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首页> 外文期刊>Contributions to Mineralogy and Petrology >Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids
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Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids

机译：稀土和高场强元素在富铁的斜py和长晶液体之间的分配

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摘要

Rare earth elements are commonly assumed to substitute only for Ca in clinopyroxene because of the similarity of ionic radii for REE~(3+) and Ca~(2+) in eightfold coordination. The assumption is valid for Mg-rich clinopyroxenes for which observed mineral/melt partition coefficients are readily predicted by the lattice strain model for substitution onto a single site (e.g., Wood and Blundy 1997). We show that natural Fe-rich pyroxenes in both silica-undersaturated and silica-oversaturated magmatic systems deviate from this behavior. Salites (Mg# 48–59) in phonolites from Tenerife, ferrohedenbergites (Mg# 14.2– 16.2) from the rhyolitic Bandelier Tuff, and ferroaugites (Mg# 9.6–32) from the rhyolitic Rattlesnake Tuff have higher heavy REE contents than predicted by single-site substitution. The ionic radius of Fe~(2+) in sixfold coordination is substantially greater than that of Mg~(2+); hence, we propose that, in Fe-rich clinopyroxenes, heavy REE are significantly partitioned between eightfold Ca sites and sixfold Fe and Mg sites such that Yb and Lu exist dominantly in sixfold coordination. We also outline a REE-based method of identifying pyroxene/melt pairs in systems withmultiple liquid and crystal populations, based upon the assumption that LREE and MREE reside exclusively in eightfold coordination in pyroxene. Contrary to xpectations, interpolation of mineral/melt partition coefficient data for heavy REE does not predict the behavior of Y. We speculate that mass fractionation effects play a role in mineral/melt lithophile trace element partitioning that is detectable among pairs of isovalent elements with nearidentical radii, such as Y and Ho, Zr and Hf, and Nb and Ta.
机译：稀土元素通常被认为仅能替代次氯吡喃中的Ca，因为离子半径与REE〜（3+）和Ca〜（2+）的八倍配位相似。该假设对于富含Mg的斜茂铁是有效的，对于这些镁，其晶格应变模型可以很容易地预测观察到的矿物/熔体分配系数，以替代到单个位点（例如Wood和Blundy 1997）。我们表明，在二氧化硅不足的岩浆系统和二氧化硅过量的岩浆系统中，天然富铁的辉石均偏离了这种行为。特内里费岛的语音中的盐酸盐（Mg＃48–59），流纹岩Banduffer Tuff的ferrohedenbergites（Mg＃14.2–16.2）和流纹岩响尾蛇Tuff的ferroaugites（Mg＃9.6–32）具有较高的重稀土元素含量位替换。 Fe〜（2+）的六倍配位离子半径明显大于Mg〜（2+）的离子半径。因此，我们提出，在富铁的斜茂铁中，重质稀土元素在八倍的Ca位点与六倍的Fe和Mg位点之间显着分配，使得Yb和Lu主要以六倍的配位形式存在。我们还概述了基于REE的方法，该方法在具有多个液晶和液晶种群的系统中识别辉石/熔体对，这是基于以下假设：LREE和MREE仅存在于辉石中的八重配位。与预期相反，重稀土元素的矿物/熔体分配系数数据的插值不能预测Y的行为。我们推测质量分数效应在矿物/熔体亲石性痕量元素分配中起作用，这在具有几乎相同的等价元素对中可检测到半径，例如Y和Ho，Zr和Hf，以及Nb和Ta。

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