Quaternary and Late Neogene Growth of the Cucomungo Canyon Restraining Bend and Associated Deformation Rates, Death Valley-Fish Lake Valley Fault System, Western Great Basin

这项研究项目将大盆地西部死亡谷-鱼湖谷横流断裂系统的形变速率估计扩展到过去500万年，逐步分辨率为10万年，甚至可能是10000年。这项工作将集中在死亡谷-鱼湖谷断裂系统中的一个主要的约束性弯道上，该断裂系统是随着死亡谷-鱼湖谷断裂的侧向位移而形成的，断裂被转移到局部的缩短和隆起。主要目标是：(1)确定变形速率；(2)评估离散变形机制与分布式变形机制的作用；(3)描述在约束弯曲形成期间结构的三维几何和演化以及可能的垂直轴旋转。该项目涉及详细的地质填图、构造分析、地层特征、地质年代学和磁性地层-古地磁分析的综合。野外和实验室研究将确定这一主要收缩构造形成过程中的三维几何、构造演化和变形机制。对不同时间间隔的变形速率的评估利用了一个强大的年代地层框架，并根据变形模型确定了总位移和增量位移。通过将许多关键地层间隔(例如，特定的盖夫拉层和火山碎屑沉积)的高精度40Ar/39Ar年龄数据与可与天体年代学调整的新近纪地磁极性时间尺度相关联的磁极地层相结合，将获得100,000年甚至可能10,000年的时间分辨率。将这种时间信息与涉及同造山层和三维构造模型的场关系结合起来，可以在构造生长期间分辨率100至1000米的增量位移。在这些位移和时间范围内，约束性弯曲的位移和增长提供了与第四纪晚期地表位移相当的速率决定。准确估计广泛地质过程的速率对于理解地球表面在不同时间尺度上的演化至关重要。在所谓的地震周期中，由于断层的形成和地震能量的释放，大陆的变形在数万至数万年的时间里得到了更好的理解，这些信息为地震活动是否或在多大程度上在整个地质时期保持不变提供了重要的见解。不幸的是，随着时间的推移，估计主要断层系统变形速率的能力变得越来越差，这主要是由于较年轻的变形的模糊影响，以及无法测量跨断层的成熟标志单元的偏移量。在从几十万年到几百万年的地质时期内，估计世界大部分地区几万至几十万年的形变率的能力仍然难以捉摸。加强对持续数百万年的地震周期的了解需要了解地球在不同时间尺度上的历史，只有在地质结构保存完好并有能力高精度确定地质事件日期的极少数情况下才能解决这一问题。这一研究项目的预期结果将量化在目前地震活跃的广阔区域内暴露的主要地质断层系统的一部分的逐步发展，该区域是内华达山脉东部和美国西部科迪勒拉大盆地西部之间的边界。死亡谷-鱼湖谷断裂系统几百万年来一直活跃，记录了数十公里的水平位移。与根据大地测量和偏移地貌特征确定的当代和最新第四纪变形速率估计值相比较，这项研究的结果将有助于将活动构造与长期变形过程联系起来。

This research project extends deformation rate estimates for the Death Valley-Fish Lake Valley transcurrent fault system, western Great Basin, to the last 5 million years with a stepwise resolution of 100,000 and possibly 10,000 years. The work will focus on a major restraining bend in the Death Valley-Fish Lake Valley fault system that formed as lateral displacement along the Death Valley-Fish Lake Valley fault was transferred to local shortening and uplift. The primary objectives are: (1) determination of deformation rates; (2) assessment of the role of discrete versus distributed deformation mechanisms; and (3) characterization of the three-dimensional geometry and evolution of structures and possible vertical-axis rotation during formation of the restraining bend. The project involves integration of detailed geologic mapping, structural analysis, stratigraphic characterization, geochronology, and magnetostratigraphic-paleomagnetic analysis. Field and laboratory studies will define the three-dimensional geometry, tectonic evolution, and mechanisms of deformation active during the formation of this major contractional structure. Assessment of deformation rates over different time intervals utilizes a robust chronostratigraphic framework and determination of aggregate and incremental displacements from deformation models. By combining high-precision 40Ar/39Ar age data for numerous key stratigraphic intervals (e.g. specific tephra layers and volcaniclastic deposits) with a magnetic polarity stratigraphy that can be correlated with the astrochronologically-tuned Neogene geomagnetic polarity timescale, temporal resolutions of 100,000 and possibly 10,000 years will be obtained. Combining this temporal information with field relations involving synorogenic strata and three-dimensional structural models allows resolution of incremental displacements of 100 to 1,000 meters during growth of the structure. With these displacement and timing ranges, the displacement and growth of the restraining bend provides rate determinations comparable to those for late Quaternary surface displacements.Accurate estimates of the rates of a broad range of geologic processes are critical to understanding the evolution of the Earth's surface over different time scales. The deformation of continents through the formation of faults and the release of seismic energy as earthquakes, in what is known as the earthquake cycle, is becoming better understood over durations of tens to tens of thousands of years and such information provides important insights into whether or to what degree earthquake activity remains the same through geologic time. Unfortunately, the ability to estimate deformation rates on major fault systems becomes more poorly resolved with the passage of time, mainly due to the obscuring effects of younger deformation and the inability to measure offset of well-dated marker units across faults. The capacity to estimate deformation rates over durations of tens of thousands and hundreds of thousands of years in most parts of the world remains elusive for periods of geologic time ranging from hundreds of thousands and millions of years. Enhanced understanding the earthquake cycle over durations of millions of years requires unraveling Earth's history over different time scales, and can be addressed only in rare instances where geologic structures are well preserved and provide the capacity to date geologic events with high- precision. The anticipated results of this research project will quantify the progressive development of a part of a major geologic fault system exposed within the broad, currently seismically active region that is the boundary between the eastern Sierra Nevada and the western Great Basin in the western US Cordillera. The Death Valley-Fish Lake Valley fault system has been active for several millions of years and records tens of kilometers of horizontal displacement. When compared to well determined contemporary and latest Quaternary deformation rate estimates established geodetically and from offset geomorphic features, the results of this study will help tie active tectonic to long-term deformation processes.