A method of tracing hydrothermal activity in a sedimentary basin

Abstract

The application discloses a kind of sedimentary basin hydrothermal activity tracer method, belong to geochemistry and isotopic tracer field.The tracer method includes the pretreatment of mixed mineral sample, lithium element separation and purification and δ 7 Li carb Value determination;The correlation analysis of δ 7 Li carb Value and the main trace element characteristics of sample;The measurement δ 7 Li carb Value of mixed mineral sample is corrected: the correlation analysis of corrected data of mixed mineral sample and hydrothermal activity index and anti weathering index;Determine the δ 7 Li 校正后 Background value in study sequence, judge hydrothermal activity enhancement period, hydrothermal activity weakening period or non-hydrothermal dominant period by comparing lithium isotopic ratio of continuous section and background interval value difference.The method has the advantages of continuous high resolution, wide temperature range sensitive response, mechanism is clear, strong anti-interference ability and strong universality.

Description

Technical Field

[0001] This invention belongs to the field of geochemistry and isotope tracing technology, and particularly relates to a method for tracing hydrothermal activity in sedimentary basins. Background Technology

[0002] Hydrothermal activity in sedimentary basins has a crucial impact on hydrocarbon generation, mineral enrichment, and paleoenvironmental evolution. Accurately assessing the intensity of hydrothermal activity is of great significance for hydrocarbon exploration, shale gas reservoir prediction, and ore deposit genetic studies.

[0003] Currently, the tracer technologies commonly relied upon in the industry mainly cover three categories: specific minerals (such as zeolites and sodalite), elemental ratios (such as Fe / Ti), rare earth element anomalies (such as positive Eu anomalies, usually with Eu / Eu*>1.05 as the criterion), and radioactive isotopes (such as...). 87 Sr / 86 Sr), etc. However, these methods have significant drawbacks: firstly, the specificity of the indicators is generally weak. Many widely used indicators, such as the Fe / Ti ratio and 87 Sr / 86 Sr values, essentially a "hybrid indicator" of volcanic-hydrothermal activity, cannot effectively distinguish the specific properties of deep-seated material sources (such as Fe / Ti). Secondly, the sensitivity and spatiotemporal continuity of these indicators are severely lacking. For example, the formation of positive Eu anomalies typically requires high hydrothermal temperatures (>200°C), therefore it is sluggish or even unresponsive to low- and medium-temperature hydrothermal activity. More importantly, the vast majority of existing indicators (such as the first occurrence of a specific mineral or the anomalous enrichment of certain metallic elements) are recorded event-based or intermittently. They can mark the "presence" or "peak" of hydrothermal activity, but they cannot faithfully and with high resolution record the dynamic fluctuations and long-term evolution trends of the relative intensity of hydrothermal activity, like continuous curves.

[0004] In summary, there has long been a lack of a novel tracing technology in this field capable of continuously, sensitively, specifically, and with strong anti-interference capabilities for hydrothermal activity in sedimentary basins, particularly its intensity variations. This technological bottleneck limits the detailed characterization of the spatiotemporal evolution of hydrothermal activity and also hinders a deeper understanding of its role in resource enrichment and environmental evolution. Summary of the Invention

[0005] In view of the shortcomings of existing technologies, the technical problem to be solved by the present invention is that existing hydrothermal activity tracing technologies are insufficient in terms of continuity, sensitivity and specificity. The present invention proposes a tracing method for hydrothermal activity in sedimentary basins with continuous high resolution, wide temperature range sensitive response, clear mechanism, strong anti-interference ability and wide applicability.

[0006] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for tracing hydrothermal activity in a sedimentary basin, comprising the following steps:

[0008] S1. Pretreatment of mixed mineral samples, lithium separation and purification, and δ 7 Li carb Value determination;

[0009] S2, for δ 7 Li carb Correlation analysis was performed between the δ value and the major and trace element characteristics of the sample. 7 Li carb If there is no significant correlation with the major and trace element characteristics of the sample, proceed to step S3 to determine the hydrothermal intensity.

[0010] S3. The measurement δ of the mixed mineral sample is corrected using the following formula. 7 Li carb Values ​​are corrected:

[0011] δ 7 Li 校正后 =δ 7 Li carb -k×[f 碱 / (1+f 碱 )];

[0012] Among them, f 碱 The ratio of alkali minerals to calcium and magnesium carbonates;

[0013] k represents the inherent difference in fractionation values ​​between the two types of minerals, k=Δ 7 Li 碱 -Δ 7 Li 钙镁 ;

[0014] S4, δ of the mixed mineral sample 7 Li 校正后 Correlation analysis was performed on the δ values ​​with hydrothermal activity indicators and deweathering indicators to verify whether there was a synergistic relationship among the three, thereby confirming the δ 7 Li 校正后 The reliability and mechanism consistency of the response to hydrothermal activity;

[0015] S5. Determine δ in the research sequence 7 Li 校正后 The background value is used to identify the period of enhanced hydrothermal activity, the period of weakened hydrothermal activity, or the period of non-hydrothermal activity by comparing the difference between the lithium isotope ratio value of continuous segments and the background interval value.

[0016] Preferably, in step S1, the mixed mineral sample is an unweathered rock core collected from a sedimentary basin.

[0017] As a preferred option, unweathered rock cores from sedimentary basins include mudstone, shale, marl, dolomite, and evaporites containing alkali minerals.

[0018] Preferably, the specific pretreatment operation for the mixed mineral sample in step S1 is as follows:

[0019] After cleaning, drying, and crushing, the mixed mineral samples were rinsed with 0.5-1M ammonium acetate solution by shaking.

[0020] The remaining sample was then reacted with 0.5-1M acetic acid solution at room temperature with shaking for 2-6 hours. The acetic acid filtrate was collected, evaporated to dryness, and converted into a nitric acid system.

[0021] Preferably, the specific operation for lithium element separation and purification in step S1 is as follows:

[0022] A purified lithium solution was obtained using an AG50W-X12 cation exchange resin column and 0.15-0.3M hydrochloric acid as the eluent.

[0023] Preferably, the specific operation for determining the lithium isotope ratio in step S1 is as follows:

[0024] The purified lithium solution was analyzed by MC-ICP-MS using a standard-sample cross-reference method. Instrument mass fractionation calibration was performed using the international standard reference material USGS LSVEC. The results are expressed as δ 7 Li carb Value (‰) represents;

[0025] The calculation formula is: δ 7 Li carb = [( 7 Li / 6 Li) 样品 / ( 7 Li / 6 Li) LSVEC -1]×1000.

[0026] Preferably, in step S2, when the mixed mineral sample is collected from a sedimentary basin, it is necessary to confirm δ. 7 Li carb There was no significant correlation with Al / Ca, Rb / Ca, Mn / Ca, or Mg / (Ca+Mg).

