Method for measuring carbon-oxygen isotope of carbon dioxide in single inclusion

Abstract

The invention provides a single inclusion carbon dioxide carbon-oxygen isotope measurement method, and relates to the technical field of isotope measurement, and the method 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 inclusion samples to be detected at different temperatures; s3, constructing a standard model according to the Raman spectrum data of all the standard carbon dioxide samples; s4, inputting the Raman spectrum data of a to-be-detected inclusion sample at different temperatures into the standard model to obtain isotope ratio curves of the to-be-detected inclusion sample, and calculating to-be-detected carbon isotope characteristics of the to-be-detected inclusion sample according to the fact that the distance between the isotope ratio curves is in direct proportion to the difference of the carbon isotope ratios. The method has the beneficial effects that Raman spectrum detection is directly carried out in the inclusion, the limitation that a sample needs to be damaged in a traditional mass spectrometry method is avoided, and nondestructive and high-precision measurement of the carbon and oxygen isotope ratio of carbon dioxide in a single inclusion can be realized.

Description

Technical Field

[0001] The 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 that are trapped inside crystals during the formation of minerals or rocks, and contain important information such as ore-forming fluids, magma evolution, and temperature and pressure conditions. Carbon dioxide (CO2), as 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 path of geological fluids. Accurately measuring the carbon and oxygen isotope ratios of carbon dioxide in inclusions helps to reveal the formation environment of ore-forming fluids, the migration pattern of geological fluids and the geological history evolution process.

[0003] Traditional carbon and oxygen isotope measurement methods mainly rely on mass spectrometers for accurate isotope ratio analysis. These methods include gas isotope mass spectrometry (IRMS) and secondary ion mass spectrometry (SIMS), which have high sensitivity and resolution. However, traditional mass spectrometry methods usually require the extraction of carbon dioxide gas from inclusions, which often leads to the destruction of inclusions. Especially for tiny and precious geological samples, the extraction process may destroy the microstructure of the sample, thereby affecting the integrity of the sample and the accuracy of subsequent research. Usually, the carbon dioxide in the inclusion is small in volume and often under high pressure. It is very difficult to directly extract the gas components therein, especially for extremely small single inclusions (usually less than tens of microns in diameter), which is even more difficult to accurately extract and analyze without destroying the sample. In addition, in rock or mineral thin sections, the inclusions are numerous and of various shapes, usually of different sizes and buried deep in the sample. Conventional mass spectrometry methods cannot accurately locate the position and size of a single inclusion, and can often only perform overall measurements, making it difficult to obtain accurate isotope 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 spectral data of all standard carbon dioxide samples and inclusion samples to be tested at different temperatures, wherein the Raman spectral data include Fermi double peak intensity, thermal peak intensity and isotope peak intensity to be tested, and the isotope to be tested is carbon isotope or oxygen isotope;

[0008] S3. Construct a standard model based on the Raman spectral data of all standard carbon dioxide samples:

[0009] HR=kR HF +a

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

[0011] HR ＝ I HB / I x

[0012] Among them, I FD - and I FD + are the double peak intensity 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 isotope peak intensity to be measured and the right thermal peak intensity at the second exposure time, k is the slope, and a is the intercept;

[0013] 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.

[0014] Furthermore, 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.

[0015] Furthermore, in step S2, by controlling the exposure time, 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.

[0016] Furthermore, the peak intensity on the right side of the Fermi double peak at the first exposure time is 50,000-60,000, and the intensity of the thermal peak on the right side at the second exposure time is 50,000-60,000.

[0017] Furthermore, step S2 is specifically as follows: placing the sample on a hot and cold stage, placing the hot and cold stage under a microscope, turning on the laser light source, irradiating the inclusions with a predetermined power, exciting Raman scattering signals, capturing the scattered light through a spectral detection module and performing spectral analysis, and recording Raman spectral data at different temperatures.

[0018] Furthermore, the microscope is a LabRAM HR800 confocal microscope laser Raman spectrometer.

