Detrital Zircon U-Pb Dating of Cretaceous Sandstones from Amakusa-Mifune District, Central Kyushu, Japan: Provenance and Transition of Fore-arc Clastic Rocks in Cretaceous Japan

Shallow marine and non-marine Cretaceous strata of the Amakusa-Mifune area in central Kyushu, SW Japan, represent fore arc sediments of the Late Mesozoic arc-trench system along East Asia. To clarify their provenance and secular changes, U-Pb ages of detrital zircons from the Cretaceous sandstones of these units were measured. The age spectra of detrital zircons obtained from 10 sandstone samples, ranging from the Albion to Maastrichtian, clarify the following four aspects of provenance; i.e., (1) dominant exposure of Cretaceous granitoids throughout the Albian to Maastrichtian associated with minor Triassic and Paleozoic ones, (2) onset of influx of Jurassic and Paleoproterozoic zircons into the fore-arc domain in the Campanian, (3) essential resemblance in age spectra of detrital zircon to other coeval sandstones deposited in the fore-arc and intra-arc domain of East Asia (e.g. Kanmon Group on the continent side and the Monobegawa Group on the trench side), and (4) ubiquitous age spectra shared by coeval sandstones throughout SW Japan from Kanto to Kyushu along the arc. These suggest that the Cretaceous fore-arc of the East Asian margin featured the same provenance as dominant Cretaceous arc granitoids with small quantity of early-middle Mesozoic and Paleozoic granitoids from older orogen. A major change in provenance occurred in the Campanian, which allowed the influx of terrigenous elastics from much older continental sources, such as the Paleo-proterozoic basement. This probably reflects the disappearance of the pre-existing topographic barrier, which was probably composed of the uplifted Cretaceous arc batholith belt.