CN111007141B - Calcite mineral laser uranium-lead isotope dating process - Google Patents
Calcite mineral laser uranium-lead isotope dating process Download PDFInfo
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- CN111007141B CN111007141B CN201911226136.3A CN201911226136A CN111007141B CN 111007141 B CN111007141 B CN 111007141B CN 201911226136 A CN201911226136 A CN 201911226136A CN 111007141 B CN111007141 B CN 111007141B
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Abstract
The invention provides a laser uranium-lead isotope dating process for calcite minerals, which comprises a calcite sample to be detected and a standard sample rake, wherein the standard sample at least comprises an isotope fractionation correction standard sample, an age correction standard sample and a verification standard sample WC-1; carrying out laser ablation sampling on a calcite sample and a standard sample to be detected, and respectively carrying out isotope detection on the obtained ablation products; correcting the obtained isotope value by using an isotope fractionation correction standard sample; respectively calculating the test ages of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1 by using the corrected isotope values; determining an age correction factor according to the test age and the recommended age of the age correction standard sample; correcting the testing ages of the calcite sample to be tested and the verification standard sample WC-1 by using the age correction factor to obtain the final ages of the calcite sample to be tested and the verification standard sample WC-1; and judging whether the test result is valid according to whether the final age of the verification standard sample WC-1 is within the recommended age range.
Description
Technical Field
The invention relates to a laser uranium-lead isotope dating process for calcite minerals, and belongs to the technical field of dating of ancient carbonate rocks in petroleum and natural gas geological exploration.
Background
At present, the U-Pb dating method becomes the most accurate dating method in the field of geology. With the development of modern laser technology and mass spectrometry technology, laser U-Pb isotope dating methods for various minerals have been developed, and especially carbonate laser U-Pb isotope dating has recently received more and more attention. In the process of laser U-Pb isotope dating, different isotope fractionation can be generated in different instruments and different time tests due to the fact that different laser ablation time, laser spot beams, laser energy, transmission systems, different mass spectrometers, different mass spectrometer parameter settings and the like are selected in the test process. Therefore, it is necessary to correct the isotope values using homogeneous glass standards and then calculate a correction factor using a homogeneous standard of known age to make a matrix age correction. At present, homogeneous glass standards are relatively mature, include NIST610, NIST612, NIST614 and the like, and can be selected for laser U-Pb isotope detection of any mineral. Therefore, the homogeneous standard sample with known age is a key problem to be solved for developing a new mineral laser U-Pb isotope dating method, and in order to avoid matrix effect among different minerals, the mineral standard sample for matrix age correction should be as similar to the sample to be measured in lithology and age as possible.
At present, there are two major known ages of carbonate rock standards, namely ASH15E (stalagmite from Negev desert of Israel, recommended age 3.001 + -0.012 Ma) (Vaks et al, 2013; Mason et al, 2013; Nuriel et al, 2017) and WC-1 (calcite vein of Walnut canyon of 0.5km west in Whites City of New Mexico, USA, recommended age 250.4Ma-254.5Ma) (Li et al, 2014; Coogan et al, 2016; Roberts et al, 2017). The age of calcite minerals in ancient carbonate rocks is corrected by using the age-corrected mineral standards as matrixes, and the age-corrected mineral standards meet the condition of the same lithology but have limitations. The ancient carbonate rock is often in the age range of hundreds of million years, so the standard sample ASH15E is too young to meet the requirement that the age of the sample to be tested is as close as possible, and is not the optimal standard sample. Although the recommended age of the WC-1 standard sample is 250.4Ma-254.5Ma, which is closer to the age of the sample to be measured, the heterogeneity of the standard sample causes the age values of the standard sample to be different at different times, namely 250.4 +/-2.7 Ma (Q.Li et al, 2014) and 254.5 +/-3.7 Ma (Coogan et al, 2016), so that the age correction of the substrate by using the WC-1 standard sample is easy to generate the possible deviation of the result due to the heterogeneity of the standard sample.
In summary, ASH15E is too young and WC-1 itself has 3% -5% heterogeneity in both existing calcite standards, which is not the best age standard for ancient carbonate rock. In the existing ancient carbonate rock laser U-Pb isotope dating method, WC-1 is mostly adopted as a standard sample to carry out matrix age correction, on one hand, the uniformity of WC-1 is poor, and the deviation of the test result can be caused; on the other hand, the method only has one correction standard sample and lacks one verification standard sample to monitor the data accuracy.
