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首页> 外文期刊>Contributions to Mineralogy and Petrology >Rare earth element-SiO_2 systematics of island arc crustal amphibolite migmatites from the Asago body of the Yakuno Ophiolite, Japan: a field evaluation of some model predictions
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Rare earth element-SiO_2 systematics of island arc crustal amphibolite migmatites from the Asago body of the Yakuno Ophiolite, Japan: a field evaluation of some model predictions

机译：日本屋野蛇绿岩浅草的岛弧壳地闪石辉辉岩稀土元素-SiO_2系统：对一些模型预测的现场评估

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摘要

The two most commonly invoked processes for generating silicic magmas in intra-oceanic arc environments are extended fractional crystallization of hydrous island arc basalt magma or dehydration melting of lower crustal amphibolite. Brophy (Contrib Mineral Petrol 156:337-357, 2008) has proposed on theoretical grounds that, for liquids >~65 wt% SiO_2, dehydration melting should yield, among other features, a negative correlation between rare earth element (REE) abundances and increasing SiO_2, while fractional crystallization should yield a positive correlation. If correct, the REE-SiO_2 systematics of natural systems might be used to distinguish between the two processes. The Permian-age Asago body within the Yakuno Ophiolite, Japan, has amphibolite migmatites that contain felsic veins that are believed to have formed from dehydration melting, thus forming an appropriate location for field verification of the proposed REE-SiO_2 systematics for such a process. In addition to a negative correlation between liquid SiO_2 and REE abundance for liquids in excess of -65 % SiO_2, another important model feature is that, at very high SiO_2 contents (75-76 %), all of the REE should have abundances less thanthat of the host rock. Assuming an initial source amphibolite that is slightly LREE-enriched relative to the host amphibo-lites, the observed REE abundances in the felsic veins fully support all theoretical predictions.
机译：在大洋内部弧环境中产生硅质岩浆的两个最常用的过程是含水岛弧玄武岩岩浆的扩展分步结晶或下部地壳闪石的脱水熔融。 Brophy（Contrib Mineral Petrol 156：337-357，2008）从理论上提出，对于>〜65 wt％SiO_2的液体，脱水熔融应产生稀土元素（REE）丰度与SiO_2增加，而分步结晶应产生正相关。如果正确，则可以使用自然系统的REE-SiO_2系统来区分这两个过程。日本雅库诺蛇绿岩中的二叠纪-朝来星体具有闪长岩辉长岩，这些辉长岩含有长英质脉，据信是由脱水熔融形成的，因此形成了一个合适的位置，可以对这种工艺的拟议REE-SiO_2系统进行现场验证。对于超过-65％SiO_2的液体，除了液体SiO_2与REE丰度之间呈负相关关系外，另一个重要的模型特征是，在非常高的SiO_2含量（75-76％）下，所有REE的丰度应小于主岩。假设初始来源的闪石相对于宿主两性闪石略微富集了LREE，在长丝脉中观察到的REE丰度完全支持所有理论预测。

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