Abstract
Geological observations in the central part of T okunoshima in the A mami I slands, S outhwest J apan, reveal that discrete layers of serpentinite, dioritic gneiss, and amphibolite are intercalated into pelitic schist and these rock bodies form a northwest‐dipping tectonic stack. A subhorizontal psammitic schist layer overlies them. These rocks underwent ductile deformation that is denoted by penetrative foliation and mineral lineation. Microstructures of the sheared metamorphic rocks and serpentinite indicate top‐to‐the‐east, ‐southeast or ‐south (hanging‐wall up) displacements. The en echelon array of rock bodies is interpreted as a duplex with the psammitic schist layer on its top and the pelitic schist layer on its bottom. It is inferred that the serpentinite‐bearing duplex was formed due to the tectonic erosion and the subsequent accretionary growth operated in a C retaceous or older subduction zone. Tokunoshima has been considered to belong to the S himanto B elt. However, regional low‐pressure and high‐temperature type amphibolite‐facies metamorphism and related ductile deformation have not been recognized in the other areas of the S himanto B elt. There is no metamorphic rock occurrence comparable to that of T okunoshima in the neighboring islands. The metamorphic rocks in T okunoshima can be correlated to any of low‐pressure/temperature type metamorphic regions in K yushu.