A method for single inclusion carbon dioxide carbon-oxygen isotope measurement

Abstract

The application provides a single inclusion carbon dioxide carbon-oxygen isotope measurement method, relates to the technical field of isotope measurement, and comprises the following steps: S1, selecting at least two standard carbon dioxide samples; S2, obtaining Raman spectrum data of all standard carbon dioxide samples and a to-be-measured inclusion sample at different temperatures; S3, constructing a standard model according to the Raman spectrum data of all standard carbon dioxide samples; S4, inputting the Raman spectrum data of the to-be-measured inclusion sample at different temperatures into the standard model, obtaining an isotope ratio curve of the to-be-measured inclusion sample, and calculating a to-be-measured carbon isotope characteristic of the to-be-measured inclusion sample according to the fact that the interval between the isotope ratio curves is proportional to the difference between carbon isotope ratios. The application has the beneficial effect that Raman spectrum detection is directly performed on the inclusion, the limitation that a sample needs to be destroyed in a traditional mass spectrometry method is avoided, and nondestructive and high-precision measurement of the carbon-oxygen isotope ratio of carbon dioxide in a single inclusion can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of isotope measurement, and in particular to a method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion. Background Art

[0002] In geological and geochemical research, inclusions refer to tiny liquids or gases trapped inside crystals during the formation of minerals or rocks, containing important information such as ore-forming fluids, magma evolution, and temperature and pressure conditions. Carbon dioxide (CO2), a common component in inclusions, records key clues to the origin of magma and fluids, especially carbon (δ 13 C / ^δ 12 C) and oxygen (δ 18 O / δ 16 O) isotope ratios, which can provide detailed information about the source, genesis, and evolution of geological fluids. Accurately measuring the carbon and oxygen isotope ratios of carbon dioxide in inclusions helps reveal the formation environment of ore-forming fluids, the migration patterns of geological fluids, and the geological history of evolution.

[0003] Traditional carbon and oxygen isotope measurement methods rely primarily on mass spectrometry for precise isotope ratio analysis. These methods, including gas isotope mass spectrometry (IRMS) and secondary ion mass spectrometry (SIMS), offer high sensitivity and resolution. However, traditional mass spectrometry methods typically require the extraction of carbon dioxide gas from inclusions, which often results in the destruction of the inclusions. Especially for tiny and valuable geological samples, the extraction process can damage the sample's microstructure, thereby affecting the integrity of the sample and the accuracy of subsequent research. Typically, the carbon dioxide in inclusions is tiny and often under high pressure, making it extremely difficult to directly extract the gaseous components. This is especially true for extremely small single inclusions (typically less than tens of microns in diameter), which are even more difficult to accurately extract and analyze without destroying the sample. Furthermore, in rock or mineral thin sections, inclusions are numerous and diverse in shape, often varying in size and buried deep within the sample. Conventional mass spectrometry methods are unable to accurately locate the position and size of individual inclusions and are often limited to overall measurements, making it difficult to obtain precise isotopic information for a single inclusion. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion.

[0005] An embodiment of the present invention provides a method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion, comprising the following steps:

[0006] S1. Select at least two standard carbon dioxide samples with known isotopic characteristics;

[0007] S2, obtaining Raman spectrum data of all standard carbon dioxide samples and the sample of the in-situ inclusion at different temperatures, the Raman spectrum data including Fermi doublet intensity, hot peak intensity and in-situ isotope peak intensity, the in-situ isotope being carbon isotope or oxygen isotope;

[0008] S3, constructing a standard model according to the Raman spectrum data of all standard carbon dioxide samples:

[0009] HR=kR+a HF +

[0010] R HF = I HB - + I HB + / I FD - + I FD +

[0011] HR ＝ I HB / I x

[0012] wherein I FD - and I FD + are the doublet intensity at the first exposure time, I HB - and I HB + are the hot peak intensity at the first exposure time, I x and I HB are the in-situ isotope peak intensity and the right hot peak intensity at the second exposure time respectively, k is the slope, and a is the intercept;

[0013] S4, inputting the Raman spectrum data of the sample of the in-situ inclusion at different temperatures into the standard model to obtain the isotope ratio curve of the sample of the in-situ inclusion, and calculating the in-situ carbon isotope characteristics of the sample of the in-situ inclusion according to the positive correlation between the interval between the isotope ratio curves and the difference between the carbon isotope ratios.