Therefore, the technical problem to be solved in the field is to provide a novel laser uranium-lead isotope dating process for calcite minerals.
Disclosure of Invention
In order to solve the above-mentioned drawbacks and disadvantages, it is an object of the present invention to provide a calcite mineral laser uranium-lead isotope dating process that uses a calcite mineral laser uranium-lead isotope dating standard as an age correction standard. The process provided by the invention is a test flow which simultaneously uses an age correction standard sample and a verification standard sample, so that the laser method U-Pb isotope dating technology is more effectively applied to the calcite mineral dating of the ancient marine carbonate rock, and provides a tool for the development of the scientific discipline of the ancient marine carbonate rock.
In order to achieve the above purpose, the invention provides a calcite mineral laser uranium-lead isotope dating process, wherein the calcite mineral laser uranium-lead isotope dating process uses a calcite laser uranium-lead isotope dating standard sample as an age correction standard sample, uses WC-1 as a verification standard sample, and is macrocrystalline calcite filled in cracks and holes of a deep gray medium-thickness layered dolostone stratum of the Han-Wu-Shaoshui-Blakek group under the West ditch section of the Aksu region in the Tarim basin; the process comprises the following steps:
(1) preparing a calcite sample to be detected and a standard sample rake, wherein the standard sample at least comprises an isotope fractionation correction standard sample, an age correction standard sample and a verification standard sample WC-1;
(2) carrying out laser ablation sampling on the calcite sample to be detected and the standard sample, and respectively carrying out isotope detection on the obtained ablation products;
(3) correcting the isotope value obtained in the step (2) by using the isotope fractionation correction standard sample;
(4) respectively calculating the test age of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1 by using the isotope value corrected in the step (3);
(5) determining an age correction factor according to the test age and the recommended age of the age correction standard sample;
(6) correcting the testing ages of the calcite sample to be tested and the verification standard sample WC-1 by using the age correction factor to obtain the final ages of the calcite sample to be tested and the verification standard sample WC-1;
(7) and judging whether the test result is valid according to whether the final age of the verification standard sample WC-1 is within the recommended age range.
In the above process, the rake comprises the steps of:
uniformly mixing an EpoFix hardening agent and EpoFix cold-mosaic resin in a mass ratio of 1:8 to obtain glue; respectively placing a calcite sample to be detected and a standard sample into a cold-insert mold; pouring the glue into cold-inlaid dies for placing calcite samples to be measured and standard samples respectively, vacuumizing for 30-60 minutes, standing for 10-12 hours until the glue is solidified to obtain sample targets of the calcite samples to be measured and the standard samples, polishing two surfaces of the sample targets, and wiping with alcohol to remove dust on the surfaces for later use;
after the preparation of the sample target is finished, the method further comprises the following steps of performing ultra-clean treatment on the sample target: and respectively placing the sample target of the calcite sample to be measured and the sample target of the standard sample into ultrapure water, carrying out ultrasonic treatment for at least 30 minutes, taking out, leaching with the ultrapure water, and air-drying for later use.
In the above process, preferably, the macrocrystalline calcite filled in cracks and holes of the deep gray middle-thickness layered dolomite formation of the hypothalamic-wushu scholar braker group of the west channel section in the aku region of the tali basin is pure, uniform in texture, widely distributed and is a homologous contemporary diagenetic product;
the age of the macrocystallite is calibrated with the recommended age of ASH15E of 3.001Ma, and the recommended age of the obtained macrocystallite is 209.8 +/-1.3 Ma.
In the above process, preferably, the macrocalcite filled in cracks and holes of the deep gray middle-thickness layered dolomite stratum of the lower Han-Wu-system Xiao-Er Blake group of the West ditch section in Aksu region of the Tarim basin208The content of Pb is less than 0.002ppm,238the average U content reaches 0.14ppm, and the diameter of a laser beam spot can be reduced to below 50 μm by irradiating the macrocrystalline calcite with a laser beam.
In the process, the used age correction standard sample has better uniformity and is suitable for the U-Pb isotope dating of the old carbonate rock.
In the above-described process, preferably, in the step (1), the isotope fractionation calibration standards include NIST610, NST612, or NIST 64.
In the above-described process, preferably, in the step (2), the isotope detection includes: and loading the obtained denudation product into a multi-receiving plasma mass spectrometer for isotope detection.
