A dolomite standard sample development method for calibrating by age method, dolomite standard sample and its application

Abstract

The present invention provides a method for developing a dolomite standard sample for calibrating an age method, a dolomite standard sample, and its application. The development method includes: providing a dolomite candidate standard sample; providing a calcite standard sample, a zircon standard sample, and a garnet standard sample that have been verified by matrix effect; using the calcite standard sample as the main standard sample and the zircon standard sample and the garnet standard sample as the secondary standard samples, testing the age of the dolomite candidate standard sample twice, and recording the obtained test results as A and B respectively; when A and B satisfy (A-B) / B×100≤3, the dolomite candidate standard sample is used as the dolomite standard sample. The present invention establishes a standard sample development process that is free from diluents and existing standard samples, and successfully develops a dolomite standard sample.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geological exploration, and in particular to a method for developing dolomite standards calibrated by age, dolomite standards and their applications. Background Technology

[0002] Geochronology is a perennial theme in geological research, with wide applications in paleoenvironmental, paleoclimatic, and paleotectonic reconstruction, as well as geological studies of solid minerals and oil and gas deposits. Zircon U-Pb isotope dating and apatite fission track dating methods are widely used. Significant progress has been made in U-Pb isotope geochronology of carbonate minerals in recent years, and laser U-Pb dating has achieved excellent results in numerous geological cases.

[0003] Standard samples are an essential part of quality control in isotope geochemical analysis, and they are scarce resources for all laboratories. Developing high-quality standards has always been a reflection of a laboratory's level of expertise and a key to ensuring data reliability. Currently, laser U-Pb dating has resulted in a series of calcite standards for different age groups, including old, middle, and new strata. However, there are still no reliable standards for dolomite, which is the dominant mineral in ancient strata, and its development is urgently needed.

[0004] There are two main challenges in developing dolomite standards: First, the standards must be pure, with U content and U-Pb age matching the unknown sample, stable isotope measurement signals, and consistent and stable U-Pb ages (not too many phases); second, dolomite has a complex origin, and multiple phases are mixed and cannot be distinguished at the microscopic scale, making it impossible to meet the above requirements. Therefore, no one has successfully developed a reliable dolomite standard to date.

[0005] Traditionally, the development of standards requires isotope diluent calibration, but 233 U- 205 Pb diluents are extremely rare and precious. Currently, only the recommended ages of WC-1 and ASH-15 standards are determined using isotopic diluents. Very few laboratories worldwide use them. 233 U- 205 Pb diluents are primarily used for U-Pb dating of carbonate minerals for standard development or calibration with proven mature standards such as WC-1 and ASH-15. However, there are currently no reliable dolomite standards, and the applicability of calcite standards to dolomite is questionable due to matrix effects.

[0006] Therefore, innovative processes are needed to develop dolomite standard samples. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for developing dolomite standards calibrated by age method, dolomite standards and their applications, so as to solve the problem that traditional standard development cannot avoid the use of isotope diluents.

[0008] To achieve the above objectives, the present invention provides a method for developing age-calibrated dolomite standards, comprising:

[0009] Provide candidate dolomite standards;

[0010] Provides calcite, zircon, and garnet standards verified by matrix effects;

[0011] Using calcite as the primary standard and zircon and garnet as secondary standards, the age of the dolomite candidate standard was tested twice, and the test results were recorded as A and B, respectively.

[0012] When A and B satisfy (AB) / B×100≤3, the dolomite candidate standard sample is used as the dolomite standard sample;

[0013] The matrix effect verification includes:

[0014] Any two of the calcite standard, zircon standard and garnet standard are used as test sample C and test sample D respectively, and the remaining third is used as the test sample.

[0015] The age of the test sample is tested using test sample C and test sample D respectively, and the test results are recorded as C1 and D1 respectively. The true age of the test sample is recorded as E. When C1, D1, and E satisfy (C1-E) / E×100≤3 or (D1-E) / E×100≤3, the matrix effect verification is considered to be completed.

[0016] In this invention, preferably, the selected calcite, zircon, and garnet standards have the same order of magnitude U content as the dolomite candidate standards.

