COLLABORATIVE RESEARCH: Structure of the Mt. Stuart Batho- lith and Its Wall Rocks: Implications for Tilted Plutons and Cretaceous Orogenesis in the North Cascades

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Two fundamentally different models have been proposed for profound mid-Cretaceous orogenesis in northwestern Washington and southwestern Washington and southwestern British Columbia. In one, the northwest Cascade thrust system formed during the collision of Wrangellia with North America, and resulted in west- directed thrusting and burial of the Cascades crystalline core. In the other, orogenesis was the result of transpression and the crystalline core was part of a large dextral shear zone. Contro- versy also exists regarding whether paleomagnetic data from plutons indicate that the intruded terranes are far travelled or if instead the plutons have been tilted up to 35o. This project will examine the Mt. Stuart batholith and surrounding wall rocks which occupy a key position relative to the northwest Cascades thrust system and the Crystalline core. The work will involve mapping, kinematic analysis and radio- metric dating. Results are aimed at determining the amount of tilting in the region and how pluton emplacement and regional deformation change with depth. Resolution between outstanding models will have considerable implications for northwest tectonics.