Specifically, a carrier gas, a make-up gas and a sensitizing gas are used for loading the denudation product into a multi-receiving inductively coupled plasma mass spectrometer; the carrier gas is helium with the flow rate of 0.58-0.65L/min, the supplementary gas is argon with the flow rate of 0.8-1.0L/min, and the sensitizing gas is nitrogen with the flow rate of 0.005-0.010L/min.
The parameters of the multi-receiving plasma mass spectrometer are set as follows: the instrument is tuned to the highest sensitivity while reducing the yield UO/U of the oxide below 0.3%, and the fractionation of the elements is reduced to Th/U-1; the sensitivity was as follows: u is more than 500000cps/ppm, Pb is more than 400000cps/ppm,207the background of Pb is 10-100 cps,207the detection limit of Pb is less than 5 cps.
In the above-described process, preferably, in the step (2), the isotope comprises206Pb、207Pb、208Pb、232Th and238U。
in the above process, preferably, in the step (4), the calculating the test ages of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1 by using the isotope value corrected in the step (3) includes:
respectively using the calcite sample to be detected and the age correction standard sample which are corrected in the step (3) and verifying the standard sample WC-1207Pb/206Taking Pb data as a vertical axis, and taking the calcite sample to be detected, the age correction standard sample and the verification standard sample WC-1 corrected in the step (3)238U/206And (3) plotting the Pb data by a horizontal axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone and the Tera-Wassenburg harmonic line as the test age of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1.
In the above-described process, preferably, in the step (5), the age correction factor k ═ rAHX-2/rAHX-1Wherein r isAHX-1Test age, r, for the age correction standardAHX-2Correcting the recommended age of the standard for the age.
In the above process, preferably, in step (6), the age correction factor is used to correct the test ages of the calcite sample to be tested and the validation standard WC-1 to obtain the final ages of the calcite sample to be tested and the validation standard WC-1, and the process includes:
respectively carrying out the age correction on the calcite sample to be detected and the verification standard sample WC-1 which are corrected in the step (3) by using the age correction factor238U/206Performing secondary correction on the Pb data, and performing secondary correction on the calcite sample to be detected and the verification standard sample WC-1 after correction in the step (3)207Pb/206Taking Pb data as a vertical axis, and taking the calcite sample to be detected after being corrected again by the age correction factor and the verification standard sample WC-1238U/206And (3) plotting the Pb data as a horizontal axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone with the Tera-Wassenburg harmonic line as the final age of the calcite sample to be detected and the verification standard sample WC-1.
In the above process, preferably, the age correction factor is used to respectively correct the calcite sample to be measured and the validation standard sample WC-1 after being corrected in the step (3)238U/206The Pb data is corrected again, including: the calcite sample to be detected and the verification standard sample WC-1 after being corrected in the step (3)238U/206Dividing Pb data by the age correction factor respectively to obtain calcite samples to be detected and verification standard samples WC-1 corrected by the age correction factor238U/206Pb data.
In the above-mentioned process, preferably, the step (7) of determining whether the test result is valid according to whether the final age of the verification standard WC-1 is within the recommended age range thereof includes:
if the final age of the verification standard sample WC-1 is within the recommended age range, judging that the test result is correct;
and if the final age of the verification standard sample WC-1 is not within the recommended age range, judging that the test result is wrong.
In the process described above, preferably the calcite is calcite in ancient marine carbonate rock.
In the past, only WC-1 is generally adopted as an age correction standard sample in the process of the U-Pb isotope dating test of the ancient carbonate rock, and the accuracy of a test result is evaluated by lacking a verification standard sample. The invention provides a novel calcite laser uranium-lead isotope dating standard sample AHX-1, which has the recommended age of 209.8 +/-1.3 Ma, is better in uniformity than WC-1, and is more suitable for being used as an age correction standard sample. The invention also establishes a calcite mineral laser uranium-lead isotope dating process taking AHX-1 as an age correction standard sample and WC-1 as a verification standard sample based on the development of AHX-1, and adds a verification standard sample in the prior technical process to monitor whether the test result is correct or not, so that the test result is more credible.
The development of the standard sample and the new process builds a bridge and provides a core component for the extension of the carbonate rock laser method U-Pb isotope dating technology from dating of the middle and new generation of the young carbonate rock cement to dating of the ancient marine phase carbonate rock cement, and provides a tool for the development of the ancient marine phase carbonate rock sedimentary geology, the petroleum geology, the tectonic geology, the mineral deposit science and the ancient environmental science.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a specific process flow diagram of a calcite mineral laser uranium-lead isotope dating process provided in example 1 of the present invention.
