Test method for separating volcanic glass and hydrogen isotope by using heavy liquid flotation method

Abstract

The invention discloses a test method for separating volcanic glass and hydrogen isotope by using a heavy liquid flotation method. The test method comprises the following steps: S1, identifying and identifying volcanic glass under a microscope; s2, separating and extracting volcanic glass by a heavy liquid flotation method; s3, testing the volcanic glass hydrogen isotope by using TC / EA-MS; the method solves the problems of how to separate and extract volcanic glass from a volcanic rock sample by using a heavy liquid flotation method, test volcanic glass hydrogen isotope by using a TC / EA-MS analysis method and finally reconstruct the ancient height of an ancient mountain range by means of an empirical formula or a theoretical model.

Description

Technical Field

[0001] The invention relates to the field of volcanic glass and estimating ancient altitude by using stable isotopes, and in particular to a testing method for separating volcanic glass and hydrogen isotopes by using a heavy liquid flotation method. Background Art

[0002] Volcanic glass is a glassy structure fragment distributed in volcanic tuff. It is amorphous and has a density that varies depending on the chemical and physical conditions under which it is formed. It is generally 2.25-2.5g / cm 3 . The morphological characteristics of volcanic glass are an important basis for identification under a microscope. The most striking and unique features of its surface structure are the various curved surfaces or arc surfaces and the various pores on or between the curved surfaces. Together, they reflect the unique explosion and jet action during volcanic eruptions and are easily distinguished from quartz particles. Volcanic glass is transparent or nearly transparent, colorless to yellowish brown under an optical microscope. The morphology is diverse and the shape is extremely irregular. It can be seen that it has star-shaped flakes, block-shaped pores, ridges, etc. At present, the effective methods for extracting volcanic glass from volcanic ash sediments mainly include the ignition loss method, the dilute alkali method, the heavy liquid flotation method and the acidification method.

[0003] Paleoaltitude reconstruction not only helps us understand the geodynamic processes that shape the Earth's surface, but also plays an important role in understanding atmospheric circulation and the distribution of biological communities and biodiversity. In the past 20 years, with the development of various quantitative paleoaltimeters, the qualitative description of the plateau uplift process has shifted to quantitative constraints on the paleoaltitude of the plateau, which has greatly promoted the understanding of the uplift history of major orogenic belts and plateaus around the world. Among various quantitative research methods for paleoaltitude reconstruction, stable isotope paleoaltimeters are widely used due to their advantages such as a wide variety of geological carriers and continuous optimization of experimental methods. The basic principle of hydrogen and oxygen isotope paleoaltimeters is that oxygen in precipitation ( 18 The Rayleigh fractionation of deuterium (Ow) and deuterium (Dw) isotopes. The marine air mass reaches saturation during the adiabatic climb along the windward slope of the mountain and condenses to form precipitation. 18 Heavy isotopes such as O and D preferentially enter precipitation and fall to the surface, while water vapor is relatively enriched in light isotopes. 18 It is a common phenomenon that the content of O and D decreases with increasing altitude. Different geological carriers can preserve and record the hydrogen or oxygen isotope composition of ancient precipitation, thereby reconstructing the ancient altitude changes during the geological history. For oxygen isotope paleoaltimeters, the most commonly used carriers include different types of authigenic carbonate rocks, such as lacustrine carbonate rocks, soil carbonate rocks, shallow groundwater carbonate rocks, and animal and plant fossils. The geological carriers of hydrogen isotope paleoaltimeters mainly include three types: hydrous silicate minerals, volcanic glass, and plant wax alkanes.

[0004] The hydrogen isotopes of surface water in the Qinghai-Tibet Plateau are affected by altitude, water vapor sources and evaporative enrichment. Although the hydrogen isotopes of plant wax alkanes are not affected by fractionation temperature and evaporation and can be used to reconstruct the ancient altitude of the Qinghai-Tibet Plateau, the apparent fractionation coefficient (εwax-p) is difficult to determine due to drought and water stress effects on plants. The drier the climate, the higher the εwax-p value. The rhyolitic volcanic glass hydrogen isotope paleoaltimeter can effectively overcome the defects of using hydrogen and oxygen isotopes of Cenozoic paleo-soils on the Qinghai-Tibet Plateau to reconstruct ancient altitudes. The rhyolitic volcanic rock here does not refer to a type of rock with strict structural and compositional restrictions, but its geochemical characteristics and physical properties can change, but this change has little effect on the fractionation of hydrogen isotopes in the glass. Rhyolitic volcanic rocks generally carry 0.1-0.3% magmatic water when they erupt, which is then reset by hydration with environmental water (such as seawater, lake water, near-surface soil water and surface water), and become saturated with about 3-5% bound water within 1-10 ka (ka is a time unit representing 1000 years). Compared with other types of glass (such as glass in lava), glass in tuff (or volcanic ash) is more easily hydrated due to the porous structure of tuff and the fact that tuff is always deposited in underwater environments (i.e. rivers, lakes, and oceans). In this process, volcanic glass particles act like a semipermeable membrane to drive external surface water to penetrate into the interior of the glass, and H2O molecules are trapped in the glass structure. After hydration, a dense gel layer is formed near the outer edge of the volcanic glass, which prevents later alteration and exchange of hydrogen isotopes with secondary environmental water. Since H2O molecules diffuse faster than HDO molecules, hydrogen isotopes undergo isotopic fractionation during the penetration process. Assuming that isotope exchange is an equilibrium reaction, the fractionation coefficient α between environmental water (δDw) and glass water (δDvg) (water-glass) obtained from the Pliocene and Holocene volcanic glasses and the pore water (environmental water) between them is 1.0343±0.0005, thus establishing their relationship: δDw=1.0343×(δDvg﹢1000)﹣1000. Since hydrogen isotopes diffuse dynamically between volcanic glass and environmental water, the fractionation coefficient is independent of temperature, and the offset between the δDvg values ​​of volcanic glass and surrounding water at surface temperature has been experimentally determined. Depending on the sedimentary environment, the δDvg value can record the δDw value of river water, soil water, shallow groundwater or lake water. At present, the δDvg value has been widely used in the reconstruction of the paleo-elevation of the Andes Mountains in South America and the paleo-altitude research in the Cordilleras of North America, and has shown great potential.

