A method for determining the origin of granite in the Heimahe area

Abstract

The present invention discloses a method for determining the genesis of granite bodies in the Heimahe area, which belongs to the field of geological engineering technology. The method takes the Triassic granite in the Heimahe area of the eastern Kunlun Mountains as the research object, and explores the genesis of the Triassic granite in the Heimahe area from the perspective of geochemical characteristics. The steps are as follows: first, grinding the sample into powder; second, analyzing and testing the major elements and trace elements in the sample to obtain major element and trace element data; then, performing correlation analysis on the major element data, analyzing the rare earth element data in the trace elements, and making a rare earth element distribution pattern diagram based on the average value after the rare earth element standardization of the sample; finally, establishing a sample genesis discrimination model, and through comparative research, determining that the sample is of crust-mantle mixed origin. The method of the present invention provides basic data for the study of the genesis of the Triassic granite in the Heimahe area.

Description

Technical Field

[0001] The invention belongs to the technical field of geological engineering, and in particular relates to a method for determining the genesis of a granite body in the Heimahe area. Background Art

[0002] Triassic granites are widely developed in many orogenic belts in my country (Qinling-Qilian-Kunlun, etc.), and their genesis has always been a hot topic of concern for scholars at home and abroad. The Heimahe pluton is located south of the Nanshan Fault in Qinghai Lake, with an exposed area of up to 500km 2 The volcanic complex is a very important Triassic granitic complex in the northern margin of the western Qinling Mountains. The main lithology of this complex is granodiorite, but minor quartz diorite is found in the northwest, forming a gradient contact with the granodiorite. Diorite and gabbro are exposed in the southeast, making it a typical magmatic complex. This complex forms a distinct intrusive contact with the surrounding Lower Triassic Longwuhe Formation sandstones. Numerous dark microparticles (diorite) of varying shapes and sizes are present within the complex.

[0003] Currently, existing research on granite bodies mainly focuses on identifying their alteration zoning characteristics. For example, application No. 201710474613.2 discloses a geochemical method for identifying granite alteration zoning. This method calculates the alteration degree evaluation index value of each test point based on quantitative evaluation indicators to determine the alteration degree of the rock mass at each test point. Then, based on the zoning discrimination criteria, the rock mass within the same alteration degree range is divided into the same alteration zone. The rock mass is rapidly and continuously altered and zoned, and ultimately the rock mass is divided into a fully altered zone, a strongly altered zone, a moderately altered zone, a weakly altered zone, and an unaltered zone.

[0004] The origins of the Triassic granites in the East Kunlun Mountains are primarily thought to be due to ancient crustal melting, young crustal melting, crust-mantle mixing, and oceanic crust melting with sediments. These tectonic models include delamination, syn-collision, and post-collision. However, there is considerable debate about their origins. Therefore, it is necessary to develop a method for determining the origins of the granites in the Heimahe region. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the genesis of granite bodies in the Heimahe area, which can be used to determine the genesis of granite bodies in the Heimahe area based on a characteristic discrimination diagram of major and trace elements.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a method for determining the origin of granite in the Heimahe area, comprising the following steps in sequence: S1, collecting granite in the Heimahe area as a sample, and grinding the sample into powder.

[0007] S2. Analyze and test the major elements and trace elements in the powdered sample obtained in step 1 respectively to obtain major element and trace element data; the major elements include oxides of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P.

[0008] S3. Screen and analyze the major element data. The analysis includes: correlation analysis between SiO2 and oxides of Ti, Al, Fe, Mg, Ca, Na or K. The formula used is shown in formula (1).

[0009] (1).

[0010] In formula (1): is the correlation coefficient; is the number of samples; is the horizontal axis variable; is the vertical axis variable.

[0011] S4. Analyze the data of rare earth elements in the trace elements, and prepare a rare earth element distribution pattern diagram based on the average value after standardization of the rare earth elements.

