Trace elements of rutile in eclogites from CCSD main-hole:A LAICPMS study and its implication
CCSD主孔榴辉岩中金红石微量元素特征：LA-ICPMS分析及其意义

Trace elements of rutiles in eight eclogites from 200~1005m of CCSD main-hole were analyzed in-situ by LA-ICPMS. Combined our data with data of eclogites and rutiles from the literature, it is found that trace elements in rutiles from various types of eclogites have different correlations with the whole-rock chemistry. Nb and Ta contents in rutiles are significantly controlled by whole-rock compositions to degrees which in turn depend on the rock types. Cr contents in rutiles from high-Ti as well as low-Mg-Ti eclogites are positively correlated to whole-rock Cr/TiO2 ratios. In contrast, Cr contents in rutiles from Mg-rich eclogites are controlled by whole-rock MgO contents. In high-Ti and Mg-rich eclogites, whole-rock compositions have strong effects on the Zr contents in rutiles, therefore, the Zr-in-rutile thermometer does not yield meaningful temperature information in these rock types. Temperatures from Zr-in-rutile thermometer for the low-Mg-Ti eclogites are usually lower than those in peak metamorphism, which might be caused by diffusion and retrogression with the aid of fluids. In most cases, Zr contents in rutile grains from single sample are homogeneous, Zr-in-rutile temperatures represent the re-equilibrium temperature during retrograde reactions. Nb/Ta ratios of eclogites are generally lower than those in rutiles, which does not support the hypothesis that rutile-eclogite is the hidden reservoir with a superchondritic Nb/Ta ratio within the interior of the earth.