Cause determination method applied to granite body in Heimahe River region

Abstract

The invention discloses a cause judgment method applied to a granite body in a Heimahe region, and belongs to the technical field of geological engineering. According to the method, the triassic granite in the Heimahe region in the East Kunlun is taken as a research object, and the cause of the triassic granite in the Heimahe region is discussed from the perspective of geochemical characteristics. The method comprises the following steps: firstly, grinding a sample into powder; secondly, analyzing and testing major elements and trace elements in the sample to obtain major element and trace element data; performing correlation analysis on the data of the major elements, analyzing the data of the rare earth elements in the trace elements, and making a rare earth element partition pattern pattern according to the average value of the standardized rare earth elements of the sample; and finally, establishing a sample cause judgment model, and judging whether the sample is a shell and mantle mixed cause through comparative study. The method provided by the invention provides basic data for research on the causes of the Heihe Triassic granite.

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 origin has always been a hot topic of concern for scholars at home and abroad. The Heimahe rock mass is located south of the Nanshan Fault in Qinghai Lake, with an exposed area of ​​up to 500km 2 It is a very important Triassic granite complex in the northern margin tectonic belt of the West Qinling Mountains. The main lithology of the rock mass is granodiorite, but a small amount of quartz diorite is found in the northwest of the rock mass, which is in gradual contact with the granodiorite. Diorite and gabbro are exposed in the southeast, which is a typical magmatic complex. The rock mass has an obvious intrusive contact relationship with the surrounding rock, the Lower Triassic Longwuhe Formation sandstone. There are a large number of dark-colored microparticles (diorite) inclusions of various shapes and sizes inside the complex.

[0003] At present, the research on granite bodies in the prior art mainly focuses on the identification of their alteration zoning characteristics. For example, application No. 201710474613.2 discloses a geochemical identification method for granite alteration zoning. This method is based on quantitative evaluation indicators, calculates the alteration degree evaluation index value of each test point, and obtains the alteration degree of the rock body at each test point; then, according to the zoning identification criteria, the rock body in the same alteration degree range is divided into the same alteration zone, and the rock body is rapidly and continuously altered and zoned, and finally the rock body is divided into a full alteration zone, a strong alteration zone, a moderate alteration zone, a weak alteration zone and an unaltered zone.

[0004] There are several main causes of the Triassic granite in East Kunlun: melting of ancient crust, melting of young crust, crust-mantle mixing, melting of oceanic crust plus some sediments. The corresponding tectonic modes are: delamination mode, syn-collision mode, post-collision mode, etc. There is a lot of controversy about its origin. Therefore, it is necessary to study a method for determining the origin of granite bodies in the Heimahe area. Summary of the invention

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

[0006] In order to achieve the above purpose, the present invention adopts the following technical scheme: 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, including the 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 the rare earth elements are standardized.

[0012] S5. Establish a sample genesis discrimination model: S51. Prepare a sample genesis discrimination diagram, the specific steps are: select strongly incompatible elements with similar distribution coefficients among trace elements, the strongly incompatible elements include element one, element two, element three and element four, calculate the ratio of the strongly incompatible elements and standardize them, calculate the specific value of the strongly incompatible elements, and 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 Him; 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, that is, to obtain the sample's genetic discrimination diagram; in the sample's genetic discrimination diagram, draw the end members of the 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 origin of the granite body in the Heimahe area, in S1, the sample is ground into powder with a particle size of 200 meshes.

[0018] Furthermore, in the above-mentioned method for determining the origin of the granite body in the Heimahe area, in S4, a line graph is produced with the data of rare earth elements as the horizontal axis and the average value of the data of the chondrite of the sample 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 origin of granite bodies in the Heimahe area. The method selects the 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 on the rare earth elements in the trace elements are analyzed, and a rare earth element distribution pattern diagram is prepared with the average value after the rare earth elements are standardized; finally, a sample origin discrimination model is established, and through comparative research, it is determined that the samples are 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 of the single method in the prior art and human subjectivity, and can quickly, efficiently and accurately determine the genesis of the Triassic granite in the Heimahe rock body.