[0012] S5. Establish a genealogical discrimination model for the sample: S51. Prepare a genealogical discrimination diagram for the sample. The specific steps are: select strongly incompatible elements with similar distribution coefficients among the trace elements, the said strongly incompatible elements include element one, element two, element three and element four, calculate the ratio of the strongly incompatible elements and standardize them, and calculate the specific values of the strongly incompatible elements. The formula used is shown in formula (2).

[0013] Element One * = [ Element One Element Three ] sample [ Element One Element Three ] primitive mantle − Element Two * [ Element Two Element Four ] sample [ Element Two Element Four ] primitive mantle (2).

[0014] In formula (2): is Nb*; is Nb; For Ta* ; For Ta; For Th; For U.

[0015] S52. Use the calculated specific values of element one and element two as the horizontal and vertical coordinates respectively to make a scatter plot, thus obtaining the sample's genetic discrimination diagram; in the sample's genetic discrimination diagram, draw the end members of continental crust, primitive mantle, oceanic crust basalt, enriched mid-ocean ridge basalt, and normal mid-ocean ridge basalt for comparison. Through comparative study, the sample falls between the continental crust and the primitive mantle, and it is determined that the sample is of mixed crust-mantle origin.

[0016] Furthermore, in the above-mentioned method for determining the origin of the granite body in the Heimahe area, the trace elements in S2 include Y, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ta, Th and U.

[0017] Furthermore, in the above-mentioned method for determining the genesis of the granite body in the Heimahe area, in S1, the sample is ground into powder with a particle size of 200 mesh.

[0018] Furthermore, in the above-mentioned method for determining the origin of the granite body in the Heimahe area, in S4, the data of rare earth elements are used as the horizontal axis, and the average value of the data of the chondrite of the sample is taken as the vertical axis after taking the logarithm, which is the rare earth element distribution pattern diagram.

[0019] The above-mentioned method for determining the origin of the granite body in the Heimahe area is applied. In S5, the strongly incompatible elements in the trace elements are: Nb, Ta, Th and U.

[0020] Compared with the prior art, the present invention brings the following beneficial technical effects: the present invention proposes a method for determining the genesis of granite bodies in the Heimahe area, which selects granite bodies in the Heimahe area as samples, firstly obtains relevant data on the major elements and trace elements by analyzing and testing the major elements and trace elements in the samples; then, correlation analysis is performed on the relevant data in the major elements, and the relevant data in the trace elements are analyzed, and a rare earth element distribution pattern diagram is prepared using the average value after standardization of the rare earth elements; finally, a sample genesis discrimination model is established, and through comparative research, it is determined that the sample is of crust-mantle mixed origin.

[0021] The invention proposes a method for determining the genesis of the granite body in the Heimahe area, which overcomes the limitations and human subjectivity of the single method in the existing technology and can quickly, efficiently and accurately determine the genesis of the Triassic granite in the Heimahe rock body.

[0022] The method of the present invention can determine the genesis of the granite body, accurately determine the genetic type of the Triassic granite of the Heimahe rock body, and provide certain theoretical support for the study of the granite body in the Heimahe area. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the correlation analysis diagram of SiO2 and TiO2.

[0024] Figure 2 This is the correlation analysis diagram of SiO2 and Al2O3.

[0025] Figure 3 This is the correlation analysis diagram of SiO2 and Fe2O3.

[0026] Figure 4 This is the correlation analysis diagram of SiO2 and MgO.

[0027] Figure 5 This is the correlation analysis diagram of SiO2 and CaO.

[0028] Figure 6 This is the correlation analysis diagram of SiO2 and K2O.

[0029] Figure 7 This is a diagram of the distribution pattern of rare earth elements.

[0030] Figure 8 This is the sample's cause discrimination diagram. DETAILED DESCRIPTION

[0031] The present invention proposes a method for determining the genesis of granite bodies in the Heimahe region. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention will be further described below in conjunction with specific embodiments.

