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

对于华盛顿西北部、华盛顿西南部和不列颠哥伦比亚省西南部的白垩纪中期造山作用，提出了两种根本不同的模型。其中一个是弗兰格里亚与北美碰撞时形成的西北喀斯喀特冲断系统，导致喀斯喀特结晶岩心向西冲断和埋藏。另一方面，造山作用是逆压作用的结果，结晶岩心是大型右旋剪切带的一部分。关于从岩体得到的古地磁数据是否表明侵入的地体移动得很远，或者岩体是否已经倾斜到350度，也存在争议。该项目将检查斯图尔特山岩基和周围的围岩，它们相对于西北喀斯喀特冲断系统和水晶岩心占据关键位置。这项工作将包括制图、运动学分析和无线电测年。结果旨在确定该地区的倾斜程度以及岩体侵位和区域变形随深度的变化情况。杰出模式之间的分辨将对西北构造学具有重要意义。

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.