A method for regional thermal uplift identification and reconstruction based on extensional tectonic background

Abstract

The present invention belongs to the field of geological technology and discloses a method for regional thermal uplift identification and reconstruction based on extensional tectonic background. By integrating time-temperature inversion with multiple thermal chronological constraints, major and trace element and isotope geochemical analysis, and tectonic evolution modeling, it is possible to achieve a comprehensive characterization and quantitative restoration of regional thermal uplift from deep mantle thinning, magma source area tracing, thermal history evolution to shallow crust cooling path. Based on multi-temperature stage coupled inversion technology, it is possible to quantitatively evaluate the erosion rate, uplift height, and cooling time; based on accurate thermal history reconstruction and thermal uplift identification, it is possible to effectively predict the thermal maturity of high-quality source rocks, optimize the selection of oil and gas reservoirs and the positioning of closures, thereby significantly improving the success rate and economic benefits of oil and gas exploration, and has scientific research and industrial application value.

Description

Technical Field

[0001] The present invention relates to the field of geological technology, specifically to the cross-study of structural geology, geochemistry and isotope geochronology, and in particular to a method for identifying and reconstructing regional thermal uplifts based on an extensional tectonic background. Background Art

[0002] Regional thermal uplift in an extensional tectonic setting is a geological phenomenon in which the lithosphere, driven by deep tectonic activity (such as lithospheric thinning, asthenospheric upwelling, or mantle plume action), triggers widespread surface uplift. Rapid thinning of the dense lithospheric mantle causes the upwelling of asthenospheric material from the underside, which partially melts under reduced pressure, generating large-scale mafic magmatism. As the lithospheric mantle gradually separates from the base of the crust, the crust rebounds significantly under gravitational isostatic adjustments, causing rapid surface uplift. However, uplift in this tectonic setting is often mistakenly attributed to regional compression, obscuring its origin in deep extension and asthenospheric upwelling.

[0003] In-depth research on regional thermal uplift under extensional settings not only helps to reveal deep dynamic mechanisms but also provides a scientific basis for basin tectonic analysis and resource exploration. However, current research on regional thermal uplift under extensional settings still faces two major challenges: First, the causes and timing of deep thermal anomalies are difficult to determine with a single technical approach; second, accurate reconstruction of shallow crustal cooling and uplift requires higher-precision time control, which places higher demands on the integration and innovation of research methods.

[0004] In recent years, the rapid development of geochemical analysis and isotope chronology has provided strong support for the identification and reconstruction of regional thermal uplift processes. Geochemical analysis, through the interpretation of the major and trace element and isotopic characteristics of igneous rocks, can reveal the nature of the magma source, the spatiotemporal distribution of lithospheric thinning, and deep mantle activity. Multi-temperature stage coupled inversion techniques can accurately record the temporal history of crustal cooling and uplift. However, a comprehensive approach that organically integrates these two techniques to accurately identify and systematically reconstruct processes from deep thermal anomalies to shallow cooling is currently lacking.

[0005] The solution to the above problems has important theoretical and practical significance for a deeper understanding of the mechanism of continental dynamic evolution and the causes of regional sedimentary hiatus under the extensional background. It also provides key scientific guidance for the exploration of regional oil and gas resources. Summary of the Invention

[0006] This study aims to develop a method for identifying and reconstructing regional thermal uplifts in extensional tectonic settings. By coupling geochemical analysis with isotope geochronology, this method can efficiently and accurately reconstruct the evolutionary history of deep lithospheric mantle thinning and shallow crustal rebound cooling. This method provides a simple and scientific means for revealing the extensional-thermal uplift evolution of geological bodies.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] Starting from the co-evolutionary process between the deep lithosphere thinning mechanism and the shallow crust deformation response, this paper takes the magmatic rocks intruded in the extensional zone at different times as the research object and analyzes the evolutionary characteristics of the mantle source region:

[0009] S1. Collection and preparation of rock samples in the study area

[0010] Study area selection and sample collection: prioritize well-preserved basic and ultrabasic igneous rock samples with intrusion times earlier than thermal uplift; rock thin section preparation and petrographic analysis: prepare rock thin sections, conduct petrographic analysis, and select basic, ultrabasic, and plutonic igneous rocks suitable for deep mantle evolution inversion and low-temperature thermochronology analysis; separate target minerals such as apatite and zircon from the selected samples, ensuring that the purity of the separated minerals meets experimental requirements. The processed samples will be packaged and numbered for major element analysis, trace element analysis, isotope analysis, and low-temperature thermochronology testing.

[0011] S2. Whole-rock isotope dating

[0012] High-purity mineral sorting and purification separates target minerals such as zircon, apatite, feldspar, and biotite from the sample, ensuring their purity meets isotope dating requirements. Precise isotope dating analysis uses a high-precision mass spectrometer to analyze and calculate the Ar-Ar and U-Pb isotope systems, screening reliable data using error and confidence intervals to accurately date the intrusion time of the magmatic rock. LA-MC-ICP-MS testing is then performed on the same zircon to obtain the Hf isotope composition, which is used to trace the magma source. Based on the intrusion age, the magmatic activity stages are preliminarily divided and the asthenosphere upwelling is identified. Samples before and after the asthenosphere upwelling are selected for deep mantle evolution inversion, while samples before the upwelling period are used for low-temperature thermochronology analysis.

