In regions with small ocean plates and continental blocks, such as the Mediterranean in the Cenozoic and modern Indonesia, many blueschists may be stored at shallow depth in the mantle lithosphere that is newly formed during the amalgamation of small continental blocks and oceans. Melting of these blueschists at low pressures in the mixed lithosphere of this type during postcollisional relaxation may be involved in the generation of postcollisional orogenic magmas. Here, we have conducted a series of melting experiments on three blueschist samples with differing protoliths at 800–850°C, 2 GPa to investigate phase relations, mineral compositions, and trace element partitioning (using laser ablation‐inductively coupled plasma‐mass spectrometry [LA‐ICP‐MS]/nanoscale secondary ion mass spectrometry [NanoSIMS]), including the first results for clinozoisite. Dacitic/rhyolitic melts (SiO₂ 60 to 66 wt%) containing ~13 wt% volatiles are produced in all runs. Mn‐rich and Mn‐poor almandine garnets exhibit distinct rare earth element (REE) distribution patterns, while Mn‐rich garnets are effective preconcentrators of heavy REEs (HREEs) for later metamorphic processes. Melts produced from fluid‐affected blueschists of terrigenous origin show the most large‐ion lithophile element (LILE) enrichment, whereas those from terrigenous blueschists with no fluid history exhibit the lowest K/Th and Ba/Th and strongest Ce/Pb and Nb/U fractionations. Melts of blueschists derived from mid‐ocean ridge basalt (MORB) have relatively consistent, MORB‐like Ba/Th and Nb/U (~3) but the lowest Ce/Pb ratios (3.3). V/Sc and Zr/Hf ratios remain constant at ≥850°C regardless of the origin of the blueschist. Dehydration melting in new mantle lithosphere where blueschist is stored at shallow depth will significantly affect trace element behavior and should be considered carefully when examining chemical cycling and magmatism in postcollisional orogenic settings.

中文翻译：

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浅岩石圈中储存的Blueschist在碰撞后造山岩浆生成中的作用

在洋洲板块和大陆板块较小的地区，例如新生代的地中海和现代印度尼西亚，许多蓝片岩可能被浅层地藏在地幔岩石圈中，而地幔岩石圈是在大陆板块和海洋合并过程中新形成的。在碰撞后松弛过程中，这类混合岩在低压下在这种低压混合岩石中融化可能与碰撞后造山岩浆有关。在这里，我们在800-850°C，2 GPa的条件下，对三种具有不同原石的blueschist样品进行了一系列熔化实验，以研究相关系，矿物成分和痕量元素分配（使用激光烧蚀-电感耦合等离子体质谱[ LA‐ICP‐MS] /纳米级二次离子质谱[NanoSIMS]），包括clinozoisite的第一个结果。菊苣/流纹熔体（SiO₂在所有运行中均产生约60％至66％（重量）的挥发物，含量约为13％（重量）。富锰和贫锰的金刚玉石榴石表现出独特的稀土元素（REE）分布模式，而富锰石榴石是重稀土（HREE）的有效预浓缩剂，可用于后续的变质过程。来自受流体影响的陆生蓝晶产生的熔体显示出最大的离子亲石元素（LILE）富集，而来自无流体史的陆生蓝晶产生的熔体具有最低的K / Th和Ba / Th以及最强的Ce / Pb和Nb / U分馏。来自洋中脊玄武岩（MORB）的blueschist熔体具有相对一致的，类似于MORB的Ba / Th和Nb / U（〜3），但Ce / Pb比率最低（3.3）。无论blueschist的由来，V / Sc和Zr / Hf之比在≥850°C时均保持恒定。