[0017] Using calcite as the primary standard and zircon and garnet as secondary standards, the age of the dolomite candidate standard can be tested more than twice. As the number of tests increases, the results will be more reliable. However, based on the method of this invention, two measurements are sufficient to complete the test.

[0018] According to the development method of the present invention, zircon and garnet, which have very different mineral compositions and structural components, and calcite, which has good similarity to dolomite in mineral composition and structural components (i.e., similarity in U content, preferably, the U content is on the same order of magnitude), were selected. Through cross-monitoring calibration, the matrix effect was verified. That is, it can be concluded that zircon and garnet can be used to calibrate calcite. Therefore, it is easy to see that calcite, zircon, and garnet can be used to calibrate dolomite.

[0019] The above method not only avoids the matrix effect that may exist between calcite and dolomite, but also overcomes the problem of the scarcity of diluents and existing standards, and establishes a standard development process that eliminates the need for diluents and existing standards. This technical process is applicable to the development of other standards without existing standards and diluents for calibration.

[0020] According to a specific embodiment of the present invention, preferably, the method for testing the dolomite candidate standard is a laser method; preferably, the parameters of the laser beam in the laser method are: wavelength 60-100 micrometers, frequency 5-15 Hz, and energy density 2-5 J / cm². 2 .

[0021] According to a specific embodiment of the present invention, preferably, the testing instrument is calibrated using NIST-612 before the laser method test; preferably, the parameters of the testing instrument are adjusted so that the 232Th / 238U ratio of NIST-612 is close to 1.

[0022] According to a specific embodiment of the present invention, preferably, the laser method test is performed using the Energy mode of an iCap-RQ (inductively coupled plasma mass spectrometer).

[0023] According to a specific embodiment of the present invention, preferably, the method for selecting the dolomite candidate standard sample includes:

[0024] A potential dolomite standard is provided, and geochemical analysis is performed on the potential dolomite standard to determine its diagenetic alteration intensity. When the diagenetic alteration intensity meets the following conditions: the dolomite crystal has an invisible zoning structure under cathodoluminescence and trace rare earth element surface scanning, the Mn / Sr ratio is less than 1, and the error of the strontium isotope ratio obtained from three parallel sample measurements is less than 0.00001, the potential dolomite standard is used as the candidate dolomite standard.

[0025] Potential dolomite standards require pure and homogeneous texture, stable isotope measurement signals, and small U-Pb age error (not exceeding 3%).

[0026] This invention does not impose any particular restrictions on the specific location where dolomite is produced.

[0027] According to a specific embodiment of the present invention, preferably, the geochemical analysis includes one or more of the following: cathodoluminescence analysis, trace rare earth element surface scan analysis, carbon, oxygen, and strontium isotope analysis, and trace element content analysis.

[0028] According to a specific embodiment of the present invention, preferably, the development method further includes: reliability verification;

[0029] Preferably, the reliability verification method includes:

[0030] The age of a dolomite standard sample with similar U content (of the same order of magnitude) is determined by testing the dolomite standard sample. The test result is denoted as F, and the true age of the similar standard sample is denoted as G. When F and G satisfy (FG) / G×1000≤3, the dolomite standard sample is considered a reliable standard sample. The similar standard sample is selected from one of garnet, zircon, and calcite.

[0031] The reliability of the dolomite standard sample of the present invention can be further confirmed through the above reliability verification.

[0032] According to a specific embodiment of the present invention, preferably, the calcite standard sample is selected from WC-1 calcite or ASH15 calcite.

[0033] According to a specific embodiment of the present invention, preferably, the zircon standard is selected from 91500 zircon or Temora zircon.

[0034] According to a specific embodiment of the present invention, preferably, the garnet standard sample is selected from TC garnet.

[0035] According to another aspect of the present invention, a dolomite standard sample obtained according to the above-described development method is also provided.

