Collaborative Research: Arc plutonism along the Denali Fault, Alaska: Possible fault controls on incremental magma transport and assembly along a long-lived strike-slip fault

合作研究：阿拉斯加德纳利断层沿线的弧岩成体作用：断层可能控制沿长期走滑断层增量岩浆输送和聚集

• 批准号: 2121178
• 负责人: Sarah Roeske
• 金额: $ 18.56万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2121178&HistoricalAwards=false
• 关键词: Collaborative; Research; Arc; plutonism; along

Volcanoes above subduction zones almost always appear as an irregular or curvy line on the surface of the earth. Scientists have a general idea of why these “arc” volcanoes, such as the Cascade arc, create linear chains, but whether vertical faults that penetrate deep in the crust control their specific location, composition, and potential eruptive volume is a subject of much debate. Volcanoes erode quickly so a study of their large magmatic roots, called plutons, will provide a more spatially and temporally complete record to better understand whether vertical faults provide direct conduits between deeper crust, where magma is produced, and the upper crust, where magma forms a reservoir for volcanic eruptions. The Alaska Range has been shaped by subduction and translation for tens of millions of years, as southern Alaska moves westward relative to the Alaskan interior along the active Denali fault, which extends for over 2000 km and ruptured during a magnitude (Mw) 7.9 earthquake in 2002. A suite of 45-35-million-year-old arc plutons are spatially associated with the Denali fault. This proposed research will study the physical relationships of melt transport along a long-lived strike-slip fault (the Denali fault) to test how continental-scale structures may control the rates of transport of melt to the surface, geometry of pluton growth, and magma evolution. In addition, the Principal Investigators will try to use plutons analyzed during this study to provide better constraints on the long-term slip rate of the Denali fault. The project will include undergraduate students, graduate students, and professors from public universities that have diverse undergraduate programs. The tallest peak in North America, Denali (formerly Mt. McKinley), includes arc plutons of this study that are cut by the Denali fault. Outreach efforts will include developing a social media presence for the Denali fault and updating public-science dissemination exhibits at the Museum of the North in Fairbanks and Denali National Park. We will develop curriculum for the GeoForce learning community, a STEM-focused organization focused on engaging rural and first-generation students from Alaska.Crustal-scale structures are often linked to the transport of lower crustal melts through the upper crust. However, the mechanism(s) by which and if melt is transported along active strike-slip faults is still an ongoing problem in the petrology community. Distinguishing disparate mechanism(s) or combinations therein is critical for unraveling the complex interplay of granitoid petrogenesis in the upper crust, mass and thermal mantle-surface communication, and how structural processes are manifested in a petrologic system. The Denali Fault is a classic long-lived orogenic ( 2000 km) dextral strike-slip fault system with 400 km of lateral offset associated with, and perhaps localizing, arc plutonism for over ~70 My. This research project will test the hypothesis that crustal-scale faults can facilitate melt transport and pluton construction that results in systematic temporal-spatial geochemical and petrophysical patterns linked to strike-slip motion. The research will include collecting a fault-relative petrochemical and petrophysical dataset on a suite of Eocene plutons on both sides and along a ~350 km transects of the Denali Fault to evaluate how magmatic processes are manifested at the spatial and temporal scales relevant to magma transport and emplacement along an orogenic-scale strike slip fault. Field characterization combined with whole rock major and trace element geochemistry, zircon U-Pb geochronology, and O isotopic tracer analysis will be applied with these fundamental objectives: 1) identify petrographic, geochemical, isotopic, and/or structural gradients and 2) interpret results as they relate to pluton geometry as well as to the Denali Fault. In addition to testing kinematic controls on granitoid petrogenesis, these data will resolve a long-standing problem in Cordilleran geology, by evaluating a potential Denali Fault piercing point. Preliminary data indicate a possible pluton correlation may exist across the Denali Fault that would indicate an average slip rate of 8-10 mm/yr since 40 Ma, similar to the present-day dextral slip rate in this section of the fault. Data from this study will provide a recipe for distinguishing actually offset plutons from a suite of similar intrusive bodies preferentially emplaced along a fault system and help explain temporal-spatial petrochemical and petrophysical variability during continental arc assembly along strike-slip faults.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.

