【摘要】 对6个大别山超高压榴辉岩中的粒间金红石进行了显微傅立叶变换红外光谱(Micro-FTIR)观察和电子探针(EMP)分析。结果显示所有金红石颗粒都在3280cm-1和3295cm-1出现强的吸收峰,少数颗粒在约3360cm-1出现较弱且宽的峰,这3组峰都是由金红石中的结构OH引起的。与高温高压合成实验结果比较发现,3280cm-1峰主要是由Ti3++H+Ti4+取代引起的,3295cm-1峰可能是由Fe3++H+Ti4+造成的,而约3360cm-1的峰与Mg2+取代Ti4+的电荷补偿有关。由目前认为较可靠的两个金红石红外吸收系数获得结构水的含量(质量分数)分别为:161×10-6~854×10-6和202×10-6~1075×10-6,不同的IR吸收系数导致计算的水含量相差4~5倍,因此,前人所得到的金红石高水含量可能需要重新评估。与共存的石榴石和绿辉石相似,不同样品间的金红石水含量也表现出不均一分布,指示着超高压过程中有限的流体活动和快速的板块俯冲-折返过程。更多还原

【Abstract】 Intergranular rutiles from six UHP eclogites in the Dabie orogen were investigated by Micro-FTIR and EMP analysis. The results show that all grains show two strong absorbance bands at 3 280 cm-1 and 3 295 cm-1, with an occasional weak and wide absorbance band at ～3 360 cm-1, which are all ascribed to structural OH. Comparisons with the results of HT-HP experiments indicate that the 3 280 cm-1 band is caused by Ti3++H+Ti4+ substitution, the 3 295 cm-1 band is attributed to Fe3++H+Ti4+ substitution, and the ～3 360 cm-1 band is possibly related to Mg2++2H+Ti4+. The calculated water contents (expressed as H2O wt.) based on two reliable IR absorbance coefficients are 161×10-6～854×10-6 and 202×10-6～1 075×10-6 respectively, and the results will increase by about 4～5 times if other absorbance coefficients are applied. Hence the relatively high water content in literature should be considered carefully. Similar to coexisting garnet and omphacite, heterogeneous distribution of water on the outcrop scales in rutiles implies a very limited fluid mobility during UHP metamorphism and a quick subduction and exhumation process.更多还原