[0022] The method of the invention can determine the genesis of the granite body, can accurately determine the genesis 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 between SiO2 and MgO.

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

[0028] Figure 6 This is the correlation analysis diagram between 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 genesis discriminant diagram. DETAILED DESCRIPTION

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

[0032] In the description of this application, words such as "one", "two", etc. are only used to distinguish different objects, and do not limit the quantity and execution order, and words such as "one", "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 the Triassic granite in the Heimahe area of ​​East Kunlun. 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 ​​East Kunlun is a granite of mixed crust-mantle origin, and its origin is determined. 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 samples, then selecting the samples, selecting fresh and unaltered samples, and grinding the samples by a grinder to grind them into a powder with a mesh size of 200.

[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 put it into a designated paper sample bag and open it, and then put it in an oven at 105℃ to dry for 1-2 hours. After taking the sample out of the oven, put it directly into a glass desiccator for weighing. In this step, make sure that the paper sample bag is open and stable when the sample is put into the oven.

[0037] (2) Weighing: Use a 1 / 100,000 balance to weigh about 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 about 0.25 g of dried lithium metaborate and place it in the platinum crucible using a weighing spoon or weighing paper and stir with a weighing spoon to mix evenly.

[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 crucible and number them one by one, and fill the beaker with about 4 / 5 of the volume of 5% primary nitric acid; on the premise of ensuring that the exhaust is turned on, wear asbestos gloves and a helmet, open the muffle furnace, clip out a crucible, and close the door of the muffle furnace; turn on the Bunsen burner in advance to produce 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 remaining at the bottom of the crucible. Quickly pour the sample into a 50mL beaker with the same number, and place the used crucible on a metal tray to cool. Then open the muffle furnace again, clip 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, and finally adjust the volume to 2000 times the sample weight (100 g) with ultrapure water, and record the actual weight after volume adjustment. This is for the ICP-OES test of major elements.

[0040] The steps for testing trace elements are as follows: Step 1. Prepare 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; put the Teflon cup into a steel can with the perforated gasket at the bottom and the non-perforated gasket at the top, tighten the steel can, and place it in an oven and dry it at 190°C for 12 hours.

[0041] Step 2: Take out the steel can and place it in a fume hood. Unscrew the steel can. Do not take out the Teflon cup at this time to prevent the sample from spraying out. After the sample is completely cooled, take out the Teflon cup; send the Teflon cup to pretreatment, open the cup cover, and place it on a hot plate to heat at 120°C; after the sample is evaporated, add 1mL of secondary HNO3 and evaporate it, repeat twice to ensure that there is no liquid on the wall of the Teflon cup; add 1mL of secondary HNO3 and 4mL of ultrapure water in turn; put the Teflon cup into the steel can and place it in an oven at 190°C for 2h to dissolve. Transfer the solution into a constant volume bottle, dilute it to 100g with 2% HNO3 (the corresponding dilution factor is 2000), and store it in a sealed container for ICP-MS testing of trace elements.

[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 of major elements

[0044] Table 2 Data on trace elements

[0045] Step 3: Perform a preliminary screening through Excel, select the main elements with certain correlation, and select SiO2 and TiO2, Al2O3, TFe2O3, MgO, CaO or K2O for correlation analysis. At the same time, in the selection of trace elements, we selected rare earth elements for distribution mode analysis of their rare earth characteristics. We also selected strong incompatible elements and elements with similar distribution coefficients (Nb, Ta, Th, U and other elements) from the incompatible elements in the trace element data for analysis and drawing to determine their causes.

[0046] The relevant data of the major elements are 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).

[0047] (1).

[0048] In formula (1): is the correlation coefficient; is the number of samples; is the horizontal axis variable; is the vertical axis variable.

[0049] Correlation analysis between SiO2 and TiO2 Figure 1 As shown in the figure, the correlation analysis between SiO2 and Al2O3 is as follows Figure 2 As shown. The correlation analysis between SiO2 and Fe2O3 is shown in Figure 3As shown. The correlation analysis between SiO2 and MgO is shown in Figure 4 As shown in the figure. The correlation analysis between SiO2 and CaO is shown in the figure Figure 5 As shown in the figure. The correlation analysis between SiO2 and K2O is shown in the figure. 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, a 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.

