Method for constructing initial model of geodynamic numerical simulation constrained by aeromagnetic inversion

Abstract

The application discloses a method for constructing an initial model of aeromagnetic inversion constrained geodynamic numerical simulation, and relates to the field of geophysics, which comprises the following steps: obtaining aeromagnetic anomaly data of a research area and performing three-dimensional inversion to obtain the distribution of underground medium magnetization intensity; converting the magnetization intensity into bulk magnetization and obtaining the average bulk magnetization of the lower crust through vertical statistics; estimating the relative content of ferromagnetic minerals based on an empirical relationship, combining rock sample determination results to determine a threshold value, and dividing the lower crust into ferromagnesian and felsic regions; according to the composition partition results, differentially assigning mechanical parameters and density parameters to the lower crust and lithospheric mantle, wherein the mechanical parameters are realized by adjusting the dislocation creep constitutive relation, and the density parameters are realized by introducing a composition-related correction term; and integrating the composition type, mechanical parameters and density parameters to construct an initial model of geodynamic numerical simulation. The application effectively reduces the subjectivity of parameter selection and improves the physical consistency and repeatability of the model.

Description

Technical Field

[0001] This invention relates to the field of geophysics, and in particular to a method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion. Background Technology

[0002] Geodynamic numerical simulation is a crucial technique for studying the structure and tectonic evolution of the continental lithosphere. The reliability of the simulation results highly depends on the rationality of the compositional structure, mechanical parameters, and density parameters of the lower crust and lithospheric mantle in the initial model. However, under current technological conditions, the construction of initial numerical simulation models often relies on empirical assumptions or parameter values ​​from existing literature, lacking direct and effective geophysical constraints on the compositional types and spatial variations of the lower crust. This reliance on subjective experience leads to a high degree of subjectivity in the initial model conditions, which in turn affects the physical consistency and repeatability of the simulation results.

[0003] Aeromagnetic data, due to its wide coverage and high spatial resolution, has unique advantages in revealing subsurface magnetic structures and can effectively reflect the distribution characteristics of ferromagnetic minerals in the lower crust. However, in current technologies, aeromagnetic inversion results are mostly used for qualitative or semi-quantitative interpretation of magnetic structures, generally only at the level of analyzing primary geophysical parameters such as magnetization intensity or magnetic susceptibility. They fail to establish a clear quantitative conversion relationship with the identification of lower crustal composition types, and even less so to systematically incorporate compositional information into the assignment process of mechanical and density parameters in the initial model of geodynamic numerical simulation.

[0004] Therefore, how to effectively utilize aeromagnetic inversion results to identify the types of lower crustal composition and systematically introduce them into the parameter construction process of the initial model for geodynamic numerical simulation is a key problem that has not yet been solved in the existing technology. Summary of the Invention

[0005] In view of this, to address the above problems, a method for constructing an initial model for geodynamic numerical simulation based on constraints from aeromagnetic inversion results is provided. By establishing a complete technical chain from aeromagnetic data to composition identification and then to the assignment of mechanical and density parameters, the aeromagnetic data inversion results are transformed into the composition type of the lower crust, and mechanical and density parameters are assigned accordingly to improve the physical rationality and repeatability of the initial model.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion, comprising the following steps:

[0008] We acquired aeromagnetic anomaly data of the study area and performed three-dimensional inversion to obtain the three-dimensional spatial distribution of induced magnetization intensity in the subsurface medium.

[0009] The induced magnetization intensity of the underground medium is converted into the volume magnetic susceptibility of the underground medium;

[0010] The volume magnetic susceptibility is vertically statistically averaged within the depth range of the lower crust to obtain the two-dimensional spatial distribution of the average volume magnetic susceptibility of the lower crust.

[0011] Based on the known empirical relationship between the average volumetric magnetic susceptibility of the lower crust and the relative abundance of ferromagnetic minerals, the two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust is estimated.

[0012] Based on the determination of ferromagnetic mineral content in the lower crust rock samples of the study area, the composition discrimination threshold is determined. The relative content of the lower crust ferromagnetic minerals is compared with the composition discrimination threshold, and the lower crust space is divided into ferromagnesian type lower crust region and felsic type lower crust region, thus obtaining the spatial partitioning results of lower crust composition type.