FIG. 2a is a graph showing the results of AHX-1 obtained in the fourth step of example 1 of the present invention.
FIG. 2b is a diagram of the results of the WC-1 test performed by the laser ablation multi-receiver inductively coupled plasma mass spectrometer using AHX-1 as the standard in the fourth step of example 1.
Fig. 2c is a graph of results of the ASH15E test using a laser ablation multi-receiver inductively coupled plasma mass spectrometer with AHX-1 as a standard in the fourth step of example 1.
FIG. 3a is a test age chart of the age correction standard AHX-1 obtained in step (4) of example 1 of the present invention.
Fig. 3b is a test age chart of the calcite sample SS1 to be tested obtained in step (4) of example 1 according to the present invention.
FIG. 3c is a test age chart of the validation sample WC-1 obtained in step (4) of example 1 of the present invention.
Fig. 4 is a uranium-lead age chart of the calcite sample SS1 to be measured obtained in step (6) of example 1 of the present invention after correction.
Fig. 5 is a uranium-lead age chart after correction of the validation standard WC-1 obtained in step (6) of example 1 of the present invention.
Fig. 6a is a test age chart of ASH15E obtained in step (4) of comparative example 1 of the present invention.
FIG. 6b is a graph showing the test age of SS1 sample to be tested obtained in step (4) of comparative example 1 according to the present invention.
FIG. 7 is an age chart showing the corrected SS1 sample (ASH 15E as age correction standard) obtained in step (6) of comparative example 1 according to the present invention.
Detailed Description
In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.
Example 1
The embodiment provides a calcite mineral laser uranium-lead isotope dating process, wherein a calcite sample is determined to be a calcite laser uranium-lead isotope dating standard sample through prejudging, determining and verifying, the calcite sample is applied to age determination of the calcite mineral in ancient marine carbonate rocks, the calcite mineral laser uranium-lead isotope dating process taking the calcite laser uranium-lead isotope dating standard sample as a correction standard sample and WC-1 as a verification standard sample is established, and the process specifically comprises the following steps:
determination of calcite laser uranium-lead isotope year-measuring standard sample:
the first step is as follows: collecting samples: through a plurality of field outcrop profile surveys, carbonate rock samples which are pure, uniform in texture, widely distributed and are homologous and synchronous diagenetic products are searched. The sample found in this example is macrocalcite (sample name AHX-1) filled in cracks and holes of deep gray medium-thick layered dolomite stratum of the lower-cold Wushu Shaerbulake group of West ditch section (40 degrees 54 '38.10' N; 79 degrees 50 '38.10' E) of Aksu region of Tarim basin, and meets the requirements of purity, uniform texture, wide distribution and homologous contemporary diagenetic product.
The second step: pre-judging trace elements: the method comprises the following steps of (1) carrying out trace element detection on AHX-1 by using a laser inductively coupled plasma mass spectrometer (LA-ICP-MS), wherein the number of measuring points is about 2500, and the detection result shows that:206pb and207pb is the product of U decay, and the U content in the sample is (238U content) reaches 0.14ppm on average, and completely meets the detection requirement;208the Pb content is almost zero (less than 0.002ppm), which indicates that the sample has no influence of common Pb, and the trace element content data of the partial measuring points are shown in the following tables 1-1 and 1-2 is shown in the specification; the diameter of the laser beam spot can be reduced to below 50 μm, which lays a foundation for obtaining stable and reliable year measurement data; the detection result shows that the AHX-1 sample is very suitable for laser in-situ U-Pb isotope dating.
TABLE 1-1
Tables 1 to 2
The third step: determination of AHX-1 age: the age of AHX-1 is calibrated by using the recommended age of 3.001Ma of ASH15E, AHX-1 is tested at different time periods, age data of 50 groups of about 2500 measuring points are obtained, the distribution range is 207.1-210.6Ma, the data distribution is very concentrated, and the uniformity is good. The weighted average of the age data for the 50 groups was 209.8 + -1.3 Ma, thus determining an AHX-1 age of 209.8 + -1.3 Ma.
FIG. 2a is a graph of the results for a group of AHX-1 ages, as can be seen in FIG. 2a, the AHX-1 ages are 209.0 + -1.1 Ma.