[0032] In the description of this application, words such as "a", "two", etc. are used only to distinguish different objects and do not limit the quantity or execution order. In addition, words such as "a", "two", etc. do not necessarily limit differences. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0033] The sample described in the present invention is a Triassic granite from the Heimahe area of the eastern Kunlun Mountains. The origin of the Triassic granite in the Heimahe area is analyzed from the perspective of geochemical characteristics. Through analysis, it is determined that the Triassic granite in the Heimahe area of the eastern Kunlun Mountains is a granite of mixed crust-mantle origin, which realizes the discrimination of its origin. The method of the present invention provides basic data for the study of the origin of the Triassic granite in the Heimahe area.

[0034] The invention discloses a method for determining the genesis of a granite body in the Heimahe area, which specifically comprises the following steps: step 1, collecting Triassic granite in the Heimahe area as a sample, then selecting the sample, selecting fresh and unaltered samples, and grinding the sample into a 200-mesh powder by using a grinder.

[0035] Step 2: Analyze and test the major elements and trace elements in the powdered sample separately.

[0036] The steps for testing major elements are as follows: (1) Drying: Take 2-3g of sample and place it in a designated paper sample bag, open it, and place it in an oven at 105℃ for 1-2 hours. After taking the sample out of the oven, place it directly in a glass desiccator for weighing. During this step, make sure that the paper sample bag is open and stable when placing the sample in the oven.

[0037] (2) Weighing: Use a 1 / 100,000 balance to weigh approximately 50 mg of sample and place it in a platinum crucible. Record the platinum crucible number, sample number, and sample weight accurately to two decimal places. Weigh approximately 0.25 g of dried lithium metaborate and place it in the platinum crucible using a weighing spoon or weighing paper. Stir and mix thoroughly with a weighing spoon.

[0038] (3) Melting: Place the platinum crucible in a muffle furnace, set the temperature to 1050℃, and melt for 60 minutes. Take a 50mL beaker and a corresponding number for the crucible, and fill the beaker with about 4 / 5 of the volume of 5% primary nitric acid; ensure that the exhaust is turned on, wear asbestos gloves and a helmet, open the muffle furnace, pick out a crucible, and close the door of the muffle furnace; turn on the Bunsen burner in advance to generate a flame. Shake the crucible at high temperature on the Bunsen burner until the sample is fully melted into droplets and there is no sample hanging on the crucible wall or residue at the bottom of the crucible. Quickly pour the sample into a 50mL beaker with the same number. Place the used crucible on a metal tray to cool. Then open the muffle furnace again, pick out the next crucible, and perform the same operation; after use, turn off the Bunsen burner and disconnect the power supply. After sealing the beaker with sealing film, shake it in an ultrasonic cleaner for 15-20 minutes until it is completely dissolved. In this step, since the sample is not completely exploded, the outer edge of the crucible needs to be directly immersed in the acid solution in the beaker when pouring the sample to ensure that the sample is completely poured out.

[0039] (4) Volume adjustment: Transfer the sample solution to a 100 mL volumetric flask. Rinse the beaker with ultrapure water and transfer it to the volumetric flask. Finally, use ultrapure water to adjust the volume to 2000 times the sample weight (100 g). Record the actual weight after volume adjustment. This will prepare for the ICP-OES test of major elements.

[0040] The steps for testing trace elements are as follows: Step 1. Prepare and weigh 50 mg of sample in a Teflon cup, arrange the Teflon cups with weighed samples in order, open the cup lid, and add 1 mL of anti-aqua regia and 0.5 mL of HF in turn; cover the cup lid, and send the Teflon cup to the high-temperature and high-pressure sample dissolution room through the transfer window; place the Teflon cup in a steel can with the perforated gasket at the bottom and the non-porous gasket at the top, tighten the steel can, and place it in an oven at 190°C for 12 hours.

[0041] Step 2: Remove the steel container and place it in a fume hood. Unscrew the container, but do not remove the Teflon cup at this time to prevent sample spraying. After the sample has completely cooled, remove the Teflon cup. Transfer the Teflon cup to the pretreatment unit, open the lid, and heat it on a hot plate at 120°C. After the sample is evaporated to dryness, add 1mL of secondary HNO3 and evaporate to dryness. Repeat twice to ensure that there is no liquid on the wall of the Teflon cup. Then, add 1mL of secondary HNO3 and 4mL of ultrapure water. Place the Teflon cup back into the steel container and place it in an oven at 190°C for 2 hours to reconstitute. Transfer the solution to a constant volume flask and dilute it to 100g with 2% HNO3 (corresponding to a dilution factor of 2000). Store in a sealed container for trace element analysis by ICP-MS.