[0013] S3. Geochemical analysis

[0014] Major element analysis: The igneous rock samples selected in steps S1 and S2 are analyzed for major elements to determine the rock type and basic chemical composition of the magma. Trace element analysis: The trace element data of the igneous rock samples are obtained. The rare earth element (REE) and high field strength element (HFSE) data of the basic igneous rocks are combined with the changes in the K / Yb and Dy / Yb ratios to reveal the transformation of the magma source region and the thinning of the lithospheric mantle. Sr-Nd-Hf isotope analysis: By analyzing the Sr-Nd-Hf isotope composition of basic igneous rocks and combining the spatiotemporal distribution and evolution characteristics of the magma, the time node of the lithospheric thinning is reconstructed, revealing the entire process of thermal uplift from initial lithospheric thinning to asthenospheric mantle upwelling.

[0015] S4. Low-temperature thermochronological analysis and multi-thermochronological constraints on time-temperature history inversion

[0016] According to steps S2 and S3, deep-seated intrusive igneous rock samples that predate lithospheric thinning and regional thermal uplift were screened, and apatite or zircon single crystals were selected. He gas accumulated within the crystals was released using a laser heating system and accurately quantified using a mass spectrometer. Simultaneously, the remaining crystals were analyzed by ICP-MS to determine the U, Th, and Sm contents, and the cooling age of the samples was calculated using the (U-Th) / He age formula. HeFTy software was used to perform a multi-thermal chronologically constrained time-temperature history inversion of the sample's time-temperature history. Boundary conditions were based on the closure temperatures of different chronological systems. Monte Carlo simulations were used to randomly simulate 100 eligible time-temperature paths, from which the optimal path was selected as the time-temperature curve of the thermal evolution of the rock mass.

[0017] S5. Time Series Analysis of Thermal Uplift Identification and Uplift Rate

[0018] The start and end times of thermal uplift, the cooling rate, the height of thermal uplift, and the rate of thermal uplift can be determined by the time nodes of lithosphere thinning and magma source area transformation in step S3, the temperature T and time t of the high and low temperature turning points of the temperature-time curve obtained in step S4, and the paleo-geothermal gradient TD.

[0019] Cooling rate calculation formula:

[0020]

[0021] Thermal uplift height calculation formula:

[0022]

[0023] Thermal uplift rate calculation formula:

[0024]

[0025] The present invention has the following beneficial effects:

[0026] This method efficiently and accurately identifies and quantitatively evaluates regional thermal uplifts in extensional tectonic settings, overcoming the difficulties of identification and low quantification in traditional methods due to data scarcity. It also effectively avoids the limitation of basin analysis in which sedimentary hiatuses in extensional settings are misinterpreted as compressional settings caused by tectonic inversion. By integrating time-temperature inversion with multi-thermal chronological constraints, major and trace element and isotope geochemical analysis, and tectonic evolution modeling, it enables a comprehensive characterization and quantitative restoration of regional thermal uplifts, from deep mantle thinning, magma source tracing, thermal history evolution, to shallow crustal cooling pathways.

[0027] The present invention is based on multi-temperature stage coupled inversion technology, which can quantitatively evaluate the erosion rate, uplift height and cooling time, provide a high-precision time-temperature (tT) evolution curve, reliably characterize the uplift rate and cooling history of different thermal uplift stages, and significantly improve the accuracy of regional structural analysis and resource exploration.

[0028] This method also avoids the misinterpretation of sedimentary discontinuities as compressional backgrounds, a common problem in traditional basin analysis. It is simple and efficient, with flexible data acquisition and a highly effective analysis process. Compared to complex seismic profile interpretation and deep drilling, it is less expensive and suitable for sedimentary basins with a sufficient geological survey foundation. Based on precise thermal history reconstruction and thermal uplift identification, this method can effectively predict the thermal maturity of high-quality source rocks, optimize the selection of oil and gas reservoirs and the location of traps, and thus significantly improve the success rate and economic benefits of oil and gas exploration. It has important scientific research and industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of the present invention for identifying and reconstructing regional thermal uplift processes based on extensional tectonic background;

[0030] Figure 2 igneous rock zircon Value vs. Age Graph;

[0031] Figure 3 Primitive mantle-normalized trace element distribution maps of igneous rocks from the lithosphere and asthenosphere sources;

[0032] Figure 4 Mantle phase equilibrium diagram and rare earth element distribution characteristics under melting depth-pressure conditions;

[0033] Figure 5 Schematic diagram of the Sr-Nd-Hf isotope distribution characteristics of igneous rocks and the transition of their mantle source regions;

[0034] Figure 6 Result diagram of coupled inversion simulation of multiple temperature stages of igneous rocks;

[0035] Figure 7Histograms of different sections in eastern Shandong;

