Exposed Deep Crust Geological Cross-sections was added to Your Favorites!
Hidakasanmyaku Erimo Tokachi NP, Hokkaido
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Plate collision shoved buried crust upward, exposing an east–west geological slice more than 20 km thick. Few places reveal an island arc’s deep interior so continuously at the surface.
The rocks read like a depth chart laid sideways: deep-crust granulite in the west gives way eastward to amphibolite, gneiss and hornfels formed at progressively shallower levels.
Some western granulite records a furnace-like past: mineral analysis estimates about 800°C and 7.5 kbar, evidence that these rocks formed in the lowermost crust before being exposed.
Many plutons are frozen magma chambers, not just rock masses. Their preserved features let geologists investigate how magma was replenished, mixed and changed underground.
This cross-section preserves two magma lineages: melts from deep crust formed tonalite and granite, while mantle-derived magmas formed gabbro and diorite.
Zircon dating points to at least 2 major thermal pulses, around 37 and 19 million years ago. This deep-crust story unfolded in separate bouts, not one simple burst.
Sillimanite tonalite collected at nearby Chipira Beach contains striking column-like crystals. The rock formed when tonalitic magma intruded biotite gneiss in the middle crust.