[0027] Preferably, in step S3, the value of k is 0.1‰-1.0‰.

[0028] Preferably, in step S4, the hydrothermal activity indicators include:

[0029] Europium positive anomaly: Eu / Eu*=2Eu N / (SmN + Gd N );

[0030] Among them, Eu N 、Sm N and Gd N The contents of Eu, Sm, and Gd after PAAS standardization;

[0031] Alkali mineral content: refers to the total content of alkali minerals; abnormal enrichment of alkali minerals often indicates the input of deep hydrothermal substances.

[0032] Anti-weathering indicators include:

[0033] Self-generated silicon content: Si auto =Si 样品 -Al 样品 ×3.11;

[0034] 3.11 represents the background Si / Al ratio in the upper crust, with positive values ​​indicating non-clastic authigenic silica, directly reflecting the concentration of soluble silica in water.

[0035] The Li / Al and K / Al ratios are significantly higher than the UCC background values, providing direct geochemical evidence for the formation of lithium- and potassium-rich authigenic clay minerals through reverse weathering.

[0036] Preferably, in step S4, δ is analyzed through system analysis. 7 Li 校正后 By establishing a chain of evidence for the synergistic changes of multiple indicators, based on the correlation between hydrothermal activity indicators and deweathering indicators:

[0037] If δ 7 Li 校正后 A significant positive correlation between δ and hydrothermal activity indicators and anti-weathering indicators indicates that δ 7 Li 校正后 It can effectively respond to the anti-weathering effect driven by hydrothermal activity, and its reliability as a tracer of hydrothermal activity has been verified. It can proceed to step S5 for hydrothermal intensity identification.

[0038] Preferably, in step S5, the background value is δ of the segment without obvious hydrothermal index. 7 Li carb The average value indicates that the stratigraphic zone without obvious hydrothermal indicators is one that simultaneously meets the following criteria: Eu / Eu* < 1.05, alkali mineral content < 5%, and anti-weathering index: Si auto Layers with K / Al in the range of 3±3%, Li / Al in the range of 0.3±0.3%, and Li / Al in the range of 3±3 ppm / %;

[0039] When the δ of the continuous segment 7 Li carbWhen the average value is greater than the sum of the background value and twice the standard deviation, it is identified as a period of enhanced hydrothermal activity.

[0040] When the δ of the continuous segment 7 Li carb When the mean value equals the sum of the background value and twice the standard deviation, it is identified as a non-hydrothermal dominant period;

[0041] When the δ of the continuous segment 7 Li carb When the average value is lower than the sum of the background value and twice the standard deviation, it is identified as a period of weakened hydrothermal activity.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention provides a method for tracing hydrothermal activity in sedimentary basins, applicable to various marine and terrestrial environments with hydrothermal silica input and carbonate deposition. This method represents a breakthrough from event labeling to process characterization, and is a significant technological innovation for refined and quantitative tracing of hydrothermal activity in sedimentary basins, offering the following significant advantages:

[0044] Continuity and high resolution: It enables continuous and high-resolution tracing of hydrothermal activity in stratigraphic profiles, overcoming the limitations of event-based indicators;

[0045] Hydrothermal indicators are highly specific: δ 7 Li carb It is highly positively correlated with hydrothermal-specific indicators such as Eu / Eu*, which can effectively distinguish it from other deep processes such as volcanic activity;

[0046] The mechanism is clear and has good universality: based on "hydrothermal-soluble silica-reverse weathering-δ 7 Li carb The universal geochemical mechanism of "increase" makes the method applicable to marine and terrestrial sedimentary environments with hydrothermal silica input and carbonate deposition, such as rift basin alkaline lakes, back-arc basins, and passive continental margins. Through the correlation verification in step S4, it can be further confirmed whether the specific study area meets the prerequisites for the application of the method, ensuring the reliability of the identification results.

[0047] Strong anti-interference ability: Through multiple quality controls such as sequential leaching, mineral correction and diagenetic assessment, it can effectively extract the original sedimentary signals. Attached Figure Description

[0048] Figure 1 The δ provided in the embodiments of the present invention 7 Li carb A schematic diagram illustrating the correlation analysis between the values ​​and the major and trace element characteristics of the sample; where... Figure 1 A is the sample δ 7 Li carb Scatter plot of correlation with Al / Ca; Figure 1 B is δ 7 Li carb Scatter plot of correlation with Rb / Ca; Figure 1 C is δ 7 Li carb Scatter plot of correlation with Mn / Ca; Figure 1 D is the sample δ 7 Li carb Scatter plot of correlation with Mg / (Ca+Mg);

[0049] Figure 2 The sample δ provided in the embodiment of the present invention 7 Li carb With δ 7 Li 校正后 Correlation scatter plot;

[0050] Figure 3 The sample δ provided in the embodiment of the present invention 7 Li carb A scatter plot showing the correlation between classic hydrothermal vents and anti-weathering indices, where... Figure 3 A is the sample δ 7 Li carb Scatter plot of correlation with Eu / Eu*; Figure 3 B is δ 7 Li carb Scatter plot showing the correlation between the total content of alkali minerals closely related to hydrothermal activity; Figure 3 C represents the sample δ 7 Li carb With Si auto Correlation scatter plot; Figure 3 D is Si auto Scatter plot of correlation with Eu / Eu*; Figure 3 E is δ 7 Li carb Scatter plot of correlation with K / Al; Figure 3 F is the sample δ 7 Li carb Scatter plot of correlation with Li / Al;

[0051] Figure 4 The δ provided in the embodiments of the present invention 7 Li carb Si auto Plot showing the variation of K / Al, Li / Al, Eu / Eu*, alkali mineral content, and the ratio of alkali minerals to calcium and magnesium carbonates with depth. Detailed Implementation

[0052] The technical solutions in specific embodiments of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are merely some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0053] This invention provides a method for tracing hydrothermal activity in sedimentary basins, comprising the following steps:

[0054] S1. Pretreatment of mixed mineral samples, lithium separation and purification, and δ 7 Li carb Value determination;

[0055] S2, for δ 7 Li carb Correlation analysis was performed between the δ value and the major and trace element characteristics of the sample. 7 Li carb If there is no significant correlation with the major and trace element characteristics of the sample, proceed to step S3 to determine the hydrothermal intensity.

