A Method for Determination of La-q-icp-ms U-Th-Pb Age of Monazite 10μm Small Beam Spots

Abstract

The invention discloses a method for measuring the age of monazite 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb. First, a standard solution sample with a concentration of 1 ppb is directly introduced into a quadrupole inductively coupled plasma mass spectrometer, and the Optimize the instrument parameters so that the response intensity of 205Tl is greater than 200,000cps / ppb, the relative standard deviation is 1% to 2%, the double charge is less than 1.5%, and the oxide yield is less than 1%; and then the artificial glass NIST 610 solid standard is introduced by laser ablation The sample is sent to the quadrupole inductively coupled plasma mass spectrometer, matching the carrier gas of the laser and the carrier gas of the quadrupole inductively coupled plasma mass spectrometer, so that the count of 238U reaches the highest; and then the monazite standard sample 44069 is introduced by laser ablation To the quadrupole inductively coupled plasma mass spectrometer, the laser energy density used is 3J / cm2, the pulse frequency is 4Hz, and the monazite U‑Th‑Pb age is determined with a small laser beam spot of 10 μm. The invention greatly improves the spatial resolution of the monazite LA-Q-ICP-MS U-Th-Pb age determination, and meets the monazite test requirements.

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...

AI Technical Summary

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

Images