[0013] Based on the spatial partitioning results of the lower crust composition types, differentiated mechanical parameters are assigned to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, and differentiated values ​​are assigned to the density parameters of the lower crust and the lithospheric mantle.

[0014] The obtained spatial partitioning results, mechanical parameters, density parameters of the lower crust, and density parameters of the lithospheric mantle are jointly incorporated into the geodynamic numerical simulation to construct an initial geodynamic numerical simulation model that includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle.

[0015] As a further aspect of the present invention, the conversion relationship between the induced magnetization intensity of the underground medium and the volume magnetic susceptibility of the underground medium is as follows:

[0016] ;

[0017] in, For underground media in spatial coordinates The volume magnetic susceptibility at a given location is a dimensionless parameter. The value represents the induced magnetization intensity of the underground medium at the corresponding location, expressed in units of... ; ρ is the magnetic permeability in vacuum; The background geomagnetic field intensity of the study area.

[0018] As a further aspect of the present invention, the calculation formula for the vertical statistical averaging of the volume magnetic susceptibility within the lower crust depth range is as follows:

[0019] ;

[0020] in, In horizontal position From depth arrive The average volumetric magnetic susceptibility of the lower crust within the range; and These are the upper boundary depth of the lower crust and the lower boundary depth of the lower crust, respectively.

[0021] As a further aspect of the present invention, the two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust is estimated using the following formula:

[0022] ;

[0023] in, The relative abundance of ferromagnetic minerals in the lower crust; The empirical conversion factor between bulk magnetic susceptibility and the relative content of ferromagnetic minerals is 0.033.

[0024] As a further aspect of the present invention, the lower crustal rock sample in the study area is an exposed lower crustal rock sample within the study area, and the formula for calculating the composition discrimination threshold is:

[0025] ;

[0026] in, The component discrimination threshold; Number of rock samples; For the first The relative content of ferromagnetic minerals measured in each rock sample.

[0027] As a further aspect of the present invention, when dividing the lower crustal space into a ferromagnesian type lower crustal region and a felsic type lower crustal region, if In this case, the lower crustal space is identified as a ferromagnesian type lower crustal region; if In this case, the lower crust space is identified as a felsic type lower crust region.

[0028] As a further aspect of the present invention, when assigning differentiated mechanical parameters to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, the viscous deformation of the lower crust is described by a dislocation creep constitutive relation, wherein:

[0029] ;

[0030] In the formula, Strain rate, representing the rate of rock deformation; The equivalent deviatoric stress that drives rock deformation; As a pre-index factor; Stress index; To activate energy; This represents the pressure value of the confining pressure of the rock. To activate the volume; This is the universal gas constant; This refers to absolute temperature.

[0031] As a further aspect of the present invention, when assigning differentiated values ​​to the density parameters of the lower crust, a reference density of the lower crust is selected. As a baseline density, it is combined with a component-related density correction term. Calculate the actual density of the lower crust. The calculation formula is:

[0032] ;

[0033] Among them, the lower crust reference density Take as When the Earth's crust is identified as a ferromagnesian type lower crustal region, a positive density correction value is used. This makes the actual density of the lower crust... Increase; when the lower crust is identified as a felsic type lower crust region, take the negative density correction value. This makes the actual density of the lower crust... Decrease.

[0034] As a further aspect of the present invention, when differentiating the density parameters of the lithospheric mantle, the baseline density of the lithospheric mantle is... Using expressions related to temperature and pressure:

[0035] ;

[0036] in, The reference density for the lithospheric mantle is given by a value of [value missing]. ; For reference temperature, the value is [value to be filled in]. ; For reference pressure, the value is [value to be filled in]. ; The mantle temperature at different depths of the mantle; Mantle pressure at different depths of the mantle; The coefficient of thermal expansion is denoted as , and its value is . ; The compressibility factor is denoted by , and its value is . ;

[0037] Based on lithospheric mantle baseline density Combined with component-related density correction terms The actual density of the lithospheric mantle was calculated. The calculation formula is:

[0038] ;

[0039] In the lithospheric mantle located beneath the ferromagnesian lower crust, the heavier iron elements are extracted into the lower crust, resulting in a negative density correction value. This makes the actual density of the lithospheric mantle... Decrease; In the lithospheric mantle located beneath the felsic lower crust, heavier iron is retained more in the lithospheric mantle, so a positive density correction value is used. This makes the actual density of the lithospheric mantle... Increase.

