blueschist formations

Supplement to blueschist facies: Blueschists are generally considered to be diagnostic of former subduction zones, because they imply relatively high pressure conditions relative to the temperature (compared to normal geothermal gradients). This low temperature, high pressure prograde metamorphic path is exposed in the US westcoast Franciscan facies series. Blueschists terranes are typically found within young orogenic belts in faulted contact with rocks of the higher-temperature greenschist facies (rarely eclogite facies). The rocks are typically metamorphosed oceanic sediments and basaltic oceanic crust. In addition to the circum-Pacific Franciscan complex, Japanese chains, and New Caledonia, blueschists are also well exposed in Alpine-Himalayan chains in Greece, Turkey.

formations: Ring Mountain blueschist (foreground); Rand Mountains blueschist; folded blueschist from near the type locality of glaucophane on Syros, Greece; eclogite clast wrapped by blueschist (10 cm), isoclinal folding in blueschist with limbs attenuated by shearing (40 cm); refolded isoclinal folds in blueschist (20 cm), 2; high pressure blueschist and eclogite of the Maksutovo Complex, Urals, wp; blueschist boulder, Lake Pillsbury; Japan; webpages: The Franciscan Complex