Method for determining metamorphic times of medium-low-grade metamorphic rocks
By using the U-PB annual method of phosphorus 区 通过 通过 通过 to determine the deterioration era of low-level metamorphic rocks, the problem of accuracy and reliability of traditional albumin annual method in such rocks is solved. The accurate measurement in the era of rock deterioration.
Patent Information
- Application Number
- CN202411476022.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-22
- Publication Date
- 2025-01-24
AI Technical Summary
Traditional isotope dating has problems of low accuracy and reliability in determining the metamorphic era of medium and low-order metamorphic rocks.
By obtaining medium and low-level metamorphic rocks containing limestone, obtaining aphalite particles after treatment, U-PB U-PB in the micro-bellite region determine multiple sets of U-PB isotope data, and then determine the age of aluminite. Determine the deterioration era of low -level metamorphic rocks.
This method can accurately measure the deterioration era of low -level metamorphic rocks, improve the accuracy and reliability of the determination results, and provide reliable data support for geological research.
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Figure CN119355100A_ABST
Abstract
Description
Technical Field
[0001] The embodiments of the present application relate to the technical field of chemical analysis, and in particular to a method for determining the metamorphic age of medium and low-grade metamorphic rocks. Background Art
[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.
[0003] The most commonly used method for determining the metamorphic age of metamorphic rocks is the isotope dating method of its minerals. The mineral to be tested is formed during the metamorphic process. During the formation process, the parent isotopes around it decay into daughter isotopes and solidify into the mineral to be tested. The age of the mineral is calculated by measuring the content of parent and daughter isotopes in the mineral to be tested, and according to the decay law that after the formation of the mineral to be tested, the number of radioactive isotopes (parent) isolated from the surrounding environment gradually decreases, and the number of stable isotopes (daughter) produced by decay gradually increases in the mineral, thereby determining the metamorphic age of the metamorphic rock.
[0004] Since the metamorphic environment of low- and medium-grade metamorphic rocks is relatively special, there are certain limitations in determining the metamorphic age of low- and medium-grade metamorphic rocks using traditional isotope dating methods, resulting in low accuracy and reliability of the measurement results. Summary of the invention
[0005] A brief overview of the present application is provided below in order to provide a basic understanding of certain aspects of the present application. It should be understood that this overview is not an exhaustive overview of the present application. It is not intended to identify the key or important parts of the present application, nor is it intended to limit the scope of the present application. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.
[0006] An embodiment of the present application provides a method for determining the metamorphic age of intermediate and low-grade metamorphic rocks, the method comprising the following steps: S1: obtaining a plurality of intermediate and low-grade metamorphic rocks containing apatite; S2: processing the intermediate and low-grade metamorphic rocks to obtain a plurality of apatite particles; S3: determining a plurality of groups of U-Pb isotope data based on apatite micro-area U-Pb dating of the obtained plurality of apatite particles; S4: determining the age of apatite based on the plurality of groups of U-Pb isotope data; S5: determining the metamorphic age of the intermediate and low-grade metamorphic rocks based on the age of apatite.
[0007] The method for determining the metamorphic age in the embodiment of the present application can obtain apatite from low- and medium-grade metamorphic rocks, and apatite can reflect the metamorphic information of metamorphic rocks in a low-temperature metamorphic environment. The age of apatite can be determined by U-Pb dating of apatite micro-areas, and the metamorphic age of low- and medium-grade metamorphic rocks can be further determined. The metamorphic age of low- and medium-grade metamorphic rocks can be accurately measured, and reliable data support can be provided for regional geological structure research, ore deposit formation mechanism and sedimentary basin analysis. BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Other objects and advantages of the present application will become apparent from the following description of the embodiments of the present application with reference to the accompanying drawings, and will help to provide a comprehensive understanding of the present application.
[0009] Figure 1 The present invention is a flowchart of a method for determining the metamorphic age of low- and medium-grade metamorphic rocks according to an embodiment of the present application.
[0010] Figure 2 : This is the state of apatite particles under the cathode luminescence image according to one embodiment of the present application.
[0011] Figure 3 It is a schematic diagram of the concordant age of apatite determined based on 32 sets of U-Pb isotope data according to an embodiment of the present application.