[0040] As a further aspect of the present invention, when constructing an initial geodynamic numerical simulation model that includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle, the spatial partitioning results of the lower crust composition type are introduced into the model as material type identifiers to define the rheological models, mechanical parameter sets, and densities of the lower crust and lithospheric mantle used in different spatial units; the mechanical parameters of the lower crust and lithospheric mantle are constructed as a spatially partitioned mechanical parameter field to control the deformation mode and intensity distribution of the lower crust and lithospheric mantle; the spatial distribution of the actual density parameters of the lower crust and lithospheric mantle is used as the initial density field of the lithosphere system and introduced into the model to characterize the buoyancy and gravity effects of the lower crust and lithospheric mantle, thus forming an initial model for geodynamic numerical simulation calculation.

[0041] Compared with existing technologies, the method for constructing an initial model for geodynamic numerical simulation based on constraints from aeromagnetic inversion results provided by this invention has the following advantages:

[0042] 1. A quantitative constraint relationship was established between the aeromagnetic inversion results and the composition type of the lower crust.

[0043] By performing three-dimensional inversion of aeromagnetic anomalies, converting magnetization intensity to volume magnetic susceptibility, and performing vertical statistical processing of the magnetic susceptibility of the lower crust, combined with the empirical relationship between volume magnetic susceptibility and the relative content of ferromagnetic minerals, spatial discrimination of the ferromagnetic and felsic composition types of the lower crust can be achieved.

[0044] 2. The composition type of the lower crust is directly incorporated into the mechanical parameter assignment process of the initial model of the geodynamic numerical simulation.

[0045] Based on the composition type of the lower crust, differentiated rheological models and mechanical parameters are assigned to the lower crust and its synergistic lithospheric mantle medium. This allows the differences in lower crust composition to be incorporated into the initial model of geodynamic numerical simulation in the form of parameters, breaking through the assumption of spatial homogeneity of the mechanical properties of the lower crust in traditional models.

[0046] 3. The composition-related assignment of density parameters of the lower crust and its underlying lithospheric mantle was realized.

[0047] Based on the determination of the lower crust composition type, the density of the lower crust and the density of the lithospheric mantle are assigned different values ​​to make the iron-magnesian and felsic lower crust regions exhibit different physical characteristics in terms of density parameters, and to reflect the influence of the difference in lower crust composition on the density structure of the underlying lithospheric mantle.

[0048] 4. A systematic method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion results has been developed.

[0049] By coordinating the incorporation of lower crustal composition types, mechanical parameters, and density parameters of the lower crust and lithospheric mantle into the initial model construction process of geodynamic numerical simulation, the subjectivity of initial model parameter selection is reduced, the physical consistency and repeatability of model construction are improved, and the application value of aeromagnetic data in the field of geodynamic numerical simulation is expanded.

[0050] These or other aspects of the invention will become more apparent from the following description of embodiments. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. In the drawings:

[0052] Figure 1 This is a flowchart of a method for constructing an initial model for geodynamic numerical simulation with aeromagnetic inversion constraints according to the present invention.

[0053] Figure 2 This is a sub-flowchart of the lower crust composition discrimination and partitioning in the initial model construction method of geodynamic numerical simulation with aeromagnetic inversion constraints according to the present invention.

[0054] Figure 3 This is a flowchart illustrating the assignment of mechanical parameters in a method for constructing an initial model for geodynamic numerical simulation with aeromagnetic inversion constraints according to the present invention. Detailed Implementation

[0055] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0056] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0057] See Figures 1 to 3 As shown, one embodiment of the present invention provides a method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion, comprising the following steps:

[0058] Step S10: Obtain aeromagnetic anomaly data of the study area and perform three-dimensional inversion to obtain the three-dimensional spatial distribution of the induced magnetization intensity of the underground medium.