[0036] According to another aspect of the present invention, an application of the aforementioned dolomite standard sample in the development of U-Pb isotope dating technology is also provided. The scope of application of the present invention includes providing standard sample support for the development and application of laser-based and solution-based dolomite U-Pb isotope dating technologies. Attached Figure Description

[0037] Figure 1 The flowchart of the method for developing dolomite standards calibrated by the age method of the present invention is shown.

[0038] Figure 2 The measured age of zircon standard 91500 is shown.

[0039] Figure 3 The age of calcite standard AHX-1D, determined using zircon as a standard value, is shown.

[0040] Figure 4The age of garnet standard TC-13, determined using zircon standard as a normalized value, is shown.

[0041] Figure 5 The age of garnet standard QC-04, determined using zircon standard as the normalized value, is shown.

[0042] Figure 6 The measured age of calcite standard AHX-1D is shown.

[0043] Figure 7 The age of zircon sample 91500 is shown, with calcite standard as the normalized value.

[0044] Figure 8 The age of garnet standard TC-13, measured using calcite standard as the normalized value, is shown.

[0045] Figure 9 The age of the dolomite candidate standard GT2-1, calculated for the first time using calcite standard as the normalized value, is shown.

[0046] Figure 10 The age of the dolomite candidate standard GT2-1, calculated a second time using calcite as the standard value, is shown. Detailed Implementation

[0047] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0048] Example 1

[0049] A method for developing age-calibrated dolomite standards, the flowchart of which is as follows: Figure 1 As shown, it includes the following steps:

[0050] Acquisition of potential S100 dolomite standards

[0051] The collected potential standards were first analyzed by cathodoluminescence, trace rare earth element surface scanning, and carbon, oxygen, and strontium isotope and trace element content. Based on the oxygen isotope, strontium isotope, and strontium content, as well as the characteristics of cathodoluminescence and rare earth element surface scanning, it was determined that the diagenetic alteration intensity of dolomite was relatively weak. That is, the dolomite crystals did not have obvious zoning structure under cathodoluminescence and trace rare earth element surface scanning, the Mn / Sr ratio was less than 1, and the error of the strontium isotope ratio obtained from three parallel samples was less than 0.00001. Therefore, it can be used as a candidate standard.

[0052] Verification of S200 matrix effect

[0053] First, zircon standards with very large differences in mineral composition and structural components but similar U content were selected as monitoring standards. The ages of existing calcite and garnet standards were then tested. Specifically, the age of the standards was determined by laser ablation inductively coupled plasma mass spectrometry.

[0054] like Figure 2 The measured age of zircon standard sample 91500 is 1062.4 ± 0.4 Ma;

[0055] like Figure 3 Using zircon as a standard value, the age of calcite standard AHX-1D was measured to be 240.0±1.2 Ma, which is very close to its true age of 236.9±1.6 Ma;

[0056] like Figure 4 Using zircon as a standard value, the TC-13 age of the garnet standard was measured to be 125.20±0.56 Ma, which is very close to its true age of 126.2±2.3 Ma;

[0057] like Figure 5 Using zircon as a standard value, the age of garnet standard QC-04 was measured to be 129.34±0.39 Ma, which is very close to its true age of 130±1 Ma;

[0058] Then, using the age of the calcite standard sample as the standardized value, the ages of the zircon and garnet standard samples were calculated;

[0059] like Figure 6 The measured age of the calcite standard AHX-1D is 236.87 ± 0.82 Ma;

[0060] like Figure 7 Using calcite as a standard value, the age of zircon at 91500 was measured to be 1067.7 ± 2.4 Ma, which is very close to its true age.

[0061] like Figure 8 Using calcite as a standard value, the TC-3 age of the garnet standard was measured to be 126.77±0.52 Ma, which is very close to its true age of 126.2±2.3 Ma;

[0062] Through interactive monitoring and calibration, zircon and garnet, which have very different mineral compositions and structural components, yielded age results that were close enough to the true values ​​for calcite. It can be concluded that zircon and garnet can be used to calibrate calcite. Since calcite and dolomite have better similarities in mineral composition and structural components, it is easy to conclude that calcite, zircon, and garnet can also be used to calibrate dolomite.

