A Papua New Guinea Rock Was Unexpectedly Hot at 45 Kilometers Beneath Earth, Scientists Discover Something 90 Kilometers Down
Rock records its underground journey
An international team led by Göttingen University studied eclogite, a red and green rock formed under the intense pressure of subduction zones. Minerals in the rock retain clues about the conditions it encountered as it descended.
Heat changed with depth
At about 45 kilometers below the surface, the rock had reached around 700°C, or 1,290°F. That was only 100°C cooler than its temperature farther down, despite the difference in depth.
Possible causes of the pattern
Researchers have previously found rocks that record unexpectedly high temperatures. This case, however, clearly traces a shift from unusually hot shallow conditions to comparatively colder temperatures at greater depth.
One possible cause is shearing stress as tectonic plates move against each other, which may heat shallow rocks more than scientists have assumed. The subduction zone may also have been too young to develop the expected lower temperatures; both factors could have played a role.
Key points
- The Papua New Guinea rock descended more than 90 kilometers about four million years ago.
- At roughly 45 kilometers deep, it had reached around 700°C.
- The rock’s record shows unusually hot shallow conditions followed by comparatively cold conditions at depth.
- Researchers say shearing stress and the subduction zone’s development may help explain the temperature pattern.