摘要

In the area of Muzhaerte, southwestern Tianshan, three types of rocks are exposed in the low-pressure and high-temperature belt, including gneisses, amphibolites and granulites. Due to the effect of anatexis, various sizes of felsic leucosomes appear in the rocks. However, the age of the anatexis forming the felsic leucosomes has not been well constrained. In this paper, petrography and zircon cathodoluminescence image were studied in detail. Different zircon micro areas in three felsic leucosome samples were selected for LA-ICP-MS zircon U-Pb dating to constrain the time of low-pressure and high-temperature belt in the southwestern Tianshan. New growth zircons in the felsic leucosome show planar or weakly oscillatory zonings and low Th/U ratios. The morphological and internal structural features of zircons suggest that their growths were associated with partial melting. The age of anatexis from the felsic leucosome is 276.5 +/- 2.0 Ma, 272.0 +/- 1.7Ma and 265.5 +/- 1.5Ma, representing the formation age of low-pressure and high-temperature belt. The Early to Middle Permian ages correspond to the widespread post-collisional magmatism events in the southwestern Tianshan orogen. Our studies suggest that the southwestern Tianshan orogen have got into post-collision orogenic evolution stage of lithospheric thinning and crustal extension in the Early Permian. On the other hand, we also got a group of inheritable zircons ages of 421.8 +/- 3.2Ma in the anatectic felsic leucosome. This age consists with one of the major peak ages in the host rock sillimanite-garnet-biotite-plagioclase gneiss, and it shows that felsic leucosome could come from partial melting of the sillimanite-garnet-biotite-plagioclase gneiss, corresponding to the magma events of the Late Silurian in South Tianshan.

  • 出版日期2014-10
  • 单位中国地质科学院; 天津地质矿产研究所