[0036] Figure 8 Schematic diagram of the coupling between deep lithospheric thinning and shallow thermal uplift. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] S1. Collection and preparation of rock samples in the study area

[0039] First, through literature research, geological map interpretation, and geochemical data analysis, representative study areas consistent with extensional tectonic settings were identified. Sampling sites were then determined in conjunction with field geological surveys. Sampling decisions were carefully considered based on the specific research objectives and geological contexts. While basic igneous rocks are key for studying the petrology and geochemistry of mantle sources, low-temperature thermochronology requires samples that are not limited to igneous rocks. However, if the objective is to investigate the dynamics of regional thermal uplift and extensional settings, igneous rock samples (particularly intrusive rocks) are preferred among the three major rock types (igneous, metamorphic, and sedimentary). Furthermore, to ensure that the samples accurately record the cooling and erosion history of the crust during regional thermal uplift, igneous rocks predating the thermal uplift are preferred to avoid interference from later magmatic intrusions or other thermal events. If the igneous rocks are in contact with sedimentary or metamorphic rocks of known age, their approximate formation time can be inferred from intrusive relationships. During sampling, representative rock samples with good preservation and minimal weathering were selected. The sampling site coordinates, lithology, geological setting, and other information were carefully recorded and numbered. The collected samples are preliminarily cleaned to remove the weathered layer and surface impurities, retaining the fresh and complete rock parts.

[0040] Thin sections of igneous rock samples were prepared using the methods outlined in the Petroleum and Natural Gas Industry Standard SY / T5913-2004, "Rock Section Preparation Methods," for subsequent petrographic characterization. A polarizing microscope and camera system were used to examine the color, texture, structure, and mineralogy of each thin section. Based on GB / T17412.1-1998, "Classification and Nomenclature of Igneous Rocks," and SY / T5368-2000, "Identification of Rock Thin Sections" (see Table 1), basic and ultrabasic igneous rocks were initially selected for inversion of deep mantle evolution, while plutonic igneous rocks were used for low-temperature thermochronological analysis. Samples were typically cut into analytically suitable blocks and rock powder using cutting equipment for whole-rock geochemical and isotopic chronological analysis.

[0041] For whole-rock samples and low-temperature thermochronology testing, heavy liquid separation, magnetic separation, and hand sorting are used to isolate target minerals such as apatite and zircon from the samples, ensuring that the purity of the separated minerals meets experimental requirements. The processed samples will be packaged and numbered for major element analysis, trace element analysis, isotope analysis, and fission track and (U-Th) / He dating, providing high-quality data support for subsequent geochemical analysis and geochronological studies.

[0042] Table 1 Classification criteria for igneous rocks

[0043]

[0044] S2. Whole-rock isotope dating

[0045] During the first step of sample selection, acid dissolution is used to extract target minerals (such as feldspar, biotite, zircon, and apatite) from rock blocks or rock powder. This process requires strict control of acid dissolution conditions to avoid interference with the mineral's isotopic composition, thereby ensuring the extracted minerals meet the required purity for dating. Following extraction, the mineral samples undergo further chemical purification to remove impurities that could affect isotope determination, ensuring highly accurate isotope ratio analysis.

[0046] The purified mineral samples are then sent to high-precision isotope analysis instruments (such as multi-collector mass spectrometers and laser mass spectrometers) for isotopic analysis. Based on different isotopic systems, the emplacement age of the magmatic rock can be determined. By analyzing the isotope ratios (U / Pb, Ar / Ar, etc.) in the magmatic rock samples, the emplacement time of the magmatic rock can be accurately determined, providing a scientific basis for the selection of samples for subsequent geochemical and cryochronological analyses. Combining these two methods allows for the development of multi-temperature stage coupled inversion techniques.

[0047] In order to improve the accuracy and reliability of whole-rock isotope dating analysis results, the standard error (SE) and confidence interval (CI) analysis methods were used to further screen and verify the samples.

[0048] The standard error measures the range of variation of the sample mean and reflects the accuracy of the sample estimate. Its calculation formula is:

[0049] in, s is the sample standard deviation, which measures the degree of dispersion of the data; n is the sample size, which represents the number of independently measured data points.

[0050] The confidence interval is used to indicate the uncertainty range of an estimated value, usually a 95% confidence interval, indicating that there is a 95% probability that the true value falls within the interval. The calculation formula is:

[0051] in, is the sample mean; t Determined by sample size and confidence level; SE is the standard error.

[0052] According to the analysis results of standard errors and confidence intervals, samples with smaller errors and narrower confidence intervals were selected for further geochemical analysis and isotope dating tests.

[0053] The zircon samples that have been U-Pb dated were analyzed by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to obtain high-precision Hf isotope compositions. The value changes significantly due to negative anomalies Transformed into positive anomaly , indicating that the lithosphere is thinning, mantle-derived materials are injected, and the asthenosphere is upwelling actively ( Figure 2 The emplacement age is combined with the preliminary classification of magmatic activity stages and the identification of asthenosphere upwelling. Samples before and after the asthenosphere upwelling are selected for deep mantle evolution inversion, and samples before the upwelling period are used for low-temperature thermochronological analysis.

