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).