[0019] Furthermore, the hot and cold stage is a CAP500 hot and cold stage.

[0020] Furthermore, the step S2 also includes using a preset algorithm to perform signal denoising and peak identification to obtain Raman spectrum data.

[0021] Furthermore, in step S2, the inclusion sample to be tested is cut or polished by thin sections to expose the inclusions.

[0022] Further, the isotope to be detected is 13 C.

[0023] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention are:

[0024] 1. A single inclusion carbon dioxide carbon-oxygen isotope measurement method of the present invention can perform Raman spectroscopy detection on the carbon dioxide in the inclusion without destroying the inclusion structure, use Raman spectral data of two standard carbon dioxide samples with known isotopic characteristics to build a standard model, input the Raman spectral data of the inclusion 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, and directly perform Raman spectroscopy detection in the inclusion, which overcomes the dependence of traditional methods on sample amount and avoids the limitation of traditional mass spectrometry that requires sample destruction, and can achieve non-destructive and high-precision measurement of the carbon and oxygen isotope ratio of carbon dioxide in a single inclusion, providing more accurate and convenient technical support for the fields of geology and geochemistry.

[0025] 2. A single inclusion carbon dioxide carbon-oxygen isotope measurement method of the present invention has a high resolution Raman spectrum and can distinguish 12 C and 13 C. 16 O and 18O isotope ratios, using isotope calibration and δ 13 C and δ 18 The carbon and oxygen isotope values ​​are obtained by the method of 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 It is a schematic diagram of Raman spectrum 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 It is the Mann spectrum data diagram of the inclusion sample to be tested;

[0029] Figure 4 It is a schematic diagram of the method for obtaining the characteristic peaks and thermal peaks of carbon and oxygen isotopes 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 curves of two standard carbon dioxide samples;

[0031] Figure 6 The present invention is a method for measuring the carbon-oxygen isotopes 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] In order to make the purpose, technical solution and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in conjunction with the accompanying drawings. The following is a preferred embodiment of the present invention, which is intended to provide a basic understanding of the present invention, but is not intended to confirm 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 as 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, so 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 proportional relationship.

[0038] It should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to 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 is described by taking the measurement of carbon isotopes as an example. 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 the standard carbon dioxide samples can be flexibly set to multiple, such as 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 double peak 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 section cutting or polishing. Make sure 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. Use a high-magnification objective lens to observe the specific position and morphology of the inclusion to ensure that the laser can be accurately concentrated on the carbon dioxide gas area in the sample 3. Run the temperature control system 9 of the hot and cold stage 4 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 measure the Raman spectral data, so that 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 measure the Raman spectral data.

[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 the spectrum is analyzed 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 Jobin Yvon 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, and 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 displacement of each substance. The electric precision three-dimensional mobile platform 5 is a fully automatic motor-controlled movement with a minimum moving step of 0.1 μm, which fully meets the needs of measuring different positions of the sample 3. The spectral data acquisition software can remove the baseline of the collected spectral data, automatically mark the peak position, fit the spectrum peak, and calculate the center frequency shift, half-height width, spectrum intensity and integrated area of ​​the spectrum peak, which fully meets the needs of Raman spectrum test processing.

[0046] The hot and cold stage 4 is a CAP500 hot and cold stage manufactured by Linkam, with a controllable temperature range of -190-500°C. The temperature rise part is controlled by a K-type high-precision thermocouple 7, and the temperature drop part is controlled by the external liquid nitrogen and the liquid nitrogen extraction speed automatically adjusted by the control system. The temperature control accuracy is related to the temperature control range, which is ±0.2°C in the range of 25-100°C and ±0.5°C in the range of 100-300°C. The hot and cold stage 4 is equipped with a silver pad cover 6 that can wrap the analysis sample to facilitate more sensitive perception of temperature changes so as to adjust the position of the sample 3 so that it is evenly heated.

