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首页> 外文期刊>Contributions to Mineralogy and Petrology >Hidden melting signatures recorded in the Troodos ophiolite plutonic suite: evidence for widespread generation of depleted melts and intra-crustal melt aggregation
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Hidden melting signatures recorded in the Troodos ophiolite plutonic suite: evidence for widespread generation of depleted melts and intra-crustal melt aggregation

机译：Troodos蛇绿岩深成岩套件中记录的隐藏融化特征：贫化融化物和地壳内融化物聚集的广泛证据

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摘要

The main plutonic complex of the Troodos ophiolite, north of the Arakapas Fault Zone, has been re-examined both from field and geochemical perspectives. Ion microprobe analyses of clinopyroxene crystal cores show that the range of melt compositions added to the lower crust far exceeds that of published lavas in the main Troodos massif. This suggests that the lower crust acted as a filter into which a large range of melt compositions were added and out of which a homogenised (and generally fractionated) derivative was extracted. This crustal-level aggregation homogenised diverse melt fractions from a broad range of degrees of melting. Depleted melts with U-shaped rare earth element (REE) patterns were a significant component of the melts added to the crust, but because of their low incompatible element abundances, mixing with less depleted melts prior to eruption masked their signature in the lavas. The discovery that highly depleted melts constituted a significant component of the melts added to the Troodos crust, but not of the lavas, demonstrates that the spatial distribution of lava-types is not necessarily a good indicator of where different parental melt compositions are generated within the mantle. Compared with normal mid-ocean ridge basalts, the Troodos parental melts were (1) generally depleted in immobile incompatible trace elements, (2) less depleted in light REE (LREE) than would be expected for the concomitant depletion in middle and heavy REE, (3) enriched in Sr with respect to the LREE and (4) more oxidised. Modelling of these characteristics suggests a mantle source that had previously lost a significant melt fraction under relatively reducing conditions. This was followed by remelting under more oxidising conditions in an environment in which Sr and LREE were added to the source consistent with previous models of a supra-subduction zone setting.
机译：阿拉卡帕斯断层带以北的Troodos蛇绿岩的主要深成岩复合体已经从野外和地球化学的角度进行了重新审查。斜辉石晶体核的离子微探针分析表明，添加到下地壳中的熔体成分范围远远超过Troodos断层中已发表的熔岩的范围。这表明下层地壳起着过滤器的作用，向其中加入了大范围的熔体成分，并从中提取出均质的（通常是分馏的）衍生物。这种地壳水平的聚集体从很宽的熔融度范围内均化了各种熔融组分。具有U形稀土元素（REE）模式的贫化熔体是添加到地壳中的熔体的重要组成部分，但由于其不相容元素含量低，在喷发之前与贫化的熔体混合较少，掩盖了它们在熔岩中的特征。高度贫乏的熔体构成了Troodos地壳中熔体的重要组成部分，而不是熔岩的重要发现，表明熔岩类型的空间分布并不一定是指示不同母体熔体成分在何处产生的良好指标。地幔。与正常的洋中脊玄武岩相比，Troodos亲本熔体的贫化程度通常是（1）不相容的不相容微量元素，（2）轻稀土（LREE）的贫化程度要比中等和重稀土的同时耗竭的预期少， （3）相对于LREE富含Sr，并且（4）氧化程度更高。这些特征的模型表明，地幔源以前在相对还原的条件下损失了大量熔体。随后在与以前的超俯冲带环境模型一致的条件下，在将Sr和LREE添加到源中的环境中，在更高的氧化条件下进行重熔。

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