[0063] S300 determination based on dolomite standard using calcite standard.

[0064] Based on the above verification results of the base effect, calcite standard samples can be used as standardized values ​​for dolomite standard sample determination.

[0065] Specifically, the AHX-1D calcite standard, which is likely to be of similar age to the candidate dolomite standard, was selected as the main standard, and zircon 91500 and garnet were selected as secondary standards. First, the instrument parameters were optimized using NIST-612 to make the NIST 232Th / 238U ratio close to 1. Then, the candidate dolomite standard was measured twice on an iCap-RQ using an 80-micron laser beam, 10 Hz, and 6.60 mJ energy in Energymode.

[0066] For samples older than 100 million years, an age difference of no more than 30 million years is considered similar. If the results show that the ages of dolomite and calcite are not similar, then a calcite standard sample with a closer age needs to be selected for re-measurement.

[0067] like Figure 9 The GT2-1 age of the first dolomite candidate standard sample was calculated to be 253.8 ± 2.2 Ma, with the calcite standard sample being the standardized value.

[0068] like Figure 10 The calcite standard is standardized, and the second calculated age of the dolomite candidate standard GT2-1 is 248.1±2.6 Ma;

[0069] (253.8-248.1) / 253.8×100=2.24, which shows that the ages of the two dolomite candidate samples are close enough to meet the conditions for being used as standard samples.

[0070] Test method:

[0071] Laser carbon and oxygen isotope analysis was performed at LA-IRMS. The laser equipment (LA) consisted of an Nd:YAG (yttrium aluminum garnet) near-infrared laser, a cooling system, a microscopic imaging system, and a gas transport and separation system. The ND:YAG laser output a near-infrared coherent laser beam with a wavelength of 1064 nm and a beam size better than 20 μm. A krypton lamp was used as the pump energy for the ND:YAG laser, with an operating current of 7-20 A, producing 7-40 W of output energy. The sample penetration depth was 30-50 μm. The stable gas isotope instrument model was Detla V Advantage. Helium was used as the carrier gas during laser ablation. The laser reacted with carbonates to produce CO2 gas. After impurity gas separation and purification, pure CO2 gas was obtained and then analyzed by isotope mass spectrometry. The laser beam diameter and current used in this analysis were 20 μm and 14–20 A, respectively. The laser was continuously wound (CW) output. The standard samples used for data calibration were the national standard GBW04405 and the laboratory internal standard 811. Data processing was performed using Thermo Fisher Scientific ISODAT 3.0 software and is expressed in PDB format. The testing accuracies for δ13C and δ18O were ±0.1‰ and ±0.2‰, respectively. A laser beam diameter of 500 μm was used to test only the cores of fine-grained and medium-to-coarse-grained dolomite. Residual shadows of identifiable original grains and cement within some coarse-grained dolomite were also tested. Dolomite crystals and calcite cement in limestone were tested as a comparison.

[0072] Strontium isotope analysis was performed using solid-state mass spectrometry and IVP-MS (X Series II). 100–150 mg of powder sample was weighed and dissolved in a 1:1 mixture of HNO3 and HF at 190 °C for 48 hours. Strontium isotopes were extracted using a standard procedure (Baadsgard, 1987) and analyzed, with NBS987 as the standard. The average error for the 87Sr / 86Sr ratio was ±0.5 × 10⁻⁶. -5 .

[0073] Trace rare earth element analysis was performed on whole-rock powder samples using inductively coupled plasma mass spectrometry (ICP-MS) with a Thermo Fisher iCAP RQ model and a CETAC 560 autosampler. 50–100 mg of powder sample was dissolved in a mixture of 0.6 mL HNO3 and 2.5 mL HF at 185 °C for 72 hours. After drying, the solution was reacted with 4 mL of a 20% mixed acid (HCl:HNO3 = 4:1) at 130 °C for 3 hours. After removing the acid, the dissolved product was analyzed using a standard procedure in the ICP-MS. The standard was USGS W-2a, and the sample solution contained four internal standards: Rh, In, Re, and Bi. The accuracy was 0.1 ppb, with an error of ±5%.