[0054] This process ensures sample representativeness and effectively documents the temporal characteristics of regional lithospheric thinning and asthenosphere upwelling, providing key data for studying the initiation and duration of the thermal uplift, as well as the thermal evolution of the lithosphere and crust. Furthermore, the whole-rock isotope dating results provide the necessary temporal constraints for subsequent geochemical analysis and coupled inversion of multiple temperature stages.

[0055] S3. Geochemical analysis

[0056] 3.1 Major element analysis

[0057] First, major element analysis is performed on the igneous rock samples selected in steps 1 and 2, measuring the contents of various oxides (such as SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, and TiO2). This major element data can be used to determine the basic chemical characteristics of the rocks and classify them. During the analysis, standardized processing and reference to existing igneous rock databases can be used to identify the rock type and source. SiO2 content can be used to determine the acidity or alkalinity of the magma (Table 1). High SiO2 content (>65%) indicates acidic magma, while low SiO2 content (45-52%) indicates basic magma. The ratios of MgO, Fe2O3, and CaO help distinguish the magma source and its degree of evolution. Based on this comparison and evaluation, suitable samples are selected for subsequent testing.

[0058] 3.2 Identification of lithosphere thinning using trace element analysis

[0059] Taking the mantle-derived basic igneous rocks from different source areas in the study area as the research objects, through trace element analysis, we can provide key information for revealing the characteristics of the magma source area and the depth of mantle melting. The distribution of rare earth elements has strong geological stability, especially the ratio of light rare earth elements to heavy rare earth elements, which can effectively reflect the genesis and evolution of the magma source area. If the mantle source area of ​​igneous rocks in a certain area is initially a deep source area of ​​the lithosphere and gradually transforms to a shallow layer until it finally transforms into the asthenosphere, the lithosphere in the area will undergo thinning and be accompanied by the upwelling of the asthenosphere, because the normal asthenosphere will not melt until the thickness of the lithosphere is reduced to about 80 kilometers or less. The inversion of the lithosphere thinning process mainly consists of the following steps:

[0060] The enrichment and depletion information of rare earth and trace elements can be used to infer the genesis mechanism of the samples and the evolution process of the lithospheric mantle: (1) The characteristics of the magmatic rocks in the lithospheric mantle source area are analyzed by collecting lithospheric trace element data through literature research and database. The magmatic rocks derived from the lithospheric mantle usually show the characteristics of enriched large ion lithophile elements (LILE) and light rare earth elements (LREE), accompanied by significant negative anomalies of Nb, Ta, and Ti. In contrast, the magmatic rocks derived from the asthenospheric mantle show the enrichment of high field strength elements (HFSE) and heavy rare earth elements (HREE), light rare earth elements (LREE), and the anomalies of Nb, Ta, and Ti are not obvious. According to the age information of the samples, the variation intervals of the two source sample points are established in the original mantle spider diagram respectively ( Figure 3); (2) The trace element composition of the sample is usually determined by experimental analysis (such as ICP-MS, LA-ICP-MS) to obtain the mass fractions of 27 elements Rb, Ba, Th, U, Nb, Ta, K, Ce, La, Pb, Pr, Nd, Zr, Sm, Sr, P, Hf, Eu, Gd, Dy, Ti, Tb, Ho, Er, Yb, Tm, Lu (unit: ppm), and the measured sample element concentration values ​​are compared with the standardized values ​​of the primitive mantle (Formula 3); (3) By importing the standardized data into the OriginLab software, the primitive mantle standardized curves of rare earth and trace elements are generated according to the magmatic activity period analyzed in step 2. During the same magmatic activity period, if the number of magmatic rock samples from the lithospheric mantle source region is greater than that from the asthenospheric mantle source region, the mantle source region of this period is defined as the lithospheric mantle; conversely, if the number of magmatic rock samples from the asthenospheric mantle source region is greater, the mantle source region of this period is defined as the asthenospheric mantle; (4) According to the different depths and pressures of aluminum-rich minerals, mantle peridotite can be divided into different stable zones, from deep to shallow, namely garnet (>80km), spinel (30~80km) and plagioclase (<30km). Among them, spinel and garnet are two key mineral phases in the vertical section of the lithosphere, and they have significantly different distribution coefficients for rare earth elements. Spinel lherzolite is usually located below the crust at a depth of about 50km. In this stable zone, the heavy rare earth element Yb is strongly incompatible with spinel. Therefore, the melt in the spinel stable zone has a low Dy / Yb ratio (<1.5). As the depth increases, the lower part is garnet lherzolite. In this stable zone, Yb is strongly compatible with garnet, resulting in the melt produced by partial melting usually having a high Dy / Yb ratio (>2.5). By analyzing the systematic changes in the ratios of K / Yb and Dy / Yb, and using the mantle melting map to cast points, the source type, melting depth and degree of different igneous rocks can be determined ( Figure 4 ), further evidence of lithosphere thinning.

