Magma Source Evolution Following Subduction Initiation: Evidence From the Element Concentrations, Stable Isotope Ratios, and Water Contents of Volcanic Glasses From the Bonin Forearc (IODP Expedition 352)
Magma Source Evolution Following Subduction Initiation: Evidence From the Element Concentrations, Stable Isotope Ratios, and Water Contents of Volcanic Glasses From the Bonin Forearc (IODP Expedition 352)
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DOI：
10.1029/2020gc009054
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发表时间：
2021-01-01
影响因子：
3.5
通讯作者：
Pearce, Julian A.
中科院分区：
文献类型：
--
作者：
Coulthard, Daniel A., Jr.;Reagan, Mark K.;Pearce, Julian A.
前往小笠原弧的国际海洋发现计划第352次考察队钻探了太平洋板块西缘沿着俯冲开始后立即喷发的火山岩序列。在这次考察中收集的原始火山玻璃进行了主要和微量元素，卤素，硫，氢和氧同位素的分析，其目标是表征参与生成新生上板块地壳的俯冲物质的流体和熔体。最古老的熔岩（弧前玄武岩[FAB]）的不相容微量元素组成与全球最枯竭的洋中脊玄武岩相似。大多数FAB是在海底扩张过程中，在近海沟，超俯冲带的环境中，只有少量的参与不同的，一般稀释的富水流体从俯冲板块减压熔融。玻安岩系玻璃富集俯冲板块活动的不相容微量元素，但强烈亏损其他元素，如中重稀土元素。这些特点是由于代玻安岩主要是由通量熔融涉及富水熔体首先来自俯冲玄武质地壳的前缘，然后从俯冲地壳和沉积物。这些熔体是在低压下产生的，因为浅的胚胎板从海沟附近的热软流圈中提取热量。FAB-通过玻安岩序列的地幔源的逐步耗尽表明，软流圈地幔仍然被困在新生的俯冲板块的菲律宾海板块下的俯冲的第一个几百万年。
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.