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

合作研究：古代和主动位移转移的变形率和运动学，中央沃克巷，西部大盆地

• 批准号: 0208219
• 负责人: John Oldow
• 金额: $ 16.61万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-06-15 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208219&HistoricalAwards=false
• 关键词: Collaborative; Research; Deformation; Rates; Kinematics

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.

晚新生代变形广泛分布在美国西部相连的北美板块边缘，从圣安德烈亚斯断层系向东延伸，穿过莫哈韦沙漠，进入盆地和山脉。东加州剪切带和西部大盆地的步行者巷形成了一个构造活动带，可容纳北美和太平洋板块之间约25%的相对运动。从莫哈韦沙漠开始，位移被带到北部，在内华达州南部山脉以东，在西部和东部由欧文斯谷和熔炉溪断层系统界定的狭窄变形带中。从内华达州中部山脉的纬度向北，变形带扩大到包括大盆地西北部的步行者巷和内华达州中部地震带。Sierra内华达州表现为一个具有10-14 mm/年的西北向运动的连贯构造块体，并形成大盆地分布变形带的西边界。内华达州中西部下方有一个复杂的活动构造格局，位移从加州东部剪切带转移到步行者巷和内华达州中部地震带。综合地质、地震和GPS大地测量结果表明，中央步行者巷（CWL）是一个位移传递系统，连接着阶梯状的西北向横断层。位移传递系统的发展超过了一个时期的13马，并进行了至少50公里的右侧运动，从炉溪断层系统的东部加州的CWL的右侧故障。古位移转移伴随着中地壳岩石在横向构造之间的伸展步距中的折返，并伴随着垂直轴旋转和上下板块组合的倾斜。该传输系统仍然活跃，位于古代结构西北部50 × 120公里的区域之下。根据现有的工作，大地测量确定的速度场的CWL的比较是不容易调和与目前的理解，在该地区的断层位移，并指出在比较大地测量和地质位移场的困难。此外，自~13 Ma开始，位移传递系统的持续活动提供了利用地质和大地测量技术评估古代和活动变形速率的机会。PI建议对中央步行者巷进行综合大地测量和地质调查，以解决两个问题：（1）在一个横断层系统步距内，伸展转换的三维几何形状和位移历史是什么？（2）在转换系统内，对古构造和活动构造进行的大地测量、地震和地质调查的位移速率和运动学估算是否具有可比性？中央步行者巷非常适合这项研究，原因如下：（1）该地区地震活跃，位移传递断层系统存在明确的地震震源机制，（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大地网记录到一个复杂的现今位移场，其差异滑动量约为10 mm/yr，（4）在出露良好的伸展龟背构造的折返历史中保留了位移传递系统的地质演化，（5）伸展杂岩上板块组合中的同造山期火山岩和沉积岩记录了与断层位移有关的前进倾斜历史，（六）在初步的古地磁研究中，（7）该区区域地质编图比较成熟，为位移史重建提供了良好的控制条件。这些元素将允许位移转移的运动学特性，并提供机会，直接比较变形运动学和速率在地质和大地测量的时间间隔。PI将利用详细的地质测绘、结构分析、GPS大地测量、古地磁分析、地质年代学和温压调查进行综合研究，完成上述任务。研究团队（Oldow，Geissman，McClelland，McIntosh和Selverstone）拥有解决各种研究主题的专业知识，其中两名研究人员（Oldow和Geissman）在该领域拥有丰富的工作经验。通过建立在以前的研究，这种综合调查将建立的面积限制的张性断层系统，文件变量之间的几何关系的主要和次要的故障系统，确定断块运动的运动历史，并制定一阶估计的现代和古代位移。