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首页> 外文期刊>Contributions to Mineralogy and Petrology >Partial melting of fertile peridotite fluxed by hydrous rhyolitic melt at 2-3 GPa: implications for mantle wedge hybridization by sediment melt and generation of ultrapotassic magmas in convergent margins
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Partial melting of fertile peridotite fluxed by hydrous rhyolitic melt at 2-3 GPa: implications for mantle wedge hybridization by sediment melt and generation of ultrapotassic magmas in convergent margins

机译：2-3 GPa含水流纹岩熔体熔解的肥沃橄榄岩的部分融化：沉积物熔体对地幔楔杂交的影响以及会聚边缘超钾质岩浆的产生

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We investigated the melting behavior of peridotite fluxed with 25 wt% of H2O-bearing rhyolitic sediment melt (1.8 wt% bulk H2O), by performing experiments from 1100 to 1300 degrees C at 2 GPa and 1050-1350 degrees C at 3 GPa. The apparent solidus of our bulk composition lies between 1100 and 1150 degrees C at both pressures, which is at a higher temperature than the vapor-saturated solidus and close to the pargasite dehydration solidus of peridotite. With increasing temperature, reacted melt fraction increases from 20 to 36 wt% from 1200 to 1300 degrees C at 2 GPa and 7 to 24 wt% from 1225 to 1350 degrees C at 3 GPa. Orthopyroxene is present as a residual phase in all the experiments, while olivine is present as a residual phase in all the experiments at 2 GPa only. Amphibole is absent above 1100 degrees C at both pressures, clinopyroxene disappears above 1200 and 1300 degrees C at 2 and 3 GPa, respectively, and garnet (only present at 3 GPa) melts out above 1300 degrees C. Upon reaction with the mantle wedge and subsequent melting of the hybrid rock, subducted sediment-derived rhyolites evolve in composition to a nepheline-normative ultrapotassic leucitite, similar in major element composition to ultrapotassic lavas from active arcs such as Sunda and inactive arcs such as in the Roman Magmatic Province. Fluxing peridotite with H2O versus H2O-bearing sediment melt at similar pressures does not appear to have an effect on isobaric melt productivity, but does have significant effect on melting reactions and resultant melt composition, with influx of sediment melt adding K2O to the system, thereby stabilizing phlogopite, which in turn buffers the reacted melt to ultrapotassic compositions. Previous experimental studies, along with this study, find that phlogopite can be stable near the hotter core of the mantle wedge and, hence, is likely to be subducted to deeper mantle, thereby influencing deeper cycling of volatiles and large ion lithophile elements. Also, because D-Rb(phl/melt) D-Sr(phl/melt) and D-Nd(phl/melt), D-Sm(phl/melt) 1, long-term stability of phlogopite in the mantle can create 'enriched mantle' domains (epsilon Sr and epsilon Nd >= 0).
机译：我们通过在2 GPa下从1100到1300摄氏度和在3 GPa下从1050到1350摄氏度进行实验，研究了用25 wt％的含H2O的流纹质沉积物熔体（1.8 wt％的体积H2O）助熔的橄榄岩的熔融行为。在两种压力下，我们的整体组合物的表观固相线都在1100至1150摄氏度之间，该温度高于蒸气饱和固相线的温度，并且接近橄榄岩的复合沸石脱水固相线。随着温度的升高，反应的熔体分数在2 GPa下从1200到1300摄氏度从20到36 wt％，从1225到1350摄氏度在3 GPa增长7到24 wt％。在所有实验中，邻苯二甲酚作为残留相存在，而在所有实验中，橄榄石仅作为残留相存在于2 GPa。在两种压力下，高于1100°C的时候都没有闪石，高于1200和1300°C时在2和3 GPa时，环庚二烯会消失，而石榴石（仅在3 GPa时存在）会在1300°C以上融化。随后混合岩融化，俯冲沉积物衍生的流纹岩的成分演变成霞石型超钾质白云岩，其主要元素成分与来自活跃弧（如Sun他（Sunda））和非活跃弧（如罗马岩浆省）的超钾熔岩相似。在相似的压力下用H2O与含H2O的沉积物熔体熔解橄榄岩似乎对等压熔体生产率没有影响，但对熔解反应和最终的熔体组成有显着影响，沉积物熔体的涌入将K2O添加到系统中，从而稳定的金云母，继而将反应的熔体缓冲成超钾的成分。先前的实验研究以及这项研究发现，金云母在地幔楔的较热核附近可能是稳定的，因此很可能被俯冲到更深的地幔中，从而影响了挥发物和大型离子亲石元素的更深循环。同样，由于D-Rb（phl / melt） D-Sr（phl / melt）和D-Nd（phl / melt），D-Sm（phl / melt） 1，金云母在水中的长期稳定性地幔可以形成“富集的地幔”域（εSr和εNd> = 0）。

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