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首页> 外文期刊>Contributions to Mineralogy and Petrology >Analysis of experimental data on divalent cation diffusion kinetics in aluminosilicate garnets with application to timescales of peak Barrovian metamorphism, Scotland
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Analysis of experimental data on divalent cation diffusion kinetics in aluminosilicate garnets with application to timescales of peak Barrovian metamorphism, Scotland

机译：铝硅酸盐石榴石中二价阳离子扩散动力学的实验数据分析及其在苏格兰高峰Barrovian变质时间尺度上的应用

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摘要

We present a new statistical framework to analyze the diffusion data for divalent cations (Fe, Mg, Mn, and Ca) in aluminosilicate garnet using published experimental data and an Arrhenius relationship that accounts for dependence on temperature, pressure, garnet unit-cell dimension, and oxygen fugacity. The regression is based on Bayesian statistics and is implemented by the Markov chain Monte Carlo approach. All reported experimental uncertainties are incorporated, and the data are weighted by the precision of the experimental conditions. We also include a new term, the inter-experiment bias, to compensate for possible inconsistencies among experiments and to represent any experimental variability not explicitly presented in the Arrhenius relationship (e.g., water content, defect density). At high temperatures where most experiments were conducted, the diffusion coefficients calculated with the new parameters agree well with previous diffusion models (e.g., Chakraborty and Ganguly in Contrib Mineral Petrol, 111: 74-86, 1992; Carlson in Am Mineral, 91: 1-11, 2006). However, the down-temperature extrapolation leads to notable differences at lower temperatures for common petrological applications. For example, at 600 degrees C, the diffusion coefficients of Fe and Mn are one half-to-one order of magnitude faster and the diffusion coefficient of Ca is about one order of magnitude slower than calculated with parameters in Carlson (2006). Our statistical analysis also provides well-defined uncertainty bounds for timescale estimates based on garnet diffusion profiles. Application of the newly derived coefficients indicates that the timescale of the thermal peak of Barrovian metamorphism (Dalradian belt of Scotland) is about four to seven times longer than that estimated using previously published diffusion coefficients. The peak is still geologically brief, however-of the order of 10(6) years (0.75 Myr +0.70/-0.36 Myr; +/- 1 sigma). This brevity requires pulsed advective heat input, as provided by syn-orogenic mafic magmatism in these rocks.
机译：我们提供了一个新的统计框架，用于使用已发布的实验数据和Arrhenius关系分析铝硅酸盐石榴石中二价阳离子（Fe，Mg，Mn和Ca）的扩散数据，该关系关系到温度，压力，石榴石晶胞尺寸，和氧气逸度。回归基于贝叶斯统计，并通过马尔可夫链蒙特卡洛方法实现。纳入所有报告的实验不确定性，并通过实验条件的精度对数据进行加权。我们还加入了一个新术语，即实验间偏差，以补偿实验之间可能出现的不一致性，并代表未在Arrhenius关系中明确呈现的任何实验变异性（例如，水含量，缺陷密度）。在进行大多数实验的高温下，使用新参数计算的扩散系数与以前的扩散模型非常吻合（例如，Chakraborty和Ganguly in Contrib Mineral Petrol，111：74-86，1992; Carlson in Am Mineral，91：1 2006年11月11日）。但是，低温外推法会导致普通岩石学应用在较低温度下的显着差异。例如，在600摄氏度下，Fe和Mn的扩散系数快一半到一个数量级，而Ca的扩散系数要比用Carlson（2006）中的参数计算的速度慢约一个数量级。我们的统计分析还为基于石榴石扩散曲线的时间尺度估计提供了明确定义的不确定性界限。新推导的系数的应用表明，Barrovian变质（苏格兰的达拉迪安带）的热峰的时间尺度比使用先前发布的扩散系数估计的时间尺度长约四到七倍。但是，该峰值在地质上仍然很短暂-约为10（6）年（0.75 Myr + 0.70 / -0.36 Myr; +/- 1 sigma）。为了简短起见，需要脉冲对流热输入，这是由这些岩石中的造山带镁铁质岩浆作用所提供的。

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