[0042] The relevant data of major elements of the samples measured according to the above method are shown in Table 1, and the relevant data of trace elements are shown in Table 2.

[0043] Table 1 Data related to major elements

[0044]

[0045] Table 2 Data on trace elements

[0046]

[0047] Step 3: Perform an initial screening using Excel, selecting major elements with certain correlations. For example, we selected SiO2 for correlation analysis with TiO2, Al2O3, TFe2O3, MgO, CaO, or K2O. Furthermore, for trace element selection, we used rare earth elements (REEs) to analyze their distribution patterns. We also selected highly incompatible elements with similar distribution coefficients (such as Nb, Ta, Th, and U) from the incompatible trace element data and plotted them to identify their origins.

[0048] The relevant data of the major elements were screened and analyzed, including the correlation analysis between SiO2 and the oxides of Ti, Al, Fe, Mn, Mg, Ca, Na, K or P. The formula used is shown in formula (1).

[0049] (1).

[0050] In formula (1): is the correlation coefficient; is the number of samples; is the horizontal axis variable; is the vertical axis variable.

[0051] Correlation analysis between SiO2 and TiO2 Figure 1 As shown in the figure, the correlation analysis between SiO2 and Al2O3 is as follows Figure 2The correlation analysis between SiO2 and Fe2O3 is shown in Figure 3 The correlation analysis between SiO2 and MgO is shown in Figure 4 The correlation analysis between SiO2 and CaO is shown in Figure 5 The correlation analysis between SiO2 and K2O is shown in Figure 6 As shown. Figures 1 to 6 It can be seen that the present invention uses a linear regression equation and a correlation coefficient to represent its correlation. Correlation analysis is a statistical method used to measure the relationship between two or more variables. In correlation analysis, the correlation coefficient is usually used to describe the degree of relationship between variables. The value of the correlation coefficient is usually between -1 and 1. The closer the correlation coefficient is to 1, the greater the correlation between the two variables. If the correlation coefficient between two variables is 1, they are completely positively correlated; if the correlation coefficient is -1, they are completely negatively correlated; if the correlation coefficient is 0, there is no correlation between them. The detailed calculation method is shown in formula (1), R is the correlation coefficient, 、 For two variables.

[0052] Step 4: Trace element analysis includes rare earth element distribution pattern diagram, such as Figure 7 As shown in the figure, the average value of the rare earth elements in the sample data in Table 2 after standardization is used to make a rare earth element distribution pattern diagram, that is, the rare earth elements are used as the horizontal axis, and the average value of the sample data / chondrite data is taken as the vertical axis to make a line graph, which is the rare earth element distribution pattern diagram of the Heimahe rock body.

[0053] Step 5: Establish a sample genesis discrimination model and make a sample genesis discrimination diagram. The specific steps are: select strongly incompatible elements with similar distribution coefficients among trace elements, the said strongly incompatible elements include element 1, element 2, element 3 and element 4, calculate the ratio of the strongly incompatible elements and standardize them, and calculate the specific value of the strongly incompatible elements. The formula used is shown in formula (2).

[0054] Element One * = [ Element One Element Three ] sample [ Element One Element Three ] primitive mantle − Element Two * [ Element Two Element Four ] sample [ Element Two Element Four ] primitive mantle (2).

[0055] In formula (2): is Nb*; is Nb; For Ta*; Element three is Ta; element four is U.

[0056] A scatter plot is made with the specific values of element one and element two obtained by calculation as the horizontal and vertical coordinates, respectively, to obtain the sample's genetic discrimination diagram; in the sample's genetic discrimination diagram, the end members of the continental crust, primitive mantle, oceanic crust basalt, enriched mid-ocean ridge basalt, and normal mid-ocean ridge basalt are drawn for comparison. Through comparative study, the sample falls between the continental crust and the primitive mantle, and it is determined that the sample is of crust-mantle mixed origin.

