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 determine U-238,U-234,Th-232,Th-230 concentrations and their rat ios in whole rocks and minerals separated from Quaternary Maanshan, Dayings han and Heikongshan volcanic rocks of Tengchong volcanic field,Yunnan Provi nce, China. The U-238-Th-230 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). Th e 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 t hat the HP-TIMS method is reliable and has high precision. Besides, a proce dure of HP-TIMS analysis of young volcanic rocks in China is set up prelimi narily.