[0061]

[0062] Csample is the concentration of an element in the sample (ppm); Cprimitivemantle is the standard concentration of the element in the primitive mantle (usually taken from McDonough and Sun, 1995).

[0063] 3.3 Isotope Analysis (Sr-Nd-Hf)

[0064] By analyzing the Sr-Nd-Hf isotopic compositions of igneous rocks, combined with the temporal and spatial distribution of magmatic activity, we can reveal the timing and depth of lithospheric thinning, as well as the spatial characteristics of thermal anomalies. In particular, analyzing the genesis of igneous rocks can further clarify the interaction between the lithospheric and asthenospheric mantle during thinning, thus providing important insights into mantle dynamics and regional tectonic evolution.

[0065] First, the Sr-Nd-Hf isotope data of mantle-derived samples in the study area were collected through literature research and databases, and their ages were recorded. The ages were calculated using formulas 4, 5, and 6, respectively. ratio, and values, and make diagrams of their distribution characteristics in different mantle source regions and crustal materials ( Figure 5 ), which can be used to judge the process of lithosphere thinning. Magmatic rocks in the asthenosphere source region usually show The ratio is low (<0.705) and 、 The positive value (>0) reflects that it comes from the relatively primitive asthenospheric mantle, while the magmatic rocks in the lithospheric source region have a higher Ratio (>0.705) and and The negative anomaly (<0) reflects its long-term enrichment and evolution. During the thinning of the lithosphere, the upwelling of the asthenospheric mantle can lead to changes in the magma source, manifested as a shift in the Sr-Nd-Hf isotope composition of igneous rocks toward the asthenospheric mantle.

[0066]

[0067] Is the current sample 87 Sr / 86 Sr ratio; In the sample 87 Rr and 86 Sr The ratio of yes 87 The decay constant of Rr; t is the emplacement age of the sample, obtained by isotope dating.

[0068]

[0069] is the neodymium isotope ratio of the sample; is the neodymium isotope ratio of CHUR, which is approximately 0.512638; t is the time of emplacement of the sample (usually determined by isotope dating).

[0070]

[0071] is the hafnium isotope ratio of the sample; is the neodymium isotope ratio of CHUR, which is approximately 0.512638; t is the time of emplacement of the sample (usually determined by isotope dating).

[0072] As the lithosphere thins, the material of the asthenosphere mantle rises and participates in partial melting. The magma from the asthenosphere gradually becomes dominant, and its isotopic composition will show Reduce and and This change reflects the gradual transition of the magma source from the lithospheric mantle to the asthenospheric mantle, and is an important indicator of the lithospheric thinning process. This process can be seen in the path indicated by the arrow. Figure 5 It indicates that the isotopic composition of igneous rocks gradually shifts from the lithospheric mantle characteristics to the asthenospheric mantle characteristics.

[0073] Determine the Sr-Nd-Hf isotope ratio of the sample by mass spectrometry (such as TIMS or MC-ICP-MS), and calculate it based on the dating results of the sample in step 2. Ratio and 、 Value, calculate the data to the point to Figure 5 (1) If the sample data points are concentrated in the igneous rock area of ​​the lithosphere source region and show a high 87 Sr / 86 Sr ratio (about 0.706-0.708) and 、 The negative value is abnormal, which indicates that the magma mainly comes from the enriched lithospheric mantle, indicating that the lithosphere in the study area is relatively stable and has not yet undergone significant thinning; (2) As the lithosphere thins, the asthenosphere mantle material gradually rises and participates in the magma generation, which is manifested as the sample data points shifting towards the magmatic rock area of ​​the asthenosphere source. At this time, the magma 87 Sr / 86 The Sr ratio decreased to about 0.703-0.705, while 、 Positive values ​​indicate an increased contribution of the original characteristics of the asthenospheric mantle to the magma. If the data point is located in the transition zone between the lithosphere and asthenosphere source, it indicates that the magma may have been formed by a mixture of materials from both regions, further indicating that the lithosphere is thinning and is being influenced by upwelling asthenospheric material.

[0074] S4 Low-temperature thermochronological analysis and multi-thermochronological constraints on time-temperature history inversion

[0075] 4.1 (U-Th) / He low-temperature thermochronology analysis

[0076] (1) For the apatite or zircon crystals selected in the first step, single crystals with regular morphology and few inclusions are selected based on their transparency, shape, and inclusions. The single crystals can be rescreened under a stereomicroscope or polarizing microscope to minimize interference from foreign impurities or cracks. (2) The selected single crystals are placed in a small molybdenum cup or quartz tube and heated in a dedicated inert gas environment or vacuum environment (such as laser heating or resistance furnace heating) to release the He gas in the crystal. The released He gas is quantitatively measured using a high-precision mass spectrometer (such as a thermal ionization mass spectrometer or a static mass spectrometer). Generally, repeated heating is required to ensure complete He release. At the same time, standard samples (international or internal company standards) are used for process calibration, and instrument drift, background signal and other factors are corrected in a timely manner; (3) The same crystal or the same batch of crystals that have completed He release are taken, and the U, Th and Sm contents are measured by chemical digestion and inductively coupled plasma mass spectrometry (ICP-MS) or other equivalent means to ensure that the dissolution process is complete, and internal and external standard calibration methods (such as matching standard solutions or geological standards) are used to ensure measurement accuracy. When the U, Th and Sm contents are high or low, they can be adjusted to a concentration range suitable for ICP-MS analysis by dilution or concentration; (4) Based on the measured He content and U, Th and Sm concentration data, the (U-Th) / He age is calculated. t , calculation formula:

[0077]

[0078] in: t is the (U-Th) / He age of the sample; is the decay constant of the corresponding element; 4 He is the measured helium content; 238 U, 235 U, 232 Th is the content of uranium and thorium in the sample; 147 Sm is the content of samarium in the sample; S f is the decay factor of samarium.

[0079] 4.2 Multi-thermochronological constraints for time-temperature history inversion simulations

[0080] Using the software HeFTy, which has a thermal history simulation function, a comprehensive inversion of U-Pb, Ar-Ar, and (U-Th) / He age data was performed based on Monte Carlo and genetic algorithms. (1) Boundary constraints were imposed based on the multi-thermal chronological data obtained in steps S2 and S41: zircon U-Pb (700-900℃) for the high-temperature stage, biotite Ar-Ar (350-500℃) for the medium-temperature stage, and zircon and apatite (70-196℃) (U-Th) / He ages for the low-temperature stage; (2) The age data of the samples were input into the software separately, and relevant parameters (such as mineral closure temperature, annealing model, diffusion model, crystal size correction, etc.) were set according to the sample properties. The initial geothermal gradient, burial depth, and surface temperature conditions required for the simulation process were set, and reasonable prior information (such as constrained cooling paths, possible thermal events, etc.) was set based on the geothermal flow, tectonic background, or previous research results of the study area. According to the geological background and research objectives, it is necessary to select appropriate annealing models (such as apatite: Ketcham or Laslett model; zircon: different fission track annealing models) and He diffusion models (such as Farley model or Flowers model) for fitting; (3) Perform multiple iterative operations through the software to obtain the possible cooling path distribution and qualified path (U-Th) / He age data, etc. Compare and analyze the simulation curves or statistical results obtained in different iterative processes, such as the best fitting path, better fitting path, lower fitting path and key nodes of thermal history evolution (such as obvious cooling events or warming events), etc. ( Figure 6 If the simulation results deviate significantly from the geological background information, the a priori constraints should be appropriately modified or other thermochronological, structural geological, or petrographic evidence should be supplemented for comprehensive verification and correction to derive the cooling path or temperature-time (Tt) evolution curve.

[0081] S5. Time Series Analysis of Thermal Uplift Identification and Uplift Rate

[0082] Thermal uplift is the result of the combined effects of lithosphere thinning and asthenosphere upwelling ( Figure 8Its early stages are characterized by lithospheric thinning. During this period, deep magmatic activity is primarily driven by partial melting of the lithospheric mantle. The resulting mafic magmatic rocks exhibit geochemical characteristics and associated Sr-Nd-Hf isotopic compositions derived from a lithospheric mantle source. As the lithospheric mantle thins, the asthenospheric mantle upwells and partially melts, gradually shifting the source of the mafic magmatic rocks from the lithospheric mantle to the asthenospheric mantle. Gravitational isostatic adjustments in the crust following lithospheric thinning, accompanied by the action of the hot mantle, cause crustal rebound and thermal uplift, bringing deep samples into the shallow crust. During this process, cooling ages recorded in minerals provide an indicator of the onset of thermal uplift. In the later stages, as thermal uplift progresses and the decompression and cooling of the asthenospheric mantle are completed, the thermal uplift triggered by the asthenospheric upwelling leads to lithosphere regeneration and regional thermal subsidence. During this period, the cooling of shallow crustal rock samples slows for a period of time.

[0083] Based on the above background, thermal uplift can be effectively identified by combining the geochemical characteristics of the magma source area and low-temperature thermochronology techniques through the following methods:

[0084] 1. Judgment of time nodes:

[0085] Based on the inversion results of the cooling path or time-temperature (tT) evolution curve in step S4, when the curve shows a significant rapid cooling stage in the high temperature range, this usually indicates rapid crystallization of deep magma and emplacement of rock mass;

[0086] Subsequently, the cooling rate of the curve slows down in the medium temperature range and is coupled with the initial time of basic magma activity in the asthenosphere source area. This turning point represents the time node of lithospheric thinning and asthenosphere upwelling.

[0087] 2. Definition of the start and end of the heat treatment:

[0088] In the low temperature range, if the curve shows that the cooling rate accelerates again, the turning point marks the starting time of thermal uplift (t1, unit: Ma), and the corresponding temperature is recorded as T1 (unit: °C);

[0089] As time goes by, the cooling path will continue to maintain a rapid cooling trend until the late stage of geological evolution. Due to the effect of heat subsidence, the curve gradually shows a slowdown in cooling rate or even a rise in temperature. This turning point is defined as the end time t2 of thermal uplift, and the corresponding temperature is recorded as T2. Its cooling rate ( R C , unit: ℃ / Ma) is calculated using Formula 8. The geothermal gradient T of the study area at stages t1 and t2 is obtained through literature research. D1 and T D2(Unit: °C / Km), the thermal uplift height H (unit: Km) is calculated as formula 9, the thermal uplift rate (Unit: m / Ma) The calculation method is formula 10.

