An international team of researchers from the University of Göttingen has discovered that one rock sample has followed a path that does not fit the usual models.
The rock in question is an eclogite from Papua New Guinea. Four million years ago, this stone sank more than 90 kilometers beneath the Earth's surface in a subduction zone.
Analysis of mineral inclusions showed that at a depth of about 45 kilometers the rock had already heated to approximately 700 °C. This is noticeably higher than existing thermal models predict.
At the 90-kilometer mark, the temperature was about 800 °C — already within the range of "cold" subduction. Thus, as it descended, the temperature gradient changed from unexpectedly hot to relatively cold.
"Finding such a transition from hot to cold subduction came as a surprise, since it contradicts our current thermal models of subduction zones," noted Dr. Jan Schönig of the Göttingen Centre for Earth Sciences.
Possible causes of the excess heat at shallow depths are additional heating due to shear stresses between the plates or insufficient time for the subduction zone to cool. Both factors could have played a role.
Precise data on temperatures in subduction zones are important for understanding earthquakes, volcanic activity and the long-term carbon cycle.
The main conclusion of the study and its main "claim to fame" is that scientists have for the first time clearly demonstrated that the process of tectonic plates sinking (subduction) can radically change its temperature regime as it goes deeper, and the old models did not take this into account.
Why this changes the rules of the game (global significance)
- Reassessment of the tectonics of the past: If many ancient rocks that we considered evidence of "cold" subduction actually passed through a hot phase, then our ideas about how plate tectonics worked millions and billions of years ago may be wrong.
- Forecasting catastrophes: The temperature regime of a subduction zone directly affects exactly how earthquakes will occur (whether they will be deep and powerful or shallow) and how the mantle will melt, feeding volcanoes.
- The carbon cycle: Temperature determines how much carbon (in the form of carbonates) will sink deep into the mantle and how much will return to the atmosphere through volcanoes. This is the key to understanding the Earth's long-term climate.
The results were published in the journal Nature Geoscience on 1 October 2026. The study was supported by the German Research Foundation (DFG).
