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对大别山金河桥超高压榴辉岩中的金红石进行了电子探针微量元素分析,得出其Zr含量为37~118μg·g-1,并且同一薄片内不同颗粒之间的Zr含量存在明显差别.应用压力校正的金红石Zr含量温度计,以压力上限4.1GPa计算得到的温度(595~678℃)仍比石榴石-绿辉石Fe-Mg配分温度(846±70)℃低200~250℃,但是比石英-金红石矿物对氧同位素温度及U-Pb体系封闭温度高150~200℃.这指示,金红石中Zr的扩散速率明显比Pb和O慢,与已知的实验研究结果一致,表明金红石Zr温度高于U-Pb同位素定年体系冷却年龄对应的封闭温度.超高压岩石折返过程中降压扩散和流体参与下的退变质重结晶可能是造成金红石Zr含量降低而没有记录峰期温度的主要因素.金红石粒间Zr含量的显著差别表明,金红石中Zr的配分可能处于差异性扩散和退化不平衡状态.
The electron probe microelement analysis of rutile in the UHH eclogite from the Jinsheqiao Dabie Mountains shows that the Zr content is 37 ~ 118μg · g-1, and there is a significant difference between the Zr content of different particles in the same sheet The temperature (595 ~ 678 ℃) calculated by the pressure-corrected rutile Zr content thermometer with pressure upper limit of 4.1GPa is still 200 ~ 250 ℃ lower than that of the garnet-omphacite Fe-Mg (846 ± 70) ℃, But higher than the oxygen isotope temperature of quartz-rutile minerals and the sealing temperature of U-Pb system by 150 ~ 200 ℃, which indicates that the diffusion rate of zirconium in rutile is obviously slower than that of Pb and O. This is consistent with the known experimental results that rutile The Zr temperature is higher than the sealing temperature corresponding to the cooling age of the U-Pb isotopic dating system.The depressurization diffusion and the degenerated recrystallization under the hydrofracturing of UHP rocks may be the main reason for the decrease of Zr content of rutile without recording the peak temperature Factors. Significant differences in the intergranular Zr content of rutile suggest that the partitioning of Zr in rutile may be in a state of differential diffusion and degradation.