[0090] Cooling rate calculation formula:

[0091]

[0092] Thermal uplift height calculation formula:

[0093]

[0094] Thermal uplift rate calculation formula:

[0095]

[0096] Taking the Jiaobei and Sulu regions in eastern Shandong as an example,

[0097] Based on igneous rock zircon Values ​​and U-Pb age diagram ( Figure 2 ), showing that around 121Ma in the Early Cretaceous, the magmatic rocks in this region began to show geochemical characteristics of the asthenospheric mantle source. Through the analysis of trace elements in basic magmatic rocks, in the primitive mantle standardized trace element diagram ( Figure 3 ), it can be seen that around 121Ma, the trace element characteristics of magmatic rocks evolved from the island arc type of the lithospheric mantle to the ocean island type of the asthenospheric mantle. Figure 4 Evidence of rapid thinning of the lithospheric mantle and upwelling decompression melting of the asthenospheric mantle, and Figure 5 The characteristics of the intermediate magma source area transforming from lithospheric mantle to asthenospheric mantle indicate that during this period the region was in an extensional tectonic setting and the lithospheric mantle underwent rapid thinning.

[0098] Using the software HeFTy with thermal history simulation function, based on Monte Carlo and genetic algorithms, a comprehensive coupled inversion of U-Pb, Ar-Ar and (U-Th) / He multi-type age data was performed, and the simulation paths of multiple temperature stages were obtained ( Figure 6 ). Based on the optimal fitting results, 127–116 Ma was determined to be the regional thermal uplift period. The cooling rate of this stage was calculated to be 14.5°C / Ma using formulas 8, 9, and 10; combined with literature data, the geothermal gradient was 45°C / km at 127 Ma and 58°C / km at 116 Ma, and the thermal uplift height was calculated to be about 3.1 km, with a thermal uplift rate of 281.8 m / Ma. This process contributed to the sedimentary hiatus in the eastern Shandong region under the extensional background ( Figure 7 ).

[0099] Previous studies have shown, using qualitative or semi-quantitative methods, that during the Early Cretaceous (approximately 125–108 Ma), the lithosphere in the region rapidly thinned, with the asthenospheric mantle upwelling and decompression melting. This resulted in crustal rebound due to gravitational isostasis, a phenomenon known as thermal uplift. This result is consistent with the conclusions of this patent, demonstrating the high accuracy and reliability of the method employed. More importantly, this patent, through quantitative geochemical data, accurately identifies the process of thermal uplift triggered by lithosphere thinning and asthenospheric upwelling in an extensional tectonic setting. Furthermore, it accurately calculates the cooling rate, uplift height, and uplift rate during the thermal uplift period, providing a more direct and objective basis for identifying regional thermal uplift events in an extensional setting and reconstructing their tectonic setting.

[0100] Those skilled in the art will understand that the discussion of the above embodiments is merely illustrative and is not intended to limit the scope of the present invention to these examples. Within the spirit and principles of the present invention, the technical features of the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and many other variations exist for the various aspects of the present invention described above, which are not provided in detail for the sake of clarity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for identifying and reconstructing regional thermal uplift based on extensional tectonic background, characterized in that: The following steps are involved: S1. Rock sample collection and rock thin section preparation in the study area: Prioritize the collection of igneous rock samples in good preservation and formed during the study period. Prepare rock thin sections for petrographic analysis. Select basic igneous rocks suitable for deep mantle evolution inversion and deep-seated intrusive rock samples suitable for low-temperature thermochronology analysis. Fragment, remove alteration, and size-select these rocks to meet the requirements of subsequent mineral sorting and geochemical testing. S2. Whole-rock isotope dating: Separate target minerals such as zircon, apatite, feldspar, and biotite from the sample to ensure their purity meets isotope dating requirements. Analyze Ar-Ar and U-Pb isotope systems using a high-precision mass spectrometer and calculate ages. Reliable data are selected using error and confidence intervals to accurately date the intrusion time of the magmatic rock. LA-MC-ICP-MS analysis was then performed on the same zircon to obtain Hf isotope compositions, which were used to trace the magma source. Based on the intrusion age, the magmatic activity phases were preliminarily divided and the asthenospheric upwelling was identified. Samples from before and after the asthenospheric upwelling were used to invert deep mantle evolution, while samples from before the upwelling phase were used for low-temperature thermochronology analysis. S3. Geochemical analysis: Major element analysis: The igneous rock samples selected in steps S1 and S2 are analyzed for major elements to determine the rock type and basic chemical composition of the magma; Trace element analysis: The trace element data of the igneous rock samples are obtained, and the rare earth element (REE) and high field strength element (HFSE) data of the S31 intermediate-basic igneous rocks are combined with the changes in the K / Yb and Dy / Yb ratios to reveal the transformation of the magma source region and the thinning of the lithospheric mantle; Sr-Nd-Hf isotope analysis: By analyzing the Sr-Nd-Hf isotope composition of the basic igneous rocks and combining the spatiotemporal distribution and evolution characteristics of the magma, the time node of the lithospheric thinning is reconstructed, revealing the whole process of thermal uplift from initial lithospheric thinning to asthenospheric mantle upwelling; S4. Low-temperature thermochronological analysis and multi-thermal chronological constraint time-temperature history inversion: According to steps S2 and S3, deep-seated intrusive igneous rock samples that predate the lithospheric thinning and regional thermal uplift are selected, and apatite or zircon single crystals are selected. The He gas accumulated inside the crystals is released by a laser heating system and quantitatively measured by mass spectrometry. At the same time, the remaining crystals are analyzed by ICP-MS to determine the contents of U, Th, and Sm. The cooling age of the sample was calculated using an age formula. HeFTy software was used to perform a multi-thermal chronologically constrained time-temperature history inversion of the sample's time-temperature history. The boundary conditions were based on the closure temperatures of different chronological systems. Monte Carlo simulation was used to randomly simulate 100 time-temperature paths that met the conditions, and the optimal path was selected as the time-temperature curve of the rock mass's thermal evolution. S5. Time series analysis of thermal uplift identification and uplift rate: Determine the start and end times of thermal uplift, the cooling rate, the thermal uplift height, and the thermal uplift rate through the time nodes of lithosphere thinning and magma source area transformation in step S3, the temperature T and time t of the high and low temperature turning points of the temperature-time curve obtained in step S4, and the paleo-geothermal gradient TD.

