Improved method for determining U-Pb age of micron-sized sphene

Abstract

The invention belongs to the field of geological dating, and particularly relates to an improved method for determining the U-Pb age of micron-sized sphene. According to the invention, the matrix effect related to the dating Fe2O3 content of sphene is confirmed; a large number of tests show that the 206Pb / 238U ratio obtained by the TIMS (TIMS (Thermal Ionization Mass Spectrometer)) and SIMS (Secondary Ion Mass Spectrometer) of the sphene standard sample is strongly correlated with the Fe2O3 mass fraction, so that a simplified method for directly correcting the 206Pb / 238U ratio of an unknown sample is established, and the 207Pb / 235U age is corrected by adopting a similar principle. The deviation between the age of the sphene after correction and the reference age is reduced from 12.3% to 0.4%, which indicates that the corrected age result is more accurate; by adopting the method, the natural sphene with the Fe2O3 content of 0.019-38.31% can be accurately obtained, and the method has the advantages of high accuracy and simple correction process.

Description

Technical Field

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

[0002] Titanite (CaTiSiO5), as a common uranium-bearing accessory mineral, is widely distributed in intermediate-acid and alkaline intrusive rocks, metamorphic rocks, and various hydrothermal deposits. As an important geochronological dating tool, it has important application value in studying the petrogenesis and evolution process of rocks. However, due to the characteristics of multi-stage growth of most titanite minerals and generally small particle sizes (usually 5-100 μm, with the main body concentrated around 10 μm), high-precision in-situ micro-area dating techniques are required to accurately analyze the age information of different stages of titanite.

[0003] Currently, the high-precision titanite dating methods 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 method has its technical characteristics and limitations.

[0004] The ID-TIMS technique requires acid digestion of titanite samples, chromatographic separation and purification of U and Pb, and then mass spectrometry determination. Although this method can obtain relatively high data accuracy, its pretreatment process is complex and time-consuming (>2 weeks), making it difficult to meet the analysis requirements of a large number of samples. More importantly, as an overall analysis method, ID-TIMS inevitably mixes multi-stage growth components when analyzing titanite with a 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 method U-Pb dating. In addition, this method cannot simultaneously obtain trace element composition information.

[0005] The LA-ICP-MS technique does not require single mineral sorting and can directly perform in-situ analysis on rock thin sections. However, limited by the spatial resolution, this method can usually only effectively measure particles with a diameter greater than 30 μm, and the titanite particle size in most rocks is relatively small, so the practical application of this technique is greatly limited.

[0006] In contrast, the secondary ion mass spectrometry (SIMS) technique has the advantages of small sample consumption and long-term repeatable analysis. Considering the characteristics of low U content and high common lead content in titanite, high-precision and high-spatial-resolution ion probes are used for in-situ micro-area analysis, which can effectively avoid inclusion interference and obtain more reliable dating results. In the prior art, using the CAMECA 1280 type ion probe, by establishing the measurement of the lead-uranium ion ratio and 56 Fe 16 O +The correlation of signal intensity is corrected, and then the U-Pb age of titanite is calculated. However, this method has the following limitations: 1) The data processing flow is complex, requiring operators to have professional knowledge of instrument principles and data analysis, which is not conducive to wide promotion; 2) The applicable correction range is narrow, only applicable to titanite samples with Fe2O3 content between 0.25% and 11.4%; 3) It is significantly affected by matrix effects. Changes in the chemical composition of titanite will introduce large age correction deviations, seriously affecting the accuracy of dating results. Summary of the Invention

[0007] In view of the above defects, the purpose of the present invention is to provide an improved method for determining the U-Pb age of micron-scale titanite. This method determines the matrix effect related to the Fe2O3 content in titanite dating, and at the same time discovers that the 206 Pb / 238 U ratio obtained by TIMS (TIMS is Thermal Ionization Mass Spectrometer) and SIMS (SIMS is Secondary Ion Mass Spectrometry) tests of titanite reference materials shows a strong correlation with the mass fraction of Fe2O3. Based on the above discoveries, an improved method is provided, specifically as follows:

[0008] An improved method for determining the U-Pb age of micron-scale titanite, comprising the following steps:

