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Durham University

Department of Earth Sciences

Profile

Publication details for Professor Yaoling Niu

Zhang, G.B., Zhang, L.F., Song, S.G. & Niu, Yaoling (2009). UHP metamorphic evolution and SHRIMP geochronology of a coesite-bearing meta-ophiolitic gabbro in the North Qaidam, NW China. Journal of Asian Earth Sciences 35(5): 310-322.

Author(s) from Durham

Abstract

We have for the first-time observed the well-preserved coesite inclusions in a kyanite-eclogite from the
Shaliuhe terrane of the North Qaidam ultra-high pressure (UHP) metamorphic belt, NW China. This provides
convincing evidence for UHP metamorphism for the North Qaidam eclogite. Detailed petrography
indicates that the kyanite-eclogite records complex metamorphic histories that can be broadly described
in terms of three stages: (1) a pre-peak metamorphic stage characterized by the mineral assemblage of
Grt + Amp + Pl + Qtz at P = 0.49–0.67 GPa and T = 410–490 C; (2) a peak eclogite-facies stage with a mineral
assemblage of Grt + Omp + Ky + Phn + Rt ± Qtz/Coe at P = 2.7–3.4 GPa and T = 610–700 C; (3) a retrograde
‘‘stage” represented by reaction texture which includes the garnet reaction rims, the breakdown of
omphacite, the symplectitic breakdown of kyanite, the retrograded garnet amphibolite assemblage and
the latest greenschist-facies overprint. Zircon U–Pb SHRIMP dating shows the peak UHP metamorphic
age of the kyanite-eclogite to be 440 Ma. These data indicate that the kyanite-eclogite had ever been
subducted to mantle depth of 100 km in the end of the Ordovician. All these observations allow the construction
of a P-T path for the kyanite-eclogite, suggesting a cold geothermal gradient and rapid subduction,
ultimately followed by rapid exhumation in response to continental collision in Shaliuhe terrane and
throughout the North Qaidam UHP metamorphic belt.