Tracking the Late Mesozoic Strike-Slip System of the Western U.S. Cordillera

大规模的走滑断层作用越来越被认为是包括北美科迪勒拉山脉在内的造山带发展过程中的一个重要过程。 这些断层可以容纳大量的断层位移，并以复杂的方式重新排列它们的相对位置，从而形成一组断层，其关系难以破译。 造山带中的区域性走滑断层活动也可以对古代板块的相互作用产生重要的认识。 在北美科迪勒拉山脉，前新生代走滑断层被认为在岩石的运输和组装中发挥了重要的结构作用，但所提出的走滑事件的具体细节陷入了不确定性和争议。 关键的问题涉及到走滑边界的位置，以及沿着它们的位移量、方向和时间。 这些不确定性必须解决之前，任何可靠的古地理和古构造重建的前新生代Cordillera.This项目的重点是西部内华达州剪切带系统（WNS），最近确定的主要构造边界在俄勒冈州东南部和西北部内华达州。 到目前为止，沿着WNS获得的数据表明，它容纳了几个100公里的右旋位移的外侧岩石在中生代晚期，它可能会连接到其他两个重要的中生代晚期构造边界，鲑鱼河缝合线西部爱达荷州和莫哈韦雪湖断层的中部和南部的内华达州在加州。 该项目正在通过各种新的研究更严格和更广泛地检验这些结论。 如果关于边界的初步假设是正确的，它将对北美科迪勒拉的古地理和古构造重建和解释产生深远的影响。 (1)WNS的详细测绘、构造和地质年代学研究正在向南延伸到内华达州西部的盖拉赫地区，这将扩大对边界的认识，使其走向距离超过200公里。 (2)从盖拉赫地区到俄勒冈州东南部，WNS沿着微生物的分布、起源和意义正在确定中。 这些地层和结构上不同的岩石构造组合可能是断层片沿沿着WNS走滑系统的走向向北拖曳。 (3)正在测试拟议的跨走滑系统的连接，以确定是否推断的意义和位移量是有效的，以及是否推断的WNS，莫哈韦雪湖断层和鲑鱼河缝合线之间的连续性可以更严格地支持。 (4)走滑位移和变形的时间沿着WNS正在确定各种地质年代学研究。

Large-scale strike-slip faulting is increasingly recognized as an important process in the development of orogenic belts, including the North American Cordillera. These faults can accommodate substantial displacement of terranes and shuffle their relative positions in complex ways, resulting in a collage of terranes whose relationship is difficult to decipher. Regional strike-slip faulting in orogenic belts can also yield crucial insight into ancient plate interactions. In the North American Cordillera, pre-Cenozoic strike-slip faulting is believed to have played an important structural role in terrane transport and assembly, but the specifics of proposed strike-slip episodes are mired in uncertainty and controversy. Key questions involve the location of strike-slip boundaries, and the amount, sense, and timing of displacement along them. These uncertainties must be resolved before any reliable paleogeographic and paleotectonic reconstructions of the pre-Cenozoic Cordillera can be generated.This project is focusing on the western Nevada shear zone system (WNS), a recently identified major tectonic boundary in southeast Oregon and northwest Nevada. Data obtained so far along the WNS suggest that it accommodated several 100 km dextral displacement of outboard terranes in the late Mesozoic, and that it likely connects up with two other important late Mesozoic tectonic boundaries, the Salmon River suture of western Idaho and the Mojave-Snow Lake fault of the central and southern Sierra Nevada in California. This project is testing these conclusions more rigorously and extensively by a variety of new studies. If initial hypotheses concerning the boundary are correct, it will have far-reaching implications for paleogeographic and paleotectonic reconstructions and interpretations of the North American Cordillera.Specific research being done in this project is as follows. (1) Detailed mapping, structural, and geochronologic studies of the WNS are being extended south into the Gerlach area of western Nevada, which will expand knowledge of the boundary to a strike distance of over 200 km. (2) Distribution, origin, and significance of microterranes along the WNS are being determined from the Gerlach area to southeast Oregon. These stratigraphically and structurally distinct lithotectonic assemblages may be fault slices dragged northward along anastomosing strands of the WNS strike-slip system. (3) Proposed terranes linkages across the strike-slip system are being tested to determine whether the inferred sense and amount of displacement is valid, and whether the inferred continuity between the WNS, Mojave-Snow Lake fault, and Salmon River suture can be more rigorously supported. (4) Timing of strike-slip displacement and deformation along the WNS are being determined by a variety of geochronologic studies.