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Crystallization thermometers for zircon and rutile

机译：锆石和金红石结晶温度计

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摘要

Zircon and rutile are common accessory minerals whose essential structural constituents, Zr, Ti, and Si can replace one another to a limited extent. Here we present the combined results of high pressure–temperature experiments and analyses of natural zircons and rutile crystals that reveal systematic changes with temperature in the uptake of Ti in zircon and Zr in rutile. Detailed calibrations of the temperature dependencies are presented as two geothermometers—Ti content of zircon and Zr content of rutile—that may find wide application in crustal petrology. Synthetic zircons were crystallized in the presence of rutile at 1–2 GPa and 1,025–1,450°C from both silicate melts and hydrothermal solutions, and the resulting crystals were analyzed for Ti by electron microprobe (EMP). To augment and extend the experimental results, zircons hosted by five natural rocks of well-constrained but diverse origin (0.7–3 GPa; 580–1,070°C) were analyzed for Ti, in most cases by ion microprobe (IMP). The combined experimental and natural results define a log-linear dependence of equilibrium Ti content (expressed in ppm by weight) upon reciprocal temperature: $$log ({text{Ti}}_{{{text{zircon}}}}) = (6.01 pm 0.03) - frac{{5080 pm 30}}{{T;(hbox{K})}}.$$ In a strategy similar to that used for zircon, rutile crystals were grown in the presence of zircon and quartz (or hydrous silicic melt) at 1–1.4 GPa and 675–1,450°C and analyzed for Zr by EMP. The experimental results were complemented by EMP analyses of rutile grains from six natural rocks of diverse origin spanning 0.35–3 GPa and 470–1,070°C. The concentration of Zr (ppm by weight) in the synthetic and natural rutiles also varies in log-linear fashion with T −1: $$log ({text{Zr}}_{{{text{rutile}}}}) = (7.36 pm 0.10) - frac{{4470 pm 120}}{{T;(hbox{K})}}.$$ The zircon and rutile calibrations are consistent with one another across both the synthetic and natural samples, and are relatively insensitive to changes in pressure, particularly in the case of Ti in zircon. Applied to natural zircons and rutiles of unknown provenance and/or growth conditions, the thermometers have the potential to return temperatures with an estimated uncertainty of ±10 ° or better in the case of zircon and ±20° or better in the case of rutile over most of the temperature range of interest (∼400–1,000°C). Estimates of relative temperature or changes in temperature (e.g., from zoning profiles in a single mineral grain) made with these thermometers are subject to analytical uncertainty only, which can be better than ±5° depending on Ti or Zr concentration (i.e., temperature), and also upon the analytical instrument (e.g., IMP or EMP) and operating conditions.
机译：锆石和金红石是常见的辅助矿物，其基本结构成分Zr，Ti和Si可以在一定程度上相互替代。在这里，我们介绍了高压-高温实验以及对天然锆石和金红石晶体的分析的综合结果，揭示了锆石中Ti和金红石中Zr吸收随温度的系统变化。温度相关性的详细校准以两个地热仪表示-锆石中的Ti含量和金红石中的Zr含量-可能在地壳岩石学中得到广泛应用。在存在金红石的情况下，合成的锆石在1–2 GPa和1,025–1,450°C下从硅酸盐熔体和水热溶液中结晶，并通过电子探针（EMP）分析所得晶体的Ti。为了扩大和扩展实验结果，在大多数情况下，通过离子微探针（IMP）分析了由5个天然岩石制成的锆石，其中5个天然岩石具有良好的约束但来源广泛（0.7–3 GPa； 580–1,070°C）。实验结果和自然结果的组合确定了平衡Ti含量（以重量ppm表示）对温度的对数线性依赖性：$$ log（{text {Ti}} _ {{{text {zircon}}}}} = （6.01 pm 0.03）-压裂{{5080 pm 30}} {{T;（hbox {K}）}}。$$在类似于锆石的策略中，在锆石和石英的存在下生长了金红石晶体（或含水硅质熔体）在1–1.4 GPa和675–1,450°C下，并通过EMP分析Zr。对EMP分析的结果得到了补充，该EMP分析来自六种不同来源的天然金红石晶粒，其跨度为0.35–3 GPa和470–1,070°C。合成金红石和天然金红石中Zr的浓度（重量ppm）也以对数线性方式随T -1 而变化：$$ log（{text {Zr}} _ {{{text {rutile}} }}）=（7.36 pm 0.10）-frac {{4470 pm 120}} {{T;（hbox {K}）}} .. $$锆石和金红石标定在合成样品和天然样品中彼此一致，并且对压力变化相对不敏感，尤其是在锆石中的Ti情况下。应用于来源和/或生长条件未知的天然锆石和金红石时，温度计具有返回温度的潜力，锆石的不确定度估计为±10°或更高，而金红石型则为±20°或更高。感兴趣的大多数温度范围（约400–1,000°C）。用这些温度计估算的相对温度或温度变化（例如，根据单个矿物颗粒的分区分布）仅受分析不确定性的影响，取决于Ti或Zr浓度（即温度），其不确定性可能优于±5°。 ，以及分析仪器（例如IMP或EMP）和操作条件。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2006年第4期|413-433|共21页
  • 作者

    E. B. Watson; D. A. Wark; J. B. Thomas;

  • 作者单位

    Department of Earth Environmental Sciences Rensselaer Polytechnic Institute;

    Department of Earth Environmental Sciences Rensselaer Polytechnic Institute;

    Department of Earth Environmental Sciences Rensselaer Polytechnic Institute;

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