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首页> 外文期刊>Contributions to Mineralogy and Petrology >Differences in grain growth of calcite: a field-based modeling approach
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Differences in grain growth of calcite: a field-based modeling approach

机译：方解石晶粒长大的差异：基于场的建模方法

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Normal grain growth of calcite was investigated by combining grain size analysis of calcite across the contact aureole of the Adamello pluton, and grain growth modeling based on a thermal model of the surroundings of the pluton. In an unbiased model system, i.e., location dependent variations in temperature-time path, 2/3 and 1/3 of grain growth occurs during pro- and retrograde metamorphism at all locations, respectively. In contrast to this idealized situation, in the field example three groups can be distinguished, which are characterized by variations in their grain size versus temperature relationships: Group I occurs at low temperatures and the grain size remains constant because nano-scale second phase particles of organic origin inhibit grain growth in the calcite aggregates under these conditions. In the presence of an aqueous fluid, these second phases decay at a temperature of about 350 ℃ enabling the onset of grain growth in calcite. In the following growth period, fluid-enhanced group II and slower group III growth occurs. For group II a continuous and intense grain size increase with T is typical while the grain growth decreases with T for group III. None of the observed trends correlate with experimentally based grain growth kinetics, probably due to differences between nature and experiment which have not yet been investigated (e.g., porosity, second phases). Therefore, grain growth modeling was used to iteratively improve the correlation between measured and modeled grain sizes by optimizing activation energy (Q), preexponential factor (k_0) and grain size exponent (n). For n = 2, Q of 350 kJ/mol, k_0 of 1.7 * 10~(21) μm~n s~(-1) and Q of 35 kJ/mol, k_0 of 2.5 * 10~(-5) μm~n s~(-1) were obtained for group II and III, respectively. With respect to future work, field-data based grain growth modeling might be a promising tool for investigating the influences of secondary effects like porosity and second phases on grain growth in nature, and to unravel differences between nature and experiment.
机译：方解石的正常晶粒生长是通过将方解石在Adamello岩心接触金极上的粒度分析与基于岩浆环境热模型的晶粒生长模型相结合来进行研究的。在无偏模型系统中，即温度-时间路径中与位置有关的变化中，在所有位置的正变质和逆变质期间分别发生了晶粒生长的2/3和1/3。与这种理想情况相反，在现场示例中，可以区分三组，它们的特征是晶粒尺寸与温度之间的关系变化：第一组出现在低温下，并且晶粒尺寸保持恒定，因为在这些条件下，有机源抑制了方解石聚集体中晶粒的生长。在含水流体的存在下，这些第二相在约350℃的温度下衰减，从而使方解石晶粒开始生长。在随后的生长期中，发生了液流增强的II组和较慢的III组生长。对于第二组，典型的是随着T连续而剧烈地增大晶粒尺寸，而对于第三组，晶粒的增长随着T减小。观察到的趋势均与基于实验的晶粒生长动力学无关，这可能是由于自然与实验之间的差异所致，尚未进行研究（例如，孔隙度，第二相）。因此，晶粒长大建模被用于通过优化活化能（Q），前指数因子（k_0）和晶粒大小指数（n）来迭代地改善测量和建模晶粒之间的相关性。对于n = 2，Q为350 kJ / mol，k_0为1.7 * 10〜（21）μm〜ns〜（-1）和Q为35 kJ / mol，k_0为2.5 * 10〜（-5）μm〜ns分别为组II和III获得〜（-1）。对于未来的工作，基于田间数据的谷物生长模型可能是一种有前途的工具，可用于研究孔隙度和第二相等次要影响对自然谷物生长的影响，并揭示自然与实验之间的差异。

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