[0009] S1. Use an ion probe to obtain the lead-uranium ratio and iron signal intensity of each reference material, standard sample, and sample to be tested; where the number of standard samples ≥ 2; then perform the first correction through the reference material, that is, instrument fractionation correction, to obtain the corrected lead-uranium ratio of the standard sample and the corrected lead-uranium ratio of the sample to be tested;

[0010] S2. Construct a functional relationship of the standard sample: Use the ratio of the reference lead-uranium ratio to the corrected lead-uranium ratio of the standard sample as the ordinate, and the ratio of the iron signal intensity of the standard sample to the reference material as the abscissa to construct a functional relationship to obtain a correction curve;

[0011] S3. Substitute the iron signal intensity of the sample to be tested, the first-corrected lead-uranium ratio of the sample to be tested, and the iron signal intensity of the reference material used in the first correction into the above correction curve to obtain the second-corrected lead-uranium ratio, and determine the lead-uranium age of the sample to be tested according to the second-corrected lead-uranium ratio.

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

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

[0014] Among them, ( 206 Pb / 238 U) TIMS is the reference lead-uranium ratio of each standard sample, ( 206 Pb / 238 U) SIMS is the calibrated lead-uranium ratio of each standard sample, 56 Fe 16 The Fe

[0015] Further, after obtaining the second calibrated 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 .

[0016] The beneficial effects of the present invention are as follows: The present invention confirms the matrix effect related to the Fe2O3 content in sphene dating; and through a large number of tests, it is found that the 206 Pb / 238 U ratio obtained by TIMS (TIMS is Thermal Ionization Mass Spectrometer) and SIMS (Secondary Ion Mass Spectrometry (SIMS)) tests of the sphene reference material shows a strong correlation with the mass fraction of Fe2O3. Based on this, a simplified method for directly calibrating the 206 Pb / 238 U ratio of unknown samples is established, and the 207 Pb / 235 U age is calibrated by a similar principle. The deviation between the calibrated sphene age and the reference age is reduced from 12.3% to 0.4%, indicating that the calibrated age result is more accurate; by using this method, natural sphenes with Fe2O3 content ranging from 0.019% to 38.31% can be accurately obtained, which has the advantages of high accuracy and simple calibration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the calibration curve constructed in Example 1 of the present application;

[0018] Figure 2 is the deviation percentage between the calibrated age and the true age of the sample to be tested in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following describes the specific embodiments of the present invention to facilitate the 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 of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

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

[0021] S1. Use an ion probe to obtain the lead-uranium ratio and iron signal intensity of each reference material, standard sample, and sample to be measured; where the number of standard samples ≥ 2; then perform a first calibration on the reference material, that is, instrument fractionation calibration, to obtain the lead-uranium ratio of the standard sample and the lead-uranium ratio of the sample to be measured after calibration with the reference material.

[0022] S2. Construct a functional relationship of the standard sample: Use the ratio of the reference lead-uranium ratio to the calibrated lead-uranium ratio of the standard sample as the ordinate, and the ratio of the iron signal intensity of the standard sample to the reference material as the abscissa to construct a functional relationship to obtain a calibration curve.

[0023] S3. Substitute the iron signal intensity of the sample to be measured, the lead-uranium ratio of the sample to be measured after the first calibration, and the iron signal intensity of the reference material 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 measured according to the second calibrated lead-uranium ratio.