[0005] Therefore, rhyolitic volcanic glass paleoaltimeters have the advantages of being unaffected by temperature, having strong isotope preservation ability, and being easy to determine the age, which greatly simplifies the tests and assumptions when using paleoaltimeters. Moreover, by comparing the hydrogen isotopes of volcanic glass of the same or different eras with modern hydrogen isotopes on a large scale to reconstruct paleoaltitude changes, the uncertainty of altitude estimates caused by complex water vapor sources can be reduced to a large extent, which is of great significance for reconstructing the paleoaltitude of ancient mountains. The study of volcanic glass has achieved fruitful results in the reconstruction of paleoaltitudes and climate change in the Sierra Nevada region of North America, the Andes Plateau, and the Cascade Mountains in the United States. However, domestic research is still in the initial development stage.

[0006] Prior art 1

[0007] Turney, CSM (1998). Extraction of rhyolitic component of Veddemicrotephra from minerogenic lake sediments. Journal of Paleolimnology 19:199–206.

[0008] This technique describes a method for extracting rhyolitic microvolcanic ash from inorganic late glacial lake sediments. The technique was successfully applied by Lowe & Turney (1996) and is an improvement on the method described by Pilcher & Hall (1992) for Holocene peat sediments. The method proposes to use the density difference between acidic volcanic glass and other minerals to extract the rhyolitic microvolcanic ash with non-toxic and recyclable heavy liquid Na6 (H2W 12 O 40 )·H2O (sodium polytungstate) was used as a density flotation medium to extract volcanic ash from mineral-rich British lake sediments. The specific operating procedures are as follows: ① The sample was manually crushed in a crucible and heated to 550°C to remove organic matter, then dried in a dryer at 105°C overnight to remove moisture, cooled and weighed; ② The sample and crucible were then placed in a furnace at 650°C for 4 hours for organic matter ashing (combustion). After ashing is completed, the crucible is cooled in a dryer and reweighed to determine the loss on ignition. ③ The sample was transferred to a 15ml centrifuge tube and 10% HCl solution was added to dissolve any soluble inorganic matter (such as carbonates). ④ The solution was poured through 75μm and 24μm cell sieves to separate particulate volcanic ash and other sediments. ⑤ The volcanic ash sample was sieved at a relative density of 2.40g / cm 3 Centrifuge twice in sodium polytungstate solution at 2500 rpm for 20 minutes. Take out the upper liquid after centrifugation (volcanic ash density <2.40 g / cm 3The ash was further separated by centrifugation at 2500 rpm and a brake rate of 9 for 15 minutes at this stage. The supernatant (diluted sodium polytungstate) can be collected and filtered for reuse, and the sediment (density <2.40 g / cm 3 ⑥ The residue at the bottom of the centrifuge tube (density> 2.40g / cm 3 ) at a relative density of 2.50 g / cm 3 Centrifuge twice at 2500rpm for 20 minutes in sodium polytungstate. After each treatment, pour the upper layer into a conical centrifuge tube filled with distilled water and centrifuge at 2500rpm and brake speed 9 for 15 minutes. 3 The residue is diluted with distilled water and the supernatant is recovered by centrifugation (2500rpm, brake speed 9, centrifugation for 15 minutes). As in stage 5, it is processed or stored according to whether it needs further analysis. ⑧ The upper liquid of stage ⑥ is further centrifuged three times in distilled water at the same speed to completely remove and recover sodium polytungstate. According to these steps, the particulate volcanic ash is separated from other fine-grained sediments (such as diatoms, minerals, unburned organic matter) at the bottom of the centrifuge tube and concentrated and purified.

[0009] Disadvantages of the prior art 1

[0010] Turney's (1988) method provides a detailed method for extracting volcanic glass, but this technology still has the following shortcomings:

[0011] 1. In step ②, heating at 650°C is used to incinerate the organic matter. Under this condition, the chemical composition of the volcanic glass will change. Therefore, other methods need to be considered to remove the organic matter, such as lowering the heating temperature or using chemical reagents to remove the organic matter.

[0012] 2. This technology uses 2.40g / cm 3 The flotation density of rhyolitic microparticles of volcanic glass in lake sediments is 2.7 g / cm2, but it is not clear whether it is applicable to other regions and different types of volcanic ash (for example, the density of basaltic ash is > 2.7 g / cm2). 3 ), so specific analysis is needed to select the appropriate heavy liquid density.

[0013] 3. The sample particle size will affect the extraction effect of volcanic glass. This method uses a particle size of 75μm-24μm, which may not be the optimal particle size for flotation volcanic glass.

[0014] 4. This technique has cumbersome steps and is slow when preparing a large number of samples.

