Quantifying Changes in Erosion and Relief with Detrital Apatite (U-Th)/He Thermochronlogy and Cosmogenic Nuclides

项目概述用碎屑磷灰石（U-Th）/He热年代学和宇宙成因核素量化侵蚀和地貌变化技术说明：本研究使用综合碎屑磷灰石（U-Th）/He热年代学和沉积物中的宇宙成因核素，对加州南部Sierra内华达州流域侵蚀的分布和速率进行了详细研究。 我们的第一条研究线提出，碎屑磷灰石（U-Th）/He冷却年龄可以作为沉积物示踪剂，从而被用来测试是否一套陡峭的集水区，以增加的大小和复杂性，侵蚀均匀或占主导地位的点源侵蚀过程。我们的第二条研究路线比较了现代河流沉积物与较老沉积物（特别是保存在洞穴中的河流沉积物）的冷却年龄分布，以调查地形和流域高程的时间变化。我们使用一个三维热模型解释碎屑颗粒年龄分布从沉积物上解释的等温线的地形弯曲的影响。 此外，我们建议使用宇宙成因的10 Be和26 Al浓度在河流和洞穴沉积物中，调查流域平均侵蚀速率的时空变化。碎屑磷灰石（U-Th）/He热年代学和宇宙成因核素是容易集成的工具，因为它们利用来自同一袋河砂的不同矿物。 通过开发和整合这些工具在碎屑环境中，并利用丰富的以前（U-Th）/He数据和一组过时的洞穴，我们调查的地形演变的南部山脉内华达州，加州，从最早的上新世到今天。我们的综合热计时和宇宙成因的方法很容易适用于其他设置。例如，我们开发的碎屑磷灰石（U-Th）/He方法将确定该技术对较老矿床的适用性（例如，更广泛的意义：该项目解决地质学家和外行都非常感兴趣的山脉中地球表面演化的基本问题。 我们的研究应该有助于回答如何陡峭的山谷在内华达山脉内华达州侵蚀，他们侵蚀和产生沉积物的速度，以及如何在山谷内的海拔分布已经根据气候变化（如重复冰川）在过去的200万年演变。 此外，我们将开发的地球化学工具应该证明在较长时间尺度（200万年）内量化山区地形和侵蚀速率变化的整体努力中是有价值的。 对科学界更广泛的意义包括开发地球化学工具（磷灰石（U-Th）/He热年代测定法）的新应用，以及将该技术与其他更传统的地球化学工具（例如宇宙成因同位素）相结合。 与本项目相关的职业发展和培训包括培训和准备博士后科学家在学术界的职业生涯。 该研究还将促进至少一名本科生完成与本项目相关的高级论文。公共宣传和K-12教育将以以下形式进行：（1）红杉-国王峡谷国家公园的国家公园服务口译员的教育，负责向公园游客讲授内华达州南部山脉的地质和景观，以及（2）小学教师的参与，以提高对地球科学当前研究主题以及新课程计划和课程材料的认识。

PROJECT SUMMARYQuantifying changes in erosion and relief with detrital apatite (U-Th)/He thermochronlogy and cosmogenic nuclidesTechnical Description: This study performs a detailed study of the distribution and rates of catchment erosion in the southern Sierra Nevada of California using integrated detrital apatite (U-Th)/He thermochronometry and cosmogenic nuclides in sediment. Our first line of research proposes that detrital apatite (U-Th)/He cooling ages can act as sediment tracers, and thus be used to test whether a suite of steep catchments, in order of increasing size and complexity, are eroding uniformly or are dominated by point source erosion processes. Our second line of research compares the distribution of cooling ages from modern river sediments with those from older deposits, specifically river sediments preserved in caves, to investigate temporal changes in relief and catchment hypsometry. We use a 3D thermal model to account for the influence of the topographic bending of isotherms on interpreted detrital grain-age distributions from sediment. In addition, we propose to use cosmogenic 10Be and 26Al concentrations in river and cave sediments to investigate spatial and temporal changes in catchment-average erosion rates. Detrital apatite (U-Th)/He thermochronometry and cosmogenic nuclides are easily integrated tools because they utilize different minerals from the same bag of river sand. By developing and integrating these tools in detrital settings, and by exploiting a wealth of previous (U-Th)/He data and a set of well-dated caves, we investigate the topographic evolution of the southern Sierra Nevada, California, from the earliest Pliocene to today. Our integrated thermochronometric and cosmogenic approach is readily applied to other settings. For example, our development of the detrital apatite (U-Th)/He approach will determine the suitability of this technique for older deposits (e.g., sedimentary basins) for quantifying paleorelief and paleoerosion rates in orogenic belts around the world.Broader Significance:This project addresses fundamental problems in evolution of the Earth's surface in a mountain range of keen interest to geologists and laypersons alike. Our research should help answer how steep mountain valleys in the Sierra Nevada erode, the rates at which they erode and produce sediment, and how the distribution of elevation within valleys has evolved in light of climate change (e.g. repeated glaciations) over the last 2 million years. Furthermore, the geochemical tools we will develop should prove valuable in the overall effort of quantifying topography and erosion rate changes in mountain belts over longer timescales (2 million years). Broader significance to the scientific community include development of a new application of a geochemical tool (apatite (U-Th)/He thermochronometry) and integration of this technique with other more conventional geochemical tools (e.g. cosmogenic isotopes). Career development and training associated with this project includes training and preparation of a postdoctoral scientist for a career in academia. The study will also facilitate at least one undergraduate student completing a senior thesis associated with this project. Public outreach and K-12 education will occur in the form of (1) education of National Park Service interpreters at Sequoia-Kings Canyon National Parks charged with teaching park visitors about the geology and landscapes of the southern Sierra Nevada, and (2) involvement of an elementary school teacher to development an awareness of current research topics in the Earth sciences as well as new lesson plans and course materials.