[0024] In this embodiment, the reference material and the standard sample refer to sphene reference materials with known ages and sources in the prior art, such as sphene reference material BLR-1 (age is 1047 Ma, 206 Pb / 238 U TIMS ratio is 0.074303 ± 0.000087), sphene reference material Ontario (age is 1048.4 Ma, 206 Pb / 238 U TIMSThe ratio is 0.07429 ± 0.00012 (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 ratios of these reference materials have been made public. To distinguish their roles in the data processing of this invention, they are divided into reference materials and reference samples. The reference materials are used for fractionation correction of the instrument (instrument fractionation correction is a well-known technical means in the art). This is because during the ionization of lead and uranium ions by the aforementioned ion probe, lead and uranium elements are not ionized in the inherent ratio in the sample. For example, after the U in titanite is ionized by bombardment with primary ion O 2- The ratio of UO 2+ / UO + / U + is 3:6:1, while almost all Pb is ionized to Pb + . The differences in ionization efficiencies of different elements, the differences in the proportions of different ionic forms of the same element after ionization, and the differences in various ion transmission efficiencies result in the Pb + / U + measured by the secondary ion mass spectrometry receiver being different from the true Pb / U value of the sample, which is called the instrument fractionation effect. This effect will show obvious changes due to the different matrices (crystal structures or chemical compositions) of the samples being analyzed, which is called the matrix effect. Due to the existence of the matrix effect, in situ microanalysis must use a sample with the same crystal structure and chemical composition as the unknown sample and with a uniform elemental or isotopic composition of the elements to be analyzed as a reference material to correct the elemental content and isotope ratio of the unknown sample. The reference sample is tested by an ion probe to obtain the lead-uranium ratio (Pb + / U + ). After being corrected by the reference material with matrix matching, the corrected lead-uranium ratio can be obtained, which is called the first corrected lead-uranium ratio.

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

[0026] In this embodiment, the number of reference samples can be two or more. The more reference samples there are, the more reliable the constructed curve will be.

[0027] It is understandable that, for the convenience of measuring the lead-uranium ratio and iron signal intensity of the sample by the ion probe, the present application preferably prepares the standard sample and the sample to be tested into a sample target, and then performs tests after pretreatment. The pretreatment method is a conventional method in the art. For example, it is preferably:

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

[0029] Embed the sphene standard substance, the standard sample and the sample to be tested into 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 the sample

[0031] In the first step, polish the surface of the sample with 0.25-micron polishing paste. In the second step, clean the surface of the sample with clean water. In the third step, place the sample in a beaker containing alcohol and ultrasonically clean the sample for three minutes using an ultrasonic instrument. In the fourth step, dry the sample in a drying oven for one hour.

[0032] (3) Plating a conductive material

[0033] Specifically, use a gold plating instrument of model Q150TE from Quorum Company to plate a continuous gold film on the exposed side surface of the above-mentioned cleaned round sample. To ensure good conductivity of the sample, the coating thickness is 20 nm - 50 nm. For example, it can be 20 nm or 45 nm, etc.

[0034] (4) Using a secondary ion mass spectrometer to test the signals required for sphene

[0035] Specifically, place the above sample target in the sample chamber of a secondary ion mass spectrometer, use an oxygen ion source and focus it on the sphene sample on the sample target in a Gaussian light manner to generate secondary ions of the sphene sample; make the secondary ions of the sphene sample 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 + successively pass through an electric field and a magnetic field to reach the ion signal detection system.

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

[0037] 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.

[0038] After that, substituting the determined iron signal intensity of the sample to be tested into the function, the lead-uranium ratio of the sample to be tested can be obtained, and thus the lead-uranium age formula is: wherein, λ 238 is the decay constant, λ 238 = 1.55125×10 -10 , and the lead-uranium age of the sample to be tested is obtained. In this embodiment, by discovering that the TIMS (TIMS means thermal ionization mass spectrometer) of the standard substance has a strong correlation with the 206 Pb / 238 U ratio and the mass fraction of Fe2O3 obtained by SIMS (secondary ion mass spectrometry (SIMS) test), a simplified method for directly correcting the 206 Pb / 238 U ratio of unknown samples is established, and a similar principle is used to correct the 207 Pb / 235 U age. The corrected age is more consistent with the reference age, and the age deviation from the reference age is reduced from 12.3% (without correction by this method) to 0.4% (corrected by this method); using this method, natural sphene with Fe2O3 content in the range of 0.019% - 38.31% can be accurately obtained, with the advantages of high accuracy and simple correction process.

[0039] The technical effects of this application will be verified through specific embodiments below. Embodiment 1

[0040] The information of the titanite used in this embodiment is shown in Table 1.