[0012] Figure 4 It is a schematic diagram of the weighted average age of apatite determined based on 32 sets of U-Pb isotope data according to an embodiment of the present application.
[0013] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION
[0014] Exemplary embodiments of the present application will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary from implementation to implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is only a routine task for those skilled in the art who benefit from the content of this application.
[0015] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, only the device structure and / or processing steps closely related to the scheme according to the present application are shown in the accompanying drawings, while other details that are not very relevant to the present application are omitted.
[0016] The inventors of the present application discovered that since the metamorphic process of low- and medium-grade metamorphic rocks usually occurs under low-temperature and low-pressure environmental conditions, traditional isotope dating methods such as zircon U-Pb dating and muscovite Ar-Ar dating, in which minerals such as zircon and muscovite are usually formed in high-temperature and high-pressure environments, are difficult to retain zircon, muscovite and other minerals in the low- and medium-grade metamorphic rocks when applied to the determination of the metamorphic age of low- and medium-grade metamorphic rocks, and accurate geological information cannot be obtained therefrom, resulting in low accuracy and reliability of the metamorphic age determination results of the low- and medium-grade metamorphic rocks determined based on these methods.
[0017] Based on this, the embodiment of the present invention proposes a method for determining the metamorphic age of medium and low-grade metamorphic rocks, such as Figure 1 As shown, the method includes the following steps S1 to S5.
[0018] S1: Obtain multiple low- and medium-grade metamorphic rocks containing apatite.
[0019] S2: Process low- and medium-grade metamorphic rocks to obtain multiple apatite particles.
[0020] S3: Determine multiple sets of U-Pb isotope data based on the apatite micro-area U-Pb dating of multiple apatite particles obtained.
[0021] S4: Determine the age of apatite based on multiple sets of U-Pb isotope data.
[0022] S5: Determine the metamorphic age of intermediate and low-grade metamorphic rocks based on the age of apatite.
[0023] The method for determining the metamorphic age in the embodiments of the present application can obtain apatite from low- and medium-grade metamorphic rocks, and apatite can reflect the metamorphic information of metamorphic rocks in a low-temperature metamorphic environment. The age of apatite can be determined by U-Pb dating of apatite micro-areas, and the metamorphic age of low- and medium-grade metamorphic rocks can be further determined. The metamorphic age of low- and medium-grade metamorphic rocks can be accurately measured, and reliable data support can be provided for regional geological structure research, ore deposit formation mechanism and sedimentary basin analysis.
[0024] In some embodiments, in step S1, representative low- and medium-grade metamorphic rocks covering different geological units and metamorphic degrees are obtained to obtain a complete time series of the metamorphic process of the low- and medium-grade metamorphic rocks to ensure the reliability of the test results.
[0025] In some embodiments, step S2 may further include the following steps S21 to S23.
[0026] S21: Process low- and medium-grade metamorphic rocks to obtain low- and medium-grade metamorphic rock particles.
[0027] S22: Process low- and medium-grade metamorphic rock particles to obtain thin sections.
[0028] S23: Obtain multiple apatite particles from optical thin sections using heavy liquid sorting.
[0029] In this embodiment, the low- and medium-grade metamorphic rocks are first crushed into particles, and then the low- and medium-grade metamorphic rock particles are ground into thin slices. Apatite particles are separated from the thin slices using a heavy liquid separation method, thereby facilitating subsequent apatite micro-area U-Pb dating tests.
[0030] In step S21, pollutants on the surface of low- and medium-grade metamorphic rock particles are processed to avoid interference with the subsequent step of taking cathode luminescence images to determine the measurement point positions, thereby ensuring the accuracy of the test results. For example, the processing can be carried out by washing, drying, etc.
[0031] In step S22, when processing low- and medium-grade metamorphic rock particles to obtain thin slices, the thin slices of predetermined thickness can be obtained by grinding the low- and medium-grade metamorphic rock particles. The processing method can be using a rock slicer or manual processing.