[0014] Further, in the step S4, the isotope ratio curves of the two standard carbon dioxide samples closest to the isotope ratio curve of the sample of the in-situ inclusion are selected, and the in-situ carbon isotope characteristics of the sample of the in-situ inclusion are calculated according to the positive correlation between the interval between the isotope ratio curves and the difference between the carbon isotope ratios.

[0015] Further, in the step S2, the Fermi doublet intensity at the first exposure time is controlled to be no more than 60000, and the right hot peak intensity at the second exposure time is controlled to be no more than 60000 by controlling the exposure time.

[0016] Further, the peak intensity on the right side of the Fermi doublet under the first exposure time is 50000-60000, and the right side thermal peak intensity under the second exposure time is 50000-60000.

[0017] Further, the step S2 is specifically: placing the sample on the cooling and heating table, placing the cooling and heating table under the microscope, turning on the laser light source, irradiating the inclusion with a predetermined power, exciting the Raman scattering signal, capturing the scattered light through the spectrum detection module and performing spectrum analysis, and recording the Raman spectrum data at different temperatures.

[0018] Further, the microscope is a LabRAM HR800 type confocal microscopic laser Raman spectrometer.

[0019] Further, the cooling and heating table is a CAP500 cooling and heating table.

[0020] Further, the step S2 further comprises signal denoising and peak identification using a preset algorithm to obtain the Raman spectrum data.

[0021] Further, the sample to be measured in the step S2 is cut or polished by a wafer to expose the inclusion.

[0022] Further, the isotopes to be measured are 13 C.

[0023] The technical scheme provided by the embodiment of the application has the following beneficial effects:

[0024] 1. The single inclusion carbon dioxide carbon-oxygen isotope measurement method can perform Raman spectrum detection on the carbon dioxide in the inclusion without damaging the structure of the inclusion, utilize the Raman spectrum data of two standard carbon dioxide samples with known isotopic characteristics to construct a standard model, input the Raman spectrum data of the inclusion into the standard model to obtain the isotopic ratio curve of the sample to be measured, and calculate the to-be-measured carbon isotope characteristics of the sample to be measured according to the fact that the interval between the isotopic ratio curves is proportional to the difference between the carbon isotope ratios, so that the Raman spectrum detection is directly performed on the inclusion, the dependence on the sample quantity in the traditional method is overcome, the limitation that the sample needs to be damaged in the traditional mass spectrometry method is avoided, and nondestructive and high-precision measurement of the carbon-oxygen isotope ratio of carbon dioxide in a single inclusion can be realized, thereby providing more accurate and convenient technical support for the geological and geochemical fields.

[0025] 2. The single inclusion carbon dioxide carbon-oxygen isotope measurement method has high resolution, and can distinguish 12 C and 13 C, 16 O and 18O isotope differences, so as to accurately measure the isotope ratio, use isotope calibration, and use δ 13 C and δ 18 The carbon and oxygen isotope values ​​are obtained by the ratio of the Raman peak intensity of O to the thermal peak. Compared with the previous method of using mixed sample calibration factors, the test accuracy is greatly improved, and the accuracy is increased by 10 to 20 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of Raman spectroscopy data measurement in a method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion of the present invention;

[0027] Figure 2 This is an optical photograph of carbon dioxide fluid inclusions taken with a 350x objective lens;

[0028] Figure 3 is the Mann spectrum data diagram of the inclusion sample to be tested;

[0029] Figure 4 This is a schematic diagram of the method for obtaining carbon and oxygen isotope characteristic peaks and thermal peaks in Raman spectroscopy data;

[0030] Figure 5 It is a schematic diagram of the isotope ratio curve of the inclusion sample to be tested and the isotope ratio curve of two standard carbon dioxide samples;

[0031] Figure 6 The present invention is a method for measuring the carbon-oxygen isotope composition of carbon dioxide in a single inclusion. 13 C isotope characteristic measurement results diagram;

[0032] Figure 7 The existing mixed sample calibration factor method is used to 13 C isotope signature measurement results.

