LA-ICP-MS zircon U-Pb dating of monzogranite in Bayintolgoi, Gobi-Altay, Mongolia, and its geological implications

Bayintolgoi region in Mongolia is located in the southern South-Gobi-Altay tectonic zone. In this region, tectonic move-ment is active and intermediate-acidic intrusive rocks are well developed. Analysis of LA-ICP-MS zircon U-Pb ages was conduct-ed for zircons from monzogranite in Bayintolgoi, Mongolia. As revealed by the cathodoluminescence images, all the zircons from monzogranite are euhedral-subhedral and have oscillatory zoning, with almost all the zircons having high Th/U ratios. These charac-teristics suggest a magmatic genesis of the analyzed zircons. 30 zircons yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 300.2± 0.9Ma. The results show that the monzogranite was formed in Upper Carboniferous and there existed a tectonic-magmatic event in the Middle Variscan. These data provide new evidence for the Upper Carboniferous orogeny in South-Gobi-Altay tectonic zone.