Application of Ti-in-zircon and Zr-in-rutile thermometers to constrain high-temperature metamorphism in eclogites from the Dabie orogen, central China
Application of Ti-in-zircon and Zr-in-rutile thermometers to constrain high-temperature metamorphism in eclogites from the Dabie orogen, central China
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应用锆石钛和金红石锆温度计抑制大别造山带榴辉岩高温变质作用
DOI：
10.1016/j.gr.2013.10.011
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发表时间：
2015
影响因子：
6.1
通讯作者：
Rolfo F.
中科院分区：
文献类型：
--
作者：
Deng Liangpeng;Gu Xiaofeng;Groppo C.;Rolfo F.
中国中部大别造山带北部的超高压（UHP）榴辉岩在三叠纪大陆深俯冲和随后的折返过程中经历了复杂的变质演化。榴辉岩在折返过程中受到多次减压和重结晶过程的强烈影响，因此使得峰值变质条件的确定特别具有挑战性。最近校准的锆石钛温度计和金红石锆温度计提供了估计峰值和峰值后温度的新工具。锆石 UHP 矿物域内的金红石的 Zr 含量为 1030−4310 ppm，记录温度范围为 880−1080 °C，峰值温度为 970 °C。高压 (HP) 含矿物域内的金红石含有 800−5800 ppm 的 Zr 含量，温度范围为 780−1030 °C，平均值为 873 °C。麻粒岩相矿物锆石边缘中的金红石产生的温度为 845 °C。相比之下，石榴石中的金红石内含物的 Zr 含量较低，为 100−800 ppm，产生的温度较低为 600−850 °C。锆石的 UHP 和 HP 矿物地幔域的 Ti 含量为 2.15–97.8 ppm，锆石中 Ti 的温度为 620−1020 °C。锆石边缘区域的 Ti 含量较低（< 7 ppm），表明温度为 650−700 °C，但两个麻粒岩相过度生长边缘的温度为 793−840 °C。因此，变质锆石不同区域的大多数温度都< 800 °C，一般在 650 ± 50 °C 左右。对于锆石的 UHP 和 HP 域，很少有温度测量值 > 900 °C。因此，本研究结合之前发表的数据表明，该地区的榴辉岩经历了从超高压榴辉岩相到高压麻粒岩相变质阶段的长期高温（HT）变质演化。这种长期的高温演化加上缓慢的冷却和部分熔化可能解释了该地区罕见的超高压痕迹的保存。石榴石和锆石中的高压/超高压矿物包裹体经历了不同程度的减压分解或退化。因此，石榴石和锆石中的锆石中的Ti浓度和金红石中的Zr浓度也可能通过重结晶或部分熔融而发生强烈改变。因此，只有少数锆石记录了它们的实际结晶温度。相比之下，锆石中的金红石包裹体通常限定更高的温度。因此，我们认为锆石中的金红石包裹体是最适合进行 HT 估计的候选物，特别是在强烈退变的榴辉岩中。
Ultrahigh-pressure (UHP) eclogites from the northern Dabie orogen, central China underwent a complex metamorphic evolution during Triassic continental deep subduction and subsequent exhumation. The eclogites were strongly affected by multiple decompression and re-crystallization processes during exhumation, thus making the determination of peak metamorphic conditions particularly challenging. The recently calibrated Ti-in-zircon and Zr-in-rutile thermometers provide new tools to estimate the peak and post-peak temperatures. Rutiles within UHP mineral-bearing domains of zircon have Zr contents of 1030−4310 ppm and record a temperature range of 880−1080 °C, with a peak at 970 °C. Rutiles within high-pressure (HP) mineral-bearing domains contain Zr contents of 800−5800 ppm and define a temperature range of 780−1030 °C with an average value of 873 °C. Rutiles in granulite-facies mineral-bearing rims of zircon yield a temperature of 845 °C. In contrast, rutile inclusions within garnet have lower Zr contents of 100−800 ppm, yielding lower temperatures of 600−850 °C. The UHP and HP mineral-bearing mantle domains of zircon have Ti contents of 2.15–97.8 ppm, yielding Ti-in-zircon temperatures of 620−1020 °C. Ti contents in the rim domains of zircon are low (< 7 ppm), indicating a temperature of 650−700 °C, except for two granulite-facies overgrowth rims which yield a temperature of 793−840 °C. Thus, most of the temperatures for different domains of metamorphic zircons are < 800 °C and generally lie around 650 ± 50 °C. Few measures of temperature are the > 900 °C for the UHP and HP domains of zircon. Therefore, this study combined with the previously published data suggests that the eclogites in the region experienced a protracted high-temperature (HT) metamorphic evolution from UHP eclogite-facies to HP granulite-facies metamorphic stages. This long-lived HT evolution coupled with slow cooling and partial melting may explain the rare preservation of UHP traces in the area. HP/UHP mineral inclusions in garnet and zircon experienced variable degrees of decompression breakdown or retrogression. Therefore, also Ti concentrations in zircons and Zr concentrations in rutiles within garnet and zircon may have been strongly modified by re-crystallization or partial melting. As a result, only few zircons record their actual crystallization temperatures. In comparison, the rutile inclusions in zircon generally define higher temperatures. We therefore suggest that rutile inclusions in zircon are the most suitable candidates for HT estimates, especially in strongly retrogressed eclogites.
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