Abstract Central aims of IODP Expedition 352 were to delineate and characterize the magmatic stratigraphy in the Bonin forearc to define key magmatic processes associated with subduction initiation and their potential links to ophiolites. Expedition 352 penetrated 1.2 km of magmatic basement at four sites and recovered three principal lithologies: tholeiitic forearc basalt (FAB), high-Mg andesite, and boninite, with subordinate andesite. Boninites are subdivided into basaltic, low-Si, and high-Si varieties. The purpose of this study is to determine conditions of crystal growth and differentiation for Expedition 352 lavas and compare and contrast these conditions with those recorded in lavas from mid-ocean ridges, forearcs, and ophiolites. Cr# (cationic Cr/Cr+Al) vs. TiO2 relations in spinel and clinopyroxene demonstrate a trend of source depletion with time for the Expedition 352 forearc basalt to boninite sequence that is similar to sequences in the Oman and other suprasubduction zone ophiolites. Clinopyroxene thermobarometry results indicate that FAB crystallized at temperatures (1142–1190 °C) within the range of MORB (1133–1240 °C). When taking into consideration liquid lines of descent of boninite, orthopyroxene barometry and olivine thermometry of Expedition 352 boninites demonstrate that they crystallized at temperatures marginally lower than those of FAB, between ~1119 and ~1202 °C and at relatively lower pressure (~0.2–0.4 vs. 0.5–4.6 kbar for FAB). Elevated temperatures of boninite orthopyroxene (~1214 °C for low-Si boninite and 1231–1264 °C for high-Si boninite) may suggest latent heat produced by the rapid crystallization of orthopyroxene. The lower pressure of crystallization of the boninite may be explained by their lower density and hence higher ascent rate, and shorter distance of travel from place of magma formation to site of crystallization, which allowed the more buoyant and faster ascending boninites to rise to shallower levels before crystallizing, thus preserving their high temperatures.

中文翻译：

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在 IODP 远征 352 到博宁前弧期间回收的玄武岩和博宁岩的矿物成分和热气压测量

摘要 IODP Expedition 352 的中心目标是描绘和表征博宁前弧的岩浆地层，以定义与俯冲开始相关的关键岩浆过程及其与蛇绿岩的潜在联系。352 号探险队在四个地点穿透了 1.2 公里的岩浆基底，并恢复了三种主要岩性：拉斑前弧玄武岩 (FAB)、高镁安山岩和博宁岩，以及次要安山岩。Boninites细分为玄武岩，低Si和高Si品种。本研究的目的是确定远征 352 熔岩的晶体生长和分化条件，并将这些条件与大洋中脊、前弧和蛇绿岩中记录的条件进行比较和对比。Cr#（阳离子 Cr/Cr+Al）对比 尖晶石和单斜辉石中 TiO2 的关系表明，Expedition 352 前弧玄武岩到博宁岩序列的源头随着时间耗尽的趋势与阿曼和其他超俯冲带蛇绿岩中的序列相似。单斜辉石热气压测量结果表明 FAB 在 MORB (1133–1240 °C) 范围内的温度 (1142–1190 °C) 下结晶。考虑到松岩下降的液体线时，Expedition 352 松岩的斜方辉石气压测量法和橄榄石温度测量法表明，它们的结晶温度略低于 FAB 的温度，介于 ~1119 至 ~1202 °C 和相对较低的压力（~0.2- 0.4 对比 FAB 的 0.5–4.6 kbar）。博石岩斜方辉石的高温（低硅博石岩为~1214°C，高硅博石岩为1231-1264°C）可能表明斜方辉石快速结晶产生的潜热。松岩的较低结晶压力可以解释为它们的密度较低，因此上升速度较高，以及从岩浆形成地点到结晶地点的行进距离较短，这使得更有浮力和上升速度的松岩上升到较浅的水平在结晶之前，从而保持它们的高温。