(Table T1) Mineral composition of turbidite sands and sandstones from ODP Leg 190 sites

During Ocean Drilling Program Leg 190 several turbidite successions in the Nankai Trough were drilled through including Pleistocene trench fill (Sites 1173 and 1174), Pleistocene-Pliocene slope basin deposits and underlying trench fill (Sites 1175 and 1176), Miocene Shikoku Basin deposits (Site 1177), and upper Miocene trench fill (Site 1178). Sands from the Pleistocene trench-fill succession of the Nankai Trough are of mixed derivation with significant monomineralic components (quartz and feldspar) and mafic to intermediate volcanic rock fragments, in addition to sedimentary and less abundant metamorphic detritus. They have a source in the Izu collision zone in central Honshu. Sands from the slope and accreted trench fill at Sites 1175 and 1176 are dominated by quartz with less abundant feldspar, sedimentary rock fragments, and only minor volcanic and metamorphic rock fragments. In contrast to the trench turbidites of Sites 1173 and 1174, these sands are very quartzose with characteristic radiolarian chert fragments. Volcanic rock fragments are mainly of silicic composition. Potential sources of these sands are uplifted subduction complexes of southwest Japan. Sands from the accreted trench turbidites at Site 1178 have clast types similar to those at Sites 1175 and 1176. In contrast, however, framework detrital modes are distinctive, with Site 1178 sands having substantially lower total quartz contents and more abundant fine-grained sedimentary rock fragments. These sands were also probably derived from the island of Shikoku, but their composition indicates that sedimentary rocks were abundant in the source area and these may have been Miocene forearc basin successions that were largely removed by erosion. Erosional remnants of Miocene forearc basin deposits are present on the Kii Peninsula east-northeast of Shikoku. Erosion followed a phase of exhumation of the Shimanto Belt indicated by apatite fission track ages at ~10 Ma. Sand in the lower-upper Miocene turbidites of the lower Shikoku Basin section at Site 1177 is more varied in composition, with the upper part of the unit similar to Site 1178 (i.e., rich in sedimentary rock fragments) and the lower part similar to those at Sites 1175 and 1176 (i.e., rich in quartz with some silicic volcanic rock fragments). Sands from the lower part of the Miocene turbidite unit were derived from a continental source with plutonic and volcanic rocks, possibly the inner zone of southwest Japan.

大洋钻探计划（Ocean Drilling Program, ODP）第190航次在南海海槽（Nankai Trough）钻获多套浊积岩序列（turbidite successions），涵盖更新世（Pleistocene）沟槽充填物（trench fill，站位1173与1174）、更新世-上新世斜坡盆地沉积及下伏沟槽充填物（站位1175与1176）、中新世（Miocene）四国盆地（Shikoku Basin）沉积（站位1177），以及晚中新世沟槽充填物（站位1178）。南海海槽更新世沟槽充填序列中的砂体具有混合物源特征，含显著的单矿物组分（石英与长石）、基性至中性火山岩岩屑，此外还发育沉积岩岩屑及少量变质岩岩屑，其物源来自本州中部的伊豆碰撞带（Izu collision zone）。站位1175与1176的斜坡及增生沟槽充填砂体以石英为主，长石、沉积岩岩屑含量较低，仅含少量火山岩与变质岩岩屑。与站位1173、1174的沟槽浊积岩砂体不同，这类砂体富石英，且特征性含有放射虫燧石岩屑；火山岩岩屑主要为硅质成分，其潜在物源为日本西南部抬升的俯冲杂岩。站位1178的增生沟槽浊积岩砂体的碎屑类型与站位1175、1176相似，但骨架碎屑模式（framework detrital modes）存在显著差异：站位1178砂体的总石英含量显著更低，且细粒沉积岩岩屑更为丰富。这类砂体大概率同样源自四国岛（Shikoku），但其组分特征表明物源区沉积岩十分发育，这些沉积岩可能为中新世弧前盆地序列，后大多被侵蚀移除。四国东北偏东的纪伊半岛（Kii Peninsula）尚存中新世弧前盆地沉积的侵蚀残余体。磷灰石裂变径迹年龄（apatite fission track ages）显示，四地块在约10 Ma时经历了抬升剥蚀阶段，随后发生侵蚀作用。站位1177的四国盆地下段晚中新世浊积岩砂体的组分更为多样：该单元上段与站位1178相似（即富沉积岩岩屑），下段则与站位1175、1176类似（即富石英，含少量硅质火山岩岩屑）。中新世浊积岩单元下段的砂体源自含深成岩与火山岩的大陆物源，可能为日本西南部内带。