Collaborative Research: Clockwise block rotation in the Pacific Northwest and sinistral movement on the Lewis & Clark zone

一般说来，北美大陆的西部是在过去2亿年里由大块地壳碰撞组装而成的。这些碰撞很可能是整个美国西部形成山带、显著的火成岩活动和产生矿藏的原因。该项目将从爱达荷州和蒙大拿州的岩石收集数据，以测试新的想法，以解释落基山脉北部和太平洋西北部造山事件的时间和起源。要测试的想法包括地壳运动的类型，这些地壳运动的时间，以及与之相关的岩石的变形。根据这些想法得出的预测包括爱达荷州、俄勒冈州和蒙大拿州的大部分地区存在顺时针旋转。爱达荷州和蒙大拿州的Lewis&Amp；Clark带--一个大规模的走滑断层--可能是这些顺时针旋转的结果。为该项目进行的工作将包括收集样本，以测量岩石形成时记录的地球磁场方向，并分析这些岩石中的矿物以确定其年龄。这些数据将检验对变形时间和相关火成岩活动的预测。这项工作将由两所大学的教员团队、三名研究生和几名本科生完成。该提案是一项简单的古地磁测试，旨在测试蓝山及其邻近的劳伦蒂亚地区--俄勒冈州东部、华盛顿东南部、爱达荷州中部，可能还有蒙大拿州西南部--是否在晚白垩世-古近纪作为一个连贯的地块顺时针旋转约30°。将在不同的地点进行一系列的古地磁分析，以测试是否发生了顺时针旋转，如果发生了，地壳块体的空间范围是什么。不同年龄岩石的古地磁分析将测试顺时针旋转发生的时间，将其与劳伦西亚西缘的运动和大陆内部的收缩变形联系起来。其影响有三个方面。首先，顺时针旋转可以为太平洋西北西部边缘的右旋地体平移提供独立的证据。其次，顺时针旋转可能解释了Lewis和Clark线的激活，Lewis和Clark线是一个与板块边缘倾斜的主要走滑系统。顺时针旋转的时间应该作为该结构上左侧与右侧运动历史的指南。第三，与蓝山相邻的劳伦亚地块的旋转可能在空间和时间上与其类型所在地的拉莱米式变形相关联，这可能为有关前陆变形的问题提供信息。这项工作将支持来自西华盛顿大学和威斯康星大学麦迪逊分校的三名研究生。它还将支持本科生的研究，并为每所大学的本科生提供顶峰体验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

GeneralThe western portion of the North American continent was assembled by collision of large blocks of crust over the past 200 million years. These collisions are likely responsible for the formation of mountain belts, significant igneous activity, and production of mineral deposits throughout the western United States. This project will gather data from rocks in Idaho and Montana to test new ideas to explain the timing and origin of the mountain building events in the northern Rocky Mountains and Pacific Northwest. The ideas to be tested include the type of crustal movement, the timing of those crustal movements, and the deformation of rocks associated with it. Predictions resulting from these ideas include the existence of clockwise rotation of large portions of Idaho, Oregon, and Montana. The Lewis & Clark zone of Idaho and Montana - a large-scale strike-slip fault - may have resulted from these clockwise rotations. The work conducted for this project will include collection of samples to measure the direction of the Earth’s magnetic field recorded when the rocks formed, and to analyze minerals in these rocks to determine their age. This data will test predictions for the timing of deformation and of associated igneous activity. The work will be done by a team of faculty at two universities, three graduate students, and several undergraduate students.The proposal is a straightforward paleomagnetic test of whether the Blue Mountains and Adjacent Laurentia – the region of eastern Oregon, southeastern Washington, central Idaho, and possibly southwestern Montana – rotated ~30° clockwise as a coherent block in the Late Cretaceous-Paleogene. A series of paleomagnetic analyses will be conducted on different locations to test whether the clockwise rotation happened and, if so, what is the spatial extent of the crustal block. Paleomagnetic analyses of different ages of rocks will test when the clockwise rotation occurred, to correlate it to motions along the western margin of Laurentia and contractional deformation in the continental interior. The implications are three-fold. First, clockwise rotation could provide independent evidence for dextral terrane translation along the western margin of the Pacific Northwest. Second, the clockwise rotation may explain the activation of the Lewis and Clark line, a major strike-slip system that is oblique to the plate margin. The timing of clockwise rotation should act as a guide to the history of left-lateral vs. right-lateral movement on that structure. Third, the rotation of the Blue Mountains- Adjacent Laurentia block may be spatially and temporally correlated with Laramide-style deformation in its type locality, it could inform questions about foreland deformation. The work will support three graduate students from Western Washington University and the University of Wisconsin-Madison. It will also support undergraduate student research and a capstone experience for undergraduate students at each university.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.