The fourth step: verification of AHX-1 age: WC-1 and ASH15E were tested for age using a laser ablation multi-receiver inductively coupled plasma mass spectrometer (LA-MC-ICPMS) using AHX-1 as a standard to determine the ages of the two samples, which were 258.5 + -4.7 Ma and 2.981 + -0.041 Ma, respectively (as shown in FIGS. 2b and 2 c), and both within the error range of the recommended ages of the two samples, which demonstrated that the recommended age of AHX-1 was 209.8 + -1.3 Ma, which is true.
In addition, it can be seen from FIG. 3a that the data points for AHX-1 are substantially near the intersection point under the harmonic line, the effect of normal lead is small, the error of the test age is significantly smaller than that of WC-1 and ASH15E, indicating that AHX-1 has better uniformity.
The laser uranium-lead isotope dating process of calcite mineral comprises the following steps:
the age of the calcite standard sample AHX-1 to be measured is closer to the age of the old carbonate rock to be measured than ASH15E, and the homogeneity of the calcite standard sample AHX-1 is better than that of WC-1, so that the age correction standard sample AHX-1 serving as the old carbonate rock age measurement is more suitable than ASH15E and WC-1. The original calcite laser U-Pb isotope dating technology is optimized through the development of a calcite standard sample AHX-1, two age standard samples are used in the technology, wherein the AHX-1 is used as an age correction standard sample to carry out matrix age correction, and the WC-1 is used for verifying the accuracy of standard sample monitoring data, so that the reliability of a test result is improved. As shown in fig. 1, the calcite mineral laser uranium-lead isotope dating process flow taking AHX-1 as an age correction standard sample and WC-1 as a verification standard sample comprises the following steps:
(1) calcite sample SS1 and standard sample system harrow that awaits measuring, wherein the standard sample includes three: isotopic fractionation of a calibration standard (one of NIST610, NST612, NIST 64), age calibration standard AHX-1, validation standard WC-1;
(2) carrying out laser ablation sampling on a sample to be detected and a standard sample and loading an ablation product into a multi-receiving plasma mass spectrometer for carrying out206Pb、207Pb、208Pb、232Th and238detecting U-isozyme;
(3) correcting the measured isotope value by using an isotope fractionation correction standard sample;
(4) respectively carrying out the following operations on an age correction standard sample AHX-1, a calcite sample SS1 to be detected and a verification standard sample WC-1, and carrying out isotope correction on the samples207Pb/206Pb data and238U/206pb data plotted to238U/206Pb on the horizontal axis, in207Pb/206Drawing by taking Pb as a vertical axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone with the Tera-Wassenburg harmonic line as the test ages of an age correction standard AHX-1, a calcite sample SS1 to be tested and a verification standard WC-1, wherein the test ages are 194.09 +/-0.99 Ma, 423.8 +/-4.5 Ma and 235.8 +/-4.3 Ma (shown in a figure 3a, a figure 3b and a figure 3c respectively);
(5) calculating age correction factor, k 209.8/rAHX-11.0809, wherein rAHX-1194.09Ma is the actual measurement age of the age correction standard sample AHX-1, and 209.8Ma is the recommended age of the age correction standard sample AHX-1;
(6) using calcite sample SS1 to be tested and validation standard WC-1238U/206Dividing the Pb value by an age correction factor (k-1.0809) to obtain a calcite sample SS1 to be measured and a verification standard sample WC-1 corrected by the age correction factor238U/206Pb value, calcite sample SS1 to be measured and verification standard WC-1 corrected by age correction factor238U/206Pb is a horizontal axis, and the calcite sample SS1 to be detected and the verification standard sample WC-1 after correction in the step (3) are used207Pb/206And Pb is plotted as a vertical axis, an isochrone is fitted, and the age of a lower intersection point obtained by intersecting the isochrone and the Tera-Wassenburg harmonic line is determined as the corrected age, namely the final age, of the calcite sample SS1 to be detected and the verification standard WC-1, wherein the corrected age of the calcite sample SS1 to be detected is shown in figure 4, and the corrected age of the verification standard WC-1 is shown in figure 5.
(7) From the results of fig. 5, it can be seen that the final age of the standard sample WC-1 is verified to be within the error range of the recommended age, so that the result of the current age is determined to be correct, and the age of the calcite sample to be measured is 456.1 ± 4.9 Ma.
