Mineralogy and geochemistry of volcanic ash at Japan Trench from DSDP Legs 87 and 57@en

Volcanogenic sediments were obtained from Site 584, located on the midslope of the Japan Trench. Occurrences of volcanic ash in the diatomaceous mudstones increase within sediments dated 6-3 Ma. The frequency pattern and the sediment accumulation rate obtained at Site 584 are similar to those of Site 440 and to those of Sites 438 and 439, located on the upper slope basin. Explosive volcanism increased during the Pliocene and late Miocene in relation to the intrusion of Tertiary granites and uplift of the Tohoku Arc (northeastern Japan Arc). Hygromagmaphile element concentration shows that the glass does not belong to a unique series, and a comparison with Nankai Trough data distinguishes at least two different evolutionary lines.研究从日本海沟中段坡地的584站位获取了火山成因沉积物（volcanogenic sediments）。在年代为6~3 Ma的沉积物中，硅藻质泥岩内的火山灰产出量显著升高。该站位获得的频率分布模式与沉积物堆积速率，与位于上坡盆地的440站位以及438、439站位的对应结果高度相似。上新世至晚中新世时期，爆发式火山作用强度增加，这与第三纪花岗岩的侵入活动以及东北日本弧（Tohoku Arc，日本东北部弧）的隆升存在关联。亲湿岩浆元素（hygromagmaphile elements）的浓度特征表明，该套火山玻璃并非来自单一演化系列；通过与南海海槽（Nankai Trough）的相关数据对比，可区分出至少两种不同的演化路径。