Method for uranium lead dating of baddeleyite by using secondary ion mass spectroscopy

Abstract

The invention discloses a method for determining uranium lead age of baddeleyite by using secondary ion mass spectroscopy, which belongs to the field of secondary ion mass spectroscopy dating method in geochronology and particularly relates to a method applied to a large secondary ion mass spectrometer having oxygen blowing conditions. In the measurement method described by the invention, the degree of vacuum in a sample cavity of the spectrometer is enabled to reach 1E-8Torr at first, and an oxygen leak valve is then opened to blow the oxygen with the purity of 99.99% to the surface of the sample so that the oxygen partial pressure of the sample cavity reaches 1E-5Torr. The method of the invention can reduce the optical axis effect, which is exhibited by secondary ion mass spectroscopy during the uranium-lead dating of baddeleyite, to be below 2%, thus the accuracy of uranium-lead age when the baddeleyite is subjected to secondary ion mass chromatographic analysis is significantly improved. After uranium-lead measurement ratio is obtained, uranium-lead fractionation correction is performed by adopting a linear relation between ln(Pb+ / U+) and ln(UO2+ / U+) in order to obtain accurate age.

Description

technical field [0001] The invention relates to a method for determining the age of baddeleyite uranium-lead by using a secondary ion mass spectrometer (SIMS), and belongs to the category of secondary ion mass spectrometry mineral dating methods in geochronology. Background technique [0002] Secondary ion mass spectrometry is an advanced method for micro-area in situ analysis, which has the advantages of high sensitivity, high spatial resolution and high precision. The accelerated primary ion beam is used to focus and bombard the surface of the sample to be tested, the surface components of the sample are sputtered, and some of the sputtered atoms, molecules and atomic groups are ionized to form secondary ions. After the secondary ions are accelerated by high pressure on the surface of the sample, they enter the mass spectrometer for mass analysis, and the element and isotope information of the sample in the micro area is obtained. When using SIMS analysis, the yields of d...

AI Technical Summary

Problems solved by technology

For baddeleyite, due to its extremely small particles, it is impossible to ensure that the optical axes of all particles have the same orientation during sample preparation, that is, the direction of the SIMS primary ion beam incident on the surface of each sample is different from the direction of the respective optical axes. , the distribution of uranium-lead ratio observed by measuring is too discrete to be suitable for practical application

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