Extension and Volcanism During Propagation of the Northwest Basin and Range into Southeastern Oregon

北美西部的盆地山脉省是北美板块在科罗拉多高原和内华达州山脉之间延伸的产物。 正断层使谷底（盆地）相对于相邻的山峰（山脉）下降。这一提议的一个主要目标是解决这个问题：这个壮观的地区何时成为北美景观的一部分？在北纬39度左右的内华达州，这个省的宽度在三个主要的增量中向西增加了大约100公里，分别是2600万到2200万年前，大约1500万到1400万年前，以及1000万到300万年前。 步行者巷是一个广泛的走滑和走滑断层带，位于沿着盆地和山脉省的西部边界，在2600万年前开始，显然在900万年前向北传播，接近北纬41度的南部喀斯喀特山脉。 虽然在内华达州，盆地和山脉在东西和南北方向的增长是相对众所周知的，当盆地和山脉式断层“到达”俄勒冈州时，很少有数据限制。 Grunder和Meigs正在对两个关键问题进行为期3年的调查--盆地和山脉是何时在俄勒冈州东南部形成的？还有，是什么因素限制了它在俄勒冈州的生长？ 他们能够回答这些问题，是因为盆地和山脉的发展都是在火山活动之前和伴随着火山活动。 火山岩是解决这些问题的核心，因为它们很容易用传统的同位素测年技术测年。 研究的重点是盆山正断层与火山岩的关系。 在一个给定的地方，伸展开始的时间可以确定，例如，取决于断层是否可以显示为更老，更年轻，或与给定的火山单位的就位同时代。 有了这些限制，研究人员能够确定盆地和山脉何时扩展到俄勒冈州南部，以什么速度发生扩张，以什么速度个别断层增长，以及正常断层是否受火山活动模式控制，或者相反，断层是否控制火山活动发生的地方。 这些数据有助于正在进行的关于火山作用在世界各地的盆地和山脉型省份的发展中的作用的辩论。 此外，他们提供了一个新的角度对断层的速度，这有助于限制地震的危害造成的正断层东南部的人口中心俄勒冈州（包括克拉马斯福尔斯，拉克维尤，和弯曲）。其他的社会效益包括在俄勒冈州州立大学培训研究生和本科生，扩大代表性不足的群体对科学的参与，以及将研究成果与正在进行的盆岭地球物理研究相结合，包括EarthScope。

The spectacular corrugated landscape known as the Basin and Range Province in western North America is the product of extension of the North American Plate largely between the Colorado Plateau and the Sierra Nevada. Normal faults drop valley bottoms (the 'basins') relative to adjacent mountain peaks (the 'ranges'). A major goal of this proposal addresses the question: when did this spectacular region become a part of the North American landscape? In Nevada at approximately 39 degrees North, the province grew about 100 kilometers incrementally westward in width in three main increments, at 26 to 22 million years ago, approximately 15 to 14 million years ago, and 10 to 3 million years ago. The Walker Lane, a broad zone of strike-slip and oblique-slip faulting that lies along the western boundary of the Basin and Range Province, initiated after 26 million years ago and apparently propagated northward approaching the southern Cascade Range at 41 degrees North after 9 million years ago. Whereas the growth of the Basin and Range in east-west and north-south directions is relatively well known in Nevada, few data constrain when Basin and Range-style faulting "arrived" in Oregon. Grunder and Meigs are conducting a 3-year investigation into two key questions--When did the Basin and Range form in southeastern Oregon? And, what factors limited how far into Oregon it grew? They are able to answer these questions because the development of the basins and ranges was both preceded and accompanied by volcanic activity. Volcanic rocks are central to resolving the questions because they are easily dated using conventional isotopic dating techniques. The essential observation of this study is the relationship between Basin and Range normal faults and volcanic rocks. Timing of the initiation of extension at a given place can be identified, for example, depending on whether faults can be shown to be older, younger, or coeval with emplacement of a given volcanic unit. With these constraints, the investigators are able to determine when the Basin and Range propagated into southern Oregon, at what rate that expansion occurred, at what rate individual faults have grown, and whether the normal faulting was controlled by the pattern of volcanism or, conversely, whether the faults controlled where volcanism occurred. These data contribute to the ongoing debate about the role of volcanism in the development of Basin and Range-type provinces around the world. Moreover, they provide a new perspective on the rate of faulting, which helps constrain the seismic hazard posed by normal faults to the population centers of southeastern Oregon (including Klamath Falls, Lakeview, and Bend). Additional societal benefits include the training of graduate and undergraduate students at Oregon State University, broadening of participation of underrepresented groups in science, and integration of research results with ongoing geophysical studies in the Basin-Range, including EarthScope.