[0056] S3. The measurement δ of the mixed mineral sample is corrected using the following formula. 7 Li carb Values ​​are corrected:

[0057] δ 7 Li 校正后 =δ 7 Li carb -k×[f 碱 / (1+f 碱 )];

[0058] Among them, f 碱 The ratio of alkali minerals to calcium and magnesium carbonates;

[0059] k represents the inherent difference in fractionation values ​​between the two types of minerals, k=Δ 7 Li 碱 -Δ 7 Li 钙镁 ;

[0060] S4, δ of the mixed mineral sample 7 Li 校正后 Correlation analysis was performed on the δ values ​​with hydrothermal activity indicators and deweathering indicators to verify whether there was a synergistic relationship among the three, thereby confirming the δ 7 Li 校正后 The reliability and mechanism consistency of the response to hydrothermal activity;

[0061] S5. Determine δ in the research sequence 7 Li 校正后The background value is used to identify the period of enhanced hydrothermal activity, the period of weakened hydrothermal activity, or the period of non-hydrothermal activity by comparing the difference between the lithium isotope ratio value of continuous segments and the background interval value.

[0062] Specifically, in step S2, for δ 7 Li carb Correlation analysis was performed between the δ value and the major and trace element characteristics of the sample. 7 Li carb If the recorded δ0.05 values ​​show a significant correlation with the major and trace element characteristics of the sample, it is determined that the sample has been affected by later diagenetic alteration or terrigenous clastic contamination. 7 Li carb The signal cannot represent the information of the original sedimentary water body; if δ 7 Li carb There was no significant correlation with the major and trace element characteristics of the sample, ruling out the influence of later diagenetic alteration on the original δ¹⁸O₂. 7 Li carb After superimposing and modifying the signals, proceed to step S3 for hydrothermal intensity identification.

[0063] It should be noted that existing tracer technologies have significant drawbacks: First, the specificity of the indicators is poor, particularly for the Fe / Ti ratio, etc. 87 Sr / 86 Commonly used indicators such as Sr values ​​are mostly mixed indicators of volcanic and hydrothermal activity, which cannot effectively distinguish the specific nature of the source of deep materials. Secondly, the sensitivity and spatiotemporal continuity of these indicators are severely lacking. For example, the formation of positive Eu anomalies usually requires high hydrothermal temperatures (>200°C), so it is sluggish or even unresponsive to low- and medium-temperature hydrothermal activity. More importantly, most existing indicators are recorded in an event-based or intermittent manner, only able to indicate the presence or absence of hydrothermal activity and its peak value, making it difficult to continuously and with high resolution trace the dynamic fluctuations and long-term evolution trends of the relative intensity of hydrothermal activity.

[0064] To address the aforementioned issues, this patent targets existing hydrothermal activity tracing technologies (such as hydrothermal minerals like sodium borosilicate, Eu anomalies, etc.). 87 Sr / 86 To address the shortcomings of δ¹⁴Sr in terms of continuity, sensitivity, and specificity, a method based on deposited lithium carbonate isotopes (δ¹⁴Sr) is proposed. 7 Li carb A new tracing method for [the study] has been developed. Its core theory lies in the fact that hydrothermal activity introduces large amounts of soluble silicon into sedimentary water, significantly promoting "anti-weathering" and driving the formation of authigenic clay minerals (such as illite). This process strongly and preferentially fixes light lithium isotopes (…). 6 Li), leading to the enrichment of heavy lithium isotopes in the residual water and the carbonate precipitates therein ( 7 Li), so that δ 7 Li carb The value increases systematically. Therefore, δ7 Li carb The value forms a positive correlation with the soluble silica flux and deweathering intensity of hydrothermal input, becoming a continuous record of hydrothermal activity. Compared to traditional indicators, δ... 7 Li carb It possesses unique advantages: 1) Continuous high resolution: It can acquire continuous curves, finely characterizing the dynamic evolution of hydrothermal intensity; 2) Wide temperature range sensitive response: It is equally sensitive to medium and low temperature hydrothermal activity, overcoming the limitation of Eu anomalies only indicating high temperatures; 3) It can effectively distinguish hydrothermal signals from continental weathering signals through matching clastic indicators (such as Al / Ca), and the influence of diagenetic alteration is eliminated through rigorous experimental procedures; 4) Strong universality: Its "hydrothermal-silicon input-reverse weathering-lithium fractionation" mechanism is applicable to various marine and terrestrial environments with hydrothermal silicon input and carbonate deposition. This method achieves a breakthrough from event labeling to process characterization, and is an important technological innovation for the refined and quantitative tracing of hydrothermal activity in sedimentary basins.

[0065] In a preferred embodiment, in step S1, the mixed mineral sample is an unweathered rock core collected from a sedimentary basin.

[0066] In a preferred embodiment, the unweathered rock core of the sedimentary basin includes mudstone, shale, marl, dolomite, and evaporite containing alkali minerals.

[0067] This method can directly process mixed mineral samples, avoiding the cumbersome process of manually selecting single minerals (such as pure calcite) in traditional methods. It is especially suitable for scenarios where carbonate and silicate minerals are closely coexisting in fine-grained sedimentary rocks and are difficult to physically separate, significantly expanding the application scope of lithium isotope tracing technology.

[0068] In a preferred embodiment, the specific operation of pretreatment of the mixed mineral sample in step S1 is as follows:

[0069] After cleaning, drying, and crushing, the mixed mineral samples were rinsed with 0.5-1M ammonium acetate solution by shaking.

[0070] The remaining sample was then reacted with 0.5-1M acetic acid solution at room temperature with shaking for 2-6 hours. The acetic acid filtrate was collected, evaporated to dryness, and converted into a nitric acid system.

[0071] The specific steps for 'converting to a nitric acid system' are as follows: Evaporate the collected acetic acid filtrate to dryness at a temperature below 60°C (to avoid lithium isotope fractionation or sample loss due to high temperatures). Add 1 to 2 mL of concentrated nitric acid to the evaporated residue, and evaporate again to dryness to destroy residual organic matter and convert the sample to nitrate form. Subsequently, add an appropriate amount (e.g., 2 mL) of dilute nitric acid (e.g., 0.5 M to 1.0 M) to dissolve the residue for subsequent column separation.

[0072] The above technical solution specifies that the mixed mineral sample is first leached with a 0.5-1M ammonium acetate solution, then treated with a 0.5-1M acetic acid solution, and finally converted to a nitric acid system. This sequential leaching process achieves stepwise extraction and targeted purification of lithium: ammonium acetate removes adsorbed and exchangeable lithium through ion exchange, eliminating its interference with carbonate lattice lithium; acetic acid selectively dissolves carbonate minerals (calcite, dolomite, and alkali carbonates), releasing the native lithium signal representing the ancient water body while avoiding damage to silicate minerals; and the nitric acid conversion adjusts the extraction medium to a nitric acid system suitable for subsequent ion exchange separation. The above concentration ranges (ammonium acetate > 0.5 M, acetic acid > 0.5 M) ensure sufficient extraction of the target phase, while the upper limits (ammonium acetate < 1.5 M, acetic acid < 1.0 M) prevent the dissolution of non-target phases. This process, in conjunction with subsequent diagenetic alteration testing (step S2) and mineral phase correction (step S3), constitutes a triple-protection mechanism to ensure the final measured δ 7 Li 校正后 The value accurately reflects the information of the original sedimentary water body.

