An improved method for determining microscale zircon u-pb ages

Abstract

The present invention belongs to the field of geological dating, and specifically relates to an improved method for determining the U-Pb age of micron-scale sphene. The present invention confirms the matrix effect related to the Fe2O3 content in sphene dating; and after extensive testing, it is found that the TIMS (thermal ionization mass spectrometer) and SIMS (secondary ion mass spectrometry (SIMS)) test results of sphene standard samples are similar. 206 Pb / 238 The U ratio is strongly correlated with the Fe2O3 mass fraction. Based on this, a direct calibration method for unknown samples was established. 206 Pb / 238 Simplified method of U ratio and correction using similar principles 207 Pb / 235 The deviation between the corrected sphene age and the reference age was reduced from 12.3% to 0.4%, indicating that the corrected age result is more accurate. This method can accurately obtain natural sphene with Fe2O3 content between 0.019% and 38.31%, with the advantages of high accuracy and simple calibration process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of geological dating, and particularly relates to an improved method for determining micron-scale titanite U-Pb age. BACKGROUND

[0002] Titanite (CaTiSiO5) is a common uranium-bearing accessory mineral, which is widely distributed in intermediate-acid and alkaline intrusive rocks, metamorphic rocks and various types of hydrothermal deposits. As an important tool for geological dating, it has important application value in the study of rock genesis and evolution process. However, due to the characteristics of multi-stage growth of most titanite minerals and the generally small particle size (usually 5-100 μm, mainly around 10 μm), high-precision in-situ micro-area dating technology is needed to accurately analyze the age information of different stages of titanite.

[0003] At present, the high-precision dating methods of titanite reported internationally mainly include isotope dilution thermal ionization mass spectrometry (ID-TIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS), each of which has its own technical characteristics and limitations.

[0004] ID-TIMS technology needs to dissolve and digest the titanite sample by acid, and then measure the mass spectrum after U and Pb are separated and purified by chromatography. Although this method can obtain high data precision, the pretreatment process is complex and time-consuming (> 2 weeks), which is difficult to meet the analysis needs of a large number of samples. More importantly, as a whole analysis method, ID-TIMS inevitably mixes multi-stage growth components when analyzing titanite with complex zoning structure, and it is difficult to eliminate the interference of U-rich mineral inclusions on the dating results, resulting in a low success rate of conventional solution U-Pb dating. In addition, this method cannot obtain trace element composition information synchronously.

[0005] The LA-ICP-MS technology can directly analyze in-situ in rock thin sections without single mineral sorting. However, due to the limitation of spatial resolution, this method can only effectively measure particles with a diameter greater than 30 μm, and most of the titanite in rocks has a small particle size, so the practical application of this technology is greatly limited.

[0006] In contrast, the secondary ion mass spectrometry (SIMS) technology has the advantages of small sample consumption and long-term repeated analysis. In view of the characteristics of low U content and high ordinary Pb content of titanite, high-precision and high-spatial-resolution ion probe can be used for micro-area in-situ analysis to effectively avoid the interference of inclusions and obtain more reliable dating results. In the prior art, CAMECA 1280 type ion probe is used to establish the measurement of lead and uranium ion ratio and 56 Fe 16 O +The U-Pb age of sphene is then calculated by correcting the correlation between the signal intensity and the sphene signal. However, this method has the following limitations: 1) The data processing process is complex, requiring the operator to have professional knowledge of instrument principles and data analysis, which is not conducive to widespread application; 2) The applicable correction range is narrow, applicable only to sphene samples with Fe2O3 contents between 0.25% and 11.4%; 3) It is significantly affected by matrix effects, and changes in the chemical composition of sphene can introduce large age correction bias, seriously affecting the accuracy of the dating results. Summary of the Invention

[0007] In view of the above-mentioned drawbacks, the present invention aims to provide an improved method for U-Pb dating of micron-scale sphene, which determines the matrix effect related to the Fe2O3 content in sphene dating and finds that the TIMS (thermal ionization mass spectrometry) and SIMS (secondary ion mass spectrometry) measurements of sphene reference materials are similar. 206 Pb / 238 The U ratio is strongly correlated with the Fe2O3 mass fraction. Based on the above findings, an improved method is provided, specifically:

