Dolomite standard sample development method for age method calibration, dolomite standard sample and application of dolomite standard sample

Abstract

The invention provides a development method of a dolomite standard sample calibrated by an age method, the dolomite standard sample and application of the dolomite standard sample. The development method comprises the following steps: providing a dolomite candidate standard sample; providing a calcite standard sample, a zircon standard sample and a garnet standard sample which are verified by a matrix effect; taking a calcite standard sample as a main standard sample, taking a zircon standard sample and a garnet standard sample as auxiliary standard samples, testing the age of the dolomite candidate standard sample twice, and respectively recording obtained test results as A and B; and when A and B meet the condition that (A-B) / B * 100 is less than or equal to 3, taking the dolomite candidate standard sample as the dolomite standard sample. According to the invention, a standard sample development process without a diluent and an existing standard sample is established, and the dolomite standard sample is successfully developed and obtained.

Description

Technical Field

[0001] The invention relates to the field of geological exploration of petroleum and natural gas, and in particular to a method for developing a dolomite standard sample calibrated by an age method, a dolomite standard sample and an application thereof. Background Art

[0002] Geochronology is an eternal theme in geological research and can be widely used in paleoenvironment, paleoclimate, paleotectonic reconstruction and geological research on solid minerals, oil and gas minerals. Zircon U-Pb isotope, apatite fission track and other geochronological methods are widely used. Carbonate mineral U-Pb isotope geochronology has made significant progress in recent years, and laser U-Pb dating has achieved good application results in many geological examples.

[0003] Standard samples are a necessary part of isotope geochemical analysis quality control and are scarce for all laboratories. Developing high-quality standard samples has always been a reflection of laboratory level and the key to ensuring data reliability. At present, the calcite standard samples for laser U-Pb dating have formed a series of standard samples of different ages, such as old, medium and new, but there is no reliable standard sample for dolomite, which occupies a dominant position in ancient strata, and it is urgently needed to be developed.

[0004] There are two difficulties in developing dolomite standards: on the one hand, the standard must be pure, the U content and U-Pb age must match the unknown sample, the isotope measurement signal must be stable, and the U-Pb age must be consistent and stable (not too many periods). On the other hand, dolomite has a complex origin, and multiple periods of mixing cannot be distinguished at the microscopic scale, which cannot meet the above requirements. Therefore, no one has yet successfully developed a reliable dolomite standard.

[0005] Traditionally, the development of standards requires isotope dilution calibration, but 233 U- 205 Pb diluent is extremely rare and precious. Currently, only the recommended ages of WC-1 and ASH-15 standards are calibrated with isotope diluent. Very few laboratories in the world use 233 U- 205 Pb diluent is mainly used for U-Pb dating of carbonate minerals, or for calibration with proven WC-1 and ASH-15 mature standards. However, there is no reliable dolomite standard, and there is a matrix effect problem whether calcite standards can be used for dolomite.

[0006] Therefore, it is necessary to innovate the process and develop dolomite standard samples. Summary of the invention

[0007] In view of the problems existing in the prior art, the object of the present invention is to provide a dolomite standard sample development method for calibrating by age method, a dolomite standard sample and its application, so as to solve the problem that the traditional standard sample development cannot avoid the use of isotope diluent.

[0008] To achieve the above object, the present invention provides a method for developing a dolomite standard sample calibrated by an age method, which comprises:

[0009] Provide candidate dolomite standards;

[0010] Provide calcite, zircon and garnet standards with matrix effect verified;

[0011] Using a calcite standard sample as a main standard sample, and using a zircon standard sample and a garnet standard sample as secondary standards, the age of the dolomite candidate standard sample is tested twice, and the test results obtained are 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] Wherein, the matrix effect verification includes:

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

[0015] The age of the tested sample is tested with the test sample C and the test sample D respectively, and the test results are recorded as C1 and D1 respectively. The real age of the tested 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 deemed to be completed.

[0016] In the present invention, preferably, the selected calcite standard sample, zircon standard sample and garnet standard sample have U contents of the same order of magnitude as the dolomite candidate standard sample.

[0017] With the calcite standard as the main standard, and the zircon standard and the garnet standard as the secondary standards, the age of the dolomite candidate standard can be tested more than twice. As the number of tests increases, the result will be more reliable. However, based on the method of the present invention, two measurements are sufficient.

[0018] According to the development method of the present invention, zircon and garnet with very large differences in mineral composition and structural components are selected, and calcite with good similarity (that is, similarity in U content, preferably, U content is of the same order of magnitude) with dolomite mineral composition and structural components is selected, and the matrix effect is verified by interactive monitoring calibration. That is, it can be concluded that zircon and garnet can be used to calibrate calcite. Therefore, it is easy to know that calcite, zircon and garnet can be used to calibrate dolomite.

[0019] Through the above method, not only the possible matrix effect between calcite and dolomite is avoided, but also the problem of scarcity of diluents and existing standards is overcome, and a standard development process that is free from diluents and existing standards is established. This technical process is suitable for 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 sample is a laser method; preferably, the parameters of the laser beam in the laser method are a wavelength of 60 to 100 microns, a frequency of 5 to 15 Hz, and an energy density of 2 to 5 J / cm 2 .

