Monazite 10-micron small-beam-spot LA-Q-ICP-MS U-Th-Pb age determination method

Abstract

The invention discloses a monazite 10-micron small-beam-spot LA-Q-ICP-MS U-Th-Pb age determination method. The method includes the steps that a standard solution sample with the concentration of 1 ppb is directly led into a four-level-rod inductively coupled plasma mass spectrometer, the instrument parameters are optimized, the response strength of <205>T1 is larger than 200,000 cps/ppb, the relative standard deviation is 1% to 2%, the double charges are smaller than 1.5%, and the yield of oxidation is smaller than 1%; an artificial glass NTSI 610 solid standard sample is led into the four-level-rod inductively coupled plasma mass spectrometer in a laser ablation mode, carrier gas of a laser and carrier gas of the four-level-rod inductively coupled plasma mass spectrometer are matched, and counting of <238>U reaches the maximum; a monazite standard sample 44069 is led into the four-level-rod inductively coupled plasma mass spectrometer in a laser ablation mode, the density of laser energy is 3 J/cm<2>, the impulse frequency is 4 Hz, and the age of monazite U-Th-Pb is determined through a 10-micron small laser beam spot. By means of the method, the space resolution ratio of monazite LA-Q-ICP-MS U-Th-Pb age determination is increased, and the testing requirement of monazite is met.

Description

technical field [0001] The invention belongs to the technical field of geological testing, and in particular relates to a monazite 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb age determination method. Background technique [0002] Monazite ((LREE,Th)PO 4 ) is a mineral enriched in light rare earths, which widely exists in sedimentary rocks, metamorphic rocks and intermediate-acid igneous rocks, and is also a relatively common hydrothermal accessory mineral. Monazite usually has high Th and U content, low ordinary Pb content and high Pb closure temperature (~750℃), and is a commonly used geological chronometer. What is particularly noticeable is that monazite is sensitive to environmental changes during geological processes, and can easily record hydrothermal activity information. Its composition domains not only record the occurrence times of different geological events, but also can clearly reflect geological processes and The history of hydrothermal activity and its U-Th-P...

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Problems solved by technology

[0004] The purpose of the present invention is to provide a method for measuring the age of monazite 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb, aiming at solving the problem that monazite particles are usually small and have complex component partitions, and the current 32 μm larger beam The spot can only obtain the mixed U-Th-Pb age, the data is inaccurate and meaningless, and even causes wrong geological interpretation, while the 10μm small beam spot will lead to insufficient test sensitivity and poor detection signal stability. At the same time, with As the denudation pit deepens, the detection signal will drop sharply, resulting in a sharp increase in the degree of element fractionation, making it difficult to accurately determine the age of monazite U-Th-Pb

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