[0015] Prior art 2

[0016] Gong,B.,2010.A ​​TC / EA-MS online technique of determining mineral watercontent and hydrogen isotope and its application to UHP metamorphic rock in the Dabie-Sulu orogenic belt:[Dissertation].University of Science andTechnology of China(in Chinese)

[0017] Technical solution of prior art 2

[0018] This technology introduces an online continuous flow analysis method for high temperature cracking elements and isotopes, which successfully analyzes natural hydrous minerals with extremely low water content and nominally anhydrous minerals. The principle of the method is as follows:

[0019] The TC / EA-MS analysis method is based on the principle of high temperature thermal decomposition and carbon reduction. Under high temperature and He (helium) conditions, a small amount of water vapor released from the water-containing sample enters the reaction furnace with the glassy carbon reducing agent along with the He carrier gas. At 1450°C, the sample water vapor and the glassy carbon reducing agent react as follows: H2O+C→H2+CO

[0020] The reaction products H2 and CO and the mixed gas enter the gas chromatography column with the He carrier gas to achieve separation. The separated H2 enters the isotope gas mass spectrometer with He to obtain the H isotope composition of the sample. The thermal cracking and carbon reduction technology in the TC / EA-MS analysis method is based on the improvement of the continuous flow mass spectrometry analysis method and the trace sample extraction technology. This analysis method can be used to analyze the H content and H isotope composition in inorganic samples with extremely low water content (0.01 ml of water).

[0021] Disadvantages of the second prior art

[0022] This technology has successfully analyzed the content and hydrogen isotope composition of different forms of water in garnets from the Dabie-Sulu orogenic belt, but research on stable hydrogen isotopes in volcanic glass has not been reported. Summary of the invention

[0023] In order to solve the problems existing in the prior art, the present invention provides a testing method for separating volcanic glass and hydrogen isotopes using heavy liquid flotation, which solves the problem of how to separate and extract volcanic glass from volcanic rock samples using heavy liquid flotation, and test the hydrogen isotopes of volcanic glass through TC / EA-MS analysis method, and finally reconstruct the ancient height of ancient mountains with the help of empirical formulas or theoretical models.

[0024] The technical solution of the present invention is as follows:

[0025] A test method for separating volcanic glass and hydrogen isotopes using heavy liquid flotation comprises the following steps:

[0026] Step S1: Identify and authenticate volcanic glass under a microscope;

[0027] Step S2: separating and extracting volcanic glass by heavy liquid flotation;

[0028] Step S3: Testing volcanic glass hydrogen isotopes using TC / EA-MS

[0029] Preferably, step S1 specifically includes:

[0030] The volcanic rock samples are made into rock slices, and the presence of volcanic glass is observed based on its microscopic characteristics, and rock samples containing volcanic glass are selected for further analysis.

[0031] Preferably, step S2 includes the following sub-steps:

[0032] Sub-step S21: crush the samples into 100-60 mesh and put them into beakers respectively;

[0033] Sub-step S22: Add 30% H2O2 solution to each beaker in small amounts and multiple times, and stir thoroughly. Let it stand for 4 hours to allow the reaction to complete and remove organic minerals. After the reaction is complete, use a mesh to filter the upper liquid and put the filtered water into a waste liquid bucket for recycling. Add distilled water or deionized water to repeatedly wash the sample 3-5 times to remove excess H2O2 solution and impurities after the reaction;

[0034] Sub-step S23: Add 10% HCl to the beaker to immerse the sample, stir thoroughly and soak overnight to dissolve all soluble inorganic salts. After the reaction is completed, filter out the supernatant and put the filtered water into a waste liquid bucket for recycling. Wash the sample repeatedly 3-5 times with distilled water or deionized water to remove the remaining HCl solution and impurities;

[0035] Sub-step S24: drying the cleaned sample overnight to remove moisture, and weighing the sample to obtain a weight m1;

[0036] Sub-step S25: Prepare sodium polytungstate solution to make its density reach 2.50 g / cm 3 about;

[0037] Sub-step S26: Transfer the sample after impurities are removed into a 10 ml centrifuge tube and add the prepared heavy liquid, and put the centrifuge tube into a centrifuge at 2500 rpm for 20 minutes;

[0038] Sub-step S27: After centrifugation, take the upper clear liquid to observe whether there is volcanic glass floating. If it does not float, it means that the density of the heavy liquid is too small and needs to be further evaporated. If a large amount of material is observed to float, it means that the density of the heavy liquid is too large and needs to be diluted with water. Due to the different properties of the samples, the density of volcanic glass may vary. After many experiments, it was found that when the density of the heavy liquid is 2.47g / cm 3 It can effectively float out volcanic glass;

[0039] Sub-step S28: Take out the supernatant and pour it into another centrifuge tube. This part will be used to purify volcanic glass. Add 2.47g / cm 3 Place the centrifuge tube in a centrifuge and centrifuge at 2500 rpm for 20 minutes. The volcanic glass will float in the centrifuge tube, while the remaining impurities will sink to the bottom of the tube.

