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首页> 外文期刊>Contributions to Mineralogy and Petrology >Polycrystalline calcite to aragonite transformation kinetics: experiments in synthetic systems
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Polycrystalline calcite to aragonite transformation kinetics: experiments in synthetic systems

机译：多晶方解石到文石的转化动力学：合成系统中的实验

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The kinetics of the calcite to aragonite transformation have been investigated using synthetic poly-crystalline calcite aggregates, with and without additional minerals present. The reaction progresses as a function of time were measured at four temperature/ pressure conditions: (1) 550 deg C/1.86 GPa; (2) 600 deg C/ 2.11 GPa; (3) 650 deg C/2.11 GPa, and (4) 700 deg C/ 2.29 GPa. Experiments reveal that Mg-calcite and Fe-calcite transforms to aragonite at considerably slower rates than pure calcite, and that Sr-bearing calcite and calcite + quartz aggregates transform at significantly higher rates than pure calcite. The reaction progresses vs. time data for pure calcite were fitted to Cahn's grain-boundary nucleation and interface-controlled growth model. Evidence for interface-controlled growth is pro-vided by petrographic observations of grain boundaries. The activation energy for aragonite growth from the synthetic polycrystalline calcite determined in this study is significantly lower than that previously determined from a natural marble. The discrepancy in rates and activation energy may be attributed to the nature of grain boundaries, to deformational strain or the presence of impurities in the studied samples, and likely to uncertainties in experimental conditions. The results of this study imply that the variation of local petrologic conditions, in addition to temperature, pressure and grain size, may play an important role in determining the rates for the calcite to aragonite transformation in nature.
机译：方解石向文石转变的动力学已使用合成的多晶体方解石聚集体进行了研究，有无其他矿物存在。在四个温度/压力条件下测量反应随时间的变化：（1）550℃/ 1.86 GPa; （2）600摄氏度/ 2.11 GPa; （3）650摄氏度/2.11 GPa，（4）700摄氏度/ 2.29 GPa。实验表明，Mg-方解石和Fe-方解石以比纯方解石慢得多的速率转变为文石，而含Sr的方解石和方解石+石英聚集体的转化率明显高于纯方解石。将纯方解石的反应进度与时间数据拟合为Cahn的晶界成核和界面控制的生长模型。界面观察生长的证据是由晶界的岩石学观察提供的。在这项研究中确定的合成多晶体方解石对文石生长的活化能明显低于以前从天然大理石中测定的活化能。速率和活化能的差异可能归因于晶粒边界的性质，所研究样品中的形变应变或杂质的存在以及实验条件的不确定性。这项研究的结果表明，除了温度，压力和晶粒尺寸外，当地岩石学条件的变化可能在确定自然中方解石向文石转化的速率方面也起着重要作用。

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