2. The method for regional thermal uplift identification and reconstruction based on extensional tectonic background according to claim 1 is characterized in that: In step S2, the standard error calculation formula is: ; Among them, s is the sample standard deviation, which measures the degree of dispersion of the data; n is the sample size, which represents the number of independently measured data points; The confidence interval is calculated as follows: ; in, is the sample mean; t is determined by the sample size and confidence level; SE is the standard error.

3. The method for regional thermal uplift identification and reconstruction based on extensional tectonic background according to claim 1 is characterized in that: In step S4, The age formula is: ; Where: t is the sample age; is the decay constant of the corresponding element; is the measured helium content; is the content of uranium and thorium in the sample; is the content of samarium in the sample; S f is the decay factor of samarium.

4. The method for regional thermal uplift identification and reconstruction based on extensional tectonic background according to claim 1 is characterized in that: In step S4, the specific method of multi-thermal chronological constraints is as follows: the high temperature stage is constrained by zircon U-Pb age between 700 and 900 degrees Celsius, the medium temperature stage is constrained by biotite Ar-Ar age between 350 and 500 degrees Celsius, and the low temperature stage is constrained by zircon and apatite. Aged and restrained between 70 and 196 degrees Celsius.

5. The method for regional thermal uplift identification and reconstruction based on extensional tectonic background according to claim 1 is characterized in that: In step S5, the specific steps for judging the start and end time of thermal uplift are as follows: through the time-temperature curve of thermal evolution in step S4, the curve shows a rapid cooling in the high temperature interval, indicating deep magma crystallization and rock intrusion, and the cooling in the medium temperature interval slows down, and the turning point is coupled with the initial time of basic magma activity in the asthenosphere source area. This turning point serves as the time point of lithosphere thinning and asthenosphere upwelling, and the cooling in the low temperature interval accelerates again. This turning point is used as the starting time of thermal uplift. t 1 , at this time the high temperature record is T 1 After the turning point, the curve will continue to maintain a rapid cooling trend. After a geological period, the cooling rate will slow down or the temperature will rise due to thermal subsidence. This turning point is the end of the thermal uplift. t 2 The turning point low temperature record is T 2 .

6. The method for regional thermal uplift identification and reconstruction based on extensional tectonic background according to claim 1 is characterized in that: In step S5, the calculation formulas for cooling rate, thermal uplift height and thermal uplift rate are: Cooling rate calculation formula: ; in, Rc is the cooling rate, unit is ℃ / Ma; T 1 is the temperature at the beginning of thermal uplift, T 2 is the temperature at the end of thermal uplift, in °C; t 1 is the starting time of thermal uplift, t 2 is the end time of thermal uplift, unit: Ma; Thermal uplift height calculation formula: ; in, H is the thermal uplift height, in km; T 1 is the temperature at the beginning of thermal uplift, T 2 is the temperature at the end of thermal uplift, in °C; T D1 is the geothermal gradient at the onset of thermal uplift, T D2 is the geothermal gradient at the end of thermal uplift, in ℃ / Km; Thermal uplift rate calculation formula: ; in, v is the thermal uplift rate, in m / Ma; H is the thermal uplift height, in km; t 1 is the starting time of thermal uplift, t 2 is the end time of thermal uplift, unit: Ma.

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