[0040] Sub-step S29: repeating sub-step S28 twice to ensure that the supernatant after centrifugation is substantially volcanic glass;

[0041] Sub-step S210: dilute the supernatant in sub-step S29 with distilled water and put it into a centrifuge. After centrifugation, the volcanic glass sinks to the bottom of the tube, and the upper heavy liquid is poured into a glass bottle for recycling;

[0042] Sub-step S211: The volcanic glass extracted in sub-step S210 is repeatedly washed with distilled water for 3-5 times and then placed in a fume hood for air drying. At this time, we obtain pure volcanic glass, and weigh it as m2. m2 / m1 is the volcanic glass extraction rate;

[0043] Sub-step S212: adding distilled water to the residue and the remaining heavy liquid at the bottom of the centrifuge tube in sub-steps S27, S28, and S29, and centrifuging at a speed of 2500 rpm for 20 minutes, and repeating the operation three times; after the centrifugation, pouring the upper clear liquid into a glass bottle for recycling, the purpose of repeating the operation is to recover all the sodium polytungstate solution as much as possible, and the heavier substances that sink to the bottom of the centrifuge tube are processed or stored according to whether they need to be further analyzed;

[0044] Sub-step S213: continuously evaporating the recovered sodium polytungstate solution at a temperature of 60° C.-100° C. for several hours to increase its density, and storing it in a dust-free environment after cooling for subsequent use;

[0045] Sub-step S214: crush each sample to <120 mesh, 120-100 mesh, and >60 mesh, and repeat the above sub-steps S21 to S213 to compare the volcanic glass extraction rates at different mesh sizes. The comparative experimental results show that the volcanic glass extraction rate is the highest when the sample particle size is 100-60 mesh;

[0046] Preferably, the liquid obtained in sub-step S25 is called heavy liquid, and the preparation of the heavy liquid includes the following sub-steps:

[0047] Sub-step S251: put sodium polytungstate with purity>99% into a glass cup and add deionized water to dissolve it, use a heating plate to heat it to a transparent state, and use a glass rod to stir continuously to completely dissolve the sodium polytungstate molecules in the deionized water;

[0048] Sub-step S252: adding a certain amount of deionized water according to the configuration ratio of sodium polytungstate;

[0049] Sub-step S253: After cooling, measure the density of the solution with a hydrometer, and add deionized water or sodium polytungstate according to the result until the density of the heavy liquid reaches 2.50 g / cm 3 ;

[0050] Sub-step S254: store the prepared heavy liquid in a dust-free closed environment.

[0051] Preferably, step S3 includes the following sub-steps:

[0052] Sub-step S31: pre-heating the volcanic glass sample at 90° C. for 12 hours to remove water adsorbed on the surface of mineral particles;

[0053] Sub-step S32: Under high temperature conditions, a small amount of water vapor is released from the volcanic glass and enters the high-temperature carbon reaction furnace of the glassy carbon reducing agent along with the He carrier gas. At 1450° C., the water vapor reacts with the glassy carbon reducing agent;

[0054] Sub-step S33: the reaction products H2 and CO and the mixed gas enter the gas chromatography column with the He carrier gas for separation;

[0055] Sub-step S34: the separated H2 and He enter into an isotope gas mass spectrometer to obtain the H isotope composition of the volcanic glass;

[0056] Sub-step S35: Obtain the water content of volcanic glass by integrating the area and time of the sample signal peak. To calculate the water content of minerals, use a reference material with known water content and calculate using the following equation:

[0057] k-factor: k=(w ref ×m ref ) / A ref ,

[0058] Wherein, w, m and A represent the weight percentage of hydrogen isotope in the sample, the weight of the sample and the integrated area of ​​the signal peak respectively; the subscript ref represents the reference material.

[0059] Using reference materials, the k-factor was obtained by mass spectrometry and the total water content of the volcanic glass was calculated according to the equation:

[0060] w sam =(k×A sam ) / m sam ,

[0061] The subscript sam represents the volcanic glass sample; A sam Represents the integrated area of ​​each sample signal peak, m sam Indicates the sample weight,

[0062] Sub-step S36: Establish a volcanic glass hydrogen isotope paleoaltimeter using empirical formulas and theoretical models.

[0063] The technical effects of the test method for separating volcanic glass and hydrogen isotopes by heavy liquid flotation are as follows:

[0064] 1. The present invention establishes a complete process for separating and extracting volcanic glass from volcanic tuff samples in the Qinghai-Tibet Plateau for the first time, expanding the scope of application of the method; based on the density difference between volcanic glass and other minerals, the present invention selects sodium polytungstate solution as a density flotation meter, which can better separate volcanic glass from other minerals under a high-speed centrifugal environment, and obtains the optimal heavy liquid density and sample particle size for extracting volcanic glass through comparative experiments, and the extraction rate can reach up to 14.5%.

[0065] 2. This invention applies TC / EA-MS technology to hydrogen isotope testing of volcanic glass on the Qinghai-Tibet Plateau for the first time. This method successfully tests the stable hydrogen isotopes and water content of volcanic glass and reconstructs the ancient altitude history of the Qinghai-Tibet Plateau, filling the gap in domestic research on volcanic glass hydrogen isotope paleoaltimeters.

[0066] 3. With the help of volcanic glass hydrogen isotope paleoaltimeters, we have shifted from qualitatively describing the uplift process of plateaus to quantitatively constraining the ancient heights of plateaus, which has greatly promoted the understanding of the uplift history of major orogenic belts and plateaus around the world. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a microscopic characteristic image of volcanic glass in the rock slice of the present invention.

[0068] Figure 2 The present invention is a flow chart of purifying volcanic glass in volcanic rock by heavy liquid flotation method.

[0069] Figure 3 It is a diagram of the TC / EA-MS analysis system of the present invention.

