Evidence of former stishovite in UHP eclogite from the South Altyn Tagh, western China

• Published in: Earth and planetary science letters 2018-02, Vol.484, p.353-362
• Main Authors: Liu, Liang, Zhang, Jun-Feng, Cao, Yu-Ting, Green, Harry W., Yang, Wen-Qiang, Xu, Hai-Jun, Liao, Xiao-Ying, Kang, Lei
• Format: Article
• Language: English
• Subjects: eclogite; quartz paramorphs; South Altyn; stishovite; ultra-deep subduction
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2017.12.023

We report here for the first time long prism/needle-shaped polycrystalline quartz aggregates and square/parallelogram-shaped single-phase quartz inclusions in omphacite and garnet of ultrahigh pressure (UHP) eclogite from the Yinggelisayi area in the South Altyn UHP belt. Based on their morphology and mineral composition, these quartz inclusions in omphacite and garnet are quartz paramorphs after stishovite. The minimum peak pressure of the eclogite is estimated to be >8–9 GPa at 800–1000 °C based on the stability field of stishovite. This new evidence, together with previous discovery of kyanite + spineal exsolutions in former stishovite of the pelitic gneiss from the same region, suggests a ultra-deep subduction and exhumation of the South Altyn continental rocks to/from mantle depths in the stability field of stishovite. Evidence of ultra-deep subduction of continental materials might be more common and diverse than previous thought. •Long prism shaped polycrystalline quartz aggregates are found in Omp and Grt of eclogite.•These polycrystalline quartz aggregates are quartz paramorphs after stishovite.•New mineralogical evidence for former stishovite in UHP metamorphic rocks.•The Altyn continental crust subducted to mantle depths in the stability field of stishovite.•Ultra-deep subduction (>300 Km) of continental materials might be more common.