[0041] Table 1 Information of titanite

[0042]

[0043]

[0044] The above are all age reference materials of titanite developed by isotope dilution thermal ionization mass spectrometry (ID-TIMS). 206 Pb / 238 U TIMS The ratio is known. In this embodiment, BLR-1 (grain 1) and MDED1 are used as reference materials to correct the instrumental fractionation to obtain the first corrected Pb / U ratio. BLR-1 (grain 2), Pakistan (grain 1), T3 (grain 1), and Ontario are used as standard samples to construct a calibration curve. Pakistan (grain 2) and T3 (grain 2) are used as the substances to be measured. By constructing the 206 Pb / 238 relationship between the U ratio and the iron signal intensity to calculate the ages of Pakistan (grain 2) and T3 (grain 2), and then compare them with the reference ages already disclosed in the prior art to observe the accuracy of the method of the present invention. Among them, Pakistan and T3 grains 1 are used to construct a regression equation, and grain 2 is used as the sample to be measured. Different grains can be regarded as different samples, and their testing positions are different. Therefore, the obtained Pb / U signal intensities and ratios can be regarded as different data. Therefore, the regression equation and the sample to be measured are different test data, and the Pb / U ratio of the sample to be measured is unknown. The specific steps are as follows:

[0045] (1) Making a sample target containing the titanite sample to be measured and the reference material: Inlay the titanite reference materials BLR-1 (grain 1), MDED1; the standard samples BLR-1 (grain 2), Pakistan (grain 1), T3 (grain 1); the substances to be measured Pakistan (grain 2), T3 (grain 2) into a circular resin sheet with a diameter of about 1 inch and a thickness of 5 mm, so that the titanite reference samples and the titanite samples to be measured are exposed on one side surface of the resin sheet.

[0046] (2) Cleaning the sample: In the first step, polish the sample surface with 0.25-micron polishing paste. In the second step, clean the sample surface with clean water. In the third step, place the sample in a beaker containing alcohol and ultrasonically clean the sample for three minutes using an ultrasonic instrument. In the fourth step, dry the sample in a drying oven for one hour.

[0047] (3) Coating with conductive material: Using a gold plating instrument of model Q150TE from Quorum Company, a continuous gold film is coated on the exposed surface of the above-mentioned 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, etc.

[0048] (4) Testing the signals required for sphene using a secondary ion mass spectrometer: The above sample target is placed in the sample chamber of the secondary ion mass spectrometer. An oxygen ion source is used and focused on the sphene sample on the sample target in a Gaussian light mode to generate secondary ions of the sphene sample; the secondary ions of the sphene sample 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 + sequentially pass through the electric field and magnetic field to reach the ion signal detection system.

[0049] (5) Determining the lead-uranium age of the sphene to be measured

[0050] The first step: Using an ion probe to test the relevant signals of the sphene, the lead-uranium ratios of the reference material, reference sample, and sample to be measured can be obtained, as well as their respective iron signal intensities 56 Fe 16 O + ;

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

[0052] Step 2: Use reference materials to perform instrumental fractionation (matrix effect) correction (first correction) on other standard samples respectively to obtain the corrected lead-uranium ratio In this example, BLR-1 (particle 1) and MKED1 (particle 1) are used as reference materials to correct the lead-uranium ratios of other standard samples respectively. The ratios obtained by correcting with BLR-1 for T3, Pakistan, and Ontario are 0.1815, 0.0028, and 0.1756 respectively; the ratios of BLR-1, T3, and Pakistan corrected by MKED1 are 0.1888, 0.1936, and 0.0031 respectively.

[0053] Step 3: Obtain a calibration curve from the calibration results of the reference materials( Figure 1 ): Construct the correlation between the lead-uranium ratio (ordinate) and the iron signal intensity ratio (abscissa) from the calibration results of the reference materials. Among them,( 206 Pb / 238 U) TIMS is the reference ratio obtained by ID-TIMS of each standard sample (in this example, BLR-1 (particle 2), Pakistan (particle 1), T3 (particle 1), Ontario (particle 1));( 206 Pb / 238 U) SIMS is the lead-uranium ratio of each standard sample after correcting the instrumental fractionation (or matrix effect) with the reference material by the ion probe in Step 2. 56 Fe 16 O ratio is the ratio of the iron signal intensity of the standard sample tested by the ion probe to the iron signal intensity of the reference material used to calibrate the matrix effect of the lead-uranium ratio.

