Collaborative Research: Testing Source vs. Crustal Processing in High-Mg# Arc Magmas by Os-O-He-Olivine Systematics

合作研究：高镁测试来源与地壳处理

• 批准号: 1921624
• 负责人: Susanne Straub
• 金额: $ 27万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1921624&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Source; vs.

'Convergent plate margins' are major interfaces of the solid Earth geochemical cycle that are fundamental to the formation and maintenance of habitable Earth. At convergent plate margins, a lithospheric plate consisting of the Earth's crust and uppermost mantle is drawn - or subducted - beneath another lithospheric plate. At around 80-140 kilometers depth, the subducted plate releases material rich in climate-active volatile elements (H2O, halogens) and 'recycles' it back to the Earth's surface via the activity of volcanoes aligned in arcs. Such arcs form the 'Pacific Ring of Fire', which is renowned for volatile-rich, devastating eruptions of silicic magmas that can cause deadly climate perturbations (e.g. Tambora 1815) and tsunamis (e.g. Krakatoa 1883, 2018), and that are a permanent major threat to human habitation on the densely populated Earth. Thus, understanding how material cycling leads to silicic, explosive arc volcanism remains a theme at the core of geoscience research. A particular challenge when studying subduction recycling is that it takes place deep in the Earth's interior (between a few and 200 km) and thus cannot be observed directly. Scientists therefore rely on indirect observations obtained from components in magmas (e.g. olivine and spinel crystals) that carry information on processes occurring at many kilometers depth within the Earth. Two US-based women (one with a disability) plan to collect such information from volcanic rocks erupted from young Mexican volcanoes, in collaboration and exchange with national and international colleagues from the US, Mexico, Scotland and France. The project will train graduate and undergraduate students with the goal to promote diversity. K-12 teachers will be engaged in order to transfer the new research results into the Earth Science curriculum for middle and high school students, and the general public will be informed at regular annual Open Days.This project focuses on olivine and its inclusions of Cr-spinel from mafic to silicic magmas in the Trans-Mexican Volcanic Belt (TMVB), a major subduction zone that is well-known for its high potential for catastrophic volcanic eruptions. Many studies propose that the silicic magmas gain their deadly explosive power through melt processing in the 45 km thick continental crustal basement on the which the TMVB is constructed. However, some studies suggest that the composition of olivine crystals contained in these magmas is inconsistent with this hypothesis. Remarkably, olivines from the central TMVB have delta18O and 3He/4He isotope signals that suggest that their host magmas were primarily formed in the mantle below the crustal basement, where they became silicic through incorporation a large amount of subducted slab material. In this project we will further test these two contrasting hypotheses by obtaining additional 187Os/188Os isotope data from olivine and bulk rocks that have been carefully selected from key locations in the central (Popocatepetl and Sierra Chichinautzin) and eastern (Serdan basin) TMVB, as well as from the rear-arc region where magmas are not significantly affected by subduction. The Os-He-O isotope ratios will be combined with data on the composition of olivine and included Cr-spinels to infer the temperatures and oxygen fugacity of olivine crystallization, enabling a holistic model on the mode of silicic melt formation. Overall, the project will provide new constraints on the connectivity between slab subduction and arc volcanism and its role in regulating the long-term evolution and maintenance of habitable Earth.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.

“会聚板块边缘”是固体地球地球化学循环的主要界面，对于宜居地球的形成和维持至关重要。在会聚板块边缘，由地壳和最上地幔组成的岩石圈板块被牵引或俯冲到另一个岩石圈板块下方。在大约 80-140 公里深度，俯冲板块释放出富含气候活性挥发性元素（H2O、卤素）的物质，并通过呈弧形排列的火山活动将其“回收”回地球表面。这些弧形成了“太平洋火环”，以富含挥发物、毁灭性的硅质岩浆喷发而闻名，这些喷发可能导致致命的气候扰动（例如 1815 年的坦博拉火山）和海啸（例如 1883 年的喀拉喀托火山、2018 年的海啸），并且是永久性的。对人口稠密的地球上人类居住的主要威胁。因此，了解物质循环如何导致硅质、爆炸性弧火山活动仍然是地球科学研究的核心主题。研究俯冲再循环时的一个特殊挑战是，它发生在地球内部深处（几公里到 200 公里之间），因此无法直接观察到。因此，科学家依赖于从岩浆成分（例如橄榄石和尖晶石晶体）中获得的间接观测结果，这些成分携带着地球内数公里深处发生的过程的信息。两名美国妇女（其中一名是残疾人）计划与来自美国、墨西哥、苏格兰和法国的国内和国际同事合作和交流，从墨西哥年轻火山喷发的火山岩中收集此类信息。该项目将培训研究生和本科生，目标是促进多样性。 K-12 教师将参与其中，以便将新的研究成果转化为中学生和高中生的地球科学课程，并将在每年定期的开放日向公众通报。该项目重点关注橄榄石及其铬内含物- 跨墨西哥火山带 (TMVB) 中从镁铁质岩浆到硅质岩浆的尖晶石，这是一个主要俯冲带，以其发生灾难性火山喷发的高潜力而闻名。许多研究表明，TMVB 所在的 45 公里厚的大陆地壳基底中的硅质岩浆通过熔融加工获得了致命的爆炸力。然而，一些研究表明这些岩浆中所含橄榄石晶体的成分与这一假设不一致。值得注意的是，来自TMVB中部的橄榄石具有δ18O和3He/4He同位素信号，表明它们的宿主岩浆主要形成于地壳基底下方的地幔中，在那里它们通过掺入大量俯冲板片物质而变成硅质。在本项目中，我们将通过从橄榄石和大块岩石中获取额外的 187Os/188Os 同位素数据来进一步测试这两个对比假设，这些数据是从 TMVB 中部（波波卡特佩特尔和 Sierra Chichinautzin）和东部（Serdan 盆地）的关键位置精心挑选的，如下以及来自弧后区域的岩浆未受到俯冲作用的显着影响。 Os-He-O 同位素比将与橄榄石和铬尖晶石的成分数据相结合，推断橄榄石结晶的温度和氧逸度，从而建立硅熔体形成模式的整体模型。总体而言，该项目将为板片俯冲和弧火山作用之间的连通性及其在调节宜居地球的长期演化和维持中的作用提供新的约束。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。

项目成果

Using Trace Elements in Olivine Phenocrysts to Test Models of Melt Differentiation at Convergent Margins: Constraints from Times Series in Monogenetic Volcanoes in the Central Transmexican Volcanic Belt

利用橄榄石斑晶中的微量元素测试汇聚边缘的熔体分异模型：跨墨西哥中部火山带单生火山时间序列的约束

• 发表时间: 2019-12
• 期刊: AGU Fall Meeting 2019
• 作者: Fleming, W.;Straub, S.M.;Gomez;Espinasa;Bindeman, I.N.;Stuart, F.M.;Batanova, V.G.
• 通讯作者: Batanova, V.G.