Estimation method of granite magma temperature

Abstract

The invention belongs to the technical field of geological rock research, and relates to a granite magma temperature estimation method, which comprises the following steps: (1) collecting a granite sample, and grinding the sample to obtain granite sample powder; (2) carrying out digestion treatment on the granite sample powder, and analyzing and testing the total rock SiO2 content in the granite sample; and (3) estimating the granite magma temperature TSiO2 according to a granite magma temperature calculation formula, wherein the calculation formula is TSiO2 =-14.16 * SiO2 (wt%) + 1723 (DEG C). The granite magma temperature calculation formula provided by the invention can more reasonably estimate the granite magma temperature according to the granite total rock SiO2 content.

Description

Technical Field

[0001] The invention belongs to the technical field of geological rock research, relates to estimating magma temperature by applying rock component composition, and specifically relates to a method for estimating granite magma temperature. Background Art

[0002] In the process of studying the origin of igneous rocks, estimating the liquidus temperature or crystallization temperature is a fundamental problem. For basalt and basaltic rocks, it is simple because experimental petrology studies have well proved that the phase transition relationship between different liquidus minerals (such as olivine, monoclinic pyroxene, plagioclase) and melts is a function of temperature, that is, the liquidus temperature is positively correlated with the MgO content in the melt. However, for granite and granite rocks, although the liquidus temperature is negatively correlated with the SiO2 content in the melt, it is not easy to calculate the liquidus temperature of granite and granite rocks because of the following difficulties: (1) Except for highly evolved granite and rhyolite glass, most granites and granite rocks cannot represent melts, but rather a mixture of melt-crystals. This is because the viscosity of granite melts is high, and the melt and the molten residue cannot be completely separated during partial melting, and the liquidus minerals cannot be completely separated from the melt during melt evolution. (2) If the component exchange reaction between minerals in granite is sensitive to temperature, then the chemical equilibrium between minerals can record the temperature conditions under which such exchange reactions occur. However, such chemical equilibrium between minerals records not the liquidus temperature of the mineral, but the cooling temperature below the solidus temperature after the mineral crystallization.

[0003] Watson and his collaborators have overcome the above difficulties to a large extent by developing a zircon saturation thermometer through rigorous experimental petrology. This zircon saturation thermometer is widely used and is considered to be "a simple and reliable method for estimating magma temperature". In the study of granite rocks, the zircon saturation thermometer is widely used as an important technical means to estimate the magma temperature of granite.

[0004] The zircon saturation thermometer is reasonable in concept, and Watson and his collaborators are reliable in correcting experimental data. However, the temperature values ​​calculated using the zircon saturation thermometer not only have large errors, but also have no practical geological significance. The reason is that the main parameters in the zircon saturation thermometer are the major element content and trace element zirconium (Zr) content of the melt, but since the melt composition is unknown, researchers usually use the whole rock composition instead of the melt composition for calculation. Granite samples rarely represent pure melts, but are a mixture of cumulates and residual melts, because the viscosity of granite melts is high and it is difficult to completely separate the melt phase and the solid phase. If all the crystals in the rock are liquidus minerals and the rock sample is large enough, the whole granite rock may represent the melt, but this assumption is unrealistic. Therefore, the calculated whole rock characteristic value (M) is completely unrelated to the characteristic value (M) that truly represents the melt. However, since the temperature value calculated by the zircon saturation thermometer in petrological experiments has no correlation with the characteristic value (M) and other composition parameters, the zircon content of the whole rock (not the M value) is the main source of error in the calculated temperature value. Since whole-rock zircon is mainly stored in zircons of different origins (crystallization, capture, inheritance) of granite, and the proportion of zircon minerals is unknown, the whole-rock zircon content cannot replace the melt Zr content, and the temperature value calculated using the whole-rock Zr content has no geological significance. Therefore, it is urgent to design a calculation formula that can easily calculate the granite magma temperature. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems existing in the prior art, and propose a method for estimating the temperature of granite magma. After summarizing the experimental petrological data, a new and more reasonable calculation formula for estimating the temperature of granite magma based on the SiO2 content of the whole granite rock is obtained: T SiO2 =-14.16×SiO2+1723(℃).

