Zircon LA-ICP-MS U-Pb dating of amphibolite in the southern margin of Altyn Tagh,China and its geological implication

Altyn Tagh Group is the oldest metamorphosed strata in the Altyn Tagh area. Because of lack of precise isotopic dating, some researchers porposed that this Group formed in Neoproterozoic and there were not existence of Neoarchean to Paleoproterozoic metamorphosed basement in Altyn Tagh area. This paper provides the zircon LA-ICP-MS U-Pb isotopic dating result of the amphibolite from Altyn Tagh Group in the southern margin of Altyn Tagh and discusses its geological significance. The CL images of zircons from the amphibolite show that most of the zircons present the typical characteristics of metamorphic zircons with multi-faceted shape structure and without girdle structure and core-rim structure of magmatic zircons and with lower Th/U ratios. Zircon LA-ICP-MS U-Pb isotopic dating give a weighted mean 207Pb/ 206Pb age of 1827±13Ma(MSWD=4.4), with 207Pb/206Pb ages ranging from(1786±10) Ma to (1877±12) Ma of 19 analysing plots and suggest that the epoch of metamorphism of the amphibolite is Later Paleoproterozoic. The new data of isotopic chronology indicated that there existed a tectothermal event which corresponds to Lüliang orogenic movement in China and maybe related to the converging or breakup event of global Columbia suppercontinent in Paleoproterozoic. The result also indicate that there are Neoarchean-Paleoproterozoic metamorphosed basement in the Altyn Tagh area and provide a new data for research Precambrian teotothermal events and the evolution of Altyn Tagh belt.