The Kurosegawa serpentinite melange zone and its role in the evolution of southwest Japan.

This zone, approx 600 km long, developed obliquely and independently from the parallel arrangement of geological units such as the Ryoke and Sanbagawa belts in the outer zone of SW Japan. Tectonic blocks enveloped wholly or partially by serpentinite are: high-P/low-T schists (352-394 m.y. old); the complex of gneiss, high-P amphibolite and granite (approx 400 m.y.); unmetamorphosed Siluro-Devonian, Carboniferous, Permian and Triassic rocks; schists of the albite-epidote-amphibolite facies (317-327 m.y.); winchite-bearing greenstone, and schists of the jadeite- glaucophane series (208-240 m.y. B.P.). The diversity in lithology and age of the tectonic blocks indicates strong lateral and vertical movements, which would be possible only by subduction zone tectonics. A possible model to explain the existence of the oldest glaucophane schist belt in Japan is the collision of a mature island arc, previously situated further SE of the Japanese islands, at some time after the paired metamorphism of the Sanbagawa-Ryoke belt and before the Cretaceous. -P.Br.