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首页> 外文期刊>The American mineralogist >Accurate predictions of microscale oxygen barometry in basaltic glasses using V K-edge X-ray absorption spectroscopy: A multivariate approach
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Accurate predictions of microscale oxygen barometry in basaltic glasses using V K-edge X-ray absorption spectroscopy: A multivariate approach

机译：使用V K-Edge X射线吸收光谱法测定玄武岩玻璃中微米氧气气压测量的准确预测：多变量方法

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Because magmatic oxygen fugacity (f(O2)) exerts a primary control on the discrete vanadium (V) valence states that will exist in quenched melts, V valence proxies for f(O2), measured using X-ray absorption near-edge spectroscopy (XANES), can provide highly sensitive measurements of the redox conditions in basaltic melts. However, published calibrations for basaltic glasses primarily relate measured intensities of specific spectral features to V valence or oxygen fugacity. These models have not exploited information contained within the entire XANES spectrum, which also provide a measure of changes in V chemical state as a function of f(O2). Multivariate analysis (MVA) holds significant promise for the development of calibration models that employ the full XANES spectral range. In this study, new calibration models are developed using MVA partial least-squares (PLS) regression and least absolute shrinkage and selection operator (Lasso) regression to predict the f(O2) of equilibration in glasses of basaltic composition directly. The models are then tested on a suite of natural glasses from mid-ocean ridge basalts and from Kilauea. The models relate the measured XANES spectral features directly to buffer-relative f(O2) as the predicted variable, avoiding the need for an external measure of the V valence in the experimental glasses used to train the models. It is also shown that by predicting buffer-relative f(O2) directly, these models also minimize temperature-relative uncertainties in the calibration. The calibration developed using the Lasso regression model, using a Lasso hyperparameter value of alpha = 0.0008, yields nickel-nickel oxide (NNO) relative f(O2) predictions with a root-mean-square-error of +/- 0.33 log units. When applied to natural basaltic glasses, the V MVA calibration model generally yields predicted NNO-relative f(O2) values that are within the analytical uncertainty of what is calculated using Fe XANES to predict Fe3+/Sigma Fe. When applied to sa
机译：因为岩浆氧逃逸度（F（O2））在离散的钒（V）价状态上施加初级控制，其将在淬火熔体中存在，V价代理F（O2），使用X射线吸收近边光谱测量（ Xanes）可以提供玄武岩熔体中的氧化还原条件的高敏感测量。然而，对玄武岩玻璃的公开校准主要涉及特定光谱特征的测量强度，以V价或氧气不足。这些模型没有利用包含在整个XANES频谱内的信息，这也提供了作为F（O2）的函数的V化学状态的变化的量度。多变量分析（MVA）对采用全Xanes光谱范围的校准模型的开发具有显着的承担。在该研究中，使用MVA局部最小二乘（PLS）回归和最小绝对收缩和选择操作员（套索）回归来开发新的校准模型，以预测直接玄武岩组合物的玻璃玻璃均线的F（O2）。然后在海洋山脊玄武岩的一套天然眼镜上和基里亚的套房测试这些模型。该模型将测量的XANES光谱特征与缓冲相对F（O2）相关联作为预测变量，避免了在用于训练模型的实验玻璃中的V价值的外部测量。还显示通过直接预测缓冲相对f（O2），这些模型还会最小化校准中的温度相对的不确定性。使用索索回归模型开发的校准，使用alpha = 0.0008的套索超级参数值，产生具有+/- 0.33对数单位的根均方误差的镍 - 氧化镍（NNO）相对f（O2）预测。当应用于天然玄武岩玻璃时，V MVA校准模型通常产生预测的NNO相对F（O2）值，该值在使用Fexanes来预测Fe3 + / Sigma Fe的基础上的分析性不确定性内。当应用于SA时

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