[0047] The Raman spectroscopy data obtained in this example are as follows Figure 4 As shown, different exposure times can be set according to the single-second Fermi double peak and thermal peak intensities as needed to obtain suitable Raman spectral data. When measuring Raman spectral data at the first exposure time, the exposure time is set according to the single-second peak intensity on the right side of the Fermi double peak, so that the Fermi double peak intensity is as large as possible, but cannot exceed 60,000. When it exceeds 60,000, the signal will be filtered and flattened. The peak intensity on the right side of the Fermi double peak can generally be selected to 50,000-60,000. When measuring Raman spectral data at the second exposure time, the exposure time is set according to the single-second peak intensity of the thermal peak on the right side, so that the thermal peak intensity on the right side is as large as possible, but cannot exceed 60,000. The thermal peak intensity on the right side at the second exposure time is generally selected to be 50,000-60,000.

[0048] In addition, the Raman spectrum data can be obtained by performing signal denoising and peak identification using the algorithm preset on the computer 8. For example, GramsSuite9 spectrum processing software can be used to extract the characteristic peak intensity signal in the spectrum. First, the Fermi double peak intensity (I FD - and I FD + ) and two thermal peak intensities (I HB - and I HB + ), and then extract the Raman spectrum data at the second exposure time 13 C peak intensity (I 13 C) and the right thermal peak intensity (I HB ).

[0049] S3. Construct a standard model based on the Raman spectral 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 intensity 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 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 in the figure, the isotope ratio curve of the inclusion sample to be tested (purple dotted line) is compared with the isotope ratio curves of two standard carbon dioxide samples (red dotted line and green dotted 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 inclusions, 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, according to the spacing and the isotope difference of the standard sample, the δ 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 can 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 can be selected. The carbon isotope characteristics of the inclusion sample to be tested can be calculated based on the fact that the spacing between the isotope ratio curves is proportional to the difference in carbon isotope ratios.

[0058] Although the present embodiment exemplifies the measurement of carbon isotopes in carbon dioxide inclusions, it is understandable that the measurement method in the present 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 the present embodiment.

[0059] Compare Figure 6 A single inclusion carbon dioxide carbon-oxygen isotope measurement method of the present invention is used to measure the carbon-oxygen isotope 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 From the measurement results of C isotope characteristics, it can be seen that the single inclusion carbon dioxide carbon-oxygen isotope measurement method of the present invention greatly improves the test accuracy, and the accuracy is improved by 10 to 20 times.

[0060] In this article, the directional words such as front, back, top, and bottom involved are defined by the positions of the parts in the drawings and the positions of the parts relative to each other, just for the sake of clarity and convenience in expressing the technical solution. It should be understood that they are relative concepts and can change accordingly according to different ways of use and placement, and the use of the directional words should not limit the scope of protection claimed in this application.

[0061] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 inclusion samples to be tested at different temperatures, wherein the Raman spectral data include Fermi double peak intensity, thermal peak intensity and isotope peak intensity to be tested, and 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: HR=kR HF +a HR ＝ I HB / I x Among them, I FD- and I FD + are the double peak intensity 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 isotope peak intensity to be measured and the right thermal peak intensity 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. A method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion as claimed in claim 1, characterized in that: 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-oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, characterized in that: 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. A method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion as claimed in claim 3, characterized in that: The peak intensity on the right side of the Fermi double peak at the first exposure time is 50,000-60,000, and the peak intensity on the right side of the thermal peak at the second exposure time is 50,000-60,000.

5. The method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion according to claim 1, characterized in that: The step S2 specifically includes: placing the sample on a hot and cold stage, placing the hot and cold stage under a microscope, turning on the laser light source, irradiating the inclusions with a predetermined power, stimulating 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. A method for measuring carbon-oxygen isotopes of carbon dioxide in a single inclusion as claimed in claim 5, characterized in that: The microscope is a LabRAM HR800 confocal laser Raman spectrometer.

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

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

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

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

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