[0070] Figure 4 The figure is the principle and flow chart of the TC / EA-MS analysis method of the present invention. DETAILED DESCRIPTION

[0071] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0072] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0073] A test method for separating volcanic glass and hydrogen isotopes using heavy liquid flotation comprises the following steps:

[0074] Step S1: Identify and authenticate volcanic glass under a microscope;

[0075] Step S2: separating and extracting volcanic glass by heavy liquid flotation;

[0076] Step S3: Testing volcanic glass hydrogen isotopes using TC / EA-MS

[0077] Step S1 of this embodiment is specifically as follows:

[0078] The volcanic rock samples are made into rock slices, and the presence of volcanic glass is observed based on its microscopic characteristics, and rock samples containing volcanic glass are selected for further analysis.

[0079] Step S2 of this embodiment includes the following sub-steps:

[0080] Sub-step S21: crush the samples into 100-60 mesh and put them into beakers respectively;

[0081] Sub-step S22: Add 30% H2O2 solution to each beaker in small amounts and multiple times, and stir thoroughly. Let it stand for 4 hours to allow the reaction to complete and remove organic minerals. After the reaction is complete, use a mesh to filter the upper liquid and put the filtered water into a waste liquid bucket for recycling. Add distilled water or deionized water to repeatedly wash the sample 3-5 times to remove excess H2O2 solution and impurities after the reaction;

[0082] Sub-step S23: Add 10% HCl to the beaker to immerse the sample, stir thoroughly and soak overnight to dissolve all soluble inorganic salts. After the reaction is completed, filter out the supernatant and put the filtered water into a waste liquid bucket for recycling. Wash the sample repeatedly 3-5 times with distilled water or deionized water to remove the remaining HCl solution and impurities;

[0083] Sub-step S24: drying the cleaned sample overnight to remove moisture, and weighing the sample to obtain a weight m1;

[0084] Sub-step S25: Prepare sodium polytungstate solution to make its density reach 2.50 g / cm 3 about;

[0085] Sub-step S26: Transfer the sample after impurities are removed into a 10 ml centrifuge tube and add the prepared heavy liquid, and put the centrifuge tube into a centrifuge at 2500 rpm for 20 minutes;

[0086] Sub-step S27: Take out the upper clear liquid and observe whether there is volcanic glass floating. If not, it means that the density of the heavy liquid is too small and needs to be further evaporated. If a large amount of material is observed to float, it means that the density of the heavy liquid is too large and needs to be diluted with water. Due to the different properties of the samples, the density of volcanic glass may vary. After many experiments, it was found that when the density of the heavy liquid is 2.47g / cm 3 It can effectively float out volcanic glass;

[0087] Sub-step S28: After centrifugation, take the supernatant and pour it into another centrifuge tube. This part will be used to purify volcanic glass. Add 2.47g / cm 3 Place the centrifuge tube in a centrifuge and centrifuge at 2500 rpm for 20 minutes. The volcanic glass will float in the centrifuge tube, while the remaining impurities will sink to the bottom of the tube.

[0088] Sub-step S29: repeating sub-step S28 twice to ensure that the supernatant after centrifugation is substantially volcanic glass;

[0089] Sub-step S210: dilute the supernatant in sub-step S29 with distilled water and put it into a centrifuge. After centrifugation, the volcanic glass sinks to the bottom of the tube, and the upper heavy liquid is poured into a glass bottle for recycling;

[0090] Sub-step S211: The volcanic glass extracted in sub-step S210 is repeatedly washed with distilled water for 3-5 times and then placed in a fume hood for air drying. At this time, we obtain pure volcanic glass, and weigh it as m2. m2 / m1 is the volcanic glass extraction rate;

[0091] Sub-step S212: adding distilled water to the residue and the remaining heavy liquid at the bottom of the centrifuge tube in sub-steps S27, S28, and S29, and centrifuging at a speed of 2500 rpm for 20 minutes, and repeating the operation three times; after the centrifugation, pouring the upper clear liquid into a glass bottle for recycling, the purpose of repeating the operation is to recover all the sodium polytungstate solution as much as possible, and the heavier substances that sink to the bottom of the centrifuge tube are processed or stored according to whether they need to be further analyzed;

[0092] Sub-step S213: continuously evaporating the recovered sodium polytungstate solution at a temperature of 60° C.-100° C. for several hours to increase its density, and storing it in a dust-free environment after cooling for subsequent use;

[0093] Sub-step S214: crush each sample to <120 mesh, 120-100 mesh, and >60 mesh, and repeat the above sub-steps S21 to S213 to compare the volcanic glass extraction rates at different mesh sizes. The comparative experimental results show that the volcanic glass extraction rate is the highest when the sample particle size is 100-60 mesh;

[0094] The liquid obtained in sub-step S25 of this embodiment is called heavy liquid, and the preparation of the heavy liquid includes the following sub-steps:

[0095] Sub-step S251: put sodium polytungstate with purity>99% into a glass cup and add deionized water to dissolve it, use a heating plate to heat it to a transparent state, and use a glass rod to stir continuously to completely dissolve the sodium polytungstate molecules in the deionized water;

[0096] Sub-step S252: adding a certain amount of deionized water according to the configuration ratio of sodium polytungstate;

[0097] Sub-step S253: After cooling, measure the density of the solution with a hydrometer, and add deionized water or sodium polytungstate according to the result until the density of the heavy liquid reaches 2.50 g / cm 3 ;

[0098] Sub-step S254: store the prepared heavy liquid in a dust-free closed environment.

