The International Ocean Discovery Program Expedition 350 drilled between two Izu rear‐arc seamount chains at Site U1437 and recovered the first complete succession of rear‐arc rocks. The drilling reached 1806.5 m below seafloor. In situ hyaloclastites, which had erupted before the rear‐arc seamounts came into existence at this site, were recovered in the deepest part of the hole (∼15–16 Ma). Here it is found that the composition of the oldest rocks recovered does not have rear‐arc seamount chain geochemical signatures, but instead shows affinities with volcanic front or some of the extensional zone basalts between the present volcanic front and the rear‐arc seamount chains. It is suggested that following the opening of the Shikoku back‐arc Basin, Site U1437 was a volcanic front or a rifting zone just behind the volcanic front, and was followed at ~ 9 Ma by the start of rear‐arc seamount chains volcanism. This geochemical change records variations in the subduction components with time, which might have followed eastward moving of hot fingers in the mantle wedge and deepening of the subducting slab below Site U1437 after the cessation of Shikoku back‐arc Basin opening.

中文翻译：

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伊豆后方火山活动的最早阶段是在国际海洋发现计划第350探险队的U1437站点上进行钻探揭示的

国际海洋发现计划探险队350在站点U1437的两条伊豆后弧海山链之间进行了钻探，并恢复了第一批完整的后弧岩。钻探达到海床以下1806.5 m。在该地点的弧后海山形成之前就已经爆发的原位破硅质岩在该孔的最深处（约15-16 Ma）被回收。在这里发现，最古老的岩石组成没有弧后海山链的地球化学特征，而是显示出与火山前缘或当前火山前线与弧后海山链之间的某些延伸带玄武岩的亲和力。建议在四国后弧盆地开放之后，U1437站点是火山前缘或火山前缘后的裂谷带，随后在〜9 Ma发生了后弧海山链火山爆发。该地球化学变化记录了俯冲分量随时间的变化，这可能是由于四国后弧盆地开放停止后，热手指向地幔楔中的东移以及U1437站点下方俯冲板的加深。