[0073] In a preferred embodiment, the acetic acid filtrate is separated by centrifugation at 3000-4000 rpm for 10-15 minutes or collected by filtration through a 0.45 μm filter membrane.

[0074] In a preferred embodiment, the specific operation of pretreatment of the mixed mineral sample in step S1 is as follows:

[0075] After being cleaned, dried, and pulverized, the mixed mineral sample was rinsed with 0.75M ammonium acetate solution by shaking.

[0076] The remaining sample was then reacted with 0.75M acetic acid solution at room temperature with shaking for 4 hours. The acetic acid filtrate was collected, evaporated to dryness, and converted into a nitric acid system.

[0077] In a preferred embodiment, the specific operation of lithium element separation and purification in step S1 is as follows:

[0078] A purified lithium solution was obtained using an AG50W-X12 cation exchange resin column and hydrochloric acid with a concentration of 0.15-0.3 M as the eluent.

[0079] The above technical solution specifies the use of an AG50W-X12 cation exchange resin column and hydrochloric acid with a concentration of 0.15 M to 0.3 M as the eluent. This is because the resin exhibits excellent affinity and separation selectivity for alkali metals. Combined with hydrochloric acid within this concentration range, lithium can be effectively separated from matrix interfering elements such as sodium, calcium, and magnesium, which are abundant in the sample. Below 0.15 M, lithium elution is too slow and peak tailing occurs, resulting in decreased recovery. Above 0.3 M, interfering elements are prematurely co-eluted, affecting the purification effect. 0.2 M is the optimal operating point within this range for balancing separation and recovery. The purified lithium solution obtained through this step shows a significant reduction in matrix effects, facilitating high-precision δ determination by subsequent MC-ICP-MS. 7 Li carb The value provides a reliable guarantee.

[0080] In a preferred embodiment, the specific operation of lithium element separation and purification in step S1 is as follows:

[0081] A purified lithium solution was obtained using an AG50W-X12 cation exchange resin column and 0.2 M hydrochloric acid as the eluent.

[0082] In a preferred embodiment, the specific operation of determining the lithium isotope ratio in step S1 is as follows:

[0083] The purified lithium solution was analyzed by MC-ICP-MS using a standard-sample cross-reference method, with the international standard reference material USGS LSVEC (δ¹³C). 7 Instrument mass fractionation calibration was performed using Li = 0‰, and the results were expressed as δ. 7 Li carb Value (‰) represents;

[0084] The calculation formula is: δ 7 Li carb = [( 7 Li / 6 Li) 样品 / ( 7 Li / 6 Li) LSVEC -1]×1000.

[0085] By adopting the above technical solution, and combining high-precision MC-ICP-MS determination with standard-sample cross-calibration, the analytical accuracy and precision of lithium isotope ratios in carbonate minerals have been significantly improved.

[0086] In a preferred embodiment, in step S2, when the mixed mineral sample is collected from a sedimentary basin, it is necessary to confirm δ. 7 Li carbThere was no significant correlation with Al / Ca, Rb / Ca, Mn / Ca, or Mg / (Ca+Mg).

[0087] By adopting the above technical solution, based on δ 7 Li carb Systematic verification and synergistic analysis with clastic indices such as Al / Ca, Rb / Ca, Mn / Ca, and Mg / (Ca+Mg) can effectively distinguish between hydrothermal and continental weathering signals, quantitatively exclude diagenetic superposition signals, and ensure the originality of the data.

[0088] In a preferred embodiment, in step S3, the value of k is 0.1‰-1.0‰.

[0089] It should be noted that classic studies, based on marine calcite, dolomite, and other calcium and magnesium carbonates, determined the lithium isotope fractionation values ​​(Δδ) relative to the water body during precipitation. 7 Li carb The concentration is approximately -5.5‰. However, the abundant sodium carbonate minerals (such as natural soda ash and sodium bicarbonate) in alkaline lakes may exhibit different fractionation effects due to their crystal structures and surface properties. Directly using measurements from mixed mineral samples (δ...) 7 Li carb This will introduce mineral-dependent systematic errors, distorting the δ¹⁴ values ​​of paleowater bodies. 7 A true reconstruction of Li and anti-weathering intensity.

[0090] Correction formula δ 7 Li 校正后 = δ 7 Li carb - k × [f 碱 / (1 + f 碱 The derivation of [] is based on the principle of mass balance. Its core idea is to treat the measured values ​​of the mixed sample as a weighted average of the contributions of calcium magnesium carbonate and alkaline carbonate, and then use mathematical transformations to uniformly correct them to the standard of "equivalent calcium magnesium carbonate". In the formula: f 碱 The ratio of alkali minerals to calcium and magnesium carbonates, obtained quantitatively by XRD, determines the correction range.

[0091] The critical coefficient k has a clear geochemical significance, representing the inherent difference in fractionation values ​​between the two types of minerals (k = Δ). 7 Li 碱 - Δ 7 Li 钙镁 k>0 means that alkali minerals are bound together. 7 Li's relative ability is stronger (or repulsive). 6Li is weaker). The k-value (0.1‰ – 1.0‰, typical value 0.4‰) is a statistical range experimentally determined by comparing and analyzing a series of samples with different mineral compositions in the study area, based on the assumption that "they were formed in similar water bodies". This correction step eliminates the bias caused by differences in mineral phases in principle and is the core quality control link to ensure the scientific validity, consistency and comparability of data in complex sedimentary environments.

[0092] In a preferred embodiment, in step S4, the hydrothermal activity indicators include:

[0093] Europium positive anomaly: Eu / Eu*=2Eu N / (Sm N + Gd N );

[0094] Among them, Eu N 、Sm N and Gd N The contents of Eu, Sm, and Gd after PAAS standardization;

[0095] Alkali mineral content: refers to the total content of alkali minerals; abnormal enrichment of alkali minerals often indicates the input of deep hydrothermal substances.

[0096] Anti-weathering indicators include:

[0097] Self-generated silicon content: Si auto =Si 样品 -Al 样品 ×3.11;

[0098] 3.11 represents the background Si / Al ratio in the upper crust, with positive values ​​indicating non-clastic authigenic silica, directly reflecting the concentration of soluble silica in water.

[0099] The Li / Al and K / Al ratios are significantly higher than the UCC background values, providing direct geochemical evidence for the formation of lithium- and potassium-rich authigenic clay minerals through reverse weathering.

