TIMS zircon U-Pb isotopic dating of Salazha Mountain granites from the North Margin of Alxa, Inner Mongolia, and its tectonic implications

The Salazha Mountain on the north margin of Alxa Block is situated at the conjunction of North China Block and Tarim Block, or between Enger Us ophiolites belt and Quaganqulu ophiolites belt. To determine its magmatic issues, the authors collected samples from distinct positions of Salazha Mountain so as to conduct TIMS zircon U-Pb isotopic dating. The result shows that the granities were formed during Indosinian period. The ages of the three sampling spots are 233.1± 5.8Ma, 228.1± 0.4Ma, and 207.7± 0.8Ma, representing the formation age of Salatoerhan granodiorite, Wuliji granite and granodiorite, respectively. A comparative analy-sis of the previous geochronologic results indicates that the Salazha granitic batholiths resulted from the superimposition of the follow-ing four magmatic stages, namely late Early Permian(273~274Ma), Early Triassic(248~252Ma), early Late Triassic(228~236Ma)and Late Triassic(207Ma). Theses magmatic activities are also seen in the Bayin-Nuoergong area, which has been taken as the margin of North China Block.