Understanding the petrologic and geochemical evolution of island arcs is important for interpreting the timing and impacts of subduction and processes leading to the formation of a continental crust. The Izu–Bonin–Mariana (IBM) Arc, western Pacific, is an outstanding location to study arc evolution. The IBM first arc (45–25 Ma) followed a period of forearc basalt and boninite formation associated with subduction initiation (52–45 Ma). In this study, we present new major and trace element data for the IBM first arc from detrital glass shards and clasts from DSDP Site 296, located on the northernmost Kyushu Palau Ridge (KPR). We synthesize these data with published literature for contemporaneous airfall ash and tephra from the Izu–Bonin forearc, dredge and piston core samples from the KPR, and plutonic rocks from the rifted eastern KPR escarpment, locations which lie within or correlate with KPR Segment 1 of Ishizuka, Taylor, Yuasa, and Ohara (2011). Our objective is to test ways in which petrologic and chemical data for diverse igneous materials can be used to construct a complete picture of this section of the Oligocene first arc and to draw conclusions about its evolution. Important findings reveal that widely varying primary magmas formed and differentiated at various depths at this location during this period. Changes in key trace element ratios such as La/Sm, Nb/Yb, and Ba/Th show that mantle sources varied in fertility and in the inputs of subducted sediment and fluids over time and space. Plutonic rocks appear to be related to early K‐poor dacitic liquids represented by glasses sampled both in the forearc and volcanic fronts. An interesting observation is that the variation in magma compositions in this relatively small segment encompasses that inferred for the IBM Arc as a whole, suggesting that sampling is a key factor in inferring temporal, across‐arc, and along‐strike geochemical trends.

中文翻译：

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九州帕劳岭DSDP站点296渐新世碎屑沉积物中火山玻璃的地球化学：解释伊豆–波宁–马里亚纳岛北部北部早期的岩浆演化

了解岛弧的岩石学和地球化学演化对于解释俯冲的时间和影响以及导致大陆结皮形成的过程非常重要。西太平洋的伊豆邦宁马里亚纳（IBM）弧是研究弧演化的绝佳地点。IBM的第一条弧线（45–25 Ma）跟随一段俯冲开始（52–45 Ma）的前臂玄武岩和贝尼石的形成。在这项研究中，我们从位于九州帕劳山脊（KPR）最北端的DSDP 296号站点的碎屑玻璃碎片和碎屑提供了IBM第一弧的主要和痕量元素的新数据。我们将这些数据与已发表的文献进行了综合，这些文献包括来自伊豆–波宁前臂的同时期飞灰和特非拉，来自KPR的挖泥机和活塞岩心样本以及来自裂谷的东部KPR陡坡的深成岩，Ishizuka，Taylor，Yuasa和Ohara（2011）的KPR第1段之内或与之相关的位置。我们的目标是测试各种火成岩材料的岩石学和化学数据可用于构造渐新世第一弧的完整图片并得出其演化结论的方法。重要发现表明，在此期间，在该位置的各个深度形成并分化出了千差万别的原生岩浆。诸如La / Sm，Nb / Yb和Ba / Th等关键微量元素比率的变化表明，地幔源的肥力以及俯冲沉积物和流体输入随时间和空间的变化而变化。古生岩似乎与前钾和火山前沿采样的玻璃代表的早期钾贫瘠的菊状液体有关。