Parameterized lattice strain models for REE partitioning between amphibole and silicate melt
Parameterized lattice strain models for REE partitioning between amphibole and silicate melt
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DOI：
10.2138/am-2017-6110
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发表时间：
2015-12
影响因子：
3.1
通讯作者：
K. Shimizu;Yan Liang;Chenguang Sun;C. Jackson;A. Saal
中科院分区：
文献类型：
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作者：
K. Shimizu;Yan Liang;Chenguang Sun;C. Jackson;A. Saal
摘要 稀土元素 (REE) 在角闪石和硅酸盐熔体之间的分布对于了解岩石圈中各种火成岩和变质过程非常重要。在本研究中，我们使用已发表的角闪石和硅酸盐熔体之间的稀土元素和 Y 实验实验数据、晶格应变模型和非线性最小二乘回归方法，将晶格应变模型中的关键分配参数（D0、r0 和 E）参数化为压力、温度以及角闪石和熔体成分的函数。本研究获得了两个模型，它们给出了几乎相同的结果。在第一个模型中，D0 取决于温度和角闪石成分：它与 Ti 含量正相关，与温度和角闪石中 Mg、Na 和 K 含量负相关。在第二个模型中，D0 仅取决于熔体成分：它与熔体中的 Si 含量呈正相关，与熔体中的 Ti 和 Ca 含量呈负相关。在矿物和熔体成分模型中，r0 与角闪石 M4 位点的铁镁质含量呈负相关，E 是常数。两个模型中 r0 方程中的系数和 E 的最佳拟合值非常相似，使我们能够通过角闪石-熔融相平衡连接这两个模型。我们的模型对地幔捕虏体中的角闪石的应用表明，仅观察到角闪石中主要元素组成的变化就可以引起角闪石熔体稀土元素分配系数的数量级变化。结合模拟弧岩浆分步结晶的实验数据，我们的模型表明：（1）在弧岩浆结晶过程中，由于角闪石和熔体的温度和成分的变化，角闪石和熔体之间的稀土元素分配系数可以变化一个数量级；（2）角闪石分步结晶在消耗弧岩浆中相对于重稀土元素和轻稀土元素的中稀土元素方面起着关键作用。
Abstract The distribution of rare earth elements (REEs) between amphibole and silicate melt is important for understanding a wide variety of igneous and metamorphic processes in the lithosphere. In this study, we used published experimental REE and Y partitioning data between amphibole and silicate melt, the lattice strain model, and nonlinear least-squares regression method to parameterize key partitioning parameters in the lattice strain model (D0, r0, and E) as a function of pressure, temperature, and both amphibole and melt compositions. Two models, which give nearly identical results, are obtained in this study. In the first model, D0 depends on temperature and amphibole composition: it positively correlates with Ti content and negative correlates with temperature and Mg, Na, and K contents in the amphibole. In the second model, D0 depends solely on the melt composition: it positively correlates with Si content and negatively correlates with Ti and Ca contents in the melt. In both the mineral and melt composition models, r0 negatively correlates with the ferromagnesian content in the M4 site of the amphibole, and E is a constant. The very similar coefficients in the equations for r0 and best-fit values for E in the two models allow us to connect the two models through amphibole-melt phase equilibria. An application of our model to amphiboles in mantle xenoliths shows that observed major element compositional variations in amphibole alone can give rise to order of magnitude variations in amphibole-melt REE partition coefficients. Together with experimental data simulating fractional crystallization of arc magmas, out models suggest that: (1) REE partition coefficients between amphibole and melt can vary by an order of magnitude during arc magma crystallization due to variation in the temperature and composition of the amphibole and melt, and that (2) amphibole fractional crystallization plays a key role in depleting the middle REEs relative to heavy REEs and light REEs in arc magmas.