Abstract
The Ultra-Tamba Terrane in the Kawanishi-Inagawa area, southeast Hyogo Prefecture, tectonically overlies the Tamba Terrane and is subdivided into the Kunisaki and Inagawa complexes (redefined) in descending structural order. The Kunisaki Complex consists of coherent clastic rocks and equivalent broken and mixed facies. The mixed facies contains variably sized blocks of clastic rock, chert, and mafic rock within a muddy matrix. Earliest Late Permian and early Late Permian radiolarians were recovered from the felsic tuff and mudstone of this complex, respectively. The Inagawa Complex consists of coherent clastic rocks and equivalent broken facies. Felsic tuff within this complex contains radiolarians of late Middle to middle Late Permian age, and the mudstone yields middle Late Permian radiolarians that indicate the youngest age of clastic rocks of the Ultra-Tamba Terrane in the study area. The lithological characteristics of the Inagawa Complex are similar to those of the Takatsuki Formation exposed to the east of the study area, which includes clastic rocks younger than those in the Inagawa Complex. The Kunisaki and Inagawa complexes represent a pile of nappes, as the latter includes clastic rocks younger than those in the former. The age, lithological features, and structural characteristics of these complexes and the Takatsuki Formation suggest an origin via progressive growth of accretionary prism.