[0059] This step involves acquiring and 3D inverting aeromagnetic anomaly data. Aeromagnetic anomaly data for the study area is acquired and then processed to be converted to geomagnetic poles. Since regional rock remanence is difficult to measure and acquire, this embodiment employs existing 3D aeromagnetic inversion technology to perform 3D inversion on the processed aeromagnetic anomaly data, ignoring the influence of remanence, to obtain the induced magnetization intensity of the subsurface medium. The three-dimensional spatial distribution, in units of .

[0060] Step S20: Convert the induced magnetization intensity of the underground medium into the volume magnetic susceptibility of the underground medium.

[0061] This step involves the conversion of magnetization intensity to volume magnetic susceptibility. The induced magnetization intensity of the subsurface medium obtained in step S10 is used as the basis for this conversion. The three-dimensional spatial distribution of the subsurface medium, assuming that magnetization is mainly induced magnetization and the influence of remanent magnetization is negligible, converts the induced magnetization intensity into the volume susceptibility of the subsurface medium. The conversion relationship between the induced magnetization intensity of the underground medium and its volume magnetic susceptibility is as follows:

[0062] ;

[0063] in, For underground media in spatial coordinates The volume magnetic susceptibility at a given location is a dimensionless parameter. The value represents the induced magnetization intensity of the underground medium at the corresponding location, expressed in units of... ; ρ is the magnetic permeability in vacuum; The background geomagnetic field intensity of the study area.

[0064] By using the conversion relationship of volume magnetic susceptibility, the induced magnetization field in the three-dimensional aeromagnetic inversion results can be uniformly converted into a volume magnetic susceptibility field with clear physical meaning, thereby obtaining the three-dimensional spatial distribution of the volume magnetic susceptibility of the subsurface medium, providing basic parameters for statistical analysis and composition identification of the lower crust magnetic field.

[0065] Step S30: Perform vertical statistical averaging on the volume magnetic susceptibility within the depth range of the lower crust to obtain the two-dimensional spatial distribution of the average volume magnetic susceptibility of the lower crust.

[0066] This step involves the vertical statistical processing of the magnetic susceptibility of the lower crust. Within the corresponding depth range of the lower crust... Internal, volume magnetic susceptibility By performing integration or statistical averaging along the vertical direction, the two-dimensional spatial distribution of the mean volumetric magnetic susceptibility of the lower crust is obtained. The formula for calculating the vertical statistical average of the volume magnetic susceptibility within the lower crustal depth range is as follows:

[0067] ;

[0068] in, In horizontal position From depth arrive The average volumetric magnetic susceptibility of the lower crust within the range; and These are the upper boundary depth of the lower crust and the lower boundary depth of the lower crust, respectively.

[0069] Step S40: Based on the known empirical relationship between the average volumetric magnetic susceptibility of the lower crust and the relative content of ferromagnetic minerals, estimate the two-dimensional spatial distribution of the relative content of ferromagnetic minerals in the lower crust.

[0070] This step is a quantitative estimation of the relative abundance of ferromagnetic minerals. It is based on the average volumetric magnetic susceptibility of the lower crust. Based on the known empirical relationship between bulk magnetic susceptibility and the relative abundance of ferromagnetic minerals, the relative abundance of ferromagnetic minerals in the lower crust is estimated. .

[0071] In this embodiment, the two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust is estimated using the following formula:

[0072] ;

[0073] in, The relative abundance of ferromagnetic minerals in the lower crust; The empirical conversion factor between bulk magnetic susceptibility and the relative abundance of ferromagnetic minerals is 0.033. This formula yields the two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust.

[0074] Step S50: Based on the determination results of ferromagnetic mineral content in the lower crust rock samples of the study area, determine the composition discrimination threshold, compare the relative content of the lower crust ferromagnetic minerals with the composition discrimination threshold, divide the lower crust space into ferromagnesian type lower crust region and felsic type lower crust region, and obtain the spatial partitioning results of lower crust composition type.

[0075] This step involves identifying the compositional type and spatially partitioning of the lower crust. The lower crustal rock samples in the study area are those exposed within the study area. The formula for calculating the compositional identification threshold is:

[0076] ;

[0077] in, The component discrimination threshold; Number of rock samples; For the first The relative content of ferromagnetic minerals measured in each rock sample.