[0006] The technical solution of the present invention is:

[0007] A method for estimating the temperature of granite magma comprises the following steps:

[0008] (1) collecting granite samples and grinding the samples to obtain granite sample powder;

[0009] (2) Digest the granite sample powder and analyze the whole-rock SiO2 content in the granite sample;

[0010] (3) Estimate the granite magma temperature T according to the granite magma temperature calculation formula SiO2 , the calculation formula is:

[0011] T SiO2=-14.16×SiO2(wt%)+1723(℃).

[0012] Furthermore, in step (2), the granite sample powder is digested by alkali fusion to obtain a sample solution for analysis.

[0013] Furthermore, the sample solution was tested and analyzed using an inductively coupled plasma spectrometer to obtain the whole-rock SiO2 content of the granite sample.

[0014] Furthermore, in the step (2), the granite sample powder is processed by a melting sheet method or a pressing sheet method to obtain a glass sheet or a sample sheet for analysis.

[0015] Furthermore, X-ray fluorescence spectrometer was used for detection and analysis to obtain the whole-rock SiO2 content of the granite sample.

[0016] Furthermore, the SiO2 content of the whole granite rock is used to calculate the granite magma temperature.

[0017] Beneficial effects of the present invention:

[0018] The present invention proposes a more accurate formula for calculating the granite magma temperature, thereby being able to more reasonably estimate the granite magma temperature based on the SiO2 content of the whole granite rock; compared with the existing zircon saturation thermometer method, the method of the present invention is more suitable for estimating the liquidus temperature of granite based on the SiO2 content of the whole granite rock.

[0019] The new empirical formula T for calculating temperature proposed by the present invention is used. SiO2 The calculated temperature values ​​can be used to compare the similarities and differences in liquidus temperatures between different samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the relationship between the abundance of major elements and temperature in the reported experimental petrological data;

[0021] Figure 2 To select the composition data of granite samples from the Qinling, Qilian and Kunlun orogenic belts, we calculated T SiO2 and T MgO ;

[0022] Figure 3 In order to combine the whole-rock major and Zr content data of granite samples collected in the Qinling, Qilian and Kunlun orogenic belts, the zircon saturation thermometer T Zr and T proposed by the present invention SiO2 The estimated formula calculates the granite magma temperature. It can be clearly seen from the figure that T SiO2The calculated values ​​have a significant correlation with the major elements of granite samples, but no obvious correlation with Zr, which is consistent with the change of equilibrium crystalline mineral phases with the change of liquidus temperature. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In order to further understand the present invention, the present invention will be further described in conjunction with the accompanying drawings and embodiments.

[0025] Example 1

[0026] The present invention provides a calculation formula for estimating the temperature of granite magma, the formula source is as follows:

[0027] The experimental petrological data (including temperature and major element data of melt) reported in the statistical literature are used to explore the correlation between the major element abundance (such as SiO2 and MgO) and temperature of andesitic and acidic magmas. The selection criteria for the experimental data are: SiO2>53wt%, MgO=0.3~6wt%, and liquidus temperature is less than 1250K.

[0028] Selected experimental petrological data are attached. Figure 1 .from Figure 1 It can be clearly seen that the temperature is negatively correlated with the SiO2 content and positively correlated with the MgO content, which indicates that as the liquidus temperature decreases, the changes in the SiO2 and MgO composition in the melt are related to the separation and crystallization of mafic minerals from the melt as the magma cools. Given the SiO2 and MgO contents, a certain degree of temperature variation may be caused by differences in the composition of the experimental petrological data. In any case, the correlation between temperature and SiO2 and MgO is very obvious.

[0029] Therefore, the selected experimental data were averaged at every interval of 3wt% SiO2 content and every interval of 1wt% MgO content, and a simple but reasonable correlation between SiO2 and liquidus temperature and between MgO and liquidus temperature was obtained, that is, T SiO2 =-14.16×SiO2(wt%)+1723(℃), T MgO =887.6×[MgO (wt%)] 0.0989 (℃), which effectively shows the important advantages of SiO2 and MgO content in reflecting the changes in liquidus temperature of intermediate and acidic magma.