[0033] In the figure: 1. Laser light source; 2. Microscope; 3. Sample; 4. Hot and cold stage; 5. Electric precision three-dimensional moving platform; 6. Thermal conductive silver cover; 7. Thermocouple; 8. Computer; 9. Temperature control system. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more apparent, embodiments of the present invention will be further described below with reference to the accompanying drawings. The following describes a preferred embodiment of the present invention among multiple possible embodiments, which is intended to provide a basic understanding of the present invention but is not intended to identify the key or decisive elements of the present invention or to limit the scope of protection.

[0035] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0036] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0037] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in the subsequent drawings. At the same time, it should be understood that for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual scale.

[0038] It should be noted that, unless otherwise specified or limited, the terms "mounted" and "connected" should be understood broadly. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0039] Please refer to Figure 1-5 The embodiment of the present invention provides a method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion, which can measure carbon isotopes or oxygen isotopes in carbon dioxide inclusions. This embodiment uses the measurement of carbon isotopes as an example for explanation. The measurement method mainly includes the following steps:

[0040] S1. Select at least two standard carbon dioxide samples with known isotopic characteristics. The number of standard carbon dioxide samples can be flexibly set to multiple. For example, in this embodiment, the number of standard carbon dioxide samples is set to two. The carbon isotopic characteristics of the standard carbon dioxide samples are known.

[0041] S2. Obtain Raman spectral data of all standard carbon dioxide samples and inclusion samples to be tested at different temperatures. The Raman spectral data include Fermi doublet intensity, thermal peak intensity and isotope peak intensity to be tested. The isotope to be tested here is carbon isotope, such as 13 C. When measuring oxygen isotopes, the isotope to be measured is the oxygen isotope.

[0042] Specifically, select rock or mineral samples containing inclusions. The samples need to be properly processed to expose the inclusions, usually by thin sectioning or polishing. Ensure that the sample surface is clean to avoid surface impurities interfering with the measurement results.

[0043] All standard carbon dioxide samples 3 and inclusion samples 3 to be tested are obtained through a microscope 2, specifically, Figure 1As shown, the sample 3 is placed on the hot and cold stage 4, and a heat-conducting silver cover 6 is placed on the sample 3. The target inclusion must be located at the light-transmitting part of the hot and cold stage 4 to ensure that the target inclusion can be observed under the microscope 2. The hot and cold stage 4 of the sample 3 is placed under the microscope 2, and a high-magnification objective lens is used to find and mark the relative position of the target inclusion in the sample 3. The position of the sample 3 is adjusted by the three-axis adjustment platform to ensure that the laser is focused on the center of the target inclusion. The specific position and morphology of the inclusion is observed using a high-magnification objective lens to ensure that the laser can be accurately concentrated on the carbon dioxide gas area in the sample 3. The temperature control system 9 of the hot and cold stage 4 is operated to adjust the temperature of the sample 3 to the required value. The temperature of the sample 3 can be adjusted to multiple temperatures in succession to perform Raman spectral data measurement. In this way, the exposure time of all standard carbon dioxide samples 3 and the inclusion sample 3 to be measured can be obtained at each temperature to perform Raman spectral data measurement.

[0044] The laser light source 1 is turned on to irradiate the inclusion with a predetermined power to stimulate the Raman scattering signal. The scattered light is captured by the spectrum detection module and spectral analysis is performed to record the Raman spectrum data at different temperatures.

[0045] Wherein, the microscope 2 is preferably a LabRAM HR800 confocal microscopic laser Raman spectrometer produced by HORIBA JobinYvon SAS. The microscopic laser Raman spectrometer is mainly composed of a laser light source 1, a spectrometer, a microscope 2 and an electric precision three-dimensional mobile platform 5. The laser light source 1 is a ventus 532 diode-pumped solid-state laser produced by Laser Quantum, which uses high-power solid-state light-emitting (1064nm) crystal frequency doubling technology to produce an ideal single-frequency TEM 00 mode 532nm laser. It is equipped with a power control unit (mpc 6000) to control the laser frequency and beam pointing to maintain stability. It is equipped with two resolution gratings of 300 scales / mm and 1800 scales / mm for signal collection in different situations. The observation lens is an Olympus 50x telephoto lens with a numerical aperture of 0.5. Neon lamps are set up at the microscope 2 and the sample 3 to correct the Raman spectrum shift of each substance. The electric precision three-dimensional motion platform 5 is fully automated with motor control, offering a minimum step size of 0.1 μm, fully meeting the needs of measuring different positions on sample 3. The spectral data acquisition software removes baselines from the collected spectral data, automatically annotates peak positions, performs spectral peak fitting, and calculates the center frequency shift, half-height width, spectral intensity, and integrated area of ​​the peak, fully meeting the needs of Raman spectroscopy testing and processing.

