GROWTH OF ARC BATHOLITH AND ASSOCIATED PROVENANCE CHANGES IN FORE-ARC: DETRITAL ZIRCON GEOCHRONOLOGY OF CRETACEOUS SANDSTONES IN JAPAN

Orogenic components of ancient arc-trench system are prone to destruction naturally by the later overprinting tectonic processes. In SW Japan, the edifice of Cretaceous arc-trench system is relatively well preserved, particularly in the pair of Ryoke (arc granitoid) and the Sambagawa (blueschist) belt. We conducted systematic analysis of Cretaceous sandstones from the Cretaceous fore-arc, intra-arc and back-arc domains, by checking their detrital zircon ages. By analyzing/comparing the age spectra of detrital zircons in >100 sandstone samples from Kyushu, Shikoku and Honshu, the following results were obtained. 1) Lower Cretaceous sandstones are dominated mostly by Cretaceous zircons. 2) Precambrian zircons are abundant in the sandstones from the back-arc domain, whereas poor to almost absent in the intra-arc and fore-arc sandstones. 3) This contract became sharp particularly after the Albian. The source of the Cretaceous zircons was obviously coeval arc granitoid belt in SW Japan, which distributed abundant terrigenous clastics to both sides of the arc. In contrast, the provenance of the Precambrian grains was obviously the continental crusts in East Asia, i.e. N. and S. China blocks merged in the mid-Triassic. The continental flux to the fore-arc domain was suppressed in the Hauterivian, and finally shut down totally by the Albian, probably owing to the rapid growth of arc crust associated with the emergence of a prominent topographic relief that became a barrier wall.