International Ocean Discovery Program Expedition 352 to the Bonin forearc drilled the sequence of volcanic rocks erupted in the immediate aftermath of subduction initiation along the western margin of the Pacific Plate. Pristine volcanic glasses collected during this expedition were analyzed for major and trace elements, halogens, sulfur, and H and O isotopes with goals of characterizing the fluids and melts of subducted materials that were involved in generating the nascent upper plate crust. Incompatible trace element compositions of the oldest lavas (forearc basalts [FAB]) are similar to those of the most depleted mid‐ocean ridge basalts globally. Most FAB were generated by decompression melting during seafloor spreading in a near‐trench, supra‐subduction zone environment with only minor involvement of diverse and generally dilute water‐rich fluids from the subducting plate. Boninite series glasses are enriched in incompatible trace elements mobilized from the subducting plate, but strongly depleted in other elements, such as the middle‐heavy rare‐earth elements. These traits are attributed to generation of boninites largely by flux melting involving water‐rich melts first derived from the leading edge of subducted basaltic crust and then from both subducted crust and sediment. These melts were generated at low pressures as the shallow, embryonic slab extracted heat from hot asthenosphere near the trench. The progressive depletion of the mantle source for the FAB‐through‐boninite sequence suggests that the asthenospheric mantle remained trapped above the nascent subducting plate for the first several million years of subduction beneath the Philippine Sea Plate.

中文翻译：

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俯冲作用开始后的岩浆源演化：来自波恩前臂的火山玻璃的元素浓度，稳定同位素比和水分含量的证据（IODP远征352）

波宁前臂的国际海洋发现计划352探险队在俯冲开始后不久沿太平洋板块西缘钻了一系列火山岩。分析了在这次探险中收集的原始火山玻璃的主要和微量元素，卤素，硫以及H和O同位素，目的是表征参与生成新生的上板壳的俯冲物质的流体和熔体。全球最古老的熔岩（前玄武岩[FAB]）的不相容微量元素组成与全球最贫化的中海脊玄武岩相似。大部分FAB都是在海沟附近海沟扩散时通过减压融化产生的，在超俯冲带环境中，只有很少的一部分来自俯冲板的多种多样且通常是稀释的富水流体。Boninite系列玻璃富含从俯冲板中迁移出来的不相容的微量元素，但大量消耗了其他元素，例如中重稀土元素。这些特征可归因于次要矿床的产生，主要是由于熔剂熔融，其中富水熔体首先来自俯冲玄武岩地壳的前缘，然后又来自俯冲地壳和沉积物。这些熔体是在低压下产生的，这是因为浅层的胚状板从沟槽附近的热软流层中吸收热量。