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New chronology of the Ningyuan alkali basalt in southern Hunan,China:Evidence from LA-ICP-MS zircon U-Pb dating
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2010
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Southern HunanMagmatic ProcessEngineeringIgneous PetrogenesisTectonic EvolutionImages.most ZirconsGeologyGeochemistryChemistryGeochronologyPetrologyNingyuan Alkali BasaltEuhedral-subhedral ShapesIgneous PetrologyEarth ScienceNew ChronologyTectonics
The zircons from Ningyuan alkali basalt show euhedral-subhedral shapes and striped absorption on their cathodolumines-cence (CL) images.Most zircons ring with a clear plate, which is the typical structure of basic igneous rocks zircon.The Th/U ratios of Baoanxu Zhongxinpu zircons range from 0.37 to 0.95 , and Baoanxu Lizhaixiang zircons range from 0.43 to 2.53, indicating that they were formed by normal crystallization of magma.U-Pb dating of 20 zircons from Baoanxu Zhongxinpu , and Baoanxu Lizhaixi-ang was made on LA-ICP-MS.The results show that the data of Zhongxinpu 34 zircons cluster around the concordia of 204～221 Ma , yielding a weighted mean 206Pb/238U age of 212.3 Ma±1.7 Ma , and that the data of Lizhaixiang 23 zircons yield a weighted mean 206Pb/238U age of 205.5 Ma±3.0 Ma , which implied that the crystallization of the Ningyuan alkali basalt occurred in Late Triassic.