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.

俯冲带上方的火山几乎总是在地球表面上显示为不规则或弯曲的线。科学家们对为什么这些“弧形”火山（例如喀斯喀特弧）会形成线性火山链有一个大致的了解，但深入地壳的垂直断层是否控制它们的具体位置、成分和潜在喷发量仍然是一个备受争议的话题。火山侵蚀速度很快，因此对其大型岩浆根（称为岩体）的研究将提供更完整的空间和时间记录，以更好地了解垂直断层是否在产生岩浆的深层地壳和岩浆形成火山喷发储库的上地壳之间提供直接通道。几千万年来，随着阿拉斯加南部相对于阿拉斯加内陆沿着活跃的迪纳利断层向西移动，阿拉斯加山脉一直受到俯冲和平移的影响。该断层延伸超过 2000 公里，并在 2002 年的一场 7.9 级地震中破裂。一组 45-3500 万年的弧岩体在空间上与迪纳利断层有关。 这项拟议的研究将研究沿着长期走滑断层（德纳利断层）的熔体输送的物理关系，以测试大陆尺度的结构如何控制熔体输送到地表的速率、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使用本研究期间分析的岩体来更好地约束德纳利断层的长期滑动率。该项目将包括来自拥有不同本科课程的公立大学的本科生、研究生和教授。北美最高峰迪纳利山（以前称为麦金利山）包括本研究中被迪纳利断层切割的弧岩体。外展工作将包括开发有关德纳利断层的社交媒体，以及更新费尔班克斯和德纳利国家公园北方博物馆的公共科学传播展览。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，致力于吸引来自阿拉斯加的农村和第一代学生。地壳尺度的结构通常与下地壳熔体通过上地壳的输送有关。然而，熔体沿着活动走滑断层输送的机制仍然是岩石学界持续存在的问题。区分其中的不同机制或组合对于揭示上地壳中花岗岩类岩石成因、质量和地幔-表面热连通以及构造过程如何在岩石学系统中表现的复杂相互作用至关重要。迪纳利断层是一个典型的长寿造山（2000 公里）右旋走滑断层系统，具有 400 公里的横向偏移，与大约 70 多年的弧形深成作用相关，并且可能是局部性的。该研究项目将验证地壳尺度断层可以促进熔体输送和岩体构造的假设，从而产生与走滑运动相关的系统时空地球化学和岩石物理模式。该研究将包括收集德纳利断层两侧和沿约 350 公里横断面的一组始新世岩体的与断层相关的石油化学和岩石物理数据集，以评估岩浆过程在与沿造山尺度走滑断层的岩浆输送和就位相关的空间和时间尺度上的表现。现场表征与全岩石主量和微量元素地球化学、锆石 U-Pb 地质年代学和 O 同位素示踪剂分析相结合，将应用于以下基本目标：1) 识别岩石学、地球化学、同位素和/或结构梯度；2) 解释与岩体几何形状以及德纳利断层相关的结果。除了测试花岗岩类岩石成因的运动学控制之外，这些数据还将通过评估潜在的德纳利断层穿孔点来解决科迪勒拉地质学中长期存在的问题。初步数据表明，德纳利断层上可能存在岩体相关性，这表明自 40 Ma 以来平均滑移率为 8-10 毫米/年，类似于目前该断层部分的右旋滑移率。这项研究的数据将提供一种方法，用于区分实际偏移的岩体与优先沿断层系统形成的一系列类似侵入体，并有助于解释大陆弧沿走滑断层聚集期间的时空石油化学和岩石物理变化。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。