在俯冲带之上的火山在地球表面上几乎总是呈现出不规则或弯曲的线条。科学家们对为什么这些“弧”火山，如喀斯喀特弧，会产生线性链有了一个大致的了解，但是是否穿透地壳深处的垂直断层控制了它们的具体位置、组成和潜在的喷发量，这是一个有很多争论的话题。火山的侵蚀速度很快，因此，对它们的大型岩浆根（称为深岩体）的研究，将提供一个空间和时间上更完整的记录，从而更好地了解垂直断层是否在岩浆产生的深层地壳和岩浆形成火山爆发储存库的上层地壳之间提供了直接通道。随着阿拉斯加南部沿着活跃的德纳里断裂带相对于阿拉斯加内陆向西移动，阿拉斯加山脉在数千万年的俯冲和平移过程中形成，德纳里断裂带延伸了2000多公里，在2002年7.9级地震中破裂。一套距今4500万年至3500万年的弧深岩体在空间上与迪纳里断裂相关。这项拟议的研究将研究沿长寿命走滑断层（德纳里断层）的熔体运输的物理关系，以测试大陆尺度的结构如何控制熔体向地表的运输速率、岩体生长的几何形状和岩浆演化。此外，主要研究人员将尝试利用本次研究中分析的岩体来更好地约束德纳里断裂的长期滑动速率。该项目将包括本科生、研究生和拥有多种本科专业的公立大学的教授。北美最高的山峰，德纳里山（以前的麦金利山），包括本研究中由德纳里断层切割的弧深岩体。外联工作将包括为德纳里断层建立一个社交媒体，并在费尔班克斯的北方博物馆和德纳里国家公园更新公共科学传播展览。我们将为GeoForce学习社区开发课程，这是一个以stem为重点的组织，专注于吸引来自阿拉斯加的农村和第一代学生。地壳尺度的构造通常与下地壳熔体穿过上地壳的运输有关。然而，在岩石学界，熔体沿着活动走滑断层运移的机制仍然是一个悬而未决的问题。区分不同的机制或其中的组合对于揭示上地壳中花岗岩类岩石成因的复杂相互作用，质量和热地幔-表面交流，以及构造过程如何在岩石学系统中表现出来至关重要。迪纳里断裂是一个典型的长寿命造山（2000公里）的右旋走滑断裂系统，其400公里的侧向偏移与70多年来的弧深成矿作用有关，可能是局部化的。该研究项目将验证地壳尺度断层可以促进熔体运输和岩体构造的假设，从而形成与走滑运动相关的系统时空地球化学和岩石物理模式。该研究将包括收集Denali断层两侧和约350公里横断面上一套始新世岩体的断层相关石化和岩石物理数据，以评估与造山带尺度走滑断层的岩浆搬运和侵位相关的岩浆过程在时空尺度上的表现。结合全岩主要元素和微量元素地球化学、锆石U-Pb年代学和O同位素示踪分析的现场表征将应用于以下基本目标：1)确定岩石学、地球化学、同位素和/或构造梯度；2)解释与岩体几何和迪纳里断裂相关的结果。除了测试花岗岩类岩石成因的运动学控制外，这些数据还将通过评估潜在的迪纳利断层穿刺点来解决科迪勒拉地质中长期存在的问题。初步数据表明，迪纳里断裂带上可能存在一种岩体相关性，表明40 Ma以来的平均滑动速率为8-10毫米/年，与该断裂带现今的右向滑动速率相似。这项研究的数据将为区分实际偏移的岩体与一组优先沿断层系统放置的类似侵入体提供一种方法，并有助于解释沿走滑断层的大陆弧组合期间的时空石化和岩石物理变化。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。