[0050] Step 4: Trace element analysis includes rare earth element distribution pattern diagram, such as Figure 7 As shown, the rare earth element distribution pattern diagram is made using the standardized average value of the rare earth elements in the sample data in Table 2, that is, with the rare earth elements as the horizontal axis and the average value of the sample data / chondrite data taken from the logarithm as the vertical axis to make a line graph, which is the rare earth element distribution pattern diagram of the Heimahe rock body.

[0051] 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 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).

[0052] 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).

[0053] In formula (2): is Nb*; is Nb; For Ta*; is Ta; element three is Th; element four is U.

[0054] A scatter plot is made with the specific values ​​of element one and element two calculated 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 plotted 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.

[0055] Take the elements Nb, Ta, Th, and U as an example. Since Nb, Ta, Th, and U are all strongly incompatible elements, and in the process of magma evolution, D Nb ≈D Ta ≈D Th ≈D U (D refers to the distribution coefficient), so the Nb* and Ta* of these samples maintain the characteristics of their source areas to a certain extent, which can reflect the characteristics of the magma source area, that is, their genesis can be determined. According to this characteristic, the Nb*-Ta* discrimination diagram is designed to determine the genesis of the Heimahe rock mass. The specific operation is: obtain trace element data through test analysis, select Nb, Th, Ta, U and other data, calculate the Nb / Th and Ta / U ratios of the samples, and standardize them at the same time. The standardized data is taken from the primitive mantle, that is, the Nb / Th and Ta / U of the samples are compared with the Nb / Th and Ta / U of the primitive mantle to obtain the values ​​of Nb* and Ta* respectively. With the Nb* of the obtained data as the horizontal coordinate and Ta* as the vertical coordinate, a scatter plot is made to obtain the Nb*-Ta* discrimination diagram of the Heimahe rock mass.

[0056] 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 mixed crust-mantle origin.

[0057] Parts not described in the present invention can be implemented by referring to the existing technology.

[0058] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope 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 in the Heimahe area as samples and grind the samples into powder; S2. Analyze and test the major elements and trace elements in the powdered sample obtained in step 1 respectively to obtain the 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, including the correlation analysis between SiO2 and oxides of Ti, Al, Fe, Mg, Ca, Na or K. The formula used is shown in formula (1): （1）； In formula (1): is the correlation coefficient; is the number of samples; is the horizontal axis variable; is the vertical axis variable; 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 the rare earth elements are standardized; S5. Establishing a sample origin discrimination model; S51, making a cause discrimination diagram of the sample, the specific steps are: Selecting strongly incompatible elements with similar distribution coefficients among trace elements, the strongly incompatible elements include element one, element two, element three and element four, calculating the ratio of the strongly incompatible elements and performing standardization, and calculating the specific values ​​of the strongly incompatible elements, the formula used is shown in formula (2): （2）； In formula (2): is Nb*; is Nb; For Ta*; For Him; for Th; for U; S52. Use the calculated specific values ​​of element one and element two as the horizontal and vertical coordinates, respectively, to make a scatter plot, that is, to obtain the sample's genetic discrimination diagram; in the sample's genetic discrimination diagram, draw the end members of the 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.

2. The method for determining the origin of granite bodies in the Heimahe region according to claim 1, characterized in that: 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.

3. The method for determining the origin of granite bodies in the Heimahe region according to claim 1 is characterized in that: In S1, the sample was ground into a powder with a particle size of 200 mesh.

4. The method for determining the genesis of granite bodies in the Heimahe region according to claim 1, characterized in that: In S4, a line graph is made with the rare earth element data as the horizontal axis and the average value of the sample's chondrite data as the vertical axis after taking the logarithm, which is the rare earth element distribution pattern diagram.

5. The method for determining the origin of granite bodies in the Heimahe region according to claim 2 is characterized in that: In S5, the strongly incompatible elements among the trace elements are: Nb, Ta, Th and U.

Images