Collaborative Research: Impact of Magmatic Underplating on the Evolution of Lower Continental Crust

合作研究：岩浆底侵对下陆壳演化的影响

• 批准号: 2317815
• 负责人: Michael Williams
• 金额: $ 20.47万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2317815&HistoricalAwards=false
• 关键词: Collaborative; Research; Impact; Magmatic; Underplating

Spectacular volcanic eruptions are visible evidence for the fundamental role of magmatism in shaping Earth’s continents. But how does magmatism create and alter the continents at great invisible depths? Earth scientists have long inferred that mafic magmas rise from the mantle and pond near the bottom of the crust in a process called “underplating”. This process produces “hot zones” in the deep continental crust which lead to melting, magma generation, and magma mixing. Few localities exist on Earth where hot zones have been uplifted and exposed at the surface for direct observation. This project explores the development and evolution of magma in an ancient hot zone of underplating, now exposed at the surface in northern Saskatchewan. This team hypothesizes that the region once existed above a major zone of underplating near the base of the continental crust. Students and scientists will collect data to understand the timing and duration of magmatism, metamorphism, and densification of the deep crust. They will develop models to better understand complex images of the lower continental crust detected by geophysicists throughout North America. The project will provide insight into the processes that lead to the formation of magmas of varying composition, the mechanisms that weaken or strengthen the deep crust, and ultimately, the processes that facilitate formation and stabilization of continental crust on Earth.Magmatic underplating is a first order petrologic and tectonic process that is central to many models for the development and evolution of continental crust. However, remote studies of the deep crust via geophysics or xenoliths commonly lack the resolution to unequivocally constrain the impacts of underplating. This project explores the hypothesis that ”intraplating”, i.e., the emplacement of mantle-derived magma into the lower continental crust above the underplate, is critical for magmatic processes (assimilation, mingling, hybridization), deformation (weakening and crustal flow), and subsequent densification +/- foundering or delamination of lower continental crust. Key insights will be gleaned from direct field observations of the most deeply exhumed section of the 20,000 km2 Athabasca granulite terrane (1.1-1.6 GPa). These exposures are inferred to have experienced 650 m.y. of lower crustal residence prior to exhumation. They represent a rare opportunity to explore crust-mantle interaction and long-term evolution of lower continental crust due to intraplating, metamorphism, melting, and densification in three distinct tectonic settings. Deliverables include: (i) constraining the timing and duration of magmatic intraplating and metamorphism in each setting, (ii) identifying and quantifying densification mechanisms, (iii) constraining the influence of metasedimentary gneisses on the composition, density, and seismic velocity structure of intraplated lower continental crust, and (iv) using field-based observations and data to develop more robust geophysical models of underplated lower continental crust. Critical geophysical goals include: (1) evaluating the degree to which the settings of underplating and intraplating can be distinguished in seismic surveys, and (2) evaluating the degree to which the integrated geophysical properties in each tectonic domain can inform more robust interpretations of the pattern of seismically fast lower crust detected beneath parts of North America. Broader impacts include: (i) Two Ph.D. and 2-4 B.S. students will carry out research projects; (ii) A virtual international workshop for Earth scientists and graduate students focused on the origin and evolution of lower continental crust will be hosted; (iii) PIs and students will convene a Lower Crustal Field Forum where participants will visit and explore the Athabasca granulite terrane and discuss general implications for lower continental crust; (iv) PIs and students will engage in Earth science outreach as part of field work in the vicinity of Stony Rapids, Saskatchewan. The goal is to involve interested teachers and students in our virtual workshop and field forum, giving them opportunities to share their own insights on the culture, people, and landscape along the edge of the Athabasca granulite terrane.This project is jointly funded by three EAR programs (Petrology & Geochemistry, Geophysics, and Tectonics) as well as the Established Program to Stimulate Competitive Research (EPSCoR).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.

壮观的火山喷发是岩浆作用在塑造地球大陆方面发挥重要作用的明显证据，但是岩​​浆作用是如何在看不见的深处创造和改变大陆的呢？地球科学家长期以来一直推断，镁铁质岩浆是从靠近底部的地幔和池塘中升起的。这个过程在大陆地壳深处产生“热区”，导致熔化、岩浆生成和岩浆混合，地球上很少有地方存在这种情况。该项目探索了古老的底侵热区的岩浆发育和演化，该热区现已暴露在萨斯喀彻温省北部的地表。学生和科学家将收集数据以了解岩浆作用、变质作用和深部地壳致密化的时间和持续时间。他们将开发模型以更好地了解地壳的复杂图像。该项目将深入了解导致不同成分岩浆形成的过程、削弱或强化深部地壳的机制，以及最终促进地壳形成和稳定的过程。岩浆底侵是一级岩石学和构造过程，是许多大陆地壳发育和演化模型的核心。然而，通过地球物理学或捕虏体对深部地壳的远程研究通常缺乏。该项目探讨了“内盘作用”这一假设，即源自地幔的岩浆进入板块下方的下大陆地壳，对于岩浆过程（同化、混合、杂交）至关重要。变形（减弱和地壳流动），以及随后的致密化+/-下大陆地壳的沉没或分层将从直接场中收集关键见解。对 20,000 平方公里阿萨巴斯卡麻粒岩地体最深处的挖掘部分（1.1-1.6 GPa）的观测表明，这些暴露在挖掘之前经历了 650 m.y 的下地壳停留，它们代表了探索壳幔相互作用的难得机会。由于三种不同构造中的内板作用、变质作用、熔融作用和致密化作用，下大陆地壳的长期演化可交付成果包括：(i) 限制每个环境中岩浆内侵蚀和变质作用的时间和持续时间，(ii) 识别和量化致密化机制，(iii) 限制变沉积片麻岩对成分、密度和地震速度结构的影响。板内下大陆地壳，以及（iv）利用实地观测和数据开发更可靠的板下下大陆地壳地球物理模型，关键地球物理目标包括： (1) 评估在地震勘探中区分底侵和内侵设置的程度，以及 (2) 评估每个构造域中的综合地球物理特性可以在多大程度上为地震快下层模式提供更稳健的解释在北美部分地区发现的地壳更广泛的影响包括：(i) 两名博士生和 2-4 名理学士学生将开展研究项目；(ii) 为地球科学家和研究生举办一个虚拟国际研讨会，重点关注地壳的起源和发展。将主办下大陆地壳的演化；(iii) PI 和学生将召开下地壳领域论坛，与会者将参观和探索阿萨巴斯卡暗示地体并讨论下大陆地壳的一般问题；(iv) PI 和学生将参与地球研究；作为萨斯喀彻温省斯托尼拉皮兹附近实地工作的一部分，科学推广活动的目标是让感兴趣的教师和学生参与我们的虚拟研讨会和实地论坛，让他们有机会分享自己对科学的见解。阿萨巴斯卡麻粒岩地体边缘的文化、人文和景观。该项目由三个 EAR 项目（岩石学与地球化学、地球物理学和构造学）以及刺激竞争性研究既定项目 (EPSCoR) 共同资助。该奖项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，NSF 的法定使命被认为值得支持。