Collaborative Research: Deformation Rates and Kinematics of Ancient and Active Displacement Transfer, Central Walker Lane, Western Great Basin

晚新生代的变形广泛分布在美国西部相邻的北美板块边缘，并从圣安德烈亚斯断层系统向东延伸，穿过莫哈韦沙漠，进入盆地和山脉。东加利福尼亚剪切带和西部大盆地的沃克巷形成了一个活跃的构造带，容纳了北美与太平洋板块之间约25%的相对运动。从莫哈韦沙漠开始，位移被带到北部，南内华达山脉以东，在一个狭窄的变形带中，由欧文斯谷和炉溪断层系统束缚在西部和东部。从内华达山脉中部纬度向北，变形带扩大到包括大盆地西北部的沃克巷和内华达中部地震带。内华达山脉是一个向西北运动10-14 mm/yr的相干构造块体，是大盆地分布变形带的西部边界。内华达中西部下部是一个复杂的活动构造模式，位移从加州东部剪切带转移到沃克巷和内华达中部地震带。综合地质、地震和GPS大地测量结果表明，中央沃克巷（CWL）是一个连接台阶状西北向横流断层的位移传递系统。位移传递系统经过约13 Ma的演化，从加州东部的Furnace Creek断裂系统向CWL的右侧断裂进行了至少50 km的右侧运动。古位移转移伴随着跨流构造之间的伸展变位中地壳岩石的掘出，伴随着上下板块组合的纵轴旋转和倾斜。该转移系统仍然活跃，位于古建筑西北50乘120公里的区域下方。在现有工作的基础上，比较大地测量速度场与目前对该地区断层位移的认识不容易协调，并指出了比较大地测量和地质位移场的困难。此外，自~13 Ma开始以来，位移传递系统的持续活动为利用地质和大地测量技术评估古代和活动的变形速率提供了机会。PI建议对Walker Lane中心进行综合大地测量和地质调查，以解决两个问题：(1)在一个横向断层系统的断层转换中发展的伸展转移的三维几何和位移历史是什么？(2)在大地测量学、地震学和地质调查中，对转移系统内的古代和活动构造的位移率和运动学估计是否具有可比性？中央沃克巷非常适合进行这项研究，原因如下：(1)该地区地震活跃，存在位移传递断层系统的明确震源机制；(2)断层暴露良好，并产生了变形运动学的初步断层滑动估计；(3)GPS大地测量网记录了一个复杂的现今位移场，其差滑量约为10毫米/年；(4)位移传递系统的地质演化记录在出露良好的张性龟背构造的发掘史中；(5)张性杂岩上板块组合的同生火山岩和沉积岩记录了与断层位移相关的渐进倾斜历史；(6)初步的古地磁调查发现了与位移转移相关的区域性广泛的差异倾斜和垂直轴旋转域；(7)区域地质编制成熟，为位移史重建提供了良好的控制。这些元素将允许表征位移传递的运动学，并提供在地质和大地测量时间间隔内直接比较变形运动学和速率的机会。PI将利用详细的地质测绘、结构分析、GPS大地测量学、古地磁分析、地质年代学和热气压调查进行综合研究，解决上述任务。研究团队（Oldow、Geissman、McClelland、McIntosh和Selverstone）拥有解决各种研究课题的专业知识，其中两名研究人员（Oldow和Geissman）在该领域拥有丰富的工作经验。在前人研究的基础上，这项综合研究将建立张性断裂系统的面积界限，记录主要和次要断裂系统之间的可变几何关系，定义断块运动的运动学历史，并对近代和古代位移进行一阶估计。

Late Cenozoic deformation is broadly distributed across the North American plate margin of the conterminous western United States and stretches from the San Andreas fault system eastward across the Mojave Desert and into the Basin and Range. The eastern California shear zone and Walker Lane of the western Great Basin form an active belt of structures accommodating about 25% of the relative motion between North America and the Pacific plate.From the Mojave Desert, the displacement is carried north, east of the southern Sierra Nevada, in a narrow zone of deformation bound on the west and east by the Owens Valley and Furnace Creek fault systems. North from the latitude of the central Sierra Nevada, the zone of deformation broadens to include the Walker Lane and central Nevada seismic belt in the northwestern Great Basin. The Sierra Nevada behaves as a coherent tectonic block with a northwest-directed motion of 10-14 mm/yr and forms the western boundary of the zone of distributed deformation in the Great Basin. A complex pattern of active structures underlies west-central Nevada where displacement is transferred from the eastern California shear zone to the Walker Lane and the central Nevada seismic belt. Integrated geologic, seismological, and GPS geodetic results indicate that the central Walker Lane (CWL) serves as an displacement transfer system linking stepped northwest-trending transcurrent faults. The displacement transfer system evolved over a period of ~13 Ma and carried at least 50 km right-lateral motion from the Furnace Creek fault system of eastern California to the right-lateral faults of the CWL. Ancient displacement transfer was accompanied by exhumation of mid-crustal rocks in the extensional stepover between transcurrent structures and was accompanied by vertical axis rotation and tilt of both upper- and lower-plate assemblages. The transfer system is still active and underlies a region 50 by 120 km immediately northwest of the ancient structures. Based on existing work, the comparison of a geodetically determined velocity field for the CWL is not easily reconciled with the current understanding of fault displacements in the region and points out the difficulty in comparing geodetic and geologic displacement fields. Furthermore, the continued activity of the displacement transfer system since inception at ~13 Ma offers presents the opportunity to assess ancient and active rates of deformation using geologic and geodetic techniques.The PI's propose an integrated geodetic and geologic investigation of the central Walker Lane to address two questions: (1) What is the three-dimensional geometry and displacement history of extensional transfer developed within a transcurrent fault system stepover?, and (2) Are displacement rate and kinematic estimates comparable between geodetic, seismological, and geologic investigation of ancient and active structures within the transfer system? The central Walker Lane is ideally suited for this study for several reasons: (1) the region is seismically active and well defined earthquake focal mechanisms exist for the displacement transfer fault system, (2) the faults are well exposed and have produced preliminary fault-slip estimates of deformation kinematics, (3) a complex present-day displacement field with ~10 mm/yr of differential slip is recorded by a GPS geodetic network, (4) the geologic evolution of the displacement transfer system is preserved in the exhumation history of well-exposed extensional turtleback structures, (5) synorogenic volcanic and sedimentary rocks in the upper-plate assemblage of the extensional complex record a history of progressive tilt associated with fault displacement, (6) regionally extensive domains of differential tilt and vertical axis rotation associated with displacement transfer are recognized in preliminary paleomagnetic investigation, and (7) regional geologic compilation of the region is mature and provides excellent control for displacement-history reconstruction. These elements will allow characterization of the kinematics of displacement transfer and offer the opportunity to directly compare deformation kinematics and rates over geologic and geodetic time intervals. The PI's will address the tasks listed above with an integrated study utilizing detailed geologic mapping, structural analysis, GPS geodesy, paleomagnetic analysis, geochronology, and thermobarometric investigation. The research team (Oldow, Geissman, McClelland, McIntosh, and Selverstone) have the expertise to address the various research topics and two of the researchers (Oldow and Geissman) have substantial experience working in the area. By building on previous studies, this integrated investigation will establish the areal limits of the transtensional fault system, document variable geometric relations between major and secondary fault systems, define the kinematic history of fault block motion, and develop first-order estimates of recent and ancient displacement.