MESOZOIC TERRANE BOUNDARIES IN THE BLUE MOUNTAINS PROVINCE OF NORTHEASTERN OREGON DETERMINED FROM GRAVITY AND MAGNETIC DATA

Gravity and magnetic data were used to investigate the structure and extent of Mesozoic and Paleozoic terranes within the Blue Mountain Province of Northeastern Oregon. The pre-Cenozoic rocks in this region provide a glimpse into Mesozoic arc-related magmatism, basin formation, and terrane accretion that is otherwise unavailable in this region. Flows from the Columbia River Basalt Group (CRBG) and related volcanics obscure much of the Blue Mountains Province (BMP) under Tertiary sedimentary and volcanic cover. The BMP consists of early Mesozoic magmatic arcs (Wallowa and Olds Ferry terranes), a mélange belt (Baker terrane) and a large Triassic-Jurassic sedimentary basin (Izee terrane). Previous analysis of gravity and magnetic data in the Izee terrane is expanded upon as we seek to answer questions regarding the upper crustal structure of the Paleozoic basement and the geometries of the Mesozoic accreted terranes. Three-2D gravity and magnetic models of selected transects across the southwestern extent of the Izee terrane were produced. These models are coupled with isostatic gravity anomaly, low-pass filtered and horizontal derivative gravity and magnetic anomaly maps to highlight the extent and geometries of Triassic and Jurassic formations. This analysis highlights more specifically the Mesozoic terranes that underlies the Tertiary sedimentary rocks of the Bear Valley and Strawberry Mountain volcanics and the correlation between the well-defined low gravity anomalies in the Izee terrane and the possible J-K felsic plutons.