[0100] It should be noted that the europium positive anomaly (Eu / Eu*>1.05) is determined by inductively coupled plasma mass spectrometry (ICP-MS), where the rare earth element content is Eu / Eu*=2Eu. N / (Sm N + Gd N Eu N 、Sm N and Gd N The values ​​are PAAS-normalized Eu, Sm, and Gd contents. Eu / Eu* > 1.05 is a key threshold for identifying medium- to high-temperature (>200°C) hydrothermal activity;

[0101] Alkali mineral content: Quantitative analysis by X-ray diffraction (XRD) indicates the total content of alkali minerals (including natural alkali, soda ash, sodium hydride, sodium carbonate calcium aluminate, sodium carbonate magnesium aluminate, sodium chloride magnesium aluminate, etc.). Abnormal enrichment of these minerals often indicates the input of deep hydrothermal materials.

[0102] Indicators of anti-weathering are used to verify the "hydrothermal-anti-weathering" mechanism chain, including: autogenous silica content (Si... auto The Si and Al content of the sample was determined by X-ray fluorescence spectroscopy (XRF), and the Si content was calculated according to the formula. auto =Si 样品 -Al 样品 The value is calculated as ×3.11, where 3.11 is the background Si / Al ratio of the upper crust (UCC). A positive value represents authigenic silica from non-clastic sources, which directly reflects the concentration of soluble silica in the water.

[0103] The Li / Al and K / Al ratios, determined by high-sensitivity ICP-MS for Li content and by XRF or ICP-MS for K and Al, are significantly higher than the UCC background values, providing direct geochemical evidence for the formation of lithium- and potassium-rich authigenic clay minerals through reverse weathering. Systematic analysis of δ... 7 Li carb The significant positive correlation between the above two types of indicators can simultaneously verify the reliability of its recording of hydrothermal events and the underlying reverse weathering driving mechanism.

[0104] In a preferred embodiment, in step S4, the system analyzes δ 7 Li 校正后 By establishing a chain of evidence for the synergistic changes of multiple indicators, based on the correlation between hydrothermal activity indicators and deweathering indicators:

[0105] If δ 7 Li 校正后 A significant positive correlation between δ and hydrothermal activity indicators and anti-weathering indicators indicates that δ 7 Li 校正后 It can effectively respond to the anti-weathering effect driven by hydrothermal activity, and its reliability as a tracer of hydrothermal activity has been verified. It can proceed to step S5 for hydrothermal intensity identification.

[0106] Specifically:

[0107] (1) If δ 7 Li 校正后 Related to hydrothermal activity indicators (Eu / Eu*, alkali mineral content) and antiweathering indicators (Si). auto If the correlation coefficients (δ, K / Al, Li / Al) show a significant positive correlation (usually defined as a Pearson correlation coefficient r ≥ 0.5, p < 0.05), it indicates that the study area meets the geological conditions of "hydrothermal input-reverse weathering dominance". 7Li 校正后 It can effectively respond to the anti-weathering effect driven by hydrothermal activity, and its reliability as a tracer of hydrothermal activity has been verified. It can proceed to step S5 for hydrothermal intensity identification.

[0108] (2) If δ 7 Li 校正后 If there is no significant positive correlation with all or most of the above indicators, it indicates that the studied stratigraphic segment may not meet the prerequisites for the application of this method. Specific reasons may include: ① lack of hydrothermal silica input, with reverse weathering not being dominant; ② the presence of other dominant lithium isotope fractionation processes in the study area (such as intense continental weathering). In this case, the use of this method for hydrothermal activity identification should be discontinued, and the sedimentary environment should be reassessed in conjunction with petrographic and other geochemical methods, or the sample screening strategy should be adjusted and reanalyzed after the cause is identified.

[0109] (3) If δ 7 Li 校正后 If a value is positively correlated only with certain indicators (e.g., correlated only with hydrothermal indicators but not with deweathering indicators), it indicates that hydrothermal input exists, but deweathering may not be dominant. δ 7 Li 校正后 The response mechanism does not fully conform to the theoretical model of this method. In this case, δ 7 Li 校正后 It can serve as a helpful reference indicator for hydrothermal activity, but it is not suitable for use alone to quantitatively determine hydrothermal intensity. It is recommended to combine it with other hydrothermal indicators for comprehensive interpretation.

[0110] In a preferred embodiment, the background value is δ of the layer without obvious hydrothermal index. 7 Li carb The average value indicates that the stratigraphic zone without obvious hydrothermal indicators is one that simultaneously meets the following criteria: Eu / Eu* < 1.05, alkali mineral content < 5%, and anti-weathering index: Si auto Layers with K / Al in the range of 3±3%, Li / Al in the range of 0.3±0.3%, and Li / Al in the range of 3±3 ppm / %;

[0111] When the δ of the continuous segment 7 Li carb When the average value is greater than the sum of the background value and twice the standard deviation, it is identified as a period of enhanced hydrothermal activity.

[0112] When the δ of the continuous segment 7 Li carb When the mean value equals the sum of the background value and twice the standard deviation, it is identified as a non-hydrothermal dominant period;

[0113] When the δ of the continuous segment 7 Li carb When the average value is lower than the sum of the background value and twice the standard deviation, it is identified as a period of weakened hydrothermal activity.

[0114] To provide a clearer and more detailed description of the method for tracing hydrothermal activity in sedimentary basins provided by the embodiments of the present invention, specific embodiments will be described below.

[0115] Example 1: Tracing Method for Hydrothermal Activity in Sedimentary Basins

[0116] Taking a sample from the central salt rock area of ​​a basin as an example, the tracing method includes the following steps:

[0117] 1) Using the central salt rock area of ​​a basin as the target stratigraphic level (approximately 305-296 Ma), 22 core samples were collected from the Feng 1st to Feng 3rd sections of five wells, including F20. The rock types included dolomite, alkali-bearing evaporite, tuffaceous mudstone, and mudstone, all containing carbonate minerals (calcite, dolomite, or alkali carbonates). Representative samples were selected, veins and weathered portions were removed, and the samples were ultrasonically cleaned, dried at low temperature, and then pulverized to <200 mesh for later use. After ultrasonic cleaning with deionized water and low-temperature (<60℃) drying, the samples were pulverized using an agate mortar or a pollution-free crusher to a particle size of less than 200 mesh (<75μm).

[0118] 2) Weigh 80 ± 20 mg of each individual sample powder obtained in step 1. First, rinse with 1 M ammonium acetate solution to remove adsorbed and exchangeable lithium. 3) Residual samples are reacted with 0.75 M acetic acid solution at room temperature for 4 hours with shaking to selectively dissolve carbonate minerals (such as calcite, dolomite, and alkali carbonates) and release lithium. After the reaction is complete, filter through a 0.45 μm filter membrane and collect the supernatant or filtrate as acetic acid leaching solution. Evaporate the collected acetic acid leaching solution to dryness at below 60°C. Add 1.5 mL of 15 M concentrated nitric acid to the residue after evaporation and evaporate again to destroy residual organic matter and convert the sample to nitrate form. Then add 2 mL of 0.75 M dilute nitric acid to dissolve the residue to obtain a nitric acid system sample solution for subsequent column separation.

