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首页> 外文期刊>Contributions to Mineralogy and Petrology >Interpreting titanite U-Pb dates and Zr thermobarometry in high-grade rocks: empirical constraints on elemental diffusivities of Pb, Al, Fe, Zr, Nb, and Ce
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Interpreting titanite U-Pb dates and Zr thermobarometry in high-grade rocks: empirical constraints on elemental diffusivities of Pb, Al, Fe, Zr, Nb, and Ce

机译：在高档岩石中解释二岩U-PB日期和Zr热量测定法：PB，Al，Fe，Zr，Nb和Ce元素扩散性的经验约束

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摘要

Length scales of compositional heterogeneity in titanite from 750 to 1000 degrees C metamorphic rocks from southern Madagascar were measured to provide empirical constraints on elemental diffusivities. The calculated Pb diffusivity is comparable to experimental estimates of Sr diffusivity; because of this, U-Pb dates from rocks that reached peak temperatures<850 degrees C should be interpreted as the time of titanite (re)crystallization, not cooling ages. The length scales of Zr diffusion are negligible (<20 mu m), even at T>900 degrees C; thus, Zr-in-titanite thermobarometry should not be reset by diffusion in all but the smallest grains in the hottest rocks. Al and Nb diffuse at similar rates to Zr. Ce and Fe diffuse slower than Pb, but faster than Zr. Differences in empirical and experimental estimates of elemental diffusivities might be related to the complexity of most natural titanite solid solutions compared to the near-end-member titanite used in experiments.
机译：测量来自马达加斯加南部750至1000摄氏度的二氧化钛中的组成异质性的长度尺度，以提供对元素扩散性的经验限制。 计算的PB扩散率与SR扩散率的实验估计相当; 因此，来自达到峰值温度<850℃的岩石的U-Pb日期应该被解释为二钛矿（RE）结晶，而不是冷却年龄的时间。 Zr扩散的长度尺度可忽略不计（<20μm），即使在t> 900℃下也是如此; 因此，Zr-In-Tianite热轨道法不应通过最热的岩石中的所有最小颗粒的扩散重置。 Al和Nb以类似的速率扩散到Zr。 CE和Fe Diffuse比Pb慢，但比Zr更快。 与实验中使用的近端构件钛矿相比，元素扩散性的实证和实验估计的差异可能与大多数天然二钛矿固溶体的复杂性有关。

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