[0054] As Figure 1 shown: ratio1 is the standard sample corrected by MKED1 (particle 1) in Step 2, ratio2 is the standard sample corrected by BLR-1 (particle 1). For example, ratio1 of BLR-1 is the 56 Fe 16 O + signal intensity of BLR-1 (particle 2) to the 56 Fe 16 O + signal intensity of MKED1 (particle 1), ratio1 of T3 is the 56 Fe 16 O + signal intensity of T3 (particle 1) to the 56 Fe 16 O +Ratio of signal intensities; ratio2ofT3 is for T3 56 Fe 16 O + Ratio of signal intensity to that of BLR-1 (particle 1) 56 Fe 16 O + Ratio of signal intensities, and so on.

[0055] Fitting is performed according to the following functional relationship ( 206 Pb / 238 U) TIMS / ( 206 Pb / 238 U) SIMS =A( 56 Fe 16 O ratio) -B , and the values of regression coefficients A and B are obtained through fitting. The A and B coefficients can be adjusted according to the test results of reference materials for each experiment. In this example, the coefficients obtained from fitting are A = 0.9957, B = 0.053, and R 2 =0.9174( Figure 1 ).

[0056] Step 3: Determine the age of the sample to be measured: The ion probe test of the sample to be measured, after being corrected in the second step, and 56 Fe 16 O + ratio are substituted into the calibration curve of the second step to obtain the calibrated Determine the lead-uranium age of the sample to be measured: Where: λ 238 is the decay constant, and λ 238 =1.55125×10 -10 .

[0057] Taking the sample to be measured Pakistan (particle 2) as an example, in the second step of this example, the ratio of the sample to be measured Pakistan (particle 2) after being corrected by BLR-1 is 0.0029. The calculated lead-uranium age is 18.5 Ma (this is the result of the first correction), which is 12.3% lower than the reference age (21 Ma); after the third step 56 Fe 16 O + After signal intensity correction, the ratio is 0.0032, and the calculated lead-uranium age is 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). Compared with the result of the first correction, the gap from the reference age is smaller, so the age result is more accurate.

[0058] Taking the sample to be measured T3 (particle 2) as an example, in the second step of this example, the ratio of the sample to be measured T3 (particle 2) corrected by MKED1 is 0.1936. The calculated lead-uranium age is 1141 Ma (this is the result of the first correction), which is 3.8% higher than the reference age (1099 Ma); after the third step 56 Fe 16 O + After the signal intensity correction, the ratio is 0.1831, and the calculated lead-uranium age is 1084 Ma ( Figure 1 )(this is the result of the second correction), which is about 1.4% lower than the reference age (21 Ma) ( Figure 2 ). Compared with the result of the first correction, the gap from 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 this application is closer to the reference value, so 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions 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-sized titanite, characterized in that, Including the following steps: S1. Obtain the lead-uranium ratio and iron signal intensity of each reference material, standard sample, and sample to be measured using an ion probe; where the number of standard samples ≥ 2; then perform a first correction through the reference material, i.e., instrument fractionation correction, to obtain the corrected lead-uranium ratio of the standard sample and the corrected lead-uranium ratio of the sample to be measured; S2. Construct the functional relationship of the standard sample: Use the ratio of the reference lead-uranium ratio to the corrected lead-uranium ratio of the standard sample as the ordinate, and the ratio of the iron signal intensity of the standard sample to the reference material as the abscissa to construct the functional relationship and obtain the correction curve; S3. Substitute the iron signal intensity of the sample to be measured, the lead-uranium ratio of the sample to be measured after the first correction, and the iron signal intensity of the reference material used in the first correction into the above correction curve to obtain the second corrected lead-uranium ratio, and determine the lead-uranium age of the sample to be measured based on the second corrected lead-uranium ratio.

2. The method according to claim 1, wherein The correction described in S1 is through instrument fractionation or matrix effect correction.

3. The method according to claim 1, wherein The functional relationship described in S2 is: ( 206 Pb / 238 U) TIMS / ( 206 Pb / 238 U) SIMS =A( 56 Fe 16 O ratio) -B ; Among them, ( 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 reference material.

4. The method according to claim 1, wherein After obtaining the second corrected lead-uranium ratio as described in S3, the formula for determining the lead-uranium age of the sample to be measured is: where λ 238 is the decay constant, and λ 238 = 1.55125×10 -10 .

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