Abstract:

Gailike gneiss, located in the Yaganbuyang-Paxialayidang area at the Azhong Block, is composed mainly of augen biotite plagioclase gneiss and two-mica monzonitic gneiss. The U-Pb dating of zircons from the gneiss using LA-ICP-MS yields an age of (886.5 ±5)Ma, which indicates the protolith of Gailike gneiss was generated at Early Neoproterozoic era. The geochemical analysis shows that major element characterized by high SiO₂, Al₂O₃ and K₂O+Na₂O contents, and low Na₂O, MgO, CaO and TiO₂ contents. A/CNK from 1.03 to 1.17, which suggest that the protolith belongs to the typical high-K calc-alkaline series with peraluminous. The protolith is riched in large ion lithophile elements of Rb, Th, K and depleted in high field strength elements of Nb, Ta, Sr, P, Hf, Ti. These characteristics are similar to values of the continental collision type granite. REE distribution patterns show negative anomaly of Eu, distinct enrichments in LREE relative to HREE. The chondrite-normalized REE patterns are rightinclined, with a clear V trough. The protolith of the gneiss was mainly from the melting of basaltic rocks in crust and generated in the syn-collisional environment. These features indicate the existence of Early Neoproterozoic tectonomagmatic activity in Altyn Tagh area, and was related to the formation of the Rodinia supercontinent. It means that a collision and convergence between the Qaidam microplate and the Tarim Plate had taken place during the Neoproterozoic time.

Key words: Gailike gneiss, LA-ICP-MS zircon U-Pb dating, geochemistry, Rodinia supercontinent, Altyn Tagh