TESTING TECTONIC MODELS IN THE EASTERN HAYFORK TERRANE IN THE KLAMATH MOUNTAINS, NORTHERN CALIFORNIA

There are debated tectonic models for what subduction looked like in North America during the Paleozoic and Mesozoic. The number of subduction zones and their polarity through time are disputed. The timing of subduction also needs more investigation to differentiate proposed models. To address this problem of conflicting models, we investigate the relatively understudied Klamath Mountains, which extend from northern California to Oregon and are made up of multiple accreted terranes. The Eastern Hayfork Terrane formed in a Late Paleozoic to Early Mesozoic subduction zone. It is strongly deformed from broken formation to block-in-matrix mélange, making it more challenging to use stratigraphic relationships to characterize the terrane. Paleomagnetism from farther east indicates the Klamath Mountains may have been oriented E-W during the Permian and Triassic. The Eastern Hayfork Terrane is primarily composed of metaclastic and metavolcanic units with significant blocks of greenstone, metalimestone, and metachert from accreted oceanic crust. There is a limited amount of age data for the Eastern Hayfork terrane. The zircon U-Pb ages of metasandstone blocks are latest Archean to early Proterozoic and are interpreted as olistoliths from older continental blocks to the east. Meta-argillites in the Sawyers Bar area have low zircon yield and poorly constrained maximum depositional ages of 201-272 Ma. Additional 1-3 Ga ages indicate continental provenance inconsistent with an intraoceanic arc. Additionally, ⁴⁰Ar/³⁹Ar data from chert argillite mélange have cooling ages of 346-360 Ma for micas and amphiboles, indicating a long history of subduction and accretion but with significant gaps. We present new U-Pb detrital zircon geochronology from broken formation blocks and mélange matrix. Maximum depositional ages and provenance from detrital zircon ages will help constrain the accretion history of the Eastern Hayfork terrane and the tectonic construction of western North America.