[0008] An improved method for determining the U-Pb age of micron-sized sphene comprises the following steps:

[0009] S1. Using an ion probe, obtain the lead-to-uranium ratio and iron signal intensity of each standard substance, standard sample, and test sample, respectively; wherein the number of standard samples is ≥ 2; then, perform a first calibration (i.e., instrument fractionation calibration) using the standard substances to obtain the corrected lead-to-uranium ratio of the standard sample and the corrected lead-to-uranium ratio of the test sample;

[0010] S2. Constructing a functional relationship for the standard sample: constructing a functional relationship using the ratio of the reference lead-uranium ratio of the standard sample to the calibrated lead-uranium ratio as the ordinate and the ratio of the iron signal intensities of the standard sample and the standard substance as the abscissa to obtain a calibration curve;

[0011] S3. Substitute the iron signal intensity of the sample to be tested, the lead-uranium ratio of the sample to be tested obtained by the first calibration, and the iron signal intensity of the standard substance used in the first calibration into the above calibration curve to obtain a second calibrated lead-uranium ratio, and determine the lead-uranium age of the sample to be tested based on the second calibrated lead-uranium ratio.

[0012] Furthermore, the correction described in S1 is correction by instrument fractionation or matrix effect.

[0013] Furthermore, the functional relationship of S2 is: ( 206 Pb / 238 U) TIMS / ( 206 Pb / 238 U) SIMS =A( 56 Fe16 Oratio) -B ;

[0014] wherein, ( 206 Pb / 238 U) TIMS is the reference lead uranium ratio of each standard sample, ( 206 Pb / 238 U) SIMS is the corrected lead uranium ratio of each standard sample, 56 Fe 16 O ratio is the ratio of the iron signal intensity of the standard sample to the iron signal intensity of the standard substance.

[0015] Further, after S3 obtains the second corrected lead uranium ratio, the formula for determining the lead uranium age of the sample to be measured is: wherein, λ 238 is the decay constant, λ 238 = 1.55125 x 10 -10 .

[0016] The present application has the beneficial effects that the present application confirms the matrix effect related to the Fe2O3 content in titanite dating; and through a large number of tests, it is found that the 206 Pb / 238 U ratio obtained by TIMS (TIMS is a thermal ionization mass spectrometer) and SIMS (secondary ion mass spectrometry (SIMS)) tests of the titanite standard substance and the Fe2O3 mass fraction present strong correlation, based on which, a simplified method for directly correcting the 206 Pb / 238 U ratio of the unknown sample is established, and the 207 Pb / 235 U age is corrected by using similar principles. The deviation between the corrected titanite age and the reference age is reduced from 12.3% to 0.4%, indicating that the corrected age result is more accurate; the natural titanite with the Fe2O3 content of 0.019% to 38.31% can be accurately obtained by using the method, and the method has the advantages of high accuracy and simple correction process. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the correction curve constructed by example 1 of the present application;

[0018] Figure 2 is the deviation percentage of the corrected age and the true age of the sample to be measured in example 1. DETAILED DESCRIPTION

[0019] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0020] The first embodiment of the present application discloses an improved method for determining the U-Pb age of micron-scale sphene, comprising the following steps:

[0021] S1. Using an ion probe, obtain the lead-to-uranium ratio and iron signal intensity of each standard substance, standard sample, and test sample, respectively; wherein the number of standard samples is ≥ 2; then, perform a first calibration (i.e., instrument fractionation calibration) on the standard substance to obtain the lead-to-uranium ratio of the standard sample and the lead-to-uranium ratio of the test sample after calibration with the standard substance;

[0022] S2. Constructing a functional relationship for the standard sample: constructing a functional relationship using the ratio of the reference lead-uranium ratio of the standard sample to the calibrated lead-uranium ratio as the ordinate and the ratio of the iron signal intensities of the standard sample and the standard substance as the abscissa to obtain a calibration curve;

[0023] S3. Substitute the iron signal intensity of the sample to be tested, the lead-uranium ratio of the sample to be tested obtained by the first calibration, and the iron signal intensity of the standard substance used in the first calibration into the above calibration curve to obtain a second calibrated lead-uranium ratio, and determine the lead-uranium age of the sample to be tested based on the second calibrated lead-uranium ratio.

