A rock with a memory
The Kumano region, part of Japan's Kii Peninsula, is famous for ancient pilgrimage routes and spiritual waterfalls. Beneath this area lies a geological story recorded in granite. The rock formations here, known as the Kumano Acidic Rocks, hold microscopic crystals that are far older than the granite that contains them. These crystals, a mineral called zircon, are resilient time capsules, recording a history of geological forces that shaped the Japanese archipelago.
The Kumano granite itself is relatively young in geological terms. It formed during the Miocene epoch, between 15.5 and 13.5 million years ago. This magmatic activity happened because the the Philippine Sea Plate beginning to subduct, or dive beneath, the Eurasian continental plate. The immense heat and pressure generated by this tectonic collision melted older rocks deep within the Earth's crust. As this molten rock, or magma, cooled and solidified to form the Kumano granite, it incorporated unmelted zircon crystals from the pre-existing rock.