Method for large-scale thematic mapping of denudation depths

Abstract

The present invention relates to denudation depth mapping. Disclosed is a method for large-scale thematic mapping of denudation depths. The method comprises: creating a site layout and route layout rule, a field sampling rule, a field observation and recording rule and a mineral separation rule for a study area; using a thermochronological study method to test and analyze a target mineral selected from each field work site; inputting analysis data into improved Low-T Thermo software to perform thermal-evolution history simulation analysis and denudation depth calculation, so as to obtain a denudation depth at each field work site; drawing a denudation depth contour map of the study area on the basis of the denudation depth at each field work site; and using a large-scale regional geological map of a standard map sheet of the study area as a base map, and superimposing the base map and the denudation depth contour map, so as to obtain a denudation depth map of the study area. The present invention can realize the mapping of denudation depths of geological bodies with a large scale, such as 1:50,000 and 1:200,000, using a standardized base map.

Description

A large-scale thematic mapping method for erosion depth

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 13, 2023, with application number 202311174354.3 and invention name “A large-scale erosion depth thematic mapping method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the field of erosion depth mapping, and in particular to a large-scale erosion depth thematic mapping method. Background Art

[0003] After the formation of a geological body, it is difficult for it to remain stationary in the long geological history. It usually moves due to tectonic action. The movement mode is horizontal and vertical. The horizontal movement of geological bodies is more valued in the field of geotectonic research, while in regional geological research and mineral deposit research, people are more concerned about the vertical movement of geological bodies. Intrusive rocks, metamorphic rocks, and metal deposits are usually formed several kilometers to tens of kilometers underground. Because of the late tectonic action, the geological body is uplifted and then exposed due to erosion and excavation. Studying the uplift and erosion and excavation process of geological bodies has the dual significance of revealing the regional geological evolution history (geotectonics) and studying the mineralization laws to promote mineral exploration. Specifically: (1) Regional geological significance: The uplift of geological bodies is usually caused by tectonic action. Studying the uplift and erosion and excavation process of geological bodies can invert the nature, scale and action process of tectonic events, thereby providing qualitative and quantitative constraints on the regional geological evolution process. (2) Research significance of the formation, preservation and change laws of mineral deposits. Mineral deposit research must not only focus on the origin and formation of mineral deposits, but also consider their preservation and changes after formation. The genetic type, production characteristics, tectonic activity, paleoclimate and paleoenvironment, uplift, and denudation of different mineral deposits all contribute to factors influencing their preservation and changes. Generally speaking, changes in mineral deposits are primarily due to changes in the deposits and ore bodies themselves, as well as changes in the environment and spatial location of the deposits. The preservation of mineral deposits is largely determined by the weathering and denudation history of the overlying rocks, and the formation of large mineral deposits is closely linked to the preservation conditions of their tectonic environment. By quantitatively calculating the uplift and denudation of mineral deposits discovered within established mineralized belts and regional geological bodies, we can provide a comprehensive assessment of the preservation and changes of mineral deposits within these belts, guiding regional mineral exploration and prospecting.

[0004] From the above, it can be seen that carrying out regional erosion depth mapping and more accurately depicting the changes in erosion depth in different parts of the region not only has theoretical significance for regional geological evolution research, but also has practical value for regional mineral exploration breakthroughs.

[0005] Furthermore, if erosion depth mapping, similar to the 1:50,000 / 1:200,000 / 1:250,000 regional surveys, could be conducted nationwide, or even globally, it would provide a comprehensive understanding of the vertical evolution of the Earth's surface. This would allow for the inversion of the Earth's deep tectonic evolutionary history and the exploration of the constraints of topographic and geomorphological changes on changes in the hydrosphere and atmosphere, providing a new avenue for studying the coordinated evolution of Earth's multiple spheres. Thermochronological geological mapping includes regional uplift rate maps, regional erosion rate maps, and regional erosion depth (amount of erosion) maps. Internationally, such mapping is performed over large areas, often covering an island or even an entire country, resulting in small-scale maps that are relatively easy to implement. However, in terms of practicality, these maps are limited to observing general trends within large regions and lack much practical value. While China has produced numerous achievements in thermochronological research, thermochronological mapping is rare. Only sporadic thermochronological maps of mining areas have been published, all of which are small-scale, irregular, and non-standard.