[0030] Although the temperature calculated by the formula summarized from the experimental data is not the actual magma temperature, for example, minerals such as amphibole have lower SiO2 and higher MgO content than real melts. The change of liquidus temperature is controlled by the phase equilibrium of the rock and ultimately by the main material composition of the rock. Therefore, the composition data of granite samples from the Qinling, Qilian and Kunlun orogenic belts are selected for comparison with T SiO2 and T MgO The formula results are as follows Figure 2 As shown, it can be clearly seen that the temperature value T calculated using the MgO content MgO (℃) than the temperature value T calculated using SiO2 content SiO2 Compared with the whole rock Zr content, the whole rock composition of granite (especially SiO2) is closer to the melt composition. Therefore, T SiO2 The temperature calculated by the formula (℃) is closer to the magma temperature.

[0031] Test Example 1

[0032] The published major and minor data of syn-collision granites in the Kunlun, Qilian and Qinling orogenic belts of China during the Mesozoic are collected. Table 1 lists the data of some granite samples.

[0033] Table 1 Main and trace data of some granite samples and calculated temperature values

[0034] Sample No. <![CDATA[SiO2(wt%)]]> MgO (wt%) Zr(ppm) <![CDATA[T SiO2 (℃)]]> <![CDATA[T MgO (℃)]]> <![CDATA[T Zr (℃)]]> DHG12-03 70.17 0.91 256 716 880 834 DHG12-10 70.07 0.82 211 717 872 804 DHG12-17 71.24 0.77 194 706 866 803 DHG12-18 69.52 0.91 258 722 881 832 DHG12-20 71.95 0.64 350 691 850 863 DHG12-24 69.94 0.77 219 725 866 804 BJZ12-03 74.58 0.22 144 662 764 771 BJZ12-04 76.60 0.16 79 632 740 721 BJZ12-05 73.47 0.20 106 670 756 754 LZG12-02 74.37 0.23 77 661 769 737 LZG12-03 72.58 0.27 115 679 781 773 LZG12-05 72.86 0.33 125 675 796 773 LZG12-07 74.44 0.22 111 660 766 761

[0035] The zircon saturation thermometer and the T SiO2 Formula for calculation;

[0036] Different from the temperature value calculated by the zircon saturation thermometer, T SiO2 The temperature value calculated by the formula is well correlated with the major elements, which is consistent with the change of mineral phase equilibrium during the melt cooling evolution. SiO2 The temperature value calculated by the formula has no correlation with the Zr content of the whole rock, indicating that Zr is not an essential element for the formation of granite. Therefore, Zr and zircon minerals cannot be used to indicate the temperature of granite magma. The data comparison results are shown in the attached Figure 3 .

[0037] Example 2

[0038] The present invention provides a method for estimating the temperature of granite magma. The specific working steps from sample collection, grinding, digestion, and testing are described in detail below:

[0039] (1) Granite sample powder preparation stage: Collect fresh granite samples in the selected research area and accurately record sampling information such as sampling location and sample number.

[0040] In the pretreatment laboratory, a cutting machine (metal slicer) is used to cut the granite sample into a rock plate, and the rock plate is ground on the diamond turntable to remove the saw marks to prevent metal contamination from the slices. Then the rock plate is washed and dried with water. Then a jaw crusher is used to put the rock plate with the saw marks into the crusher and crush it into small pieces. Then the broken rock blocks are placed in a small glass beaker according to the sample number, added with water and placed in an ultrasonic cleaner, shaken for 3 to 5 minutes, and then the water is poured out and rinsed with pure water. The washed rock blocks are placed in an oven and dried at 105°C. At this time, the spacing between the corundum jaws of the jaw crusher is adjusted to the minimum. After cleaning, the dried sample is poured into the corundum jaw plate and crushed 2 to 3 times until there are no large particles, and then placed in a new paper bag with a number. The finely crushed sample is placed in an oven and dried at 105°C. Bake at 105°C for 2 to 3 hours before grinding to ensure that the sample is sufficiently dry.

[0041] The planetary ball mill is mainly used in the sample grinding stage. Use clean tweezers to put the cleaned agate balls into the agate jars, 5 large balls and 5 small balls in each jar. Check and ensure that the jars are dry. Quickly pour in the dried finely crushed samples, cover the lid and record the numbers. At this time, the operation should be fast to ensure that the samples absorb as little water as possible after being taken out of the oven; put the agate jars into the ball mill and set the grinding time to obtain the granite sample powder for standby use.

