Geochronology for the multiple-stage metamorphism of high-pressure terrane of granulite fades from Yushugou area, south Tianshan.

A detailed investigation of mineralogy and petrology on amphiboles demonstrates that the granulite terrane of Yushugou underwent a four-stage metamorphism, i. e. , high-pressure granulite facies, medium-pressure granulite facies, amphibolite facies and greenschist facies. The sequence and the features of the metamorphism in each stage are concluded in the paper. The 40Ar- 39Ar dating obtains a plateau age of 368. 2±4. 8Ma and an isochron age of 360±10Ma. The Sm-Nd mineral-rock isotopic dating gets an isochron age of 310±5Ma by using Gra + Pl + Ilm + whole rock assemblage. Based on the dating results in this paper and literatures, the 40Ar- 39Ar age is probably the peak-stage age of high-pressure granulite facies of Yushugou terrane while the Sm-Nd age is a retrograde age of medium-pressure granulite facies. The homogenization and block temperatures of isotopes in the multiple-stage metamorphism are also mentioned in the paper.