[MIS03-P03] Shift in provenance composition of Cretaceous Japan arc: from Jurassic granitoids/accretionary complex to Cretaceous granitoids
キーワード：ウラン-鉛年代、後背地、砕屑性ジルコン、前弧、西南日本、白亜紀
U-Pb dating of detrital zircons in shallow marine/fluvial sandstones is effective in reconstructing distributary pattern of terrigenous clastics within ancient active continental margins, e.g., the differentiation of fore-arc, intra-arc, and back-arc basins. The Japan segment of Cretaceous arc-trench system in East Asia experienced an episodic formation of crustal rocks, such as arc granitoids, accretionary complexes, and blueschists; nonetheless, details in secular change of arc-related sedimentary basins and their provenance were not fully clarified. This study investigated detrital zircon chronology of the Late Jurassic and Early Cretaceous fore-arc sandstones (18 samples) in SW Japan from Kyushu to Kii peninsula, central Japan. We obtained the following results. 1) During the Late Jurassic to Valanginian (163-133 Ma), pre-Cretaceous (with Proterozoic) zircons were supplied steadily to the fore-arc domain, 2) after the Hauterivian, their abundance started to decrease, and 3) after the Albian, Cretaceous zircons predominated in the fore-arc, whereas pre-Cretaceous ones became almost absent throughout the Late Cretaceous. In contrast, in intra-arc and back-arc domains, older zircons were constantly supplied till the end-Cretaceous. This major change in provenance likely reflected the emergence of a major topographic relief composed of Cretaceous arc granitoids that performed as a significant barrier for older grain flux to the fore-arc domain. The significant arc magmatism and emplacement of voluminous arc-granitoids during the Cretaceous may have first induced surface erosion of the overlying Jurassic accretionary complexes (sandstones with abundant Proterozoic and Paleozoic detrital zircons) that were intruded by the Cretaceous granitoids primarily in mid-shallow crustal levels, and then the erosion of arc granitoids per se.