[0046] The cold and hot stage 4 is a cold and hot stage of CAP500 type manufactured by Linkam Company, and the controllable temperature range is -190-500℃. The temperature rising part is controlled by K type high precision thermocouple 7, and the temperature falling part is controlled by external liquid nitrogen and the liquid nitrogen extraction speed controlled by the control system. The control temperature precision is related to the control temperature range, and the precision is ±0.2℃ in the range of 25-100℃, and the precision is ±0.5℃ in the range of 100-300℃. The cold and hot stage 4 is equipped with a silver pad cover 6 which can wrap the analysis sample, so as to more sensitively perceive the temperature change, and adjust the position of the sample 3 to make it uniformly heated.

[0047] The Raman spectrum data obtained in the embodiment is shown in the following table: Figure 4 In which, the exposure time can be set according to the single second fermi doublet and the thermal peak intensity as required, and the suitable Raman spectrum data can be obtained. When the Raman spectrum data is measured at the first exposure time, the exposure time is set according to the single second peak intensity on the right side of the fermi doublet, so that the fermi doublet intensity is as large as possible, but cannot exceed 60000. When the fermi doublet intensity exceeds 60000, the signal will be filtered and flattened. The peak intensity on the right side of the fermi doublet is generally selected to be 50000-60000. When the Raman spectrum data is measured at the second exposure time, the exposure time is set according to the single second peak intensity of the right side thermal peak, so that the right side thermal peak intensity is as large as possible, but cannot exceed 60000. The right side thermal peak intensity at the second exposure time is generally selected to be 50000-60000.

[0048] In addition, the Raman spectrum data can also be obtained by using the preset algorithm on the computer 8 for signal denoising and peak recognition. For example, the Grams Suite 9 spectrum processing software can be used to extract the characteristic peak intensity signal in the spectrum. First, the fermi doublet intensity (I FD - and the two thermal peak intensities (I FD + ) are extracted from the Raman spectrum data at the first exposure time, and then the C peak intensity (I HB - and the right side thermal peak intensity (I HB + ) are extracted from the Raman spectrum data at the second exposure time. 13 13 HB

[0049] S3, constructing a standard model according to the Raman spectrum data of all standard carbon dioxide samples:

[0050] HR=kR HF +a

[0051] R HF =I HB - +I HB ​​​+ / I FD - +I FD +

[0052] HR ＝ I HB / I x

[0053] Among them, I FD - and I FD + are the double peak intensities at the first exposure time, I HB - and I HB + is the thermal peak intensity at the first exposure time, I x and I HB are respectively the isotope peak intensity to be measured at the second exposure time and the thermal peak intensity on the right. In this embodiment, the isotope peak intensity to be measured at the second exposure time is 13 C is the peak intensity, k is the slope, and a is the intercept.

[0054] like Figure 5 As shown, in this embodiment, the standard model is constructed by the Raman spectra of two standard carbon dioxide samples at four temperatures, and the horizontal axis in the standard model is I HB - and I HB + The sum of I FD - and I FD + The ratio of the sum of HF , the vertical axis is I HB with I 13 The ratio of C is recorded as HR.

[0055] S4. Input the Raman spectrum data of the inclusion sample to be tested at different temperatures into the standard model to obtain the isotope ratio curve of the inclusion sample to be tested, and calculate the carbon isotope characteristics of the inclusion sample to be tested based on the fact that the spacing between the isotope ratio curves is proportional to the difference in carbon isotope ratios.

[0056] like Figure 5 As shown, the isotope ratio curve of the inclusion sample to be tested (purple dashed line) is compared with the isotope ratio curves of two standard carbon dioxide samples (red dashed line and green dashed line). The slope of the isotope ratio curve in the standard model is 74.5. It is known that the spacing between the isotope ratio functions is proportional to the difference in carbon isotope ratio. In the measured carbon dioxide inclusion, δ 13 C is greater than -12.58‰, select a straight line RHF =0.0537, HR A =3.5802, HR B =3.4344, HR x =3.3929, and the δ of the carbon dioxide inclusion can be calculated based on the spacing and the isotope difference of the standard sample. 13 C=-6.29‰.

