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首页> 外文期刊>The American mineralogist >Modeling of trace elemental zoning patterns in accessory minerals with emphasis on the origin of micrometer-scale oscillatory zoning in zircon
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Modeling of trace elemental zoning patterns in accessory minerals with emphasis on the origin of micrometer-scale oscillatory zoning in zircon

机译：重点对锆石尺度振荡分区起源的附件矿物质中痕量元素分区图案的建模

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摘要

We present a numerical model of trace-element oscillatory zoning patterns formed when zircon crystallizes from silicate melt, which is also appropriate for other accessory phases with known partition and diffusion coefficients and saturation conditions. The model accounts for diffusion-controlled accessory mineral growth and the equilibrium crystallization of major mineral phases. Consideration of recent, experimentally determined dependencies of partition coefficients on temperature, we find that thermal changes provide the simplest explanations of oscillatory zoning in accessory minerals. Numerical experiments with different cooling rates explore different crystallization scenarios with and without the precipitation of other phases and/or the interface reaction of phosphorus (P) and yttrium (Y) to form xenotime. However, these processes are monotonically related to growth rate and do not cause oscillations. Minor 3-10 degrees C variations in temperature do not result in zircon dissolution, but strongly influence zircon growth and lead to variations in coeval Y, Hf, and rare earth element (REE) concentrations of up to a factor of two, comparable to those observed in nature. Such temperature variations may be very common in any igneous body in response to external factors such as replenishment by hotter magmas or convection. More significant temperature fluctuations may result in initial minor dissolution at higher temperatures during a mafic recharge event but with continuous growth afterward. At high temperature (similar to 850 degrees C) the amplitude of oscillations is relatively small that confirms observations of both less common oscillatory zoning in hot and dry volcanic rhyolites and abundant oscillations in plutonic zircons and in zircons in cold and wet crystal-rich mushes. Additional oscillations in zircon are modeled in response to oscillations of pressure on the order of +/- 35-50 bars, causing water concentration fluctuations of +/- 0.1 wt% in wate
机译：我们介绍了当锆熔体结晶时形成的微量元素振荡分区图案的数值模型，其也适用于具有已知分区和扩散系数和饱和条件的其他附件相。该模型占扩散控制的矿物生长和主要矿物阶段的平衡结晶。考虑到近期实验确定的分区系数依赖性在温度下，发现热变化提供了附件矿物中振荡分区的最简单解释。具有不同冷却率的数值实验探讨了不同的结晶情景，并且没有其他阶段的沉淀和/或磷（P）和钇（Y）的界面反应形成Xenotime。然而，这些过程与生长速率单调有关并且不会引起振荡。较小的3-10摄氏度C的温度变化不会导致锆石溶解，但强烈影响锆石生长，并导致符合型Y，HF和稀土元素（REE）浓度高达两倍的浓度，与那些相比在自然界中观察。响应于外部因素，例如通过更热的岩浆或对流，这些温度变化可能在任何火油体中非常常见。在MAFIC充电事件期间，更明显的温度波动可能导致较高温度下的初始较小溶解，但后续增长。在高温（＆类似于850℃）的振幅相对较小，证实了在冷热锆石流离失符和丰富的锆石中和Zircons中的热和干燥的火山脉灰和丰富的振荡振荡的观察糊状物。锆石中的额外振荡是响应于+/- 35-50条的顺序的压力振荡而建模的，导致水中的水浓度波动+/- 0.1wt％

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