Method for determining age of uranium-lead in zircon by using multi-receive secondary ion mass spectroscopy

Abstract

The method discloses a method for determining the age of a uranium-lead decay system in zircon by using the multi-receive secondary ion mass spectroscopy. In the method described according to the invention, a multi-receiver peak jumping receiving mode is used, so that the age of uranium-lead is measured while the accurate age of lead-lead can be obtained. At least five electron multipliers are required to be used as receivers, wherein three of the receivers simultaneously receive the isotopes of lead, and one of the receivers is used for receiving signals required by calculating the age of uranium-lead. The method is applicable to a situation that the ages of uranium-lead and lead-lead can not be simultaneously and accurately measured by using common methods because of low uranium content or extra-small uranium age.

Description

technical field [0001] The present invention is a method for determining zircon (molecular formula ZrSiO2) by using multi-receiving secondary ion mass spectrometry 4 ) The method of uranium-lead age belongs to the category of geochronological secondary ion mass spectrometer dating method. Background technique [0002] Secondary ion mass spectrometry (SIMS) is an advanced method for in situ analysis of micro-areas. The accelerated primary ion beam is used to focus and bombard the surface of the sample to be measured, the surface components of the sample are sputtered out, and some atoms, molecules and atomic groups are ionized, that is, secondary ions, which enter the mass spectrometer after high-pressure acceleration on the sample surface for analysis , to obtain the element and isotope information of the sample in the micro-area. When performing SIMS analysis, the yields of different elements or isotopes are different, that is, the signal intensity of different elements a...

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Problems solved by technology

[0014] At present, there are generally two methods for determining the age of zircon uranium-lead systems using magnetic SIMS. One is to select a measured element at a certain moment for measurement by changing the magnetic field strength. During the measurement, all measured signals Both use the same receiver. This method can measure all isotopes of uranium and lead. Through multiple sets of data collection, the uranium-lead age and lead-lead age can be obtained. However, due to factors such as integration time, instrument state drift, and primary ion beam instability, etc. The measurement error of lead-lead age is relatively large, and it is generally only suitable for applications above 1000 Ma; another method requires the use of multi-receiver SIMS, and generally at least 4 receivers are required to measure the zircon matrix signal and lead three isotopes, this method can measure 4 signals at the same time, the magnetic field strength does not need to change, the measurement integration time is long, and the influence of the fluctuation of the primary ion beam on the measurement results is reduced, so the lead-lead age with high precision can be obtained, but because there is no Uranium and its oxides are measured, so the result information obtained is too single, and the uranium-lead age cannot be obtained, so it cannot reflect the concordance of the sample, and there may be large differences in data interpretation

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