Fig. 2. (a) Location of the Altyn Tagh. (b) Geological map of the Altyn Tagh orogen (modified after Liu et al., 2002). (c) Detailed geological map of the study area showing sampling locations.
The Yinggelisayi area is located in the eastern part of the South Altyn HP-UHP metamorphic belt, near the Altyn Fault (Fig. 2b). Interlayered garnet lherzolite, garnet pyroxenite, and garnet-bearing granitic gneiss (Fig. 3a–b) form a complex lens that is 2500 m long (E-W) and 800 m wide (N-S) (Fig. 2c). The long axis of the lens and lineation in the garnet lherzolites are consistent with the gneissosity that strikes ~280° (Fig. 3c). Previous studies have shown that the Yinggelisayi garnet lherzolites have experienced UHP metamorphism. Liu et al. (2005) observed clinopyroxene exsolution in garnet from the garnet pyroxenites and proposed that the peak metamorphic conditions were >7 GPa/ ~1000°C. Dong et al. (2019) determined the peak metamorphic pressure of the mafic granulites to be 4–7 GPa based on phase equilibria. Dong et al. (2020) identified pigeonite exsolution along the (401) plane in clinopyroxene in garnetite, which constrains the minimum metamorphic conditions to 6.5–7.0 GPa/ 990°C. Liu et al. (2002) and Wang et al. (2011) used thermobarometry to constrain the metamorphic P–T conditions of the garnet lherzolites to 3.8–5.1 GPa/ 880–970°C, and 4.2–6.0 GPa/920–990°C, respectively. The Yinggelisayi garnet lherzolites also experienced HP granulite- and amphibolite-facies retrograde metamorphism (Liu et al., 2012, 2015; Gai et al., 2022).