Collaborative Research: Evaluating the Exhumation History of the Aleutians with Zircon and Apatite Thermochronology

合作研究：利用锆石和磷灰石热年代学评估阿留申群岛的发掘历史

• 批准号: 1949160
• 负责人: Claire Bucholz
• 金额: $ 3.83万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-15 至 2023-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1949160&HistoricalAwards=false
• 关键词: Collaborative; Research; Evaluating; Exhumation; History

Island arcs are chains of volcanic islands that form at subduction zone plate boundaries where one plate is being dragged beneath another, recycling old crust to the Earth’s mantle and creating new continental crust through volcanism. A central question surrounding these systems is whether processes that occur deeply in the subduction zone affect processes that are observed on the surface. This is especially debated for what drives surface uplift and related island arc exhumation and erosion. Uplift and exhumation of island arcs in other localities have been attributed to a variety of factors, from deep tectonic drivers to climate-surface interactions, with exhumation rates and erosion estimates that vary by orders of magnitude. In many locations, the arc exhumation history is difficult to study because it may be overprinted by later thermal or physical processes. The Aleutian Arc is unique in that it includes over 50 islands composed of both active and inactive volcanoes over 1,900 miles from Alaska to Russia, and has limited overprinting by secondary events. In addition, it has a volcanic history that spans 50 million years, so that the ancient magma chambers of past volcanoes are now exposed on the islands’ surfaces today. These plutonic rocks hold a record of past island uplift, exhumation, and erosion that can address key questions regarding: When were the Aleutians uplifted? When and how much has been eroded through time? Was uplift and subsequent erosion constant or cyclical? How does it vary geographically along the length of the arc? Specifically, the answers to these questions will shed light on the link between plate-scale processes and uplift; the timing and magnitude of erosion, contributing sediment and geochemical inputs to North Pacific; and the relationship between plutonic exhumation rates, geochemistry, and emplacement depth. The Aleutians have functioned as a natural laboratory to test fundamental principles regarding subduction zone evolution for more than four decades. This study will make a novel contribution to the existing extensive geochemical and geodynamic research. In terms of Broader Impacts, this award supports a new PI and engages underrepresented minority students and teachers, from the undergraduate through K-12 level. In order to quantify when and by how much the Aleutians experienced surface uplift and erosion, plutonic samples from ~10 islands that span 870 miles of arc length will be analyzed for emplacement depth and subsequent uplift rates. This work will place the exhumation history of the Central Aleutians in the context of 1) driving forces involving regional tectonics and subduction zone processes; and 2) geochemical inputs to the N. Pacific via erosion of arc material. In order to answer these questions, previously sampled and well-characterized plutonic rocks from across the central Aleutians will be characterized by pluton crystallization age, emplacement depth, and 2 or more thermochronometers with different thermal sensitivities (e.g., apatite and/or zircon, (U-Th)/He and/or fission track). Thermochronology techniques, particularly the use of multiple chronometers with different temperature sensitivities within the same sample, can constrain exhumation rates and be used to estimate erosion rates over time. Coupling the thermochronological data with emplacement depth will help constrain the amount of material eroded over that time. The timing and geographic trends revealed by these data can then be related in time and space to previously proposed drivers for uplift, including plate rotation, change in convergence angle and rate, or the development of an accretionary prism.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

岛弧是在俯冲带板块边界形成的火山岛链，一个板块被拖到另一个板块下面，将旧地壳重新循环到地幔中，并通过火山作用形成新的大陆地壳。围绕这些系统的一个中心问题是，发生在俯冲带深处的过程是否会影响在地表观察到的过程。这在驱动地表隆起和相关岛弧挖掘和侵蚀的原因上尤其有争议。其他地区岛弧的抬升和挖掘归因于多种因素，从深层构造驱动因素到气候-地表相互作用，挖掘率和侵蚀估计在数量级上存在差异。在许多地方，弧挖掘历史很难研究，因为它可能被后来的热或物理过程覆盖。阿留申弧的独特之处在于，它包括50多个由活火山和不活火山组成的岛屿，从阿拉斯加到俄罗斯，绵延1900英里。此外，它有一个跨越5000万年的火山历史，所以过去火山的古老岩浆室现在暴露在岛屿的表面。这些深成岩记录了过去的岛屿隆起、挖掘和侵蚀，可以解决以下关键问题：阿留申群岛是何时隆起的？随着时间的推移，什么时候，侵蚀了多少？隆起和随后的侵蚀是持续的还是周期性的？沿着弧长它在地理上是如何变化的？具体来说，这些问题的答案将揭示板块尺度过程与隆升之间的联系；侵蚀的时间和程度，为北太平洋提供沉积物和地球化学输入；以及探出速度，地球化学和侵位深度之间的关系。40多年来，阿留申群岛一直是检验俯冲带演化基本原理的天然实验室。这项研究将对现有广泛的地球化学和地球动力学研究作出新的贡献。就更广泛的影响而言，该奖项支持新的PI，并吸引从本科到K-12级别的未被充分代表的少数民族学生和教师。为了量化阿留申群岛在什么时候以及经历了多少地表隆起和侵蚀，将对横跨870英里弧长的约10个岛屿的深部岩浆样本进行分析，以确定侵位深度和随后的隆起速率。这项工作将把中阿留申群岛的发掘历史置于1)涉及区域构造和俯冲带过程的驱动力的背景下；2)地球化学通过弧物质的侵蚀进入北太平洋。为了回答这些问题，我们将从阿留申群岛中部取样并对其进行充分表征的深部岩石，通过岩体结晶年龄、位深和2个或更多具有不同热敏度（如磷灰石和/或锆石、(U-Th)/He和/或裂变径迹）的热时计对其进行表征。热年代学技术，特别是在同一样品中使用具有不同温度灵敏度的多个计时器，可以限制挖掘速率，并用于估计随时间推移的侵蚀速率。将热年代数据与就位深度相结合，将有助于限制这段时间内侵蚀的物质数量。这些数据揭示的时间和地理趋势可以在时间和空间上与先前提出的隆起驱动因素联系起来，包括板块旋转、辐合角和速率的变化，或增生棱镜的发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。