[0057] Take the elements Nb, Ta, Th, and U as an example. Since Nb, Ta, Th, and U are all strongly incompatible elements, and D Nb ≈D Ta ≈D Th ≈D U (D refers to the distribution coefficient). Therefore, the Nb* and Ta* values of these samples retain, to a certain extent, the characteristics of their source regions, reflecting the characteristics of the magma-generating region and, in other words, their origin. Based on this characteristic, a Nb*-Ta* discrimination diagram was designed to determine the origin of the Heimahe pluton. Specifically, the following steps were performed: Trace element data obtained through testing and analysis were selected, and the Nb / Th and Ta / U ratios of the samples were calculated. These ratios were then normalized using data derived from the primitive mantle. Specifically, the Nb* and Ta* values of the samples were compared with the primitive mantle's Nb / Th and Ta / U values to obtain the Nb* and Ta* values, respectively. A scatter plot was created, with Nb* as the horizontal axis and Ta* as the vertical axis, to produce the Nb*-Ta* discrimination diagram for the Heimahe pluton.

[0058] In order to determine its origin, it is necessary to determine whether it is of crustal origin, mantle origin, or a mixture of crust and mantle. Figure 8 As shown, the present invention draws the end members of continental crust, primitive mantle, oceanic crust basalt, enriched mid-ocean ridge basalt, and normal mid-ocean ridge basalt in the sample's genesis discrimination diagram for comparison. Through comparative study, the sample falls between the continental crust and the primitive mantle, and it is determined that the sample is of crust-mantle mixed origin.

[0059] Parts not described in the present invention can be implemented by referring to the existing technology.

[0060] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for determining the origin of granite in the Heimahe area, characterized in that: The following steps are included in sequence: S1. Collect granite samples from the Heimahe area and grind them into powder. S2. Analyze and test the major elements and trace elements in the powdered sample obtained in step 1 to obtain major element and trace element data; the major elements include oxides of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P; S3. Screen and analyze the acquired major element data. The analysis includes correlation analysis between SiO2 and oxides of Ti, Al, Fe, Mg, Ca, Na or K. The formula used is shown in formula (1): In formula (1), R is the correlation coefficient; n is the number of samples; x i is the horizontal axis variable; i is the vertical axis variable; S4. Analyze the rare earth element data in the trace elements, and use the average value of the rare earth elements after standardization to create a rare earth element distribution pattern diagram; use the rare earth element data as the horizontal axis and the average value of the chondrite data of the sample as the vertical axis after taking the logarithm to create a line graph, which is the rare earth element distribution pattern diagram; S5. Establishing a sample genesis discrimination model; S51. Prepare a generative discrimination diagram of the sample. The specific steps are as follows: Strongly incompatible elements with similar distribution coefficients among the trace elements are selected. The strongly incompatible elements include element one, element two, element three, and element four. The ratios of the strongly incompatible elements are calculated and standardized to obtain specific values of the strongly incompatible elements. The formula used is shown in formula (2): In formula (2): element 1 * is Nb*; element one is Nb; element two * is Ta*; element two is Ta; element three is Th; element four is U; S52. Using the calculated specific values of element 1 and element 2 as the horizontal and vertical coordinates, respectively, a scatter plot is created to obtain a genetic discrimination diagram for the sample; end members of continental crust, primitive mantle, oceanic crust basalt, enriched mid-ocean ridge basalt, and normal mid-ocean ridge basalt are plotted in the genetic discrimination diagram for comparison. Through comparative study, the sample falls between the continental crust and primitive mantle, and it is determined that the sample is of mixed crust-mantle origin. In S2, trace elements include Y, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ta, Th and U; the strongly incompatible elements among the trace elements are: Nb, Ta, Th and U.

2. The method for determining the genesis of granite bodies in the Heimahe region according to claim 1, wherein: In S1, the sample was ground into a powder with a particle size of 200 mesh.

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