Detrital zircon U-Pb ages of the Cretaceous Unokawa Complex in the Shimanto Belt on the central Kii Peninsula, SW Japan

Abstract

The depositional age sequence of Cretaceous accretionary complexes in the Kouyasan Belt of the Shimanto Belt (central Kii Peninsula, SW Japan) is poorly constrained owing to a lack of age data for the Unokawa Complex in this belt. We conducted U-Pb dating of detrital zircons from three sandstone samples of the Unokawa Complex. Detrital zircon U-Pb ages in this complex consist mainly of two age groups at ca. 300-100 Ma and ca. 2600-1700 Ma. The youngest single grain ages are 110-102 Ma, and the youngest cluster ages are 124-102 Ma, ranging from the Aptian to Albian. These youngest ages of the Unokawa Complex overlap (at 2σ) with those of the underlying Takaharagawa Complex but do not overlap with those of the overlying Mugitani Complex (Mg2 Unit).