内蒙古大石寨组英安岩锆石LA-ICP-MS U-Pb定年及其地质意义

ianshizhai Formation volcanic rocks has a big difference between its age and tectonic setting. A combined study of cathodoluminescence images (CL), in situ LA-ICP-MS U-Pb isotope dating and trace element analysis were carried out for zircons from the dashizhai dacite. The zircon LA-ICP-MS U-Pb analysis shows that the zircons are of typical magmatic origin with oscillatory zoning, higher concentrations of Th, U, and REE. Th/U ratios ranging from 0.51 to 1.57. Chondrite-normalized REE were loss of light rare earth elements and significant enrichment of heavy rare earth elements, has a strong positive Ce anomaly and negative Eu anomalies strongly, shows these zircons are magmatic in origin. 22 measuring points weighted average age (313 ± 2) Ma (MSWD = 2.8). The zircon U-Pb results represent the formation age of Dianshizhai Formation volcanic rocks. Combined with data made by previous works leads to the recognition that the Dashizhai Formation volcanic rocks were formed in the chasmic basin. And the Late Paleozoic sedimentary rocks which have chasmic basin characteristic were developed on chasmic basis.