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

虽然地球上的大多数火山发生在构造板块之间的边界，但许多其他火山发生在板块内部。其中一些板内火山，如夏威夷的火山，与从下地幔2500公里深处向上流动的热地幔有关。然而，另一些则有着更神秘的起源。一组火山在神秘的类别喷发熔岩，其化学成分与410公里至660公里深处的岩石融化一致。新西兰奥克兰火山区就是这种火山带的一个例子。这个项目的目标是为这些火山的融化区域成像。将利用海底和陆地上的地震仪记录的远距离地震的地震波，测量新西兰北岛和周围海洋下地幔的特性。这些结果将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。更广泛的影响包括支持本科生和研究生。本研究的目标是通过解决全新世奥克兰火山场（AVF）的起源，更好地了解产生板内火山活动的过程。AVF在空间上与俯冲带弧分离，其岩浆没有明显的俯冲熔融贡献。根据现有的地震层析成像和氦同位素，这些岩浆也没有明确地与下地幔柱相连。相反，地球化学数据提出的可能性，AVF岩浆提供了一个全球性的地幔熔融，从过渡区深处，一类板内火山作用，最近出现的端元的情况下。然而，不能排除其他过程，如与岩石圈不稳定性和小规模对流有关的上涌驱动的熔融，甚至下地幔的上涌也需要进一步评估。新的地震数据将从一个由20个美国海底宽带地震仪组成的临时阵列中收集。这些台站将由新西兰的陆地阵列和南科大（中国）的OBS部署进行补充。利用所提出的阵列，地震分析将测试是否存在地震速度和衰减异常、过渡区不连续地形以及与竞争假设相关的地震各向异性。美国的工作将与新西兰合作者的地震学和火山学分析以及南科大的地球动力学建模工作相结合。从这个综合的结果将提供估计的深度范围的熔融，挥发性的上升，以及在何种程度上，这种板内火山活动是由岩石圈，过渡带，或两者的过程驱动。一系列的关键问题将得到解决，包括：什么是从表面到过渡区深度的热结构？是否发生上升流，从什么深度开始，存在岩石圈不稳定性？当它们提升时，液体和融化物会走什么样的路径，而这些路径又是如何与大规模的流动相互作用的？如果有火山活动的话，那么远在弧后的火山活动是如何与俯冲系统相互作用的呢？该项目将支持康奈尔大学和布朗大学的研究生和本科生，包括来自历史上边缘化群体的学生。该项目的成果将纳入方案执行机构的外联和教学活动。拟议的项目将加强国际合作。该项目将使人们更好地了解火山灾害的深层驱动因素，包括年轻人（1 ka）奥克兰市区内的火山活动。该项目由海洋科学部的海洋地质学和地球物理学项目以及地球科学部的地球物理学项目支持。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。

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.