Comparative example 1
The comparative example provides a laser uranium-lead isotope dating process for calcite minerals, which takes ASH15E as an age correction standard sample to age the calcite sample to be detected in the embodiment 1, and the dating process specifically comprises the following steps:
(1) calcite sample SS1 and standard sample system harrow that awaits measuring, wherein, the standard sample includes two: isotope fractionation calibration standard (one of NIST610, NST612, NIST 64), age calibration standard ASH 15E.
(2) Carrying out laser ablation sampling on a sample to be detected and a standard sample and loading an ablation product into a multi-receiving plasma mass spectrometer for carrying out206Pb、207Pb、208Pb、232Th and238detecting U-isozyme;
(3) correcting the measured isotope value by using an isotope fractionation correction standard sample;
(4) respectively carrying out the following operations on an age correction standard sample ASH15E and a calcite sample SS1 to be measured, wherein the operations are carried out after isotope correction207Pb/206Pb data and238U/206pb data plotted to238U/206Pb on the horizontal axis, in207Pb/206Drawing by taking Pb as a vertical axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone with the Tera-Wassenburg harmonic line as the test ages of an age correction standard sample ASH15E and a calcite sample SS1 to be tested, wherein the ages are respectively 3.26 +/-0.12 Ma and 481 +/-29 Ma (shown in the figures 6a and 6b respectively);
(5) calculating age correction factor, k is 3.001/rASH15E0.9206, wherein rASH15EIs the actual measurement age of the age correction standard sample ASH15E at this time of 3.26 +/-0.12 Ma, and 3.001Ma is the recommended age of the age correction standard sample ASH 15E;
(6) using calcite sample SS1 to be tested238U/206Dividing the Pb value by the age correction factor (k-0.9206) to obtain the age-correction-factor-corrected calcite sample SS1 to be measured238U/206Pb value, and of Calcite sample SS1 to be measured which is corrected again by age-based correction factor238U/206Pb is horizontal axis, and the measured calcite sample SS1 corrected in the step (3) is207Pb/206And Pb is plotted as a vertical axis, an isochrone is fitted, and the age of a lower intersection point obtained by intersecting the isochrone and the Tera-Wassenburg harmonic line is determined as the corrected age, namely the final age, of the calcite sample SS1 to be detected, wherein the age of the calcite sample SS1 to be detected is 443 +/-27 Ma in the graph 7.
As can be seen from the results of example 1 and comparative example above, the age of the calcite sample SS1 to be tested, which was measured using ASH15E as an age correction standard, was 443 ± 27Ma, which is smaller than the test result obtained in example 1, and the comparative example 1 did not verify the standard to verify whether the result is correct, so it is very useful to add a verification standard in the test procedure.
Calcite standard WC-1 is reported at a plurality of different ages due to its heterogeneity, 250.4 + -2.7 Ma and 254.5 + -3.7 Ma respectively, so WC-1 is not the optimal age correction standard, but can be used as a verification standard, and if the yearly technical test result is within the reported age range, the test result can be considered to be correct. In addition WC-1 is closer to the age of ancient carbonate rock than ASH15E, so it is also more suitable for use as an age verification standard than ASH 15E.
The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, so that the invention is intended to cover all modifications and equivalents of the embodiments described herein. In addition, the technical features and the technical inventions of the present invention, the technical features and the technical inventions, and the technical inventions can be freely combined and used.
Claims (14)
1. The calcite mineral laser uranium-lead isotope dating method is characterized in that a calcite laser uranium-lead isotope dating standard sample is used as an age correction standard sample, and the calcite laser uranium-lead isotope dating standard sample is macrocrystalline calcite filled in cracks and holes of a deep gray medium-thickness layered dolostone stratum of the Han Wu system Showzak Bulac group under the west ditch section of the Aksu region of the Tarim basin; the method comprises the following steps:
(1) preparing a calcite sample to be detected and a standard sample rake, wherein the standard sample at least comprises an isotope fractionation correction standard sample, an age correction standard sample and a verification standard sample WC-1;
(2) carrying out laser ablation sampling on the calcite sample to be detected and the standard sample, and respectively carrying out isotope detection on the obtained ablation products;
(3) correcting the isotope value obtained in the step (2) by using the isotope fractionation correction standard sample;
(4) respectively calculating the test age of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1 by using the isotope value corrected in the step (3);
(5) determining an age correction factor according to the test age and the recommended age of the age correction standard sample;
(6) correcting the testing ages of the calcite sample to be tested and the verification standard sample WC-1 by using the age correction factor to obtain the final ages of the calcite sample to be tested and the verification standard sample WC-1;
(7) and judging whether the test result is valid according to whether the final age of the verification standard sample WC-1 is within the recommended age range.