[0099] Step S3 of this embodiment includes the following sub-steps:

[0100] Sub-step S31: pre-heating the volcanic glass sample at 90° C. for 12 hours to remove water adsorbed on the surface of mineral particles;

[0101] Sub-step S32: Under high temperature conditions, a small amount of water vapor is released from the volcanic glass and enters the high-temperature carbon reaction furnace of the glassy carbon reducing agent along with the He carrier gas. At 1450° C., the water vapor reacts with the glassy carbon reducing agent;

[0102] Sub-step S33: the reaction products H2 and CO and the mixed gas enter the gas chromatography column with the He carrier gas for separation;

[0103] Sub-step S34: the separated H2 and He enter into an isotope gas mass spectrometer to obtain the H isotope composition of the volcanic glass;

[0104] Sub-step S35: Obtain the water content of volcanic glass by integrating the area and time of the sample signal peak. To calculate the water content of minerals, use a reference material with known water content and calculate using the following equation:

[0105] k-factor: k=(w ref ×m ref ) / A ref ,

[0106] Wherein, w, m and A represent the weight percentage of hydrogen isotope in the sample, the weight of the sample and the integrated area of ​​the signal peak respectively; the subscript ref represents the reference material.

[0107] Using reference materials, the k-factor was obtained by mass spectrometry and the total water content of the volcanic glass was calculated according to the equation:

[0108] w sam =(k×A sam ) / m sam ,

[0109] The subscript sam represents the volcanic glass sample; A sam Represents the integrated area of ​​each sample signal peak; m sam Indicates the sample weight.

[0110] Sub-step S36: Establish a volcanic glass hydrogen isotope paleoaltimeter using empirical formulas and theoretical models.

[0111] When this implementation plan is implemented,

[0112] Identifying and Identifying Volcanic Glass Under the Microscope

[0113] (1) The volcanic rock samples are made into rock slices, and the presence of volcanic glass is observed based on its microscopic characteristics. Rock samples containing volcanic glass are selected for further analysis.

[0114] 2. Separation and extraction of volcanic glass by heavy liquid flotation

[0115] This method uses the density difference between volcanic glass and other minerals (quartz, feldspar, heavy minerals, etc.) to obtain sodium polytungstate solution Na6 (H2W 12 O 40)·H2O is used as density flotation medium (hydrometer) to separate and purify volcanic glass from volcanic rocks. Sodium polytungstate is a new type of inorganic heavy liquid that is non-toxic, odorless, easy to dissolve, easy to configure, and has a high recovery rate. Its density range is 1.0g / cm 3 -3.1g / cm 3 The specific operation process is as follows:

[0116] (1) Crush the samples to 100-60 mesh (250 μm-150 μm) and place them in beakers respectively;

[0117] (2) Add 30% H2O2 solution to each beaker in small amounts and stir thoroughly. Allow to stand for 4 hours to allow the reaction to complete (if the reaction is violent, the reaction time can be appropriately extended) to remove organic minerals. After the reaction is complete, use a mesh to filter the upper liquid and recycle the filtered water into a waste liquid bucket. Add distilled water or deionized water to wash the sample repeatedly 3-5 times to remove excess H2O2 solution and impurities after the reaction.

[0118] (3) Add 10% HCl to the beaker to immerse the sample, stir thoroughly and soak overnight to dissolve all soluble inorganic salts. After the reaction is completed, filter out the supernatant and put the filtered water into a waste liquid bucket for recycling. Wash the sample repeatedly with distilled water or deionized water for 3-5 times to remove the remaining HCl solution and impurities.

[0119] (4) Dry the cleaned sample overnight to remove moisture, and weigh it to obtain the weight m1.

[0120] (5) Prepare sodium polytungstate solution to make its density reach 2.50g / cm 3 About (hereinafter referred to as heavy liquid). The specific method is: put sodium polytungstate with purity>99% into a glass cup and add deionized water to dissolve it, use a heating plate to heat it to a transparent state, and use a glass rod to stir continuously to make the sodium polytungstate molecules completely dissolved in the deionized water. Add a certain amount of deionized water according to the configuration ratio of sodium polytungstate. After cooling, use a hydrometer to measure the density of the solution, and add deionized water or sodium polytungstate appropriately according to the result until the density of the heavy liquid reaches 2.50g / cm 3 . Store the prepared heavy liquid in a dust-free closed environment (Note: It is best to measure the density of the solution before use and adjust the density as required).

[0121] (6) After the impurities are removed, the sample is transferred to a 10 ml centrifuge tube and the prepared heavy liquid is added. The centrifuge tube is placed in a centrifuge and centrifuged at 2500 rpm for 20 minutes.

[0122] (7) After centrifugation, take the supernatant and observe whether there is volcanic glass floating. If it does not float, it means that the density of the heavy liquid is too low and needs to be further evaporated. If a large amount of material is observed to float (in addition to volcanic glass, there are also a large number of feldspar, quartz and other particles), it means that the density of the heavy liquid is too high and needs to be diluted with water. Due to the different properties of the samples, the density of volcanic glass may vary. After many experiments, it was found that when the density of the heavy liquid is 2.47g / cm 3 It can effectively float out volcanic glass.

[0123] (8) Take out the supernatant (rich in volcanic glass and containing a small amount of other minerals) and pour it into another centrifuge tube. This part will be used to purify the volcanic glass. Add 2.47 g / cm 3 Place the centrifuge tube in a centrifuge and centrifuge at 2500 rpm for 20 minutes. The volcanic glass will float in the centrifuge tube, while the remaining impurities will sink to the bottom of the tube.

