High-precision thermal ionization mass spectrometry dating of young volcanic rocks by using U-series method

A high precision thermal ionization mass spectrometric (HP-TIMS) technique is used to determine²³⁸U,²³⁴U,²³²Th,²³⁰Th concentrations and their ratios in whole rocks and minerals separated from Quaternary Maanshan, Dayingshan and Heikongshan volcanic rocks of Tengchong volcanic field, Yunnan Province, China. The²³⁸U-²³⁰Th isochrons are given, yielding four age values (227±20) ka (D-1, Dayingshan), (79.6±5.5) ka (D-7, Dayingshan), (21.9±3.0) ka (h-1, Heikongshan), and (7.5±1.0) ka (M-1, Maanshan). The result is not only consistent with but also preciser than those measured by the K-Ar method and the alpha spectrometry U-series method, indicating that the HP-TIMS method is reliable and has high precision. Besides, a procedure of HP-TIMS analysis of young volcanic rocks in China is set up preliminarily.