HF GEOCHEMISTRY OF ZIRCON INCLUSIONS IN RUTILE AND GARNET FROM THE CCSD

Abstract

Except zircons as intergranular grains, zircon inclusions (-10-30 μm) were also found in rutiles as well as garnets in rutile-bearing eclogites recovered from the CCSD main borehole. Backscattered electron (BSE) imaging of such zircons show that they have multi-faceted shape, homogeneous internal structure and weak BSE luminescence. Hf concentrations in these zircons was measured by Energy dispersive spectroscopy (EDS) technique. These data show that these zircons inclusions have (1) relatively high Hf concentrations with HfO2 ranging from 1.51% to 2.45 % in rutile, and 1.77% to 2.13% in garnet, respectively; (2) low Zr/Hf ratio (35.92), significantly lower than the Zr/Hf rate of zircon in mafic protolith. Relatively elevated Hf concentrations and in turn decreased Zr/Hf ratios in these zircon inclusions suggest that they might formed at UHP metamorphic conditions.