Early Jurassic zircon U-Pb age from sandstone within the accretionary complex in the southeastern Okayama Prefecture, SW Japan

Abstract

An accretionary complex of unknown age is distributed in the southeastern Okayama Prefecture, but because it is broadly covered and intruded by Cretaceous igneous rocks it rarely crops out; insufficient data are available to establish a depositional age and any correlation with the surrounding accretionary complex. In this study, U-Pb analyses of detrital zircons from sandstone in the accretionary complex were used to constrain depositional age, resulting in a youngest single grain ²³⁸U-²⁰⁶Pb age of 181.7±7.4 Ma and youngest cluster of weighted mean ages of 188.9-185.7 Ma. The detrital zircon U-Pb ages of the sandstone show that the depositional age of the accretionary complex is post Early Jurassic (Pliensbachian age).