Collaborative Research: Investigating intraplate melting processes in northwest New Zealand with seismic imaging

合作研究：利用地震成像研究新西兰西北部的板内熔融过程

• 批准号: 2241064
• 负责人: Karen Fischer
• 金额: $ 35.54万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2027-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2241064&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; intraplate; melting

While most of Earth’s volcanoes occur at the boundaries between tectonic plates, many others occur within plate interiors. Some of these intraplate volcanoes, such as those in Hawaii, are linked to hot mantle that flows upward from depths of more than 2500 km in the lower mantle. Others, however, have more enigmatic origins. One group of volcanoes in the enigmatic category erupt lavas whose chemistry is consistent with melting of rocks at depths of 410 km to 660 km. The New Zealand Auckland Volcanic Field is an example of this type of volcanic zone. The goal of this project is to image the melting region for these volcanos. This will be carried out by measuring the properties of the mantle beneath the North Island of New Zealand and the surrounding ocean using seismic waves from distant earthquakes recorded by seismometers on the ocean floor and on land. These results will be combined with numerical models and geochemical measurements to understand origins of these volcanic rocks. Broader impacts include support for undergraduate and graduate students.The goal of this study is to develop a better global understanding of the processes that produce intraplate volcanism by resolving the origins of the Holocene Auckland Volcanic Field (AVF). The AVF is spatially separated from the subduction zone arc, and its magmas do not bear obvious contributions from subduction-related melting. Neither are these magmas clearly connected to a lower mantle plume, based on existing seismic tomography and helium isotopes. Rather, geochemical data raise the possibility that the AVF magmas provide a global end-member case of mantle melting that emanates from transition zone depths, a class of intraplate volcanism that has recently emerged. However, other processes such as melting driven by upwelling related to lithospheric instabilities and small-scale convection cannot be ruled out, and even upwelling from the lower mantle needs to be further evaluated. New seismic data will be collected from a temporary array of 20 US seafloor broadband seismometers (OBSs). These stations will be complemented by New Zealand-based land arrays, and an OBS deployment from SUSTech (China). With the proposed array, seismic analyses will test for the presence or absence of seismic velocity and attenuation anomalies, transition zone discontinuity topography, and seismic anisotropy associated with the competing hypotheses. US work will be integrated with seismological and volcanological analyses by New Zealand collaborators and a SUSTech geodynamical modeling effort. Results from this synthesis will provide estimates of the depth extent of melting, volatile ascent, and the degree to which this intraplate volcanism is driven by processes in the lithosphere, transition zone, or both. A range of critical questions will be addressed, including: What is the thermal structure from surface to transition-zone depths? Does upwelling occur, and from what depth, and are lithospheric instabilities present? What pathways do fluids and melt take as they ascend, and how do those pathways interact with large-scale flow? How does volcanism far behind the arc interact with the subduction system, if at all? This project will support graduate and undergraduate students at Cornell and Brown, including students from historically marginalized groups. Results from the project will be incorporated in the outreach and teaching activities of the PIs. The proposed project will enhance international collaborations. The project will provide a better understanding of the deep drivers for volcanic hazards, including young (1 ka) volcanism within the Auckland urban area.This project is supported by the Marine Geology and Geophysics program in the Division of Ocean Sciences and the Geophysics program in the Division of Earth Sciences.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.

虽然地球上的大多数火山发生在板块之间的边界处，但许多其他火山发生在板块内部，其中一些板内火山（例如夏威夷的火山）与从下层 2500 多公里深处向上流动的热地幔有关。然而，其他火山则具有更神秘的起源，其中一组火山喷发的熔岩的化学成分与 410 公里至 660 公里深处的岩石融化一致。新西兰奥克兰火山场是此类火山带的一个例子，该项目的目标是对这些火山的融化区域进行成像，这将通过测量北岛下方的地幔特性来实现。新西兰和周围的海洋利用海底和陆地地震仪记录的遥远地震的地震波，将这些结果与数值模型和地球化学测量相结合，以了解这些火山岩的起源，包括支持。这项研究的目标是通过解决全新世奥克兰火山场 (AVF) 的起源，更好地了解板内火山作用的产生过程。AVF 在空间上与俯冲带弧分离，并且根据现有的地震层析成像和氦同位素，它的岩浆没有明显的俯冲作用，也没有与下地幔羽流明显相关。地球化学数据提出了这样一种可能性，即 AVF 岩浆提供了从过渡带深度发出的全球端元案例，这是最近出现的一类板内火山活动。然而，其他过程（例如由与岩石圈不稳定性相关的上升流驱动的熔化）。并且不能排除小规模对流，甚至还需要进一步评估来自下地幔的上升流，新的地震数据将从20个美国海底宽带临时阵列中收集。这些站将由新西兰的陆地阵列和南方科技大学（中国）部署的OBS作为补充。通过拟议的阵列，地震分析将测试是否存在地震速度和衰减异常、过渡。与美国的竞争假设相关的区域不连续性地形和地震各向异性将与新西兰合作者和南方科技大学地球动力学模型的地震学和火山学分析相结合。该综合结果将提供对熔融深度、挥发性上升以及岩石圈、过渡带或两者的过程驱动板内火山活动的程度的估计，一系列关键问题将得到解决。包括：从地表到过渡区深度的热结构是什么？是否发生上升流，从什么深度发生，以及岩石圈不稳定性存在？流体和熔体上升时采取什么路径，以及这些路径如何与大的相互作用。规模弧线后方的火山活动如何与俯冲系统相互作用（如果有的话）？该项目将支持康奈尔大学和布朗大学的研究生和本科生，包括来自历史边缘群体的学生，该项目的结果将纳入外展教学。拟议的项目将加强国际合作，使人们更好地了解火山灾害的深层驱动因素，包括奥克兰市区内的年轻（1 ka）火山活动。该项目得到了海洋局的支持。海洋科学部的地质和地球物理学项目以及地球科学部的地球物理学项目。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。