Kurosegawa terrane: disrupted remnants of a low latitude Paleozoic terrane accreted to SW Japan

Abstract

The Kurosegawa terrane is an anomalous, disrupted, predominantly Paleozoic lithotectonic assemblage of convergent continental margin affinity located between two Mesozoic terranes in SW Japan. On the basis of Silurian macrofossils in limestones and sparse Devonian plant fossils in overlying volcaniclastic sediments portions of the terrane were considered previously to represent a Silurian through Devonian sedimentary succession. Radiolarian data, together with sedimentological analysis, indicate the possibility that hiatuses may occur in this succession although their position remains indeterminate. Faunal, floral and paleomagnetic data indicate low latitude development during the Paleozoic, probably near the northern margins of Gondwana. Late Paleozoic oceanic crustal rocks are incorporated in a chaotic complex which crops out along the northern margin of the terrane. The chaotic rocks are interpreted to represent remnants of a subduction complex. Spatial relations of weakly-metamorphosed subduction complex rocks distributed along the northern side of the terrane and higher grade blueschist-bearing rocks to the south may indicate that during the Late Paleozoic to Early Mesozoic, subduction was south-directed along the northern margin of the Kurosegawa terrane. In the Jurassic, the Kurosegawa terrane underwent an oblique collision with Japan which was then part of Eurasia. Strike-slip faulting, associated with, and post-dating this collision resulted in dispersal of the Kurosegawa terrane into a narrow, discontinuous belt which transects the outer zone of SW Japan.