[0032] In some embodiments, step S2 may also include determining a plurality of pure apatite particles from a plurality of apatite particles. Specifically, the apatite particles may be observed to determine the morphology, crystal structure characteristics, and relationship between the apatite and surrounding rock minerals. For example, the apatite particles may present a relatively uniform grain distribution, fibrous or plate-like crystal morphology, etc. The observation means may be a mineral phase microscope, a polarizing microscope, etc., to screen out pure apatite particles as the basis for subsequent micro-area U-Pb dating, so as to eliminate the interference of impurity particles, thereby improving the accuracy of the dating test results.
[0033] In some embodiments, step S3 may include the following steps S31 to S34.
[0034] S31: Processing a plurality of apatite particles to obtain a corresponding plurality of epoxy resin targets.
[0035] S32: Obtain cathode luminescence images of multiple epoxy resin targets.
[0036] S33: Determine the positions of multiple measuring points according to the cathode luminescence image.
[0037] S34: Determine multiple groups of U-Pb isotope data according to the positions of multiple measuring points.
[0038] In this embodiment, apatite particles are made into epoxy resin targets and photographed as follows: Figure 2 Cathodoluminescence image of the epoxy target shown. Figure 2The state of apatite particles under the cathode luminescence image of an embodiment of the present application is shown. By observing the cathode luminescence image, the measurement point positions of multiple apatite U-Pb dating tests are determined, and the apatite U-Pb dating is performed on the marked measurement point positions to ensure the reliability of the dating test results.
[0039] In some embodiments, in step S33, multiple measuring point positions are determined according to the ring-shaped structure or homogenized region in the cathode luminescence image, that is, multiple measuring points are selected at the positions of the ring-shaped structure or homogenized region appearing in the cathode luminescence image. Apatite of metamorphic origin usually presents a specific ring-shaped structure or homogenized region in the cathode luminescence image, which reflects the recrystallization or homogenization of chemical composition experienced during the metamorphic process. Therefore, the above-mentioned method of determining the measuring point position can improve the reliability of the dating result.
[0040] In some embodiments, in step S34, the following steps S341 to S342 may be included.
[0041] S341: Determine the laser beam spot, laser frequency and density for U-Pb dating.
[0042] S342: Based on the laser beam spot, laser frequency and density, and multiple measurement point positions, apatite U-Pb multi-point measurement is performed on the apatite particles in the epoxy resin target to determine multiple groups of U-Pb isotope data.
[0043] In this embodiment, a suitable laser beam spot, laser frequency and density are first determined, and then U-Pb multi-point measurement is performed on the apatite particles in the epoxy resin target according to the marked multiple measuring point positions to obtain multiple groups of U-Pb isotope data, so as to reduce accidental errors, improve the reliability of U-Pb isotope data, and ensure the accuracy of the final metamorphic age determination results of medium and low-grade metamorphic rocks.
[0044] In step S342, the multiple sets of U-Pb isotope data are determined as multiple sets 235 U. 207 Pb, 238 U and 206 Pb content data.
[0045] In step S342, laser ablation-inductively coupled plasma mass spectrometry can be used to perform U-Pb multi-point measurement on apatite particles. For example, when laser ablation-inductively coupled plasma mass spectrometry is used to perform U-Pb multi-point measurement on apatite particles, the analysis process of laser ablation-inductively coupled plasma mass spectrometry starts with a 20-second blank gas measurement and ends 40 seconds after the laser is turned on. The laser beam is focused on the apatite surface, and the apatite particles are bombarded into small particles with a diameter of less than 100nm using high pulse energy, which form aerosols under the action of carrier gas and are transported to the plasma mass spectrometer for isotope testing.
[0046] In some embodiments, in step S343, the determined multiple sets of U-Pb isotope data are calibrated using apatite standard samples to ensure high accuracy and repeatability of the U-Pb isotope data. For example, multiple apatite standard samples such as MAD2, Otter lake, and Durango can be used to jointly calibrate the U-Pb isotope data.
[0047] In some embodiments, step S4 may include the following steps S41 to S43.
[0048] S41: Process multiple sets of U-Pb isotope data and determine multiple sets of U-Pb isotope ratios after eliminating the interference of common lead.
[0049] S42: Determine the concordant age of apatite based on the multiple groups of U-Pb isotope ratios determined in step S41.
[0050] S43: Determine the weighted average age of apatite based on the multiple groups of U-Pb isotope ratios determined in step S41.