[0124] (9) Repeat the previous step twice to ensure that the supernatant after centrifugation is basically volcanic glass.

[0125] (10) Dilute the supernatant (volcanic glass and diluted sodium polytungstate) in operation 9 with distilled water and place in a centrifuge (speed 2500 rpm, centrifugation for 10 minutes). After the centrifugation, the volcanic glass sinks to the bottom of the tube. Pour the upper heavy liquid into a glass bottle for recycling.

[0126] (11) The volcanic glass extracted in the previous step is repeatedly washed with distilled water for 3-5 times and then placed in a fume hood to air dry. At this time, we obtain pure volcanic glass and weigh it as m2. m2 / m1 is the volcanic glass extraction rate.

[0127] (12) Add distilled water to the residue (density>2.47g / cm3) and the remaining heavy liquid at the bottom of the centrifuge tube in steps 7, 8, and 9, and centrifuge at 2500rpm for 20 minutes, and repeat the operation three times. After the centrifugation, pour the supernatant (heavy liquid) into a glass bottle for recycling. The purpose of the repeated operation is to recover as much sodium polytungstate solution as possible. The heavier material that sinks to the bottom of the centrifuge tube is processed or stored according to whether it needs to be further analyzed.

[0128] (13) The recovered sodium polytungstate solution is continuously evaporated at a temperature of 60°C-100°C for several hours to increase its density, and after cooling, it is stored in a dust-free environment for subsequent use.

[0129] (14) Each sample was crushed to <120 mesh, 120-100 mesh, and >60 mesh, and all the above steps were repeated to compare the volcanic glass extraction rates at different mesh sizes. The comparative experimental results showed that the volcanic glass extraction rate was the highest when the sample particle size was 100-60 mesh.

[0130] Table 1 Results of extraction of volcanic glass from volcanic tuff in the Qinghai-Tibet Plateau by heavy liquid flotation

[0131]

[0132]

[0133] 3. Using TC / EA-MS to test hydrogen isotopes in volcanic glass

[0134] (1) Principle of the method: high temperature thermal decomposition and carbon reduction principle, H2O+C→H2+CO (same as prior art 2).

[0135] (2) Analysis system: Thermal decomposition conversion element analyzer (TC / EA), isotope gas mass spectrometer (MS), open interface. TC / EA includes: injection system, vertical tubular high temperature furnace, gas chromatography column (GC)

[0136] (3) Experimental steps:

[0137] ①Pre-heat the volcanic glass samples at 90°C for 12 hours to remove water adsorbed on the surface of mineral particles;

[0138] ② Under high temperature conditions, a small amount of water vapor is released from the volcanic glass and enters the high-temperature carbon reactor of the glassy carbon reducing agent along with the He carrier gas. At 1450℃, the water vapor reacts with the glassy carbon reducing agent;

[0139] ③ The reaction products H2 and CO and the mixed gas enter the gas chromatography column (GC) for separation along with the He carrier gas;

[0140] ④ The separated H2 and He enter the isotope gas mass spectrometer (MS) to obtain the H isotope composition of the volcanic glass;

[0141] ⑤ The water content of volcanic glass is obtained by integrating the area and time of the sample signal peak. To calculate the water content of a mineral, first use a reference material with a known water content to calculate the k-factor using the following equation: k = (w ref ×m ref ) / A ref , where w, m and A represent the weight percentage of hydrogen isotopes in the sample, the weight of the sample and the integrated area of ​​the signal peak respectively; the subscript ref represents the reference material. Using the reference material, the k-factor was obtained by mass spectrometry analysis, and the total water content of the volcanic glass was calculated according to the equation: w sam =(k×A sam ) / m sam The subscript sam represents the volcanic glass sample.

[0142] ⑥ Use empirical formulas and theoretical models to establish a volcanic glass hydrogen isotope paleoaltimeter.

Claims

1. A test method for separating volcanic glass and hydrogen isotopes using heavy liquid flotation, characterized in that: The following steps are involved: Step S1: Identify and authenticate volcanic glass under a microscope; Step S2: separating and extracting volcanic glass by heavy liquid flotation; Step S3: Use TC / EA-MS to test the hydrogen isotope of volcanic glass.

2. The testing method for separating volcanic glass and hydrogen isotopes by heavy liquid flotation according to claim 1, characterized in that: The step S1 is specifically as follows: The volcanic rock samples are made into rock slices, and the presence of volcanic glass is observed based on its microscopic characteristics, and rock samples containing volcanic glass are selected for further analysis.

