Collaborative Research: Beryllium-10 in detrital magnetite as a new tool in erosion and weathering studies

石英中的宇宙成因铍-10(10Be)被广泛用于定量测量景观中的侵蚀和风化速率。10Be在地表过程的研究中很有用，因为它只在地表附近产生，因此提供了矿物颗粒在土壤中停留时间的测量。这些停留时间可以很容易地用数百到数千年的平均侵蚀率来解释，这使得它们在景观演变和土壤可持续性研究中几乎是理想的。然而，使用石英也存在一些问题。它并不是在所有的景观中都存在，其化学制备需要使用危险的氢氟酸，限制了能够处理样品的实验室的数量。该项目将开发磁铁矿中的10Be作为一种新的工具，用于确定流域平均侵蚀和风化速率。在大多数情况下，磁铁矿的侵蚀速率与石英的侵蚀速率一样有用。然而，磁铁矿更容易从其他矿物中分离出来，其化学制备的危险和成本也要低得多。该项目的贡献将包括开发快速、成本效益高的矿物分离和化学制备技术。这应该会向一个全新的研究人员社区开放10Be的使用。该项目将在对侵蚀和风化速率进行深入研究的三个景观中测试该方法。此外，它还将探索10Be在磁铁矿和石英中的结合使用，作为一种新的、易于测量的流域平均化学风化程度的指标。不久前，测量长期侵蚀和风化速率极其困难，部分原因是与景观侵蚀的时间尺度相比，人类观察的时间尺度通常较短。在过去20年左右的时间里，像石英中的10Be这样的宇宙成因核素为测量数百至数千年的平均侵蚀和风化速率提供了新的工具。这推动了对表面过程的定量理解的一场革命。然而，测量一些地貌的侵蚀速度仍然很困难，因为首选的宇宙源目标矿物石英并不存在于所有类型的岩石中。因此，例如，很少在火山地貌中测量基于宇宙成因的侵蚀率。此外，所有关于宇宙核素的工作都是在世界各地的几十个实验室完成的，因为石英不容易为10Be的分析做准备，而且需要昂贵的专门设备来处理涉及的大量危险酸。矿物磁铁矿的使用有可能克服这些困难。10Be在其内部的产生方式与在石英中大致相同。在许多没有石英的岩石中，它以微量矿物的形式存在。此外，磁铁矿比石英更容易分离和溶解。因此，该项目开发的技术有望将10Be的使用开放给没有石英的新景观，也开放给缺乏石英分离和溶解专门设备资源的新研究人员。磁铁矿和石英的风化速率不同。这增加了一种令人兴奋的可能性，即来自同一溪流的磁铁矿和石英矿物对中的10Be将产生土壤化学风化的指数。这项研究将集中在NSF的两个关键区天文台(卢基洛和南塞拉利昂)的实地工作，从而利用现有的基础设施投资来研究风化过程及其与地质、气候和生态的关系。

Cosmogenic Beryllium-10 (10Be) in quartz is widely used to quantify rates of erosion and weathering in landscapes. 10Be is useful in the study of surface processes because it is produced only near the ground surface, and thus provides a measure of the residence time of mineral grains in soils. These residence times can be readily interpreted in terms of erosion rates averaged over hundreds to thousands of years, making them nearly ideal in studies of landscape evolution and soil sustainability. There are problems with the use of quartz, however. It is not present in all landscapes and its chemical preparation requires the use of hazardous hydrofluoric acid, limiting the number of laboratories that are able to process samples. This project will develop 10Be in magnetite as a new tool for determining catchment-averaged rates of erosion and weathering. For most purposes, erosion rates from magnetite would be just as useful as erosion rates from quartz. Magnetite, however, is easier to separate from other minerals and its chemical preparation is far less hazardous and expensive. The project's contributions will include development of rapid, cost-effective mineral separation and chemical preparation techniques. This should open the use of 10Be to a whole new community of researchers. The project will test the method in three landscapes where erosion and weathering rates have been intensively studied. In addition, it will explore the coupled use of 10Be in magnetite and quartz as a new, readily measured index of the catchment-averaged degree of chemical weathering.Not long ago, it was extremely difficult to measure long-term rates of erosion and weathering, in part because the timescales of human observation are usually short compared to the timescales of landscape erosion. Over the last 20 or so years, cosmogenic nuclides such as 10Be in quartz have provided new tools for measuring rates of erosion and weathering averaged over hundreds to thousands of years. This has fueled a revolution in quantitative understanding of surface processes. Yet measurements of erosion rates in some landscapes have remained difficult because the preferred cosmogenic target mineral, quartz, is not present in all rock types. Hence cosmogenic-based erosion rates have rarely been measured in volcanic landscapes, for example. Moreover, all of the work on cosmogenic nuclides is done in just a few dozen labs around the world because quartz is not easy to prepare for analysis of 10Be, and costly, specialized equipment is needed to handle the large volumes of hazardous acids that are involved. Usage of the mineral magnetite has the potential to overcome these difficulties. 10Be is produced within it in much the same way as it is in quartz. It is present as a trace mineral in many rocks where quartz is absent. Moreover, magnetite is easier to separate and dissolve than quartz. Hence, techniques developed in this project promise to open the use of 10Be to new landscapes where quartz is absent, and also to new researchers who lack resources for the specialized equipment of quartz separation and dissolution. Magnetite and quartz weather at different rates. This raises the exciting possibility that 10Be in the mineral pair magnetite and quartz from the same stream will yield an index of chemical weathering in soil. This research will focus on fieldwork at two of NSF's Critical Zone Observatories (Luquillo and Southern Sierra), thus capitalizing on existing infrastructure investment for studying weathering processes and their relationships with geology, climate, and ecology.