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

Brown University, Providence RI

Investigators

Abstract

While most of Earth’s volcanoes occur at the boundaries between tectonic plates, 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. 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.