磷灰石 LA-ICP-MS U-Pb 定年直接校准方法研究.

BACKGROUND: Apatite is a common U - bearing accessory mineral with a U - Pb closure temperature of ~500℃, making U - Pb dating of apatite a potentially valuable thermochronometer. However, its low U concentration, high common lead concentration and lack of reference material has limited widespread application to LA-ICP-MS dating. OBJECTIVES: To develop a technique for U-Pb dating of apatite using laser ablation sector field inductively coupled plasma-mass spectrometry (LA-HR-ICP-MS). METHODS: The U-Pb isotope ratio in apatite samples was determined by LA-HR-ICP-MS, with apatite MAD2 as the external standard to correct U - Pb and Pb - Pb elemental fractionation directly without a common Pb correction. RESULTS: Long-term U-Pb analysis of Madagascar apatite sample (MAD2) showed homogeneous distribution of U, Pb and U-Pb isotope ratios, with average contents of U and Pb ~ 23. 8×10 -6 and ~ 13. 5×10 -6, respectively and weighted average 207 Pb / 206 Pb and 206 Pb / 238U ratios of 0. 0941±0. 0006 and 0. 0794±0. 0004, respectively. Taking MAD2 apatite as a reference mineral, combined with 207 Pb-correction method, the ages of apatite samples, McClure Mountain (521±5Ma), Tory-Hill-apt (1021±16Ma), a Durango (30. 7±1. 5Ma) and Fagnshan diorite apatite (~131Ma) can be determined accurately. CONCLUSIONS: The Madagascar apatite sample (MAD2) can be used to calibrate apatite U-Pb isotope ratio measured by LA-ICP -MS directly, without common-Pb correction, similar to the calibration strategy in zircon U-Pb dating. The method greatly reduces the difficulty of data processing during apatite U-Pb dating by LA-ICP -MS, which is conducive to the wide application of the method. [ABSTRACT FROM AUTHOR]