[0119] 4) Using an AG50W-X12 (200-400 mesh) cation exchange resin column and 0.2 M hydrochloric acid as the eluent, lithium in the solution was separated and purified to remove matrix interfering elements such as sodium, calcium, and magnesium.

[0120] 5) The purified lithium solution was analyzed using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). A standard-sample cross-reference method was employed, using the international standard reference material USGS LSVEC (δ¹²HbA1c). 7 Instrument mass fractionation calibration was performed with Li = 0‰. The results are expressed as δ... 7 The Li value (‰) is expressed by the formula: δ 7 Li = [( 7Li / 6 Li) 样品 / ( 7 Li / 6 Li) LSVEC -1] × 1000. Carbonate standards (such as JDo-1) and seawater standards (such as OSIL) were inserted for process monitoring and data quality assessment in each batch of sample analysis.

[0121] 6) Diagenetic alteration examination and data screening: Parallel analysis was performed on the same batch of sample powder after crushing in step 1: one sample was used for the carbonate lithium isotope analysis in steps 1-5 (to obtain δ¹⁴ ppm). 7 Li carb One set of values ​​was used for independent whole-rock major and trace element analysis. Major elements (Al, Ca, Mg, K) were determined by XRF (500 mg sample, melt preparation), with an accuracy better than ±1% for elements >1% and better than ±10% for elements <1%. Trace elements (Rb, Mn, Sr) were determined by ICP-MS (50 mg sample, HF+HNO3 dissolution, Rh internal standard correction), with an analytical accuracy better than ±5%. Based on the above results, the ratios of Al / Ca, Rb / Ca, Mn / Ca, Mg / (Ca+Mg), and Mn / Sr were calculated and compared with δ¹⁴. 7 Li carb Perform Pearson correlation analysis on the value. If δ 7 Li carb If a sample shows a significant correlation with any of the following indicators: Al / Ca, Rb / Ca, Mn / Ca, or Mg / (Ca+Mg) (|r|≥0.5 and p<0.05), or Mn / Sr≥3, it is considered to have undergone post-processing and will be discarded, not participating in subsequent steps. It should be noted that the above elemental ratios are derived from independent whole-rock analysis, not from the purified lithium solution in step 4. Since calcium, magnesium, and aluminum have been removed in step 4, correlation testing must rely on independent analytical data from parallel samples.

[0122] like Figure 1 As shown, taking a sample from the central salt rock area of ​​a basin as an example, the δ of the sample... 7 Li carb There was no significant correlation with Al / Ca, Rb / Ca, Mn / Ca, and Mg / (Ca+Mg), indicating the influence of silicate components, Mn hydroxides, and early diagenesis on δ during the stepwise leaching process, respectively. 7 Li carb The value has no significant effect, δ 7 Li carb The values ​​are mainly controlled by the sedimentary environment and can record the original processes during the sedimentary period.

[0123] 7) Classical studies, based on marine calcite, dolomite, and other calcium and magnesium carbonates, have determined the lithium isotope fractionation values ​​(Δδ) relative to the water body during precipitation. 7 Li carb The concentration is approximately -5.5‰. However, the abundant sodium carbonate minerals (such as natural soda ash and sodium bicarbonate) in alkaline lakes may exhibit different fractionation effects due to their crystal structures and surface properties. Directly using measurements from mixed mineral samples (δ...) 7 Li carb This will introduce mineral-dependent systematic errors, distorting the δ¹⁴ values ​​of paleowater bodies. 7 Accurate reconstruction of Li and antiweathering intensity. Correction formula δ 7 Li 校正后 = δ 7 Li carb -k × [f 碱 / (1+f 碱 The derivation of [] is based on the principle of mass balance. Its core idea is to treat the measured values ​​of the mixed sample as a weighted average of the contributions of calcium magnesium carbonate and alkaline carbonate, and then use mathematical transformations to uniformly correct them to the standard of "equivalent calcium magnesium carbonate". In the formula: f 碱 The ratio of alkali minerals to calcium and magnesium carbonates, obtained quantitatively by XRD, determines the correction range. The key coefficient k has a clear geochemical significance, representing the inherent difference in fractionation values ​​between the two types of minerals (k = Δ). 7 Li 碱 - Δ 7 Li 钙镁 k>0 means that alkali minerals are bound together. 7 Li's relative ability is stronger (or repulsive). 6 Li is weaker). The k-value (0.1‰ – 1.0‰, typical value 0.4‰) is a statistical range experimentally determined by comparing and analyzing a series of samples with different mineral compositions in the study area, based on the assumption that "they were formed in similar water bodies". This correction step eliminates the bias caused by differences in mineral phases in principle and is the core quality control link to ensure the scientific validity, consistency and comparability of data in complex sedimentary environments.

[0124] To clearly demonstrate the practical application of the correction formula, a representative sample from a basin in this embodiment is used as an example for calculation. The k value used in this embodiment is 0.4‰ (a typical value obtained from statistical analysis of multiple sample pairs in the study area). 碱 The value was obtained through quantitative analysis using X-ray diffraction (XRD) and represents the ratio of the total amount of alkali minerals to the total amount of calcium magnesium carbonate (calcite + dolomite). The correction amplitude and f... 碱 The value is closely related: when f 碱 At higher levels (e.g., FN5 well 4065.5m, f 碱=31.24), the correction term is relatively large (0.388‰), δ 7 Li 校正后 Significantly lower than the measured value; when f 碱 When =0 (e.g., well F20 at m 3191.1, where the sample does not contain alkali minerals), the correction term is 0, f 碱 This is equal to the measured value. This quantitative relationship indicates that the correction formula effectively eliminates the systematic bias caused by differences in alkali mineral content, enabling samples with different mineral compositions to be compared on the "equivalent calcium magnesium carbonate" benchmark.

[0125] Figure 2 δ before and after correction 7 Li carb Data from sample δ 7 Li carb With δ 7 Li 校正后 As can be seen from the correlation scatter plot, the δ of samples with higher contents of alkali minerals and calcium and magnesium carbonates is higher. 7 Li 校正后 Significantly lower than δ 7 Li carb This results in the use of the original δ 7 Li carb Alternative methods for interpreting the data do not yield accurate results.