[0024] In this embodiment, the standard material and standard sample refer to the sphene standard material with known age and source in the prior art, such as the sphene standard material BLR-1 (age 1047Ma, 206 Pb / 238 U TIMS The ratio is 0.074303±0.000087), the sphene standard material Ontario (age is 1048.4Ma, 206 Pb / 238 U TIMSThe ratio is 0.07429 ± 0.00012) and the like (source: Ma Q., Evans N.J., Ling X.X., Yang J.H., Wu F.Y., Zhao Z.D. and Yang Y.H. (2019) Natural titanite reference materials for in situ U-Pb and Sm-Nd isotopic measurements by LA-(MC)-ICP-MS. Geostandards and Geoanalytical Research, 43, 355-384.) The reference lead-uranium ratio of these standard materials has been published. In order to distinguish the roles of the two in the data processing process of the present application, they are distinguished as standard materials and standard samples. The standard materials are used to perform instrument fractionation correction (instrument fractionation correction is a known technology in the art), because in the ion probe excitation process of lead and uranium ions, lead and uranium elements are not ionized according to the inherent ratio in the sample. For example, the U in the titanite is ionized by one ion O 2- After ionization by bombardment, UO 2+ is formed. + / U + The ratio is 3:6:1, while Pb is almost completely ionized to Pb + . The difference in ionization efficiency of different elements, the difference in the proportion of different ion forms after ionization of the same element, and the difference in the transmission efficiency of various ions, result in the difference between the Pb + / U + value measured by the secondary ion mass spectrometer and the true Pb / U value of the sample, which is called instrument fractionation effect. This effect shows obvious changes due to the difference in the matrix (crystal structure or chemical composition) of the analyzed sample, which is called matrix effect. Due to the existence of the matrix effect, micro-area in-situ analysis must use a sample with the same crystal structure and chemical composition as the unknown sample and uniform element or isotope composition as the standard material to correct the element content and isotope ratio of the unknown sample. The standard sample is tested by the ion probe to obtain the lead-uranium ratio (Pb + / U + ), and after correction by the matrix-matched standard material, the corrected lead-uranium ratio, called the first corrected lead-uranium ratio, is obtained.

[0025] The standard sample refers to the titanite standard sample used to construct the relationship between the first corrected lead-uranium ratio and the iron signal intensity ratio in the one-time test analysis process, and the sample to be tested refers to the titanite sample to be tested with unknown age.

[0026] In the present embodiment, the number of standard samples can be two or more, and the more standard samples, the more reliable the curve constructed.

[0027] It is understood that in order to facilitate the ion probe to measure the lead-uranium ratio and iron signal intensity of the sample, the present application preferably prepares the standard sample and the sample to be tested into a sample target, and then pre-treats it before testing. The pre-treatment method is a conventional method in the art, for example, preferably:

[0028] (1) Prepare a sample target containing the sphene sample to be tested and the standard substance

[0029] The sphene standard material, standard sample and sample to be tested are embedded in a circular resin sheet with a diameter of about 1 inch and a thickness of 5 mm, so that the sphene standard sample and the sphene sample to be tested are exposed on one side surface of the resin sheet.

[0030] (2) Cleaning samples

[0031] The first step is to polish the sample surface with 0.25 micron polishing paste. The second step is to clean the sample surface with clean water. The third step is to place the sample in a beaker filled with alcohol and use an ultrasonic instrument to ultrasonically clean the sample for three minutes. The fourth step is to place the sample in a drying oven and dry it for one hour.

[0032] (3) Plating conductive material

[0033] Specifically, a Q150TE gold plating machine from Quorum is used to plate a continuous gold film on the exposed surface of the cleaned wafer sample. To ensure good conductivity of the sample, the coating thickness is between 20nm and 50nm. For example, it can be 20nm or 45nm.

