金红石Zr温度计在苏鲁-大别榴辉岩研究中的应用：问题讨论

金红石Zr含量温度计在苏鲁-大别超高压榴辉岩中的应用普遍得出了比峰期变质温度明显偏低的温度值。通过对比国内外的研究,并结合岩相学的分析,认为除了超高压可能使金红石对Zr的容纳度降低外,较强的退变质和流体作用下的扩散丢失是造成金红石Zr含量降低的主要原因。同一样品不同金红石颗粒之间Zr含量和温度的显著差别说明金红石与共存锆石和石英之间的Zr配分平衡已受到退变质作用的破坏且未能达到再平衡,金红石Zr含量温度代表的是每个颗粒受不同程度退变质和扩散影响后的某个缓冲状态,其平均温度的地质意义很难界定。只有将金红石的赋存状态、岩相学分析等研究与数据本身的均匀性分析结合起来进行综合判断,才有可能对金红石Zr温度计给出合理解释。

Discussion of the Application of Zr-in-Rutile Thermometer in the Sulu-Dabie UHP Eclogites

Zr-in-rutile geo-thermometer has attracted wide attention and has been used in many cases.However,rutile temperatures derived from Zr-in-rutile thermometry in the Sulu-Dabie UHP eclogites were always lower than metamorphic peak temperatures calculated from other thermometers.In comparison with studies of domestics and overseas,and combining with the petrography observation,we considered that along with effect of the ultrahigh pressure on accommodation of Zr in rutile,retrogressive metamorphism and diffusion loss by fluid activity may be the most important factors that decrease the Zr content in rutiles.Significant differences of Zr content and temperature between different rutiles in an individual sample suggest that the high temperature equilibrium between rutile-zircon-quartz had been break off by the retrogressive metamorphism and could not gain re-equilibrium.Rutile temperature may represent some buffer state of each rutile grain after retrogressive metamorphism and diffusion to various extents;hence it is difficult to define geological meaning of average rutile temperature.Only in combination with occurrence of rutile,petrography observation and data homogeneity analysis,it is very likely to give an reasonable interpretation to the Zr-in-rutile geo-thermometer.