Press release: Two kinds of subduction recorded in one rock
No. 132 - 07.10.2026
Research team identify unusual journey deep into Earth for most recently formed ultrahigh-pressure eclogite
When two tectonic plates collide, one plate sinks below the other – a process known as “subduction”. An international research team led by Göttingen University has discovered a rock in Papua New Guinea that, four million years ago, travelled over 90 km down into a subduction zone. The rock records an unusual journey, with higher-than-expected temperature conditions at a depth of around 45 km. This change from very hot subduction at this depth to the more common colder subduction at its final depth challenges scientists’ view of the thermal structure of subduction zones. The results were published in Nature Geoscience.
Subduction zones are sites for earthquakes and volcanic activity and are also responsible for Earth’s long-term climate stabilization over millions of years – acting as a recycling valve for molecules like carbon dioxide. Due to the high pressure in subduction zones, a red-and-green coloured rock called “eclogite” forms. The researchers investigated such an eclogite by a combination of cutting-edge techniques. They found tiny inclusions of coesite – a mineral that requires ultrahigh-pressure conditions – trapped inside another mineral during the rock’s formation. The researchers conclude that the rock was deeply subducted, at least 90 km below the Earth’s surface, and experienced temperatures of around 800 °C. Most interestingly, they could reconstruct that temperatures were only 100 °C colder at half the depth. Dr Jan Schönig at Göttingen University’s Geoscience Center explains: “Finding this change from hot to cold subduction was unexpected as this contradicts our current thermal models of subduction zones.”
Rocks that record higher temperature conditions than expected have been reported before, but this is the first time a journey from a shallow to a deep depth with an accompanied change to relatively colder gradients has been shown so clearly. The possible explanations are: either rocks are getting much more heated at a shallow depth than previously assumed due to shearing stress at the plate contacts; or the subduction zone hadn’t yet had time to evolve to the lower temperatures expected; or a combination of both. This study demonstrates the need to better understand such systems in order to evaluate the effects on earthquakes, volcanic activity, and major geochemical cycles like the long-term carbon cycle. This knowledge will also shed light on how subduction has been operating over millions to billions of years and continues to operate today.
The research was supported by funding from the German Research Foundation (DFG).
Original publication: Schönig JS et al (2026). “Geothermal gradient change during subduction recorded by ultrahigh-pressure eclogite”. Nature Geoscience 2026. DOI: 10.1038/s41561-026-02110-1
Contact:
Dr Jan Schönig
University of Göttingen
Geoscience Center
Department of Sedimentology and Environmental Geology
Faculty of Geoscience & Geography
37077 Göttingen, Germany