[0126] 8) δ of all samples 7 Li carb Correlation analysis was performed on the data with classical hydrothermal and anti-weathering indicators to construct a synergistic variation model, thereby achieving cross-validation and mechanism confirmation of hydrothermal signals. Hydrothermal activity indicators included: Europium positive anomaly (Eu / Eu*>1.05): rare earth element content was determined by inductively coupled plasma mass spectrometry (ICP-MS), Eu / Eu*=2Eu. N / (Sm N +Gd N Eu N 、Sm N and Gd N The values ​​are PAAS-normalized Eu, Sm, and Gd contents. Eu / Eu* > 1.05 is a key threshold for identifying medium- to high-temperature (>200°C) hydrothermal activity;

[0127] Alkali mineral content: Quantitative analysis by X-ray diffraction (XRD) indicates the total content of alkali minerals (including natural alkali, soda ash, sodium hydride, sodium carbonate calcium aluminate, sodium carbonate magnesium aluminate, sodium chloride magnesium aluminate, etc.). Abnormal enrichment of these minerals often indicates the input of deep hydrothermal materials.

[0128] Indicators of anti-weathering are used to verify the "hydrothermal-anti-weathering" mechanism chain, including: autogenous silica content (Si... autoThe Si and Al content of the sample was determined by X-ray fluorescence spectroscopy (XRF), and the Si content was calculated according to the formula. auto =Si 样品 - Al 样品 The value is calculated as ×3.11, where 3.11 is the background Si / Al ratio of the upper crust (UCC). A positive value represents authigenic silica from non-clastic sources, which directly reflects the concentration of soluble silica in the water.

[0129] The Li / Al and K / Al ratios, determined by high-sensitivity ICP-MS for Li content and by XRF or ICP-MS for K and Al, are significantly higher than the UCC background values, providing direct geochemical evidence for the formation of lithium- and potassium-rich authigenic clay minerals through reverse weathering. Systematic analysis of δ... 7 Li carb The significant positive correlation between the above two types of indicators can simultaneously verify the reliability of its recording of hydrothermal events and the underlying reverse weathering driving mechanism.

[0130] Figure 3 For sample δ 7 Li carb A scatter plot showing the correlation between classic hydrothermal vents and anti-weathering indices, by... Figure 3 It can be seen that δ 7 Li carb It showed a strong positive correlation with both Eu / Eu* and total alkali mineral content (r = +0.71 and +0.82, respectively), cross-validating the hydrothermal signal and indicating δ 7 Li carb The Si value can effectively and continuously indicate the relative change in the intensity of hydrothermal activity. auto With δ 7 Li carb Both Eu and Eu* are significantly positively correlated (r = +0.56; +0.72), indicating that hydrothermal activity brought a large amount of soluble silicon, δ 7 Li carb The values ​​of K / Al and Li / Al were significantly positively correlated (r = +0.67; +0.78), indicating that hydrothermal activity promoted deweathering by providing a large amount of soluble silica, and the resulting authigenic clay minerals were preferentially fixed. 6 Li, which leads to the formation of δ-carbonates in water bodies. 7 The increase in Li value verified the "hydrothermal-reverse weathering-lithium fractionation" mechanism.

[0131] If only δ 7 Li carb Correlation analysis was performed with Eu / Eu*, without combining Si. auto The mechanism of anti-weathering indicators such as Li / Al and K / Al was verified. This alternative scheme can only indicate δ 7 Licarb The value shows a significant correlation with other hydrothermal parameters, but because δ cannot be determined... 7 Li carb Without understanding the mechanism of response to changes in hydrothermal activity intensity, δ cannot be determined. 7 Li carb Can this value be used as an indicator of hydrothermal activity?

[0132] 9) Identification of hydrothermal activity intensity: First, determine the δ¹⁸ t⁻¹ ... 7 Li 校正后 Background values ​​(e.g., the average μ of sections without obvious hydrothermal indicators). Identify "sections without obvious hydrothermal indicators" in the study profile—that is, sections that simultaneously meet the following conditions: Eu / Eu* < 1.05, alkali mineral content < 5%, and anti-weathering index (Si). auto K / Al and Li / Al are close to the UCC background value (autogenous silicon content Si). auto The layer segment (within the range of 3±3%, K / Al within the range of 0.3±0.3, and Li / Al within the range of 3±3 ppm / %) was used. The δ values ​​of all samples within this layer segment were taken. 7 Li 校正后 The background mean μ and standard deviation σ are calculated using the following formula: μ = (∑δ 7 Li 校正后 ) / n,σ = √[∑(δ 7 Li 校正后 - μ)² / (n-1)], where n is the number of samples in the background layer. The upper section of the Feng-3 member without obvious hydrothermal indicators (Eu / Eu* < 1.05, alkali mineral content < 5%) was selected as the basis for background value calculation. Three samples were collected in this section (3138.3m, 3187.9m, and 3191.1m from well F20), and their δ... 7 Li 校正后 The values ​​are 5.9‰, 6.5‰, and 6.5‰ respectively. Calculation process: μ = (5.9 + 6.5 + 6.5) / 3 = 6.30‰, σ = √[((5.9-6.30)² + (6.5-6.30)² + (6.5-6.30)²) / (3-1)]≈0.35‰. Therefore, the identification threshold = μ + 2σ = 6.30 + 2×0.35 = 7.00‰. Based on this standard, the δ in the profile... 7 Li 校正后Continuous stratigraphic intervals with values ​​>7.00‰ were identified as periods of enhanced hydrothermal activity. This result is in high agreement with traditional hydrothermal indicators such as positive Eu / Eu* anomalies and alkali mineral enrichment, verifying the reliability of this method. Intervals equal to the sum of the background value and twice the standard deviation were identified as non-hydrothermal dominant periods, while intervals below the sum of the background value and twice the standard deviation were identified as periods of weakened hydrothermal activity. For example, based on the absence of a positive Eu anomaly and low alkali mineral content, this is an interval without significant hydrothermal activity, and its δ... 7 Li carb The average value is 6.40 ± 0.49‰, then δ 7 Li carb Continuous layers with values ​​higher than the background value (=6.40+2*0.49=7.38‰) were identified as being in a period of enhanced hydrothermal activity.

