province, the hyper-extended area of Death Valley, CA, records the impact of multiple phases of overlapping extension, producing one of the most detailed and complete records of Cenozoic tectonism in the Basin and Range. Three distinct phases of extension observed in the broader Basin and Range are also observed in existing tectonic data in Death Valley: (1) late Cretaceous syn-orogenic extension recorded in ⁴⁰Ar/³⁹Ar thermochronology, (2) a pulse of rapid Miocene extension along low-angle detachment faults recorded by low-temperature thermochronology, and (3) a Pliocene to present phase of trans-tensional tectonism that produced the modern topography of Death Valley, as evidenced by both low-temperature thermochronology in southern Death Valley and geodetic measurements. An enigmatic fourth phase of Paleogene extensional deformation in the Death Valley region, potentially contemporaneous with metamorphic core complex development in the northern Basin and Range, is recorded in the Titus Canyon and Ubehebe Formations, the two oldest Cenozoic sedimentary units in the region. The timing and duration of this extensional phase is difficult to constrain due to significant internal structural complexity and a lack of datable tuffs within the two formations. We present new mapping, measured sections, and detrital zircon U-Pb ages from the Titus Canyon Formation that constrain the onset of extension to ~35 Ma, and which demonstrate significant tectonic and environmental changes near the Eocene-Oligocene boundary. Shifts in zircon provenance, sedimentary facies, and volcanic input within the Titus Canyon Formation at ~35 Ma coincide with the onset of extension in metamorphic core complexes farther north along the Sevier orogenic belt. The Titus Canyon Formation may therefore record the earliest evidence of Cenozoic extensional collapse in eastern California. The spatial association of the Titus Canyon Formation with thickened crust of the Sevier Orogeny reinforces the correlation between early extensional collapse and topographically driven gravitational potential energy gradients.