[0042] (2) Alkali fusion method for sample digestion: Rinse the platinum crucible and 50ml glass beaker with deionized water, place them in a fume hood to dry, and prepare 2% HNO3 to soak the 100ml constant volume bottle and injection tube, then rinse them with deionized water and dry them for use. After preparing the experimental supplies required for sample digestion, put 2-3g of granite sample ground into 200 mesh powder into a clean kraft paper envelope, place it in an oven at 105℃ for 2h, and place the sample directly into a glass desiccator after taking it out of the oven. Record the number of the platinum crucible, weigh 0.25g of lithium metaborate in the platinum crucible, and then weigh 50mg of granite sample powder, stir evenly with a weighing spoon, and record the weighed mass. Put the platinum crucible filled with sample powder into a muffle furnace at 1050℃ for 0.5h. During this period, pour 3 / 4 of 5% HNO3 into the 50ml glass beaker and record the number.

[0043] Wait for the muffle furnace setting time to end, take out the platinum crucible, shake the platinum crucible on the Bunsen burner to polymerize the sample, ensure that the sample does not stick to the bottom of the platinum crucible, and quickly put the platinum crucible into a 50ml glass beaker filled with 5% HNO3. At this time, put the open glass beaker into the ultrasonic instrument for 20s. Take the glass beaker out of the ultrasonic instrument, clamp the platinum crucible with plastic pointed tweezers and pour the sample into the small glass beaker, and rinse the plastic tweezers and platinum crucible with deionized water. The rinse liquid is connected to the 50ml glass beaker. At this time, continue to put the glass beaker into the ultrasonic instrument for 15 to 20 minutes until it is completely dissolved. Place the 100ml volumetric flask on the balance and peel it, then transfer the sample solution from the 50ml glass beaker to the 100ml volumetric flask, rinse the inner wall of the glass beaker with deionized water 3 times, pour the liquid into the volumetric flask, dilute to 100g with deionized water, record the mass, cover the volumetric flask with a lid, and write the corresponding sample number on the bottle body and the bottle cap for subsequent testing.

[0044] (3) Major element (SiO2) analysis test process: This laboratory uses an inductively coupled plasma spectrometer (5100VDV ICP-OES) produced by Agilent to test the major element content of the sample. Before starting the test, first set the plasma gas (12L / min) and nebulizer gas (0.7L / min) to purge the instrument. After a period of purge, ignite the plasma. Place the mixed element standard solution and the sample solution to be tested in the corresponding position of the automatic sampler in sequence, fill in the test sequence conditions and start the test. After the test is completed, calculate the content of the corresponding oxide according to the element content, and you can get the major element content of the granite sample.

[0045] (4) According to the formula for calculating the granite magma temperature T SiO2 =-14.16×SiO2(wt%)+1723(℃) to estimate the granite magma temperature T SiO2 .

[0046] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments, or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, modification, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for estimating the temperature of granite magma, characterized in that: The following steps are involved: (1) collecting granite samples and grinding the samples to obtain granite sample powder; (2) Digest the granite sample powder and analyze the whole-rock SiO2 content in the granite sample; (3) Estimate the granite magma temperature T according to the granite magma temperature calculation formula SiO2 , the calculation formula is: T SiO2 =-14.16×SiO2(wt%)+1723(℃)。 2. The method according to claim 1, characterized in that In the step (2), the granite sample powder is digested by alkali fusion method to obtain a sample solution for analysis.

3. The method according to claim 2, characterized in that The sample solution was tested and analyzed using an inductively coupled plasma spectrometer to obtain the whole-rock SiO2 content of the granite sample.

4. The method according to claim 1, characterized in that: In the step (2), the granite sample powder is processed by a melting sheet method or a pressing sheet method to obtain a glass sheet or a sample sheet for analysis.

5. The method according to claim 4, characterized in that X-ray fluorescence spectrometer was used for detection and analysis to obtain the whole-rock SiO2 content of the granite sample.

6. The method according to claim 1, characterized in that The SiO2 content of the whole granite rock is used to calculate the granite magma temperature.

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