Paleomagnetic characteristics of Basalts on the Devils Garden Plateau, Northeastern California

Northeastern California hosts expansive tholeiitic basalt fields of late Miocene and younger age east of the Cascade volcanic arc, and at the western boundary of the Basin and Range extensional province. The geochemistry of these volcanic units indicates a primitive mantle source with little crustal contamination. The Devils Garden Plateau is a constructional volcanic field north and west of Alturas, California with numerous mapped Tertiary basalt units with an estimated total volume of ~850 km3 (McKee et al., 1983). It is made up of older volcanic edifices which were subsequently engulfed by the voluminous Devils Garden Basalt, which forms the remarkably flat plateau-top topography, despite being disrupted by numerous Quaternary normal faults. Though there are multiple mapped eruptive sources of the Devils Garden Basalt, the size and type of vents (shields or fissures) have little topographic expression indicating low lava viscosity that remained essentially uniform over the period of its accumulation. Older vents can be easily identified suggesting a different eruptive regime. Probing the mechanism of this large-volume and spatially distributed volcanic system requires a combination of geological and geophysical techniques. Paleomagnetic field studies can correlate flows as well as provide estimates of eruption timing and duration. The long-term history of this back arc tholeiitic basaltic system at the transition into the Basin and Range extensional province provides a unique laboratory to understand the evolution of similar volcanic systems elsewhere. Precise paleomagnetic data also ground truth regional aeromagnetic interpretations and models, allowing for better spatial constraint of faults and contacts. Greater knowledge of unit distribution and age will also provide constraints on the age of faulting and its relationship to the volcanism. We present paleomagnetic results from the Devils Garden Plateau region east of Medicine Lake volcano and west of Goose Lake Valley. We find both normal and reversed remanent magnetization directions, which form directional groupings that indicate flow and unit boundaries. We will continue to evaluate previously proposed spatiotemporal distributions of the Devils Garden Basalt and the other basaltic units making up the Devils Garden Plateau.