Collaborative Research: Caught in the Act- The Petrology of Modern Lower-Crust Formation and Foundering in the North Andean Arc

合作研究：陷入困境——北安第斯弧现代下地壳形成和沉没的岩石学

• 批准号: 2131643
• 负责人: Mauricio Ibanez-Mejia
• 金额: $ 29.48万
• 依托单位: University of Arizona
• 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: 2021-05-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2131643&HistoricalAwards=false
• 关键词: Collaborative; Research; Caught; Act; Petrology

Earth's continents are thought to have mainly formed in convergent tectonic boundaries, where hydrous fluids transported to depth by subducting plates enable melting of the upper mantle and produce magmas that ultimately contribute to the growth of the overlying crust. Nevertheless, the processes responsible for driving the composition of primitive magmas generated in arc regions, which are basaltic, towards the bulk composition that characterizes Earth's continents, which are andesitic, remain intensely debated. A major difficulty in understanding these 'differentiation' processes, and how they may couple with other first-order features of convergent continental margins, is the fact that the deep roots of these magmatically-active regions are rarely exposed in the Earth's surface. However, volcanic eruptions are sometimes capable of transporting deep-sourced rock fragments - known as 'xenoliths' - to the Earth's surface, providing Earth scientists with unique glimpses of processes occurring deep within the continents that are otherwise difficult to study. In the northern segment of the Andean orogen (southern Colombia), a rare eruption from a recent volcanic vent transported an extraordinary cargo of xenolith fragments sourced from the deep roots of the arc and mantle section beneath it. Therefore, this locality presents a unique opportunity to help unravel the physical and chemical processes that operate during construction of continental crust in magmatically-active regions like the Andes. This award supports two early-career Assistant Professors and a woman who is a PhD student to conduct a detailed geochemical, petrologic and geochronologic study of these unique xenoliths, and the rare eruptions that brought them to the surface. In particular, this research focuses on the 'gravitationally unstable' root of the arc, a section of crustal (i.e., chemically differentiated) rocks with densities greater than the underlying mantle, represented by lithologies such as garnet gabbros, hornblendites, and garnet-bearing pyroxenites. Mechanical removal of density-unstable roots form the base of arcs, a process known as lithospheric foundering (aka, delamination), has not only been identified as a crucial process to explain the chemistry of Earth's continents but is also thought capable of inducing rapid changes in surface elevation, such as those driving the fast Neogene uplift of the Central Andean Plateau. Because the processes taking place in the lower orogenic crust are critical for understanding the uplift history of mountains, the geochemistry of the continents, and the geophysical imaging of the deep lithosphere, results from this investigation will have important implications for our understanding of the geochemical, structural and tectonic history of Andean-type plate margins. In addition to the scientific research products that will result from this investigation, the PIs will collaborate with the Rochester Museum and Science Center (RMSC) on activities that will: 1) explain the origin and physicochemical principles of arc volcanoes to the public of Upstate NY; and 2) continue to organize campus visits for high-school participants of RMSC's 'Next Level Science' summer camps, to provide local students with a direct opportunity to experience college and learn more about upper-level STEM education.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.

人们认为地球的大陆主要形成于会聚的构造边界，其中含水流体通过俯冲板块输送到深处，使上地幔熔化并产生岩浆，最终促进上覆地壳的生长。然而，推动弧形区域（玄武岩）产生的原始岩浆成分向地球大陆（安山岩）特征的整体成分转变的过程仍然存在激烈争论。理解这些“分化”过程以及它们如何与会聚大陆边缘的其他一级特征结合的一个主要困难是，这些岩浆活跃区域的深层根部很少暴露在地球表面。然而，火山喷发有时能够将深部岩石碎片（称为“捕虏体”）输送到地球表面，为地球科学家提供了独特的视角，了解大陆深处发生的过程，否则很难研究这些过程。在安第斯造山带北段（哥伦比亚南部），最近火山口的一次罕见喷发携带了大量来自其下方弧和地幔部分的深根的捕虏体碎片。因此，这个地点提供了一个独特的机会，可以帮助揭示安第斯山脉等岩浆活跃地区大陆地壳构造过程中的物理和化学过程。该奖项支持两名职业生涯早期的助理教授和一名女博士生对这些独特的捕虏体以及将它们带到地表的罕见喷发进行详细的地球化学、岩石学和地质年代学研究。特别是，这项研究重点关注弧的“重力不稳定”根部，这是一段密度大于下伏地幔的地壳（即化学分化）岩石，以石榴石辉长岩、角闪石和含石榴石等岩性为代表辉石岩。机械去除形成弧形底部的密度不稳定的根部，这一过程被称为岩石圈沉没（又称分层），不仅被认为是解释地球大陆化学的关键过程，而且还被认为能够引发快速变化地表海拔，例如那些推动中安第斯高原新近纪快速隆升的因素。由于下造山地壳中发生的过程对于了解山脉的隆起历史、大陆的地球化学以及深层岩石圈的地球物理成像至关重要，因此这项调查的结果将对我们了解地球化学、安第斯型板块边缘的构造和构造历史。除了本次调查产生的科学研究产品外，PI 还将与罗切斯特博物馆和科学中心 (RMSC) 合作开展以下活动：1) 向纽约州北部公众解释弧火山的起源和物理化学原理; 2) 继续组织 RMSC“Next Level Science”夏令营的高中参与者参观校园，为当地学生提供直接体验大学和了解更高水平 STEM 教育的机会。该奖项体现了 NSF 的法定使命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，并被认为值得支持。

项目成果

To sink, or not to sink: The thermal and density structure of the modern northern Andean arc constrained by xenolith petrology

下沉还是不下沉：现代北安第斯弧的热力和密度结构受到捕虏体岩石学的限制

• DOI: 10.1130/g50973.1
• 发表时间: 2023
• 期刊: Geology
• 影响因子: 5.8
• 作者: Zieman, Lisa;Ibañez-Mejia, Mauricio;Rooney, Alan D.;Bloch, Elias;Pardo, Natalia;Schoene, Blair;Szymanowski, Dawid
• 通讯作者: Szymanowski, Dawid

Reading the Isotopic Code of Heavy Elements

解读重元素同位素代码

• DOI: 10.2138/gselements.17.6.379
• 发表时间: 2021
• 期刊: Elements
• 影响因子: 4.5
• 作者: Ibañez-Mejia, Mauricio;Tissot, François L.H.
• 通讯作者: Tissot, François L.H.

Unlocking the Single-Crystal Record of Heavy Stable Isotopes

解锁重稳定同位素的单晶记录

• DOI: 10.2138/gselements.17.6.389
• 发表时间: 2021
• 期刊: Elements
• 影响因子: 4.5
• 作者: Tissot, François L.;Ibañez-Mejia, Mauricio
• 通讯作者: Ibañez-Mejia, Mauricio

Neogene precipitation, vegetation, and elevation history of the Central Andean Plateau

• DOI: 10.1126/sciadv.aaz4724
• 发表时间: 2020-08
• 期刊: Science Advances
• 影响因子: 13.6
• 作者: C. Martínez;C. Martínez;Carlos Jaramillo;C. Jaramillo;A. Correa-Metrio;W. Crepet;J. E. Moreno;A. Aliaga;Federico Moreno;M. Ibáñez-Mejia;M. Bush