[0133] Figure 4 For δ 7 Li carb Si auto Plot showing the variation of K / Al, Li / Al, Eu / Eu*, alkali mineral content, and the ratio of alkali minerals to calcium and magnesium carbonates with depth. This plot clearly illustrates the δ 7 Li carb Eu / Eu*, alkali mineral content, Si auto The co-evolution sequence of key indicators with depth (time). For example, in a basin profile, δ0 can be observed. 7 Li carb The values ​​exhibit a systematically high level (>7–9‰) at depths of 3375–4500 m, which coincides with a significant positive Eu anomaly (Eu / Eu*>1.05), high alkali mineral content, and elevated Si. auto The K / Al and Li / Al ratios are precisely coupled vertically. This phenomenon of simultaneous peak values ​​for multiple indicators constitutes a complete chain of evidence, collectively indicating a period of enhanced hydrothermal activity. Conversely, in strata with depths <3375 m, Figure 4 The results show a synergistic shift across all indicators: δ 7 Li carb The concentration decreased (>6.0–6.8‰), while the Eu positive anomaly disappeared, the content of alkali minerals decreased sharply, and the authigenic silica index declined. This section was therefore objectively defined as a "section without obvious hydrothermal indicators," with its δ... 7 Li carb The average value (e.g., 6.40 ± 0.49 ‰) naturally becomes an ideal source for calculating the background value (μ) of the region. The clear transition of the indicator curves from the "active period" to the "quiet period" in the figure not only visually verifies the geological rationality of the "background value" selection in step 9, but also proves the validity of the δ... 7 Li carbThe dynamic standard for identification based on relative background value offset (e.g., >μ+2σ) can effectively capture the onset and intensity changes of hydrothermal activity, achieving a leap from qualitative description to semi-quantitative staging.

Claims

1. A method for tracing hydrothermal activity in a sedimentary basin, characterized in that, Includes the following steps: S1. Pretreatment of mixed mineral samples, lithium separation and purification, and δ 7 Li carb Value determination; S2, for δ 7 Li carb Correlation analysis was performed between the δ value and the major and trace element characteristics of the sample. 7 Li carb If there is no significant correlation with the major and trace element characteristics of the sample, proceed to step S3 to determine the hydrothermal intensity. S3. The measurement δ of the mixed mineral sample is corrected using the following formula. 7 Li carb Values ​​are corrected: δ 7 Li 校正后 =δ 7 Li carb -k×[f 碱 / (1+f 碱 )]; Among them, f 碱 It represents the ratio of alkali minerals to calcium and magnesium carbonates. k represents the inherent difference in fractionation values ​​between the two types of minerals, k=Δ 7 Li 碱 -Δ 7 Li 钙镁 ; S4, δ of the mixed mineral sample 7 Li 校正后 Correlation analysis was performed on the δ values ​​with hydrothermal activity indicators and deweathering indicators to verify whether there was a synergistic relationship among the three, thereby confirming the δ 7 Li 校正后 The reliability and mechanism consistency of the response to hydrothermal activity; S5. Determine δ in the research sequence 7 Li 校正后 The background value is used to identify the period of enhanced hydrothermal activity, the period of weakened hydrothermal activity, or the period of non-hydrothermal activity by comparing the difference between the lithium isotope ratio value of continuous segments and the background value.

2. The tracing method according to claim 1, characterized in that, In step S1, the mixed mineral sample is an unweathered rock core collected from a sedimentary basin.

3. The tracing method according to claim 1, characterized in that, In step S1, the specific pretreatment operations for the mixed mineral sample are as follows: After cleaning, drying, and crushing, the mixed mineral sample was rinsed with 0.5-1M ammonium acetate solution by shaking. The remaining sample was then reacted with 0.5-1M acetic acid solution at room temperature with shaking for 2-6 hours. The acetic acid filtrate was collected, evaporated to dryness, and converted into a nitric acid system.

4. The tracing method according to claim 1, characterized in that, In step S1, the specific operations for lithium element separation and purification are as follows: A purified lithium solution was obtained using an AG50W-X12 cation exchange resin column and 0.15-0.3M hydrochloric acid as the eluent.

5. The tracing method according to claim 1, characterized in that, In step S1, the specific operation for determining the lithium isotope ratio is as follows: The purified lithium solution was analyzed by MC-ICP-MS using a standard-sample cross-reference method. Instrument mass fractionation calibration was performed using the international standard reference material USGS LSVEC. The results are expressed as δ 7 Li carb Value (‰) represents; The calculation formula is: δ 7 Li carb = [( 7 Li / 6 Li) 样品 / ( 7 Li / 6 Li) LSVEC -1]×1000.

6. The tracing method according to claim 1, characterized in that, In step S2, when the mixed mineral sample is collected from a sedimentary basin, it is necessary to confirm δ. 7 Li carb There was no significant correlation with Al / Ca, Rb / Ca, Mn / Ca, or Mg / (Ca+Mg).

7. The tracing method according to claim 1, characterized in that, In step S3, the value of k is 0.1‰-1.0‰.

8. The tracing method according to claim 1, characterized in that, In step S4, the hydrothermal activity indicators include: Europium positive anomaly: Eu / Eu*=2Eu N / (Sm N + Gd N ); Among them, Eu N 、Sm N and Gd N The contents of Eu, Sm, and Gd after PAAS standardization; Alkali mineral content: refers to the total content of alkali minerals; abnormal enrichment of alkali minerals often indicates the input of deep hydrothermal substances. Anti-weathering indicators include: Self-generated silicon content: Si auto =Si 样品 -Al 样品 ×3.11; 3.11 represents the background Si / Al ratio in the upper crust. A positive value indicates authigenic silica from non-clastic sources, directly reflecting the concentration of soluble silica in water. The Li / Al and K / Al ratios are significantly higher than the UCC background values, providing direct geochemical evidence for the formation of lithium- and potassium-rich authigenic clay minerals through reverse weathering.

9. The tracing method according to claim 8, characterized in that, In step S4, δ is analyzed through system analysis. 7 Li 校正后 By establishing a chain of evidence for the synergistic changes of multiple indicators, based on the correlation between hydrothermal activity indicators and deweathering indicators: If δ 7 Li 校正后 A significant positive correlation between δ and hydrothermal activity indicators and anti-weathering indicators indicates that δ 7 Li 校正后 It can effectively respond to the anti-weathering effect driven by hydrothermal activity, and its reliability as a tracer of hydrothermal activity has been verified. It can proceed to step S5 for hydrothermal intensity identification.

10. The tracing method according to claim 8, characterized in that, In step S5, the background value is δ of the section without obvious hydrothermal index. 7 Li carb The average value indicates that the stratigraphic zone without obvious hydrothermal indicators is one that simultaneously meets the following criteria: Eu / Eu* < 1.05, alkali mineral content < 5%, and anti-weathering index: Si auto Layers with K / Al in the range of 3±3%, Li / Al in the range of 0.3±0.3%, and Li / Al in the range of 3±3 ppm / %; When the δ of the continuous segment 7 Li carb When the average value is greater than the sum of the background value and twice the standard deviation, it is identified as a period of enhanced hydrothermal activity. When the δ of the continuous segment 7 Li carb When the mean value equals the sum of the background value and twice the standard deviation, it is identified as a non-hydrothermal dominant period; When the δ of the continuous segment 7 Li carb When the average value is lower than the sum of the background value and twice the standard deviation, it is identified as a period of weakened hydrothermal activity.

Images