2. The method according to claim 1, wherein macrocalcite filled in cracks and vugs of the deep gray medium-thick layered dolomitic rock formation of the West ditch section of the Aksu region of the Tarim basin is pure, homogeneous in texture, widely distributed, and a homogeneous contemporaneous diagenetic product;
the age of the macrocystallite is calibrated with the recommended age of ASH15E of 3.001Ma, and the recommended age of the obtained macrocystallite is 209.8 +/-1.3 Ma.
3. The method of claim 1 or 2, wherein the macrocalcite filled in the fissures and vugs of the deep gray medium-thickness layered dolomitic rock formations of the West ditch section of the Aksu region of the Tarim basin208The content of Pb is less than 0.002ppm,238the average U content reaches 0.14ppm, the macrocrystalline calcite is irradiated by the laser beam, and the diameter of a laser beam spot can be reduced to be below 50 mu m.
4. The method of claim 1, wherein in step (1), the isotopically fractionated calibration standards comprise NIST610, NIST612, or NIST 614.
5. The method of claim 1, wherein in step (2), the isotope detection comprises: and loading the obtained denudation product into a multi-receiving plasma mass spectrometer for isotope detection.
6. According to claimThe method of claim 1 or 5, wherein in step (2), the isotope comprises206Pb、207Pb、208Pb、232Th and238U。
7. the method according to claim 1, wherein in the step (4), the step of calculating the test ages of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1 respectively by using the isotope values corrected in the step (3) comprises the following steps:
respectively using the calcite sample to be detected and the age correction standard sample which are corrected in the step (3) and verifying the standard sample WC-1207Pb/206Taking Pb data as a vertical axis, and taking the calcite sample to be detected, the age correction standard sample and the verification standard sample WC-1 corrected in the step (3)238U/206And (3) plotting the Pb data by a horizontal axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone and the Tera-Wassenburg harmonic line as the test age of the calcite sample to be tested, the age correction standard sample and the verification standard sample WC-1.
8. The method according to claim 1, wherein in step (5), the age correction factor k = rAHX-2/rAHX-1Wherein r isAHX-1Test age, r, for the age correction standardAHX-2Correcting the recommended age of the standard for the age.
9. The method according to claim 1, wherein in the step (6), the age correction factor is used to correct the test ages of the calcite sample to be tested and the validation standard WC-1 to obtain the final ages of the calcite sample to be tested and the validation standard WC-1, and the method comprises the following steps:
respectively carrying out the age correction on the calcite sample to be detected and the verification standard sample WC-1 which are corrected in the step (3) by using the age correction factor238U/206The Pb data is corrected again, and calcite samples to be detected and verification standard samples WC-1 corrected in the step (3) are used207Pb/206Pb data is vertical axis, inCalcite sample to be detected after being corrected again by the age correction factor and verification standard sample WC-1238U/206And (3) plotting the Pb data by a horizontal axis, fitting an isochrone, and determining the age of a lower intersection point obtained by intersecting the isochrone with the Tera-Wassenburg harmonic line as the final age of the calcite sample to be detected and the verification standard sample WC-1.
10. The method according to claim 9, wherein the age correction factor is used for respectively correcting the calcite sample to be measured after being corrected in the step (3) and the verification standard WC-1238U/206The Pb data is corrected again, including: the calcite sample to be detected and the verification standard sample WC-1 after being corrected in the step (3)238U/206The Pb data is divided by the age correction factor respectively to obtain calcite samples to be detected and verified standard samples WC-1 after being corrected by the age correction factor238U/206Pb data.
11. The method according to claim 1, wherein in the step (7), judging whether the test result is valid according to whether the final age of the verification standard sample WC-1 is within the recommended age range comprises:
if the final age of the verification standard sample WC-1 is within the recommended age range, judging that the test result is correct;
and if the final age of the verification standard sample WC-1 is not within the recommended age range, judging that the test result is wrong.
12. The method according to any one of claims 1-2, 4-5, 7-11, wherein the calcite is calcite in ancient marine carbonate rock.
13. The method according to claim 3, wherein the calcite is calcite in ancient marine carbonate rock.
14. The method according to claim 6, wherein the calcite is calcite in ancient marine carbonate rock.
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