[0021] According to a specific embodiment of the present invention, preferably, before the laser method test, the test instrument is calibrated using NIST-612; preferably, the parameters of the test 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 completed using the Energy mode of 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 comprises:

[0024] A dolomite potential standard sample is provided, and a geochemical analysis is performed on the dolomite potential standard sample to determine its diagenetic transformation intensity. When the diagenetic transformation intensity satisfies that the dolomite crystal has an invisible ring structure under cathode luminescence and trace rare earth element surface scanning, the Mn / Sr ratio is less than 1, and the strontium isotope ratio error obtained by measuring three parallel samples is less than 0.00001, the dolomite potential standard sample is used as the dolomite candidate standard sample.

[0025] Potential dolomite standard samples are required to have pure and uniform texture, stable isotope measurement signals, and small U-Pb age error (no more than 3%).

[0026] The present invention has no particular limitation on the specific production location of dolomite.

[0027] According to a specific embodiment of the present invention, preferably, the geochemical analysis includes one or a combination of two or more of cathode luminescence analysis, trace rare earth element surface scanning 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 comprises: reliability verification;

[0029] Preferably, the reliability verification method includes:

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

[0031] Through the above reliability verification, the reliability of the dolomite standard sample of the present invention can be further determined.

[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 development method is also provided.

[0036] According to another aspect of the present invention, there is also provided an application of the above-mentioned dolomite standard sample in the development of U-Pb isotope dating technology. The scope of application of the present invention includes providing standard sample support for the development and application of laser and solution dolomite U-Pb isotope dating technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The flowchart of the method for developing dolomite standard samples 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 the calcite standard AHX-1D is shown, normalized to the zircon standard.

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

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

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

[0043] Figure 7 The age of the zircon standard 91500 is shown, normalized against the calcite standard.

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

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

[0046] Fig.10 The age of the dolomite candidate standard sample GT2-1 obtained by the second calculation using the calcite standard sample as the normalized value is shown. DETAILED DESCRIPTION

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

[0048] Example 1

[0049] A method for developing a dolomite standard sample calibrated by the age method is shown in the flow chart below: Figure 1 As shown, the following steps are included:

[0050] Acquisition of S100 dolomite potential standard sample

[0051] The potential standard samples collected were first subjected to cathodoluminescence and trace rare earth element surface scanning, as well as carbon, oxygen, strontium isotope and trace element content analysis. Based on the oxygen isotope, strontium isotope, strontium content, and cathode luminescence and rare earth element surface scanning characteristics, it was determined that the dolomite diagenetic transformation intensity was weak, that is, the dolomite crystals had no obvious ring structure under cathode luminescence and trace rare earth element surface scanning, Mn / Sr was less than 1, and the strontium isotope ratio error obtained from 3 parallel samples was less than 0.00001; therefore, they can be used as candidate standard samples.

[0052] Verification of S200 matrix effect

[0053] Firstly, zircon standards with very different mineral compositions and structural components but similar U contents were selected as monitoring standards to test the ages of existing calcite and garnet standards. Specifically, the age of the standards was tested using laser ablation inductively coupled plasma mass spectrometry.

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

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

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

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

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

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

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

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

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

[0063] S300 based on dolomite standard determination of calcite standard

[0064] According to the verification results of the above base effect, the calcite standard sample can be used as the standardized value to carry out the determination of the dolomite standard sample.

[0065] Specifically, an AHX-1D calcite standard with a possible age close to that of the candidate dolomite standard was selected as the primary standard, and 91500 zircon and garnet were used as secondary standards. NIST-612 was first used to optimize the instrument parameters to a NIST 232Th / 238U ratio close to 1. Then, an 80-micron laser beam, 10 Hz, and 6.60 mJ energy were used, and Energymode was used to measure the dolomite candidate standard twice on the iCap-RQ.

[0066] For samples older than 100 million years, the age difference is considered close if it does not exceed 30 million years. If the results show that the ages of dolomite and calcite are not similar, it is necessary to select a calcite standard sample with a similar age for re-measurement.

[0067] like Fig. 9 The age of the dolomite candidate standard sample GT2-1 calculated for the first time was 253.8±2.2Ma, using the calcite standard sample as the normalized value;

[0068] like Fig.10 The calcite standard was used as the normalized value, and the age of the dolomite candidate standard sample GT2-1 calculated for the second time was 248.1±2.6Ma;

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

[0070] Test method:

[0071] Laser carbon and oxygen isotope testing is performed in LA-IRMS. The laser equipment (LA) consists of a Nd:YAG (yttrium aluminum garnet) near-infrared laser, a cooling system, a microscopic imaging system, and a gas transmission and separation system. The ND:YAG laser outputs a near-infrared coherent laser beam with a wavelength of 1064nm and a beam spot size of better than 20μm. A krypton lamp is used as the pump energy source for the ND:YAG laser. The operating current is 7-20A, generating 7-40W output energy, and the sample penetration depth is 30-50μm. The stable gas isotope instrument model is Detla V Advantage. Helium is used as the carrier gas during laser ablation. The laser reacts with carbonate to produce CO2 gas. After impurity separation and purification, pure CO2 gas is obtained and enters the isotope mass spectrometer for testing and analysis. The laser beam spot and current for this analysis were 20 μm and 14-20 A, respectively. The laser used a continuous (CW) output mode. The standard samples used for analysis data correction were the national standard GBW04405 and the laboratory internal standard 811. The analysis data processing was completed using the Thermo Fisher software ISODAT 3.0 and expressed in PDB. The test accuracy of δ13C and δ18O was ±0.1‰ and ±0.2‰, respectively. The laser spot beam diameter was 500 μm. Only the inner cores of fine-grained dolomite and medium-coarse-grained dolomite were tested, and the identifiable original particles and residual shadows of cement in some coarse-grained dolomite were tested. For comparison, dolomite crystals and calcite cement in limestone were tested.

[0072] Strontium isotope test was performed on solid-state mass spectrometer 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 and tested using the conventional process (Baadsgard, 1987). The standard sample was NBS987. The average error of the 87Sr / 86Sr ratio test was ±0.5×10 -5 .

[0073] Trace rare earth elements were analyzed by whole rock powder samples and tested on an inductively coupled plasma mass spectrometer (ICP-MS), model Thermo Fisher iCAP RQ, autosampler model: CETAC 560. 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, it was reacted with 4 mL 20% mixed acid (HCl:HNO3=4:1) at 130 ° C for 3 hours. After removing the acid, the dissolved material was tested in the plasma mass spectrometer using the standard process. The test standard was USGS W-2a, and the solution on the machine contained 4 internal standards: Rh, In, Re and Bi. The test accuracy was 0.1 ppb, and the error was ±5%.

[0074] Cathodoluminescence was performed by CL8200MK5 produced by CITL, and the implementation standard was "Cathode Luminescence Identification Method for Rock Minerals" SY / T5916-2013.

[0075] Trace rare earth element surface scanning uses LA-ICP-MS to perform micro-area in-situ laser surface scanning imaging on the selected area. First, select the type of element to be tested and the element integration time; secondly, according to the mineral structure characteristics of the sample, set the surface scanning area, laser scanning beam spot, energy density, moving speed, erosion frequency, scanning line spacing and other parameters. Then, perform LA-ICP-MS micro-area in-situ laser surface scanning imaging on the machine test, and then process the data in the software Iolite and image it.

[0076] It can be seen from the examples that the method developed in the present invention can successfully develop and obtain a dolomite standard sample.

Claims

1. A method for developing a dolomite standard sample calibrated by age method, characterized in that: include: Provide candidate dolomite standards; Provide calcite, zircon and garnet standards with matrix effect verified; 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, the age of the dolomite candidate standard sample is tested twice, and the obtained test results are 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.

2. The development method according to claim 1, characterized in that: The method for testing the dolomite candidate standard sample is a laser method; Preferably, the parameters of the laser beam in the laser method are wavelength 60-100 microns, frequency 5-15 Hz, energy density 2-5 J / cm 2 .

3. The development method according to claim 2, characterized in that: Before the laser method test, the test instrument is calibrated using NIST-612; preferably, the parameters of the test instrument are adjusted so that the 232Th / 238U ratio of NIST-612 is 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 iCap-RQ.

5. The development method according to claim 1, characterized in that: The method for selecting the dolomite candidate standard sample comprises: A dolomite potential standard sample is provided, and a geochemical analysis is performed on the dolomite potential standard sample to determine its diagenetic transformation intensity. When the diagenetic transformation intensity satisfies that the dolomite crystal has no obvious ring-zone structure under cathode luminescence and trace rare earth element surface scanning, Mn / Sr is less than 1, and the strontium isotope ratio error obtained by measuring three parallel samples is less than 0.00001, the dolomite potential standard sample is used as the dolomite candidate standard sample.

6. The development method according to claim 5, characterized in that: The geochemical analysis includes one or a combination of two or more of cathode luminescence analysis, trace rare earth element surface scanning analysis, carbon, oxygen and strontium isotope analysis, and trace element content analysis.

7. The development method according to claim 1, characterized in that: The development method also includes: Reliability verification; Preferably, the reliability verification method includes: The dolomite standard sample is used to test the age of a similar standard sample, and the test result is recorded as F. The true age of the similar standard sample is recorded as G. When F and G satisfy (FG) / G×100≤3, the dolomite standard sample is used as a reliable standard sample; wherein the similar standard sample is selected from one of garnet or zircon.

8. The development method according to claim 1, characterized in that: The calcite standard sample is selected from WC-1 calcite or ASH15 calcite.

9. The development method according to claim 1, characterized in that: The zircon standard sample is selected from 91500 zircon or Temora zircon.

10. The development method according to claim 1, characterized in that: The garnet standard sample is selected from TC garnet.

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

12. Use of the dolomite standard sample according to claim 11 in the development of U-Pb isotope dating technology.

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