Tracing the origin of Southwest Japan using the Hf isotopic composition of detrital zircons from the Akiyoshi Belt

Abstract

The Permian Akiyoshi Belt, which is the oldest unmetamorphosed accretionary complex in Southwest Japan, plays an important role in understanding the origin of the Japanese Islands; however, its tectonic affinity is still not well constrained. Herein, we present the first Hf isotopic data for U–Pb dated detrital zircons of the Late Permian sandstones in the Akiyoshi Belt. Almost all the late Palaeozoic detrital zircons yielded highly positive ɛHf (t) values compatible with a juvenile source, suggesting that the major provenance of the trench sediments was from the South China block and not from the Bureya-Jiamusi-Khanka massif. We propose that in the late Palaeozoic, a block of juvenile lower crust existed outboard of the South China block, and it was being melted during the westward subduction of the Palaeo-Pacific oceanic plate to produce voluminous volcanic and plutonic rocks with positive ɛHf (t) values.