Recipient organisationUniversity of PlymouthSource-published name: University of Plymouth
Funding£21K
PeriodOct 2025 — Oct 2027
In plain English
AI plain-English summary
Tiny volcanoes on the seafloor, barely explored, are now being cored for the first time to reveal how seawater reacts with their fractured rocks. These "petit-spot" volcanoes form on the edge of the Pacific plate as it bends before diving into a subduction zone, but scientists know almost nothing about them. The key gap: when seawater percolates through fractured volcanic rock, it heats up and drives chemical reactions that change the rock’s minerals, chemistry, and physical properties—including how it behaves during earthquakes. This project will analyse newly recovered rock cores using traditional geochemistry and a novel infrared imaging technique that rapidly maps minerals and hydration levels at high resolution. If successful, the work will quantify how much petit-spot volcanism alters the oceanic lithosphere and contributes to global geochemical cycles—the movement of elements between crust, mantle, and oceans. This is fundamental science. A deeper understanding of how hydration affects rock mechanics could, in the long term, improve models of subduction zone seismicity, but the immediate value lies in filling a basic observational gap about a widespread but overlooked volcanic process.
View original technical description
IODP3 Expedition 502 “Impact of Petit-Spot Magmatism on Subduction Zone Seismicity and the Global Geochemical Cycle” targets a relatively newly discovered type of volcanism called petit-spots. These small volcanoes form on the outer edge of the subducting NW Pacific plate but we know very little about them. Expedition 502 will sample these petit-spot volcanoes in order to understand how they may influence earthquake processes (e.g how they may change the mechanical behaviour of earthquakes) and global cycling of elements between the crust, mantle and oceans, so called ‘global geochemical cycles’. Submarine volcanoes typically result in very fractured rocks that allow seawater to percolate down into the rocks. This seawater becomes heated and migrates through the rocks, driving reactions that result in changes to the minerals, chemistry and physical properties of the rocks. As petit-spot volcanoes have only limited sampling to date, we do not know the extent to which seawater might react with the rocks. In this project we will investigate this potential fluid-rock interaction using the newly recovered cores from Expedition 502 and compare these results to other submarine volcano hydrothermal systems. Project Objectives: To characterise the fluid/rock reactions that have taken place around the petit-spot volcanoes using traditional petrography and whole rock geochemistry. To create novel imaging spectroscopy mineral and hydration maps that enable the objective quantification of different alteration types and hydration levels. To determine the geochemical exchanges that have taken place in the different alteration types and scale these observations to estimate the contribution of petit-spot volcanism to global hydrothermal budgets. Our primary research objective supports Expedition 502 Objective 3, which aims to better understand heat and element transfer in the oceanic lithosphere and evaluate the role of petit-spot magmatism in global geochemical cycles. We focus specifically on quantifying the extent and nature of hydrothermal alteration in petit-spot basalts, an essential record of fluid-rock reaction in subseafloor systems. To achieve the project objectives, we will assess the distribution, abundance, and variability of newly formed hydrothermal minerals, using this to define different hydrothermal ‘types’. Integrating a range of analytical methods (eg thin section analysis, scanning electron microscopy (SEM) with high-resolution elemental mapping, bulk geochemistry via XRF, imaging spectroscopy) will enable robust characterisation of the mineralogical and chemical signatures of alteration at a range of spatial scales. High-resolution infrared imaging spectroscopy is a novel technique that is rapid and non-destructive that enables the identification of minerals at <250 µm resolution using their diagnostic signatures. Importantly, mineral signatures can be linked to the hydration states of the rock, providing a tool to quantify how hydrated the petit-spot volcanoes have become. Hydration is important when considering the mechanical properties of rocks in subduction zones. Outcomes of this project will advance our understanding on the contribution of petit-spot magmatism in altering the oceanic lithosphere and its contribution to global geochemical cycles.
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