[0051] In this embodiment, the interference of common lead is eliminated to obtain the U-Pb isotope ratio after the interference of common lead is eliminated, so as to avoid the influence of common lead content on the calculation of U-Pb age. According to the U-Pb isotope ratio after the interference of common lead is eliminated, the concordant age and weighted average age of apatite are determined to ensure the accuracy of the measurement results.
[0052] In step S41, when processing multiple sets of U-Pb isotope data and determining multiple sets of U-Pb isotope ratios after eliminating the interference of common lead, multiple sets of 235 U. 207 Pb, 238 U and 206 The Pb content data were processed to eliminate the interference of common lead, and multiple groups of U-Pb isotope ratios were obtained after eliminating the interference of common lead.
[0053] In step S42, the U-Pb isotope ratio after eliminating the interference of common lead is input into software such as Isoplot to obtain a concordant age diagram of apatite. According to the concordant age diagram of apatite, the concordant age of apatite is determined.
[0054] In step S43, the U-Pb isotope ratio after eliminating the interference of common lead is input into software such as Isoplot to obtain 206 Pb / 238 Schematic diagram of the weighted average age of U. According to the schematic diagram of the weighted average age of apatite, the weighted average age of apatite is determined.
[0055] In some embodiments, in step S5, the weighted average age of apatite and the consonant age of apatite are used to determine whether they are basically consistent within the error range. If they are basically consistent within the error range, the weighted average age of apatite and the consonant age of apatite are the metamorphic age of medium and low-grade metamorphic rocks.
[0056] In this embodiment, by combining the two U-Pb age data results of the concordant age of apatite and the weighted average age of apatite, it is determined whether the two are basically consistent within the error range. When the concordant age of apatite and the weighted average age of apatite are basically consistent within the error range, the concordant age of apatite and the weighted average age of apatite are determined as the metamorphic age of the intermediate and low-grade metamorphic rocks, thereby improving and verifying the accuracy and reliability of the metamorphic age results of the intermediate and low-grade metamorphic rocks finally determined.
[0057] The following is a specific example to further illustrate the process of determining the metamorphic age of low- and medium-grade metamorphic rocks using the method of the present invention.
[0058] Low-grade metamorphic rocks of phyllite and greenschist containing apatite were collected.
[0059] The collected low-grade metamorphic rocks are crushed into particles, and the pollutants on the surface of the low-grade metamorphic rock particles are removed by washing, drying and other treatments. The low-grade metamorphic rock particles are made into optical slices with a thickness of 0.3 mm by rock slicers and manual processing. Apatite minerals are separated from the optical slices by heavy liquid sorting. During the separation process, apatite particles are observed by mineral phase microscope and polarizing microscope to screen out pure apatite particles.
[0060] Apatite particles were made into epoxy resin targets and cathode luminescence images were taken. By observing the cathode luminescence images, 32 apatite particle test points were marked. Laser ablation-inductively coupled plasma mass spectrometry was used to perform U-Pb isotope analysis on apatite particles in epoxy resin targets. The laser beam spot was set to 40 μm, the laser frequency was set to 8 Hz, and the density was set to 4 J / cm 2The analysis process starts with a 20-second blank gas measurement and ends 40 seconds after the laser is turned on, and helium is used as the carrier gas. After the U-Pb dating of the apatite particles, 32 sets of U-Pb isotope data were obtained, that is, 32 sets of 235 U. 207 Pb, 238 U and 206 Pb content data.