[0006] Currently, no one, either domestically or internationally, has conducted erosion depth mapping of geological bodies at large scales, such as 1:50,000 and 1:200,000, with standardized base maps. Therefore, there is an urgent need to explore methods for erosion depth mapping at large scales, such as 1:50,000, 1:200,000, and 1:250,000, with standardized base maps, and to establish technical specifications for erosion depth mapping of geological bodies using thermochronological methods. This will lay the foundation for nationwide and even global erosion depth mapping at large scales, such as 1:50,000, 1:200,000, and 1:250,000, with standardized base maps.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide a large-scale erosion depth thematic mapping method, which can realize erosion depth mapping of geological bodies with large scales such as 1:50,000 and 1:200,000 with a standard base map. The data in the erosion depth map obtained is more accurate and more in line with the actual situation, so that a more realistic and accurate comprehensive evaluation of the preservation and change status of mineral deposits in the metallogenic belt can be given, and regional mineral exploration and prospecting can be guided.

[0009] To achieve the above-mentioned object, the present invention provides the following scheme: a large-scale erosion depth thematic mapping method, comprising: establishing rules for distributing field work points and work routes in a study area, and establishing field sampling rules when sampling at the field work points; establishing field observation and recording rules suitable for thermochronological research, and formulating mineral processing rules; applying thermochronological research methods to test and analyze target minerals selected at each field work point to obtain basic analysis data; inputting the basic analysis data into improved Low-T Thermo software to perform thermal evolution history simulation analysis and erosion depth calculation to obtain the erosion depth at each field work point; the improved Low-T Thermo software is based on traditional Low-T Based on the Thermo software, the Ar-Ar dating results of potassium feldspar, plagioclase Ar-Ar and hornblende Ar-Ar were added as simulation parameters; an erosion depth contour map of the study area was drawn according to the erosion depth at each field work point; and a 1:50,000 or 1:200,000 standard regional geological map of the study area was used as a base map, and the base map and the erosion depth contour map were superimposed to obtain an erosion depth map of the study area.

[0010] In one embodiment, the layout and routing rules of the field work points and work routes in the study area are created, specifically including: setting the field work points according to the accuracy of thermochronological analysis, lithologic distribution characteristics, point representativeness and uniformity; setting the work routes according to the distribution of the field work points.

[0011] In one embodiment, the field sampling rules for sampling at the field work point are created, specifically including: for intrusive rocks with an exposed area of ​​5km 2For "stock-like rock masses" within 400 meters, one thermochronological research sample shall be collected according to the surface outcrop conditions and sampling convenience; for "planar rock masses" with an elevation range of less than 400 meters in the intrusive rock, when the "planar rock mass" is a convergent rock mass, 1-2 thermochronological research samples shall be collected, and the sampling positions shall be the center of the rock mass or the highest point of the rock mass outcrop, the edge of the rock mass or the lowest point of the rock mass outcrop; when the "planar rock mass" is a long strip rock mass, 1-3 thermochronological research samples shall be collected, and the sampling positions shall be the center and both ends of the rock mass; convergent rock mass refers to rock mass The shapes are circular, elliptical, square, etc. For "three-dimensional rock bodies" in intrusive rocks, a series of thermochronological research samples are collected according to the elevation difference of 300-400 meters, and the sampling density is increased at both ends of the rock body; the elevation difference within the exposed range of the "three-dimensional rock body" is greater than 400 meters; for fault zones, control points are set along the fault zone at the center and both ends of the fault zone, and thermochronological research samples are collected on both sides of the fault at the control points; for shear zones, three control points are set along the shear zone at the center and both ends of the shear zone, and at least one thermochronological research sample is collected on each shear zone;

[0012] For metamorphic strata, collect thermochronological research samples according to the outcrop of metamorphic strata and the sampling rules for intrusive rocks; for sandstone and shallow metamorphic rocks in sedimentary strata, collect lithologic control samples or collect thermochronological research samples according to the lithology and outcrop and referring to the sampling rules for intrusive rocks; for continuous thermochronological profiles, select 1-2 profiles with large altitude differences within the map, collect thermochronological research samples according to the preset elevation difference, and make thermochronological profiles.