[0057] It should be noted that, in this embodiment, only two standard carbon dioxide samples are selected to form two isotope ratio curves. However, in other embodiments, three or more standard carbon dioxide samples may be selected to form multiple isotope ratio curves. In this case, the isotope ratio curves of the two standard carbon dioxide samples closest to the isotope ratio curve of the inclusion sample to be tested may be selected. Based on the fact that the spacing between the isotope ratio curves is proportional to the difference in carbon isotope ratios, the carbon isotope characteristics of the inclusion sample to be tested may be calculated.

[0058] Although the present embodiment illustrates the measurement of carbon isotopes in carbon dioxide inclusions, it is understandable that the measurement method in this embodiment is also applicable to the measurement of oxygen isotopes in carbon dioxide inclusions, and the measurement steps and principles are the same as those in this embodiment.

[0059] Compare Figure 6 The present invention is used to measure the carbon-oxygen isotope composition of carbon dioxide in a single inclusion. 13 C isotope signature measurements and Figure 7 The existing mixed sample calibration factor method is used to 13 The measurement results of C isotope characteristics show that the method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion of the present invention greatly improves the test accuracy, with the accuracy increased by 10 to 20 times.

[0060] In this document, directional terms such as front, back, top, and bottom are defined based on the positions of components in the accompanying drawings and relative to each other, and are intended for clarity and convenience in describing the technical solution. It should be understood that these terms are relative and may vary depending on usage and placement. The use of these directional terms should not limit the scope of protection claimed in this application.

[0061] The above embodiments and features of the embodiments may be combined with each other unless they conflict. The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion, characterized in that: The following steps are involved: S1. Select at least two standard carbon dioxide samples with known isotopic characteristics; S2. Obtaining Raman spectral data of all standard carbon dioxide samples and the inclusion samples to be tested at different temperatures, wherein the Raman spectral data include Fermi doublet intensity, thermal peak intensity, and isotope peak intensity to be tested, where the isotope to be tested is carbon isotope or oxygen isotope; S3. Construct a standard model based on the Raman spectral data of all standard carbon dioxide samples: a R HF =(I HB - +I HB + ) / (I FD - +I FD + ) HR I HB / I x Among them, I FD - and I FD + are the double peak intensities at the first exposure time, I HB - and I HB + is the thermal peak intensity at the first exposure time, I x and I HB are the intensity of the isotope peak to be measured and the intensity of the thermal peak on the right at the second exposure time, k is the slope, and a is the intercept; S4. Input the Raman spectrum data of the inclusion sample to be tested at different temperatures into the standard model to obtain the isotope ratio curve of the inclusion sample to be tested, and calculate the carbon isotope characteristics of the inclusion sample to be tested based on the fact that the spacing between the isotope ratio curves is proportional to the difference in carbon isotope ratios.

2. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: In step S4, the isotope ratio curves of two standard carbon dioxide samples closest to the isotope ratio curve of the inclusion sample to be tested are selected, and the carbon isotope characteristics of the inclusion sample to be tested are calculated based on the fact that the distance between the isotope ratio curves is proportional to the difference in carbon isotope ratios.

3. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: In step S2, the exposure time is controlled so that the Fermi double peak intensity at the first exposure time does not exceed 60,000, and the right thermal peak intensity at the second exposure time does not exceed 60,000.

4. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 3, wherein: The peak intensity on the right side of the Fermi double peak under the first exposure time is 50,000~60,000, and the intensity of the right thermal peak under the second exposure time is 50,000~60,000.

5. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: Step S2 specifically includes placing the sample on a hot / cold stage, placing the hot / cold stage under a microscope, turning on a laser light source, irradiating the inclusions at a predetermined power to stimulate Raman scattering signals, capturing the scattered light through a spectral detection module and performing spectral analysis, and recording Raman spectral data at different temperatures.

6. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 5, wherein: The microscope is a LabRAM HR800 confocal laser Raman spectrometer.

7. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 5, wherein: The hot and cold stage is a CAP500 hot and cold stage.

8. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: The step S2 further includes performing signal denoising and peak identification using a preset algorithm to obtain Raman spectrum data.

9. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: In step S2, the inclusion sample to be tested is cut or polished to expose the inclusions.

10. The method for measuring carbon and oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, wherein: The isotope to be measured is 13 C.

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