[0061] Process multiple sets of U-Pb isotope data and determine multiple sets of U-Pb isotope ratios after eliminating the interference of common lead. The following is obtained by Isoplot software: Figure 3 The schematic diagram shown, Figure 3 A schematic diagram of apatite concordant age determined according to 32 sets of U-Pb isotope data in one embodiment of the present application is shown, wherein the abscissa is 238 U / 206 Pb, the ordinate is 235 U / 207 Pb, the curve is the concordance line 1, which represents the isotope ratio change of apatite particles and the age corresponding to different ratio changes when there is no loss or gain of U or Pb in apatite particles. The ellipse is the 32 groups of apatite particles 2 tested. If the 32 groups of apatite particles 2 tested were formed in the same metamorphic era, a fitting straight line 3 can be connected. The lower intersection 4 of the fitting straight line 3 and the concordance line 1 is the concordance age of apatite 431.2±6.3Ma (MSWD=1.00; n=32), and the upper intersection 5 of the fitting straight line 3 and the concordance line 1 is the common lead composition of apatite. The following is obtained by Isoplot software: Figure 4 The schematic diagram shown, Figure 4 A schematic diagram of the weighted average age of apatite determined based on 32 groups of U-Pb isotope data in one embodiment of the present application is shown, wherein the ordinate is age, the rectangle is the 32 groups of apatite particles 2 tested, the straight line is the weighted average age line 6, and the intercept 7 between the weighted average age line 6 and the ordinate is the weighted average age of apatite 428.4±3.6Ma (MSWD=0.93), and the two are basically consistent within the error range. At this time, the consonant age of apatite and the weighted average age of apatite are determined as the metamorphic age of low-grade metamorphic rocks.
[0062] Regarding the embodiments of the present application, it should also be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other to obtain new embodiments.
[0063] The above are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. The protection scope of the present application shall be based on the protection scope of the claims.
Claims
1. A method for determining the metamorphic age of low- and medium-grade metamorphic rocks, characterized in that: The steps include: S1: obtaining a plurality of the intermediate and low-grade metamorphic rocks containing apatite; S2: processing the low- and medium-grade metamorphic rocks to obtain a plurality of apatite particles; S3: determining multiple groups of U-Pb isotope data according to the obtained apatite micro-area U-Pb dating of the multiple apatite particles; S4: determining the age of apatite according to the multiple sets of U-Pb isotope data; S5: Determine the metamorphic age of the intermediate and low-grade metamorphic rocks according to the age of the apatite.
2. The method according to claim 1, characterized in that: In step S3, the following steps are also included: S31: processing the plurality of apatite particles to obtain a corresponding plurality of epoxy resin targets; S32: obtaining cathode luminescence images of the plurality of epoxy resin targets; S33: determining positions of multiple measuring points according to the cathode luminescence image; S34: Determine multiple groups of U-Pb isotope data according to the multiple measurement point positions.
3. The method according to claim 2, characterized in that In step S33, the positions of the multiple measuring points are determined according to the ring-shaped structure or the homogenized area in the cathode luminescence image.
4. The method according to claim 2, characterized in that: In step S34, the following steps are also included: S341: Determine the laser beam spot, laser frequency and density for U-Pb dating; S342: Performing apatite U-Pb multi-point measurement on the epoxy resin target according to the laser beam spot, laser frequency and density and the positions of the multiple measurement points to determine the multiple groups of U-Pb isotope data.
5. The method according to claim 4, characterized in that In step S34, the following steps are also included: S343: Calibrate the determined multiple sets of U-Pb isotope data using apatite standard samples.
6. The method according to claim 1, characterized in that In step S1, the representative low- and medium-grade metamorphic rocks covering different geological units and metamorphic degrees are obtained.
7. The method according to claim 1, characterized in that In step S2, the following steps are also included: S21: processing the medium and low-grade metamorphic rocks to obtain medium and low-grade metamorphic rock particles; S22: processing the low- and medium-grade metamorphic rock particles to obtain optical thin sections; S23: Obtaining a plurality of apatite particles from the optical slice using a heavy liquid sorting method.
8. The method according to claim 7, characterized in that In step S2, the following steps are also included: A pure plurality of apatite particles are determined from the plurality of apatite particles.
9. The method according to claim 1, characterized in that: In step S4, the following steps are also included: S41: processing the multiple sets of U-Pb isotope data to determine multiple sets of U-Pb isotope ratios after eliminating the interference of common lead; S42: Determine the concordant age of apatite according to the multiple groups of U-Pb isotope ratios determined in step S41; S43: Determine the weighted average age of apatite according to the multiple groups of U-Pb isotope ratios determined in step S41.
10. The method according to claim 1, characterized in that In step S5, the following steps are also included: According to the weighted average age of the apatite and the concordant age of the apatite, it is determined whether the two are basically consistent within the error range. If they are basically consistent within the error range, the weighted average age of the apatite and the concordant age of the apatite are the metamorphic age of the medium and low-grade metamorphic rocks.