[0034] (4) Using secondary ion mass spectrometry to test the signal required for sphene

[0035] Specifically, the sample target is placed in the sample chamber of the secondary ion mass spectrometer, an oxygen ion source is used and Gaussian light is focused on the sphene sample on the sample target to generate secondary ions of the sphene sample; the secondary ions of the sphene sample are 56 Fe 16 O + , 40 Ca 48 Ti2 16 O4 + , 204 Pb + , 206 Pb + , 207 Pb + , 208 Pb + , 238 U + , 232 Th 16O + ,and 238 U 16 O + The ion signal passes through the electric field and the magnetic field in sequence and reaches the ion signal detection system.

[0036] In this embodiment, after obtaining the corrected lead-uranium ratio of the standard sample, the standard substance, the standard sample, and the iron signal intensity of the sample to be tested by the ion probe, a function can be constructed as described in S2; the functional relationship is ( 206 Pb / 238 U) TIMS / ( 206 Pb / 238 U) SIMS =A( 56 Fe 16 O ratio) -B ;

[0037] in,( 206 Pb / 238 U) TIMS is the reference lead-uranium ratio of each standard sample, ( 206 Pb / 238 U) SIMS is the corrected lead-uranium ratio of each standard sample, 56 Fe 16 O ratio is the ratio of the iron signal intensity of the standard sample to the iron signal intensity of the standard substance.

[0038] After that, the iron signal intensity of the sample to be tested is substituted into the function to obtain the lead-uranium ratio of the sample to be tested, and the formula based on the lead-uranium age is: Among them, λ 238 is the decay constant, λ 238 =1.55125×10 -10 , and obtain the lead-uranium age of the sample to be tested. This embodiment is obtained by TIMS (TIMS is thermal ionization mass spectrometer) and SIMS (secondary ion mass spectrometry (SIMS) test of the standard material. 206 Pb / 238 The U ratio is strongly correlated with the Fe2O3 mass fraction, and a direct calibration of unknown samples was established. 206 Pb / 238 Simplified method of U ratio and correction using similar principles 207 Pb / 235 The corrected ages are more consistent with the reference ages, with the deviation from the reference ages reduced from 12.3% (without correction using this method) to 0.4% (with correction using this method). This method can accurately obtain natural sphene with Fe2O3 contents ranging from 0.019% to 38.31%, offering the advantages of high accuracy and a simple correction process.

[0039] The following specific examples will be used to verify the technical effects of this application.

[0040] The titanate information used in this embodiment is shown in Table 1.

[0041] Table 1 Sphene information

[0042]

[0043]

[0044] The above are all sphene age reference materials developed by isotope dilution thermal ionization mass spectrometry (ID-TIMS). 206 Pb / 238 U TIMS The ratio is known. In this embodiment, BLR-1 (pellet 1) and MDED1 are used as standard materials to calibrate the instrument fractionation to obtain the first calibration lead-uranium ratio. BLR-1 (pellet 2), Pakistan (pellet 1), T3 (pellet 1), and Ontario are used as standard samples to construct a calibration curve. Pakistan (pellet 2) and T3 (pellet 2) are used as test substances. 206 Pb / 238 The relationship between the U ratio and the iron signal intensity was used to calculate the ages of Pakistan (particle 2) and T3 (particle 2), and then compared with the reference ages disclosed in the prior art to observe the accuracy of the method of the present invention. Particle 1 of Pakistan and T3 was used to construct the regression equation, and particle 2 was used as the sample to be tested. Different particles can be regarded as different samples, and their test locations are different. Therefore, the obtained lead-uranium signal intensity and ratio can be regarded as different data. Therefore, the regression equation and the sample to be tested are different test data, and the lead-uranium ratio of the sample to be tested is unknown. The specific steps are:

[0045] (1) Prepare a sample target containing the sphene sample to be tested and the standard material: embed the sphene standard materials BLR-1 (particle 1) and MDED1; the standard samples BLR-1 (particle 2), Pakistan (particle 1), and T3 (particle 1); and the test materials Pakistan (particle 2) and T3 (particle 2) into a circular resin sheet with a diameter of approximately 1 inch and a thickness of 5 mm, so that the sphene standard sample and the sphene sample to be tested are exposed on one side of the resin sheet.

[0046] (2) Cleaning the sample: The first step is to polish the sample surface with 0.25 μm polishing paste. The second step is to clean the sample surface with clean water. The third step is to place the sample in a beaker containing alcohol and use an ultrasonic instrument to ultrasonically clean the sample for three minutes. The fourth step is to place the sample in a drying oven and dry it for one hour.