[0078] The relative content of the lower crustal ferromagnetic minerals The component discrimination threshold When making comparisons, if In this case, the lower crustal space is identified as a ferromagnesian type lower crustal region; if If so, the lower crust space is identified as a felsic type lower crust region; the lower crust space is divided into a ferromagnesian type lower crust region and a felsic type lower crust region, thus obtaining the spatial zoning results of the lower crust composition type.

[0079] Step S60: Based on the spatial partitioning results of the lower crust composition types, assign differentiated mechanical parameters to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, and assign differentiated values ​​to the density parameters of the lower crust and the lithospheric mantle.

[0080] This step involves assigning values ​​to lithospheric mechanical parameters, lower crust density, and lithospheric mantle density based on the composition type of the lower crust.

[0081] In this embodiment, when assigning differentiated mechanical parameters to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, the viscous deformation of the lower crust is described by a dislocation creep constitutive relation, wherein:

[0082] ;

[0083] In the formula, Strain rate, representing the rate of rock deformation; The equivalent deviatoric stress that drives rock deformation; As a pre-index factor; Stress index; To activate energy; This represents the pressure value of the confining pressure of the rock. To activate the volume; This is the universal gas constant; This refers to absolute temperature.

[0084] For ferromagnesian lower crust regions, by selecting a smaller pre-index factor Larger activation energy and activation volume and a large stress index This adjustment causes the lower crust and lithospheric mantle in the corresponding regions to exhibit higher equivalent viscosity and yield strength. Conversely, for regions with felsic lower crust, the opposite parameter adjustment results in lower equivalent viscosity and yield strength in the lower crust and lithospheric mantle, reflecting the mechanical differences in the lower crust and lithospheric mantle caused by different lower crustal composition types. The proposed correction direction aligns with the physical laws governing lithospheric composition variations.

[0085] In this embodiment, when assigning differentiated values ​​to the density parameter of the lower crust, a reference density of the lower crust is selected. As a baseline density, it is combined with a component-related density correction term. Calculate the actual density of the lower crust. The calculation formula is:

[0086] ;

[0087] Among them, the lower crust reference density Take as When the Earth's crust is identified as a ferromagnesian type lower crustal region, a positive density correction value is used. This makes the actual density of the lower crust... Increase; when the lower crust is identified as a felsic type lower crust region, take the negative density correction value. This makes the actual density of the lower crust... The density correction direction aligns with the physical law that the density of the ferromagnesian lower crust is higher than that of the felsic lower crust.

[0088] In this embodiment, when differentiating the density parameters of the lithospheric mantle, the baseline density of the lithospheric mantle is... Using expressions related to temperature and pressure:

[0089] ;

[0090] in, The reference density for the lithospheric mantle is given by a value of [value missing]. ; For reference temperature, the value is [value to be filled in]. ; For reference pressure, the value is [value to be filled in]. ; The mantle temperature at different depths of the mantle; Mantle pressure at different depths of the mantle; The coefficient of thermal expansion is denoted as , and its value is . ; The compressibility factor is denoted by , and its value is . ;

[0091] Based on lithospheric mantle baseline density Combined with component-related density correction terms The actual density of the lithospheric mantle was calculated. The calculation formula is:

[0092] ;

[0093] In the lithospheric mantle located beneath the ferromagnesian lower crust, the heavier iron elements are extracted into the lower crust, resulting in a negative density correction value. This makes the actual density of the lithospheric mantle... Decrease; In the lithospheric mantle located beneath the felsic lower crust, heavier iron is retained more in the lithospheric mantle, so a positive density correction value is used. This makes the actual density of the lithospheric mantle... The correction direction is consistent with the physical characteristics of changes in the composition of the lithospheric mantle.

[0094] Step S70: The obtained spatial partitioning results, mechanical parameters, density parameters of the lower crust, and density parameters of the lithospheric mantle are jointly introduced into the geodynamic numerical simulation to construct an initial geodynamic numerical simulation model that includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle.

