Forearc Uplift in Northern Chile

一个构造板块下降到另一个构造板块之下的地方是地球上最大的地震和最具爆炸性的火山活动的地点。在所有这些会聚的板块边缘中，大约有一半的地方，最初形成覆盖板块下部的岩石被移走并被拖到地球深处。尽管这种构造侵蚀作用的一种表现形式是板块边缘的逐渐消失，但人们对岩石被移走的过程却知之甚少。被认为涉及的过程包括一些破碎岩石和一些产生破碎岩石从其原始位置到更大深度的流动，这似乎需要润滑流动岩石的通道。几乎没有直接观测的可能，因为这些过程发生在地球下面几十英里的地方。s表面。然而，通过研究构造侵蚀的次生后果，我们可以了解到很多东西。智利北方的海岸是一个极好的天然实验室，在那里，太平洋下面的板块下降到南美板块下面。在那里，构造侵蚀的次要后果是应力模式、重力场的空间变化和大陆表面的地形。本研究侧重于后者，即地形变化，因为随着时间的推移，随着地下物质的增加或减少，大陆表面的高度会发生变化。该项目的一个主要步骤是收集数据，说明现在沿海山区带的海拔变化。研究人员正在通过检查最初水平表面的现代方向来记录过去1000万年来地形形态的变化。此外，他们还利用一种新的方法，根据古代土壤和古代盐田中的盐的同位素，确定哪些地点高于或低于海拔约3000英尺的古代海拔。研究人员正在测试一种假设，即自1000万年前以来，地形上升了2000多英尺，形成了海岸线上壮观的悬崖，并且在过去的300万年里，研究区域向西倾斜。该项目的部分工作包括在实地研究区域收集适当的数据和样本。同时，研究团队使用在板块边界相互作用的过程和材料的数值模型来预测一组情景的地形结果。两个主要的场景进行了建模。第一种情况是，由于气候变化或板块运动的变化，破碎岩体移动的通道的物理特性或进入通道的物质数量在感兴趣的时间跨度内发生变化。 第二种情况探讨了火山弧附近发生的过程在近海岸地区的结果，因为这些遥远的过程可能掩盖了构造侵蚀的信号。的预测方案进行比较的地形历史，以确定哪些过程导致观察到的地貌。这些模型还预测了应力和重力场的模式，并与现有的测量结果进行了比较。对这些板块边界物理过程的更好理解可能有助于更好地理解在会聚板块边缘产生大地震的过程。研究结果通过期刊上的同行评审报告分享。在从事这个项目的同时，一名研究生正在学习将对地表过程的理解与对地球内部过程的理解联合收割机结合起来，使用各种方法，批判性地思考，并作为一个多元化研究团队的合作成员发展“软”技能。该项目小组包括来自智利和欧洲的地球科学合作者。直接适用于商业和政策的结果，如区域水文历史，工业矿产资源分布，以及对地震活动控制的见解，分别与水管理人员，开采盐水和蒸发岩矿物的公司以及政府机构工作人员分享。显示在PRI？地球博物馆向公众展示了总体结果。

The places where one tectonic plate descends beneath the margin of another are the sites of Earth's largest earthquakes and most explosive volcanic activity. In about half of all such convergent plate margins, rocks that originally formed the lower part of the overriding plate are removed and dragged deep into the earth. Even though one manifestation of this action of tectonic erosion is clearly visible as the progressive elimination of the plate margin, the processes by which the rocks are removed are poorly understood. The processes thought to be involved include some that break rock and some that generate a flow of broken rock from its original site to a much greater depth, which seemingly requires lubrication of a channel of flowing rock. Few direct observations are possible because the processes occur tens of miles beneath Earth?s surface. Yet much can be learned by study in active systems of secondary consequences of tectonic erosion. The coast of northern Chile is an excellent natural laboratory, where the plate underlying the Pacific Ocean descends below the South American plate. There, secondary consequences of tectonic erosion are found in patterns of stress, spatial variations in the gravity field, and the topography of the continental surface. This study focuses on the latter, topographic changes, because the continental surface would change in altitude through time as subsurface material is added or removed. One major step of this project is to gather data that illuminate the changes in altitude of what is now the coastal mountain belt. The researchers are documenting the changes of the topographic form during the last 10 million years through examination of the modern orientations of what were originally horizontal surfaces. In addition, using a new method based on isotopes in salts that occur in ancient soils and in ancient salt pans, they are determining which locations stood above or below an ancient altitude of about 3000 feet above sea level. The researchers are testing the hypotheses that the topography rose by over 2000 feet to form the spectacular cliffs of the coastline since 10 million years ago, and that the study area tilted down to the west during the last 3 million years. Part of the project work involves gathering the appropriate data and samples in the field study area.Simultaneously, the research team uses numerical models of the processes and materials that interact at a plate boundary to predict the topographic outcomes for a set of scenarios. Two principal scenarios are modeled. The first scenario is that the physical properties of a channel in which broken rock mass would move, or the amount of materials entering the channel, varied through the time span of interest, because the climate varied or because the plate movements varied. A second scenario explores the outcomes in the near-coastal region of the processes that occurred near the volcanic arc, because those distant processes might obscure the signals of tectonic erosion. The predictions of the scenarios are compared to the topographic history, to determine which processes led to the observed landforms. The models also predict patterns of stress and of the gravity field, which are compared to existing measurements.An improved understanding of these plate boundary physical processes may enable better understanding of the processes that generate major earthquakes at convergent plate margins. The findings are shared via peer-reviewed reports in journals. While working on this project, a graduate student is learning to combine understanding of surface processes with inner earth processes, to use a variety of approaches, to think critically, and also is developing "soft" skills as a collaborating member of a diverse research team. The project team includes geoscience collaborators from Chile and Europe. Results that are directly applicable to commerce and policy, such as regional hydrological history, industrial mineral resource distribution, and insights into controls on seismic activity, are shared with water managers, companies who mine brines and evaporite minerals, and government agency staff, respectively. Displays at PRI?s Museum of the Earth present to the public the general results.