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

本研究项目将大盆地西部死亡谷-鱼湖谷横向断裂系统的变形速率估计扩展到过去500万年，逐步分辨率为10万至1万年。研究的重点是死亡谷-鱼湖谷断裂系统中的一个主要抑制弯曲，该弯曲是由于沿死亡谷-鱼湖谷断裂的横向位移转移到局部缩短和隆起而形成的。主要目标是：(1)确定变形速率；(2)评估离散与分布变形机制的作用；(3)结构的三维几何特征和演化以及约束弯曲形成过程中可能的垂直轴旋转。该项目包括详细的地质填图、构造分析、地层表征、地质年代学和磁地层学-古地磁分析。野外和实验室研究将定义三维几何，构造演化，以及在这个主要收缩构造形成过程中活跃的变形机制。评估不同时间间隔的变形速率利用了一个强大的年代地层格架，并从变形模型中确定了累计位移和增量位移。通过将高精度的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性地层学相结合，将获得100,000年甚至可能10,000年的时间分辨率。将这些时间信息与同生地层和三维结构模型的场关系相结合，可以在构造生长过程中分辨出100至1000米的增量位移。有了这些位移和时间范围，抑制弯曲的位移和增长提供了可与晚第四纪地表位移相媲美的速率确定。准确估计各种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是至关重要的。在所谓的地震周期中，由于断层的形成和地震能量的释放而引起的大陆的变形，在几十年到几万年的时间里，人们对这种变形和地震能量的释放越来越了解，这些信息为了解地震活动在整个地质时期是否保持不变以及在多大程度上保持不变提供了重要的见解。不幸的是，随着时间的推移，估计主要断层系统的变形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效应和无法测量断层间的准确年代标志单元的偏移。估计世界上大部分地区在数万年和数十万年期间的变形率的能力，在数十万年到数百万年的地质时期内仍然是难以捉摸的。加强对数百万年地震周期的了解需要在不同的时间尺度上揭示地球的历史，并且只能在地质结构保存完好并提供高精度地质事件日期的极少数情况下才能解决。本研究项目的预期结果将量化一个主要地质断层系统的一部分的逐步发展，该断层系统暴露在广泛的、目前地震活跃的地区，该地区是美国西部科迪勒拉东部内华达山脉和西部大盆地之间的边界。死亡谷-鱼湖谷断层系统已经活跃了数百万年，记录了数十公里的水平位移。与已确定的当代第四纪和最新第四纪变形速率估算值相比，本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.