Mineral Compositions and P-T Conditions of the Blueschist-Mica Schist in Heilongjiang Complex

A sequence of middle-high-pressure metamorphic rocks occurs in the Heilongjiang Complex, whose representative lithology is blueschist and mica schist. Characteristic minerals of middle-high-pressure metamorphism, such as glaucophane, ferro-glaucophane and phengite (Si=3.37 to 3.463.30) are observed in the metamorphic rocks. The rock association, blueschist and mica schist, has suffered at least two stages of metamorphism. The P-T conditions are estimated to be 320 to 460 ℃ and 7.8×108 to 11×108 Pa, which correspond to early stage epidote-blueschist facies. The late stage is high-greenschist facies, which is characterized by the replacement of glaucophane and phengite by magnesium-rich (XMg=0.565 to 0.646) chlorite. The metamorphic conditions constrained by garnet mica schist are 536～598 ℃ and 6.8×108 to 9.5×108 Pa, consistent with medium temperature and middle-high pressure metamorphism.