[0047] (3) Plating conductive material: using the Q150TE model of Quorum gold plating instrument, the exposed side surface of the above clean wafer sample is plated with a continuous gold film, in order to ensure good conductivity of the sample, the thickness of the plating layer is 20-50 nm, for example, it can be 20 nm, or 45 nm, etc.

[0048] (4) Testing the signal required for zircon by secondary ion mass spectrometer: placing the above sample target into the sample chamber of the secondary ion mass spectrometer, using an oxygen ion source and focusing it on the zircon sample on the sample target in a Gaussian light mode, so as to generate secondary ions of the zircon sample; making the secondary ions of the zircon sample pass through the electric field and the magnetic field in turn to reach the ion signal detection system. 56 Fe 16 O + , 40 Ca 48 Ti2 16 O4 + , 204 Pb + , 206 Pb + , 207 Pb + , 208 Pb + , 238 U + , 232 Th 16 O + , and 238 U 16 O + reaching the ion signal detection system.

[0049] (5) Determining the lead-uranium age of the zircon to be tested

[0050] First step: testing the relevant signals of zircon by ion probe, the lead-uranium ratios of standard material, standard sample and sample to be tested, and their respective iron signal intensities can be obtained 56 Fe 16 O + ;

[0051] The test results show that the 56 Fe 16 O + signal intensities of zircon standard samples MKED1, BLR-1, Ontario are 6082, 10840, 13456 cps respectively, and the 56 Fe 16 O + signal intensities of samples to be tested T3, Pakistan are 15422, 1149 respectively.

[0052] Second step: using standard material to correct the instrument fractionation (matrix effect) of other standard samples (first correction), and obtaining the corrected lead uranium ratio In this example, BLR-1 (grain 1) and MKED1 (grain 1) are used as standard materials to correct the lead uranium ratio of other standard samples, and the BLR-1 corrected T3, Pakistan and Ontario The ratio is 0.1815, 0.0028 and 0.1756 respectively; the BLR-1, T3 and Pakistan corrected by MKED1 have The ratio is 0.1888, 0.1936 and 0.0031 respectively.

[0053] Third step: obtaining the correction curve (correlation) through the correction results of standard materials: Figure 1 Through the correction results of standard materials, the correlation between lead uranium ratio (ordinate) and iron signal intensity ratio (abscissa) is constructed, wherein, 206 Pb / 238 U) TIMS is the reference ratio obtained by ID-TIMS of each standard sample (BLR-1 (grain 2), Pakistan (grain 1), T3 (grain 1), Ontario (grain 1) in this example); ( 206 Pb / 238 U) SIMS is the lead uranium ratio of each standard sample in the second step obtained by ion probe after correction of instrument fractionation (or matrix effect) of standard materials. 56 Fe 16 O ratio is the ratio of iron signal intensity of standard sample tested by ion probe to iron signal intensity of standard material used for calibration of matrix effect of lead uranium ratio.

[0054] As shown in Figure 1 : ratio1 is the standard sample corrected by MKED1 (grain 1) in the second step, and ratio2 is the standard sample corrected by BLR-1 (grain 1), for example: ratio1 of BLR-1 is the ratio of 56 Fe 16 O + signal intensity of BLR-1 (grain 2) to 56 Fe 16 O + signal intensity of MKED1 (grain 1), ratio1 of T3 is the ratio of 56 Fe 16 O + signal intensity of T3 (grain 1) to 56 Fe 16 O +Ratio of signal intensity of T3 to T3 56 Fe 16 O + Ratio of signal intensity of BLR-1 (grain 1) to BLR-1 (grain 1) 56 Fe 16 O + Ratio of signal intensity of BLR-1 (grain 1) to BLR-1 (grain 1)

[0055] Fitting according to the following function relationship 206 Pb / 238 U) TIMS 206 Pb / 238 U) SIMS = A 56 Fe 16 O ratio) -B The values of regression coefficients A and B are obtained by fitting, and the A and B coefficients can be adjusted according to the test results of the standard substance of each experiment. In this example, the coefficient A = 0.9957 and the coefficient B = 0.053 are obtained by fitting, and R 2 = 0.9174 Figure 1 ).

