An international research team led by Göttingen University has identified an unusual thermal pattern in a rock specimen from Papua New Guinea that traveled deep into Earth’s interior approximately four million years ago. The rock descended more than 90 kilometers beneath the surface while experiencing temperatures that reached approximately 800°C at its maximum depth. The research, published in Nature Geoscience, provides new insights into heat distribution within the planet and raises questions about existing models of tectonic plate behavior.
Scientists studied the rock using advanced analytical techniques, identifying tiny crystals of coesite preserved within other minerals. These microscopic formations indicate the extreme pressures and temperatures the rock experienced during its descent. Analysis revealed that at a depth of approximately 45 kilometers, the rock had already reached temperatures around 700°C, meaning it was only about 100°C cooler at half its maximum depth. This finding contradicts conventional expectations about how temperature should increase with depth in subduction zones.
The research team determined that the rock experienced an unexpected transition from hot to relatively cooler conditions as it descended deeper into the planet. While temperatures continued to increase with depth, the rate of warming was substantially slower than existing thermal models predict. This represents the first clear reconstruction of such a transition between different thermal conditions at varying depths within a subduction zone.
The researchers propose multiple explanations for the anomalous temperature distribution. Tectonic plates may generate more heat at shallow depths than previously understood, with intense shearing forces along plate boundaries producing additional warming. Alternatively, the subduction zone may not have existed long enough to develop the cooler temperatures predicted by standard models. Both processes may have contributed to the rock’s thermal history.
Accurate understanding of subduction zone temperatures carries significant implications for evaluating earthquake and volcanic activity conditions, as well as for comprehending geochemical cycles that regulate Earth’s climate. The findings offer scientists new methodological approaches to investigating how subduction has functioned over geological timescales. The work received support from the German Research Foundation.
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