Nishisonogi Coast (Nagasaki Prefecture, Japan) is the second area on Earth discovered to have a metamorphic rock layer filled with microscopic diamonds.
The rock rich in microscopic diamonds in Nagasaki is believed to have formed 100 million years ago, during the Cretaceous period, the golden age of dinosaurs.
Microscopic diamonds have been found in various locations around the world, and it was previously thought that they could only form through continental collisions. However, geological history clearly indicates that Japan is not located in a collision zone. The recently discovered diamond-bearing rock is metamorphic rock, formed through the process of subduction of oceanic plates. Before Japan, only the Alps region in Italy was known to have this unusual type of metamorphic rock containing diamonds.
Metamorphic rock layers in Japan, filled with microscopic diamonds – (photo: NATURE).
According to researchers from Kumamoto University (Japan), the presence of microscopic diamonds indicates that the metamorphic rock here, during the complex plate tectonics of the Earth, once penetrated deep into the Earth’s crust, reaching up to 120 km below the surface; it was later brought back up from the “hellish” world to its current easily accessible location along the coast of Japan.
The diamonds are mixed with materials from the Earth’s mantle (the layer beneath the Earth’s crust) and are typically formed at temperatures around 450 degrees Celsius and pressures of about 1 to 2.8 GPa, making them the coldest diamonds ever formed.
Previously, the metamorphic rock in Nagasaki was thought to belong to a low-temperature, high-pressure metamorphic belt. However, new findings suggest that they have a distinct origin and represent a type of ultra-high-pressure metamorphic rock not found in surrounding areas. It is possible that tectonic activity has brought this region unique and rare materials.
Plate tectonics is a complex series of processes on Earth, including subduction, where one tectonic plate sinks beneath another while some deep materials are pushed up in other locations. Subduction in the oceans is believed to be a primary process that has caused the Earth’s continents to repeatedly merge into supercontinents and then break apart into the continents we see today.