[0056] Step 3: Determine the age of the sample to be tested: the ion probe test value of the sample to be tested corrected in step 2 is brought into the correction curve of step 2 to obtain the corrected and 56 Fe 16 O + ratio Determine the lead-uranium age of the sample to be tested: Wherein: λ 238 is the decay constant, λ 238 = 1.55125 x 10 -10 .

[0057] Taking the sample to be tested Pakistan (grain 2) as an example, the corrected ratio of the sample to be tested Pakistan (grain 2) is 0.0029 in step 2 of this example, and the lead-uranium age is calculated to be 18.5 Ma (this is the result of the first correction), which is 12.3% lower than the reference age (21 Ma); after step 3 56 Fe 16 O + ratio correction, the ratio is 0.0032, and the lead-uranium age is calculated to be 20.69 Ma Figure 1 ) (this is the result of the second correction), which is about 0.4% lower than the reference age (21 Ma), and compared with the first correction result, the gap with the reference age is smaller, so the age result is more accurate. ​

[0058] Taking the sample T3 (particle 2) as an example, in the second step of this example, the sample T3 (particle 2) to be tested is obtained after MKED1 correction. The ratio is 0.1936, and the calculated lead-uranium age is 1141Ma (this is the result of the first correction), which is 3.8% higher than the reference age (1099Ma). 56 Fe 16 O + After signal strength correction The ratio is 0.1831, and the lead-uranium age is calculated to be 1084 Ma ( Figure 1 ) (This is the result of the second correction) and is about 1.4% lower than the reference age (21Ma) ( Figure 2 ), compared with the first calibration result, the difference with the reference age is smaller, so the age result is more accurate.

[0059] From the above analysis, it can be seen that the sphene U-Pb age determined by the method of the present application is closer to the reference value, and thus the obtained sphene age is more accurate.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An improved method for determining the U-Pb age of micron-scale sphene, characterized in that: The steps include: S1. Using an ion probe, obtain the lead-to-uranium ratio and iron signal intensity of each standard substance, standard sample, and test sample, respectively; wherein the number of standard samples is ≥ 2; then, perform a first calibration (i.e., instrument fractionation calibration) using the standard substances to obtain the corrected lead-to-uranium ratio of the standard sample and the corrected lead-to-uranium ratio of the test sample; S2. Constructing a functional relationship for the standard sample: constructing a functional relationship using the ratio of the reference lead-uranium ratio of the standard sample to the calibrated lead-uranium ratio as the ordinate and the ratio of the iron signal intensities of the standard sample and the standard substance as the abscissa to obtain a calibration curve; S3. Substituting the iron signal intensity of the test sample and the first calibrated lead-uranium ratio of the test sample, as well as the iron signal intensity of the standard substance used in the first calibration into the calibration curve to obtain a second calibrated lead-uranium ratio, and determining the lead-uranium age of the test sample based on the second calibrated lead-uranium ratio; The standard substance and standard sample are both sphene standards of known age and origin; wherein, the standard substance is used for the first calibration; and the standard sample is used for obtaining the standard sample calibrated lead-uranium ratio after the first calibration to construct a functional relationship of the standard sample.

2. The method according to claim 1, characterized in that The correction described in S1 is performed by instrument fractionation or matrix effect correction.

3. The method according to claim 1, characterized in that The functional relationship of S2 is: 206 Pb / 238 U) TIMS / ( 206 Pb / 238 U) SIMS = A( 56 Fe 16 O ratio) -B ; in,( 206 Pb / 238 U) TIMS is the reference lead-uranium ratio of each standard sample, ( 206 Pb / 238 U) SIMS is the corrected lead-uranium ratio of each standard sample, 56 Fe 16 O ratio is the ratio of the iron signal intensity of the standard sample to the iron signal intensity of the standard substance; A and B are regression coefficients.

4. The method according to claim 1, characterized in that After obtaining the second corrected lead-uranium ratio in S3, the formula for determining the lead-uranium age of the sample to be tested is: ; Among them, λ 238 is the decay constant, λ 238 =1.55125×10 -10 .

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