[0013] In one embodiment, field observation and recording rules suitable for thermochronological research are created, specifically including: dividing the field work points into geological control points and geological observation points, and setting data description requirements for the geological control points and the geological observation points; setting the format and content of the field record book.

[0014] In one embodiment, mineral processing rules are formulated, specifically including: when crushing the target minerals, pollution-free equipment is required to be used and cross-contamination of samples is strictly prohibited; when sorting zircon, apatite, and sphene single minerals, the crystal shape must be intact, the crushing must be completed in a short time, and the samples must be screened multiple times. High-temperature heating and baking of the samples is prohibited, and the sample heating temperature must not exceed 45°C. More than 1,000 grains of each single mineral are required to be selected; when sorting silicate minerals, organic contamination is strictly prohibited during the sorting process, and the particle size is required to be 60-80 mesh, the purity is required to be above 99%, and the amount of each single mineral selected is required to reach more than 3 grams; the silicate minerals include hornblende, biotite, potassium feldspar, plagioclase, and sanidine.

[0015] In one embodiment, a thermochronological research method is applied to test and analyze the target minerals selected from each of the field work sites to obtain basic analysis data, specifically including: performing zircon, apatite (U-Th) / He dating analysis, apatite fission track dating analysis, potassium-containing silicate mineral Ar-Ar dating analysis, zircon U-Pb dating analysis, and whole-rock composition analysis on the target minerals selected from the field work sites to obtain the basic analysis data; the basic analysis data includes the thermochronological analysis test data and composition analysis data of the target minerals at each of the field work sites.

[0016] In one embodiment, the basic analysis data at each field working point is input into the improved Low-T Thermo software to perform thermal evolution history simulation analysis and erosion depth calculation to obtain the erosion depth at each field working point.

[0017] In one embodiment, an erosion depth contour map of the study area is drawn according to the erosion depth at each of the field work points; a 1:50,000 or 1:200,000 standard sheet regional geological map of the study area is used as a base map, and the base map and the erosion depth contour map are superimposed to obtain an erosion depth map of the study area, specifically comprising: constructing a TXT document based on the point information of each of the field work points and the erosion depth; selecting "discrete data gridding" in MAPGIS software to process the TXT document; drawing the erosion depth contour map using the "plane contour drawing" function in MAPGIS software based on the processed TXT document; using the "image analysis" function in "image processing" in MAPGIS to vectorize the 1:50,000 or 1:200,000 standard sheet regional geological map, and using the vectorized geological map as the base map; importing the erosion depth contour map into the corresponding area of ​​the base map to obtain the erosion depth map.

[0018] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the present invention provides a large-scale erosion depth thematic mapping method, establishes the field work points and work route layout and wiring rules, field sampling rules, field observation and recording rules, and mineral processing rules in the study area; applies the thermochronology research method to test and analyze the target minerals selected at each field work point to obtain basic analysis data; inputs the basic analysis data into the improved Low-TThermo software to perform thermal evolution history simulation analysis and erosion depth calculation, and obtains the field work depth of each field work point. The erosion depth at the point; draw the erosion depth contour map of the study area according to the erosion depth at each field work point; use the large-scale standard map regional geological map of the study area as the base map, superimpose the base map and the erosion depth contour map to obtain the erosion depth map of the study area, so as to realize the erosion depth mapping of geological bodies with large scales such as 1:50,000 and 1:200,000 and standard base maps. The data in the obtained erosion depth map is more accurate and more in line with the actual situation, so that a more real and accurate comprehensive evaluation of the preservation and change status of the mineral deposits in the metallogenic belt can be given, and regional mineral exploration and prospecting can be guided.

[0019] Figures in the specification

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] FIG1 is a flow chart of a large-scale erosion depth thematic mapping method provided by an embodiment of the present invention;

[0022] FIG2 is a thermal evolution history graph (traditional display style) provided by an embodiment of the present invention;

[0023] FIG3 is a reverse display thermal evolution history curve diagram provided by an embodiment of the present invention;

[0024] FIG4 is a diagram showing calculation results of erosion