Abstract
Eclogites from North Qaidam, China is used to constrain the stable sulfide minerals and their composition under UHP condition. Coesite is not found from the studied sample yet, and the garnet has almost homogeneous core (Grs32-35) with lower Grs and higher XMg rim. The outermost core includes Omp (Jd40-42). The P-T path constructed by Zhang et al. (2009) includes decompression heating from Coe stability field (610-700°C, 2.7-3.4GPa). Therefore, it is likely that the outermost core of Grt was formed under UHP condition. The outermost core includes Po+Ccp+Rt and this would be the stable UHP assemblage. Retrogressed matrix contains Py+Ccp+Rt+Ilm. The log[f(S2)]-log[f(O2)] diagram at 2.7GPa, 700 °C constructed after Froese (1977) constrains log[f(S2)] to be -7 to 1, and log[f(O2)] to be below -14.
