The application of Zr-in-rutile and Zr-in-titanite geothermometers to eclogites from southwestern Tianshan Mountains, Xinjiang
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    Abstract:

    LA-ICP-MS analyses of rutile and titanite from eclogites and veins from high pressure-ultrahigh pressure (HP-UHP) metamorphic belt of southwestern Tianshan Mountains in Xinjiang were carried out for testing the Zr content and calculating the Zr-in-rutile and Zr-in-titanite thermometers. Rutile inclusions in garnet mantle, coexisting with omphacite, have a narrower range of Zr values of 10~20 μg/g. The Zr content of matrix rutiles is higher than that of rutile inclusions in garnet, with Zr values being 30~50 μg/g. Titanite is the retrograde product of rutile. Zr values of titanite are homogeneous between individual grains, even among different samples, concentrated between 3 μg/g and 5 μg/g. The Zr concentrations in rutile from the veins are equivalent to those from the eclogites, or even higher. The Zr concentrations of rutile in vein are 30~60 μg/g. Rutile inclusions in garnet mantle grow in the peak pressure metamorphic stage and Zr-in-rutile thermometers gave the estimated temperature of 480~540℃ at 2.7~3.0 GPa. Matrix rutiles can re-equilibrate easily along with the increase of temperature during retrogression, and record the peak temperature condition of 530~590℃, 2.4~2.7 GPa. Rutiles in high pressure veins grow in eclogite facies metamorphism stage, and the growth temperature of vein rutile is 540~580℃, 1.5~2.1 GPa. Titanite in eclogite is the secondary product of rutile, and reaches equilibrium at about 1.0 GPa. Zr-in-titanite thermometry gave the estimated temperature of 540~560℃, recording the further isothermal decompression process. Combined with the analytical results above, the authors constructed a relatively complete clockwise p-T path, which is consistent with the result of phase equilibrium modeling. Zr in rutile from eclogites and veins can serve as a pressure indicator that suggests that the pressure has a significant effect on the Zr-in-rutile thermometry. In the specific case, combined with detailed petrographic observation and consideration of the pressure, the activity of TiO2 and SiO2, diffusion rate, retrograde metamorphism and fluid effect, Zr-in-rutile and Zr-in-titanite thermometers can give an accurate p-T estimate and p-T path.

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张丽娟,张立飞,2016,金红石和榍石Zr温度计在新疆西南天山榴辉岩中的应用[J].岩石矿物学杂志,35(5):840~854. ZHANG Li-juan, ZHANG Li-fei,2016,The application of Zr-in-rutile and Zr-in-titanite geothermometers to eclogites from southwestern Tianshan Mountains, Xinjiang[J]. Acta Petrologica et Mineralogica,35(5):840~854.

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History
  • Received:May 24,2016
  • Revised:June 12,2016
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  • Online: September 23,2016
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