3. The testing method for separating volcanic glass and hydrogen isotopes by heavy liquid flotation according to claim 1, characterized in that: The step S2 comprises the following sub-steps: Sub-step S21: crush the samples into 100-60 mesh and put them into beakers respectively; Sub-step S22: Add 30% H2O2 solution to each beaker in small amounts and multiple times, and stir thoroughly. Let it stand for 4 hours to allow the reaction to complete and remove organic minerals. After the reaction is complete, use a mesh to filter the upper liquid and put the filtered water into a waste liquid bucket for recycling. Add distilled water or deionized water to repeatedly wash the sample 3-5 times to remove excess H2O2 solution and impurities after the reaction; Sub-step S23: Add 10% HCl to the beaker to immerse the sample, stir thoroughly and soak overnight to dissolve all soluble inorganic salts. After the reaction is completed, filter out the supernatant and put the filtered water into a waste liquid bucket for recycling. Wash the sample repeatedly 3-5 times with distilled water or deionized water to remove the remaining HCl solution and impurities; Sub-step S24: drying the cleaned sample overnight to remove moisture, and weighing the sample to obtain a weight m1; Sub-step S25: Prepare sodium polytungstate solution to make its density reach 2.50 g / cm 3 about; Sub-step S26: Transfer the sample after impurities are removed into a 10 ml centrifuge tube and add the prepared heavy liquid, and put the centrifuge tube into a centrifuge at 2500 rpm for 20 minutes; Sub-step S27: After centrifugation, take the upper clear liquid to observe whether there is volcanic glass floating. If it does not float, it means that the density of the heavy liquid is too small and needs to be further evaporated. If a large amount of material is observed to float, it means that the density of the heavy liquid is too large and needs to be diluted with water. Due to the different properties of the samples, the density of volcanic glass may vary. After many experiments, it was found that when the density of the heavy liquid is 2.47g / cm 3 It can effectively float out volcanic glass; Sub-step S28: Take out the supernatant and pour it into another centrifuge tube. This part will be used to purify volcanic glass. Add 2.47g / cm 3 Place the centrifuge tube in a centrifuge and centrifuge at 2500 rpm for 20 minutes. The volcanic glass will float in the centrifuge tube, while the remaining impurities will sink to the bottom of the tube. Sub-step S29: repeating sub-step S28 twice to ensure that the supernatant after centrifugation is substantially volcanic glass; Sub-step S210: dilute the supernatant in sub-step S29 with distilled water and put it into a centrifuge. After centrifugation, the volcanic glass sinks to the bottom of the tube, and the upper heavy liquid is poured into a glass bottle for recycling; Sub-step S211: The volcanic glass extracted in sub-step S210 is repeatedly washed with distilled water for 3-5 times and then placed in a fume hood for air drying. At this time, we obtain pure volcanic glass, and weigh it as m2. m2 / m1 is the volcanic glass extraction rate; Sub-step S212: adding distilled water to the residue and the remaining heavy liquid at the bottom of the centrifuge tube in sub-steps S27, S28, and S29, and centrifuging at a speed of 2500 rpm for 20 minutes, and repeating the operation three times; after the centrifugation, pouring the upper clear liquid into a glass bottle for recycling, the purpose of repeating the operation is to recover all the sodium polytungstate solution as much as possible, and the heavier substances that sink to the bottom of the centrifuge tube are processed or stored according to whether they need to be further analyzed; Sub-step S213: continuously evaporating the recovered sodium polytungstate solution at a temperature of 60° C.-100° C. for several hours to increase its density, and storing it in a dust-free environment after cooling for subsequent use; Sub-step S214: Crush each sample to <120 mesh, 120-100 mesh, and >60 mesh, respectively, and repeat the above sub-steps S21 to S213 to compare the volcanic glass extraction rates at different mesh sizes. The comparative experimental results show that the volcanic glass extraction rate is the highest when the sample particle size is 100-60 mesh.

4. The testing method for separating volcanic glass and hydrogen isotopes by heavy liquid flotation according to claim 1, characterized in that: The liquid obtained in the sub-step S25 is called heavy liquid, and the preparation of the heavy liquid includes the following sub-steps: Sub-step S251: put sodium polytungstate with purity>99% into a glass cup and add deionized water to dissolve it, use a heating plate to heat it to a transparent state, and use a glass rod to stir continuously to completely dissolve the sodium polytungstate molecules in the deionized water; Sub-step S252: adding a certain amount of deionized water according to the configuration ratio of sodium polytungstate; Sub-step S253: After cooling, measure the density of the solution with a hydrometer, and add deionized water or sodium polytungstate according to the result until the density of the heavy liquid reaches 2.50 g / cm 3 ; Sub-step S254: store the prepared heavy liquid in a dust-free closed environment.

5. The testing method for separating volcanic glass and hydrogen isotopes by heavy liquid flotation according to claim 1, characterized in that: The step S3 comprises the following sub-steps: Sub-step S31: pre-heating the volcanic glass sample at 90° C. for 12 hours to remove water adsorbed on the surface of mineral particles; Sub-step S32: Under high temperature conditions, a small amount of water vapor is released from the volcanic glass and enters the high-temperature carbon reaction furnace of the glassy carbon reducing agent along with the He carrier gas. At 1450° C., the water vapor reacts with the glassy carbon reducing agent; Sub-step S33: the reaction products H2 and CO and the mixed gas enter the gas chromatography column with the He carrier gas for separation; Sub-step S34: the separated H2 and He enter into an isotope gas mass spectrometer to obtain the H isotope composition of the volcanic glass; Sub-step S35: Obtain the water content of volcanic glass by integrating the area and time of the sample signal peak. To calculate the water content of minerals, use a reference material with known water content and calculate using the following equation: k-factor: k=(w ref ×m ref ) / A ref , Wherein, w, m and A represent the weight percentage of hydrogen isotope in the sample, the weight of the sample and the integrated area of ​​the signal peak respectively; the subscript ref represents the reference material. Using reference materials, the k-factor was obtained by mass spectrometry and the total water content of the volcanic glass was calculated according to the equation: w sam =(k×A sam ) / m sam , The subscript sam represents the volcanic glass sample; A sam Represents the integrated area of ​​each sample signal peak; m sam Indicates the sample weight, Sub-step S36: Use empirical formulas and theoretical models to establish a volcanic glass hydrogen isotope paleoaltimeter to reconstruct the uplift history of ancient mountains.

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