[0095] This step involves constructing the initial model for geodynamic numerical simulation. When constructing the initial model, which includes the compositional differences, mechanical properties, and density structure of the lower crust and lithospheric mantle, the spatial partitioning results of the lower crustal composition types are introduced into the model as material type identifiers. This is used to define the rheological models, mechanical parameter sets, and densities of the lower crust and lithospheric mantle used in different spatial units. The mechanical parameters of the lower crust and lithospheric mantle are constructed as a spatially partitioned mechanical parameter field to control the deformation patterns and intensity distribution of the lower crust and lithospheric mantle. The spatial distribution of the actual density parameters of the lower crust and lithospheric mantle is used as the initial density field of the lithospheric system and introduced into the model to characterize the buoyancy and gravity effects of the lower crust and lithospheric mantle, thus forming the initial model for geodynamic numerical simulation calculations.

[0096] In this embodiment, the initial model for geodynamic numerical simulation, which includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle, includes the following steps:

[0097] Step S701: Establish a three-dimensional spatial mesh and material type identifier.

[0098] First, based on the study area and the resolution requirements of the research objectives, a three-dimensional spatial grid for the geodynamic model is established. Each grid cell has corresponding spatial coordinates. Then, the obtained spatial partitioning results of crustal composition types are mapped onto a 3D mesh. The spatial partitioning results of crustal composition types are identified by a grid that marks each horizontal location. Two-dimensional map of the lower crust belonging to the ferromagnesian or felsic type lower crust region.

[0099] Then, the depth range located in the lower crustal strata... Each grid cell, based on the horizontal coordinate The compositional zoning map is queried, and a material type identifier is assigned. For each grid cell located in the lithospheric mantle layer, a corresponding material identifier is assigned based on the material type of the lower crust unit directly above it. By assigning material identifiers, each grid cell in the model has a clear identity, indicating its composition and stratum.

[0100] Step S702: Construct a spatially differentiated mechanical parameter field.

[0101] In the governing equations of the numerical simulation, the dislocation creep constitutive relation is adopted: To describe the viscoplastic deformation of the lithosphere, a lookup table of mechanical parameters corresponding to material identifiers is established according to the assignment rules; the mechanical parameter lookup table is shown in Table 1.

[0102] Table 1 Mechanical Parameter Lookup Table

[0103] Material Identifier Geological meaning Pre-index factor ( ) Stress index ( ) Activation energy ( ) 1 Ferromagnetic lower crust (Smaller value) (Larger value) (Larger value) 2 Euclidean lower crust (Larger value) (Smaller value) (Smaller value) 3 The mantle corresponding to the ferromagnesian lower crust (Smaller value) (Larger value) (Larger value) 4 The mantle corresponding to the felsic lower crust (Larger value) (Smaller value) (Smaller value)

[0104] Among them, material identifier 1 represents the ferromagnesian lower crust, that is, the ferromagnesian type lower crust region; material identifier 2 represents the felsic lower crust, that is, the felsic type lower crust region; material identifier 3 represents the lithospheric mantle unit corresponding to the ferromagnesian lower crust; and material identifier 4 represents the lithospheric mantle unit corresponding to the felsic lower crust.

[0105] At the start of the simulation, based on the material type identifier of each mesh element, the corresponding set of mechanical parameters is retrieved from the lookup table, forming a non-uniform mechanical parameter field in the entire model space that strictly corresponds to the composition partition.

[0106] Step S703: Construct the initial density field of spatial differentiation.

[0107] First, the lower crust density field is calculated. Specifically, the initial density is calculated for each lower crust grid cell according to the assignment rules. The density value is obtained by adding a composition correction term to the reference density, i.e.: Density correction value for the lower crustal region of the ferromagnesian type (material identifier 1) A positive value indicates the density correction value for the lower crustal region of the felsic type (material identifier 2). It is a negative value.

[0108] Secondly, the density field of the lithospheric mantle is calculated. This is done by using the depth and geothermal gradient of each lithospheric mantle grid cell. Calculate the baseline density unaffected by composition. At the baseline density Based on this, add component correction items according to the rules. Through The actual density of the lithospheric mantle was calculated. In the lithospheric mantle located beneath the ferromagnesian lower crust, the heavier iron elements are partially extracted into the lower crust, and a negative density correction value is taken. This makes the actual density of the lithospheric mantle... Decrease; In the lithospheric mantle located beneath the felsic lower crust, heavier iron is retained more in the lithospheric mantle, so a positive density correction value is used. This makes the actual density of the lithospheric mantle... Increase.