[0074] Cathodoluminescence was performed using a CL8200MK5 manufactured by CITL, following the standard SY / T5916-2013, "Identification Method of Cathodoluminescence for Rocks and Minerals".

[0075] Trace rare earth element surface scanning was performed using LA-ICP-MS to conduct in-situ micro-area laser surface scanning imaging of selected regions. First, the elements to be tested and the integration time were selected. Second, based on the mineral fabric characteristics of the sample, the surface scanning area, laser beam spot, energy density, moving speed, ablation frequency, and scan line spacing parameters were set. Then, LA-ICP-MS micro-area in-situ laser surface scanning imaging was tested, and the data was processed and images generated in the Iolite software.

[0076] As can be seen from the embodiments, the method developed in this invention can successfully produce dolomite standard samples.

Claims

1. A method for developing age-calibrated dolomite standards, characterized in that, include: Provide candidate dolomite standards; Provides calcite, zircon, and garnet standards verified by matrix effects; Using the calcite standard as the primary standard and the zircon and garnet standards as secondary standards, the age of the dolomite candidate standard was tested twice, and the test results were recorded as A and B, respectively. When A and B satisfy (AB) / B×100≤3, the dolomite candidate standard sample is used as the dolomite standard sample; The matrix effect verification includes: Any two of the calcite standard, zircon standard and garnet standard are used as test sample C and test sample D respectively, and the remaining third is used as the test sample. The age of the test sample is tested using test sample C and test sample D respectively, and the test results are recorded as C1 and D1 respectively. The true age of the test sample is recorded as E. When C1, D1, and E satisfy (C1-E) / E×100≤3 or (D1-E) / E×100≤3, the matrix effect verification is considered to be completed. The selected calcite, zircon, and garnet standards have U contents of the same order of magnitude as the candidate dolomite standards; The development method also includes: Reliability verification; The reliability verification method includes: The age of a similar standard sample is determined by testing the dolomite standard sample, and the test result is denoted as F. The true age of the similar standard sample is denoted as G. When F and G satisfy (FG) / G×100≤3, the dolomite standard sample is considered a reliable standard sample. The similar standard sample is selected from either garnet or zircon.

2. The development method according to claim 1, characterized in that, The method for testing the dolomite candidate standard is the laser method; The laser beam parameters in the laser method are: wavelength 60–100 micrometers, frequency 5–15 Hz, and energy density 2–5 J / cm². 2 .

3. The development method according to claim 2, characterized in that, Before the laser method test, the test instrument was calibrated using NIST-612; the parameters of the test instrument were adjusted so that the 232Th / 238U ratio of NIST-612 was close to 1.

4. The development method according to claim 3, characterized in that, The laser method test was performed using the Energy mode of the iCap-RQ.

5. The development method according to claim 1, characterized in that, The method for selecting the dolomite candidate standard includes: A potential dolomite standard is provided, and geochemical analysis is performed on the potential dolomite standard to determine its diagenetic alteration intensity. When the diagenetic alteration intensity meets the following conditions: the dolomite crystals have no obvious zoning structure under cathodoluminescence and trace rare earth element surface scanning, the Mn / Sr ratio is less than 1, and the error of the strontium isotope ratio obtained from three parallel sample measurements is less than 0.00001, the potential dolomite standard is used as the candidate dolomite standard.

6. The development method according to claim 5, characterized in that, The geochemical analysis includes any combination of methods among cathodoluminescence analysis, trace rare earth element surface scan analysis, carbon, oxygen, and strontium isotope analysis, and trace element content analysis.

7. The development method according to claim 1, characterized in that, The calcite standard was selected from WC-1 calcite or ASH15 calcite.

8. The development method according to claim 1, characterized in that, The zircon samples were selected from 91500 zircon or Temora zircon.

9. The development method according to claim 1, characterized in that, The garnet standard sample was selected from TC garnet.

10. A dolomite standard obtained by the development method according to any one of claims 1 to 9.

11. The application of the dolomite standard as described in claim 10 in the development of U-Pb isotope dating technology.

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