(3) The assemblage Grt₂+Ol₃+Opx₃+Cpx₃+Amp₂+Spl (M₂) occurs in the fine-grained matrix and surrounds or is located in fractures in the coarse-grained minerals. Cpx+Opx+Amp intergrowths are only developed around coarse-grained garnet, and their compositions are almost the same as those in the fine-grained matrix. As such, we infer the intergrown and fine-grained matrix minerals represent the earlier retrograde metamorphic stage. The retrograde metamorphicP–T conditions were estimated to be 1.31–1.80 GPa and 851–893°C by Grt–Opx (Nickel & Green, 1985; Taylor, 1998) and Cr-in-spinel (O’Neill, 1981) barometry, and Opx–Cpx thermometry (Taylor, 1998; Brey & Kohler, 1990), which corresponds to the HP retrograde granulite-facies metamorphism.

(4) The final assemblage comprises Amp₃ that crystallized around the matrix amphibole, which suggests that the garnet lherzolites experienced late retrograde amphibolite-facies metamorphism (M₃). Olivine was not formed during this stage. Phase equilibria modeling of garnet lherzolite using THERMOCALC (Yang et al., 2008) showed that the olivine was not significantly affected by the pressure, but olivine became absent at 450–500°C. Given this temperature range, we infer the pressure was <1 GPa based on the amphibolite facies metamorphic stage of Spear (1993).

5. Olivine fabrics of garnet lherzolite

The Yinggelisayi garnet lherzolites contain relict protolith minerals and three metamorphic mineral assemblages. The relict protolith olivine grains are mostly rounded and undeformed, and were insufficient to obtain an ideal olivine fabric. No recrystallized olivine associated with the retrograde amphibolite-facies metamorphism (M₃) was observed. Thus the olivine fabrics in this two stages were not analyzed. The olivine fabrics of the coarse-grained porphyroblasts associated with M₁ and fine-grained olivine associated with M₂ (Fig. 5a–b) were analyzed in detail. We examined the area of olivine grains of >40,000 μm² for the coarse-grained porphyroblasts (M₁) and create a new subset in Channel 5 program. We examined an area of fine-grained olivine surrounding the garnet, clinopyroxene, and orthopyroxene porphyroblasts of 10,000–30,000 μm² and extracted the olivine size in this range in Channel 5 program for the fine-grained olivine (M₂) to fabric analysis. The results were that the coarse-grained olivine porphyroblasts exhibited as [010] axes sub-normal to the foliation and [001] axes subparallel to the lineation, which is characteristic of the B-type fabric; and the fine-grained olivine showed as [010] axes sub-normal to the foliation and [100] axes subparallel to the lineation, which is characteristic of the A-type fabric (Fig. 9).