In situ trace element geochemistry of single minerals in eclogites from the CCSD main hole (100-1100m).
CCSD主孔100-1100m榴辉岩中单矿物的原位微区微量元素地球化学研究

In situ trace element compositions of single minerals in eclogites from the CCSD main hole(100 - 1100m) were analyzed using LA-ICP-MS. Trace element partitioning between garnet and omphacite suggests that Ti and Co are controlled by Mg( for example, Dco Grt/Omp =3.43dMg Grt/Omp -0. 34), and REE, Sr and Y are controlled by Ca. Concentrations of REE, Pb and Th in omphacite are significantly controlled by presence of apatite. Petrologic and geochemical features suggest that trace element compositions of the minerals formed by retrograde metamorphism were controlled by original minerals, the mineral assemblage and fluid activity. For example, presence of epidote decreased greatly the LREE and Sr concentrations of the coexisting amphibole compared with the omphacite, parent mineral of the amphibole based on the petrologic features; and decomposition of phengite increased Rb and Ba concentrations of amphibole. MREE enrichments in the rim of garnets in several samples imply that the eclogites could suffer a shortlived heating during exhumation based on variations of partition coefficients with temperature and pressure in eclogite, as suggested by overprinting of granulite facies on eclogites and widespread partial melting of UHP rocks in the Sulu UHP terrane. On the other hand, the highly variations of Nb and Ta in rutile could provide additional evidence for the hypothesis that rutile in the eclogite was transformed from Ti-bearing magnetite during UHP metamorphism.