[0109] Finally, the calculated lower crust density field and lithospheric mantle density field are combined to form a non-uniform three-dimensional initial density field covering the entire lithosphere model.

[0110] Step S704: Output of the initial model for geodynamic numerical simulation.

[0111] The data generated in steps S701-S703 are integrated into the numerical simulation program, outputting mesh information, mechanical parameter fields, and an initial density field. The mesh information includes spatial coordinates and material type identifiers; the mechanical parameter fields are dynamically linked to the material identifiers via a lookup table; and the initial density field serves as a static three-dimensional data field input. Ultimately, an initial geodynamic numerical simulation model is generated that can be directly used for dynamic evolution simulation.

[0112] The present invention provides a method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion. This method utilizes three-dimensional inversion of aeromagnetic anomalies, conversion of magnetization intensity to volume susceptibility, and vertical statistical processing of the lower crust's magnetic susceptibility. Combined with the empirical relationship between volume magnetic susceptibility and the relative abundance of ferromagnetic minerals, it achieves spatial discrimination of the lower crust's ferromagnetic and felsic composition types. Based on the lower crust composition type, differentiated rheological models and mechanical parameters are assigned to the lower crust and its interacting lithospheric mantle medium. This allows the compositional differences of the lower crust to be incorporated into the initial model of geodynamic numerical simulation in the form of parameters, breaking through the assumption of spatial homogeneity of the lower crust's mechanical properties in traditional models.

[0113] This invention, based on the determination of the lower crust composition type, assigns differentiated values ​​to the lower crust density and lithospheric mantle density, allowing the ferromagnesian and felsic lower crust regions to exhibit different physical characteristics in terms of density parameters. This also reflects the influence of lower crust composition differences on the density structure of the underlying lithospheric mantle. By co-introducing the lower crust composition type, mechanical parameters, and density parameters of the lower crust and lithospheric mantle into the initial model construction process of geodynamic numerical simulation, the subjectivity of initial model parameter selection is reduced, the physical consistency and repeatability of model construction are improved, and the application value of aeromagnetic data in the field of geodynamic numerical simulation is expanded.

[0114] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion, characterized in that, Includes the following steps: We acquired aeromagnetic anomaly data of the study area and performed three-dimensional inversion to obtain the three-dimensional spatial distribution of induced magnetization intensity in the subsurface medium. The induced magnetization intensity of the underground medium is converted into the volume magnetic susceptibility of the underground medium; The volume magnetic susceptibility is vertically statistically averaged within the depth range of the lower crust to obtain the two-dimensional spatial distribution of the average volume magnetic susceptibility of the lower crust. Based on the known empirical relationship between the average volumetric magnetic susceptibility of the lower crust and the relative abundance of ferromagnetic minerals, the two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust is estimated. Based on the determination of ferromagnetic mineral content in the lower crust rock samples of the study area, the composition discrimination threshold is determined. The relative content of the lower crust ferromagnetic minerals is compared with the composition discrimination threshold, and the lower crust space is divided into ferromagnesian type lower crust region and felsic type lower crust region, thus obtaining the spatial partitioning results of lower crust composition type. Based on the spatial partitioning results of the lower crust composition types, differentiated mechanical parameters are assigned to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, and differentiated values ​​are assigned to the density parameters of the lower crust and the lithospheric mantle. The obtained spatial partitioning results, mechanical parameters, density parameters of the lower crust, and density parameters of the lithospheric mantle are jointly incorporated into the geodynamic numerical simulation to construct an initial geodynamic numerical simulation model that includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle.

2. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 1, characterized in that, The conversion relationship between the induced magnetization intensity of the underground medium and the volume magnetic susceptibility of the underground medium is as follows: ； in, For underground media in spatial coordinates The volume magnetic susceptibility at a given location is a dimensionless parameter. The value represents the induced magnetization intensity of the underground medium at the corresponding location, expressed in units of... ; ρ is the magnetic permeability in vacuum; The background geomagnetic field intensity of the study area.

3. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 2, characterized in that, The formula for calculating the vertical statistical average of the volume magnetic susceptibility within the lower crust depth range is as follows: ； in, In horizontal position From depth arrive The average volumetric magnetic susceptibility of the lower crust within the range; and These are the upper boundary depth of the lower crust and the lower boundary depth of the lower crust, respectively.

4. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 3, characterized in that, The two-dimensional spatial distribution of the relative abundance of ferromagnetic minerals in the lower crust is estimated using the following formula: ； in, The relative abundance of ferromagnetic minerals in the lower crust; The empirical conversion factor between bulk magnetic susceptibility and the relative content of ferromagnetic minerals is 0.

033.

5. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 4, characterized in that, The lower crustal rock samples in the study area are those exposed within the study area. The formula for calculating the composition discrimination threshold is as follows: ； in, The component discrimination threshold; Number of rock samples; For the first The relative content of ferromagnetic minerals measured in each rock sample.

6. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 5, characterized in that, When dividing the lower crust into ferromagnesian and felsic lower crust regions, if In this case, the lower crustal space is identified as a ferromagnesian type lower crustal region; if In this case, the lower crust space is identified as a felsic type lower crust region.

7. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 6, characterized in that, When assigning differentiated mechanical parameters to the lower crust and lithospheric mantle in the initial model of geodynamic numerical simulation, the viscous deformation of the lower crust is described by a dislocation creep constitutive relation, wherein: ； In the formula, Strain rate, representing the rate of rock deformation; The equivalent deviatoric stress that drives rock deformation; As a pre-index factor; Stress index; To activate energy; This represents the pressure value of the confining pressure of the rock. To activate the volume; This is the universal gas constant; This refers to absolute temperature.

8. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 7, characterized in that, When assigning differentiated values ​​to the density parameters of the lower crust, a reference density of the lower crust is selected. As a baseline density, it is combined with a component-related density correction term. Calculate the actual density of the lower crust. The calculation formula is: ； Among them, the lower crust reference density Take as When the Earth's crust is identified as a ferromagnesian type lower crustal region, a positive density correction value is used. This makes the actual density of the lower crust... Increase; when the lower crust is identified as a felsic type lower crust region, take the negative density correction value. This makes the actual density of the lower crust... Decrease.

9. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 7, characterized in that, When differentiating the density parameters of the lithospheric mantle, the baseline density of the lithospheric mantle... Using expressions related to temperature and pressure: ； in, The reference density for the lithospheric mantle is given by a value of [value missing]. ; For reference temperature, the value is [value to be filled in]. ; For reference pressure, the value is [value to be filled in]. ; The mantle temperature at different depths of the mantle; Mantle pressure at different depths of the mantle; The coefficient of thermal expansion is denoted as , and its value is . ; The compressibility factor is denoted by , and its value is . ; Based on lithospheric mantle baseline density Combined with component-related density correction terms The actual density of the lithospheric mantle was calculated. The calculation formula is: ； In the lithospheric mantle located beneath the ferromagnesian lower crust, the heavier iron elements are extracted into the lower crust, resulting in a negative density correction value. This makes the actual density of the lithospheric mantle... Decrease; In the lithospheric mantle located beneath the felsic lower crust, heavier iron is retained more in the lithospheric mantle, so a positive density correction value is used. This makes the actual density of the lithospheric mantle... Increase.

10. The method for constructing an initial model for geodynamic numerical simulation constrained by aeromagnetic inversion as described in claim 1, characterized in that, When constructing the initial model for geodynamic numerical simulation that includes the differences in composition, mechanical properties, and density structure of the lower crust and lithospheric mantle, the spatial partitioning results of the lower crust composition type are introduced into the model as material type identifiers to define the rheological models, mechanical parameter sets, and densities of the lower crust and lithospheric mantle used in different spatial units. The mechanical parameters of the lower crust and lithospheric mantle are constructed as a spatially partitioned mechanical parameter field to control the deformation mode and intensity distribution of the lower crust and lithospheric mantle. The spatial distribution of the actual density parameters of the lower crust and lithospheric mantle is used as the initial density field of the lithosphere system and introduced into the model to characterize the buoyancy and gravity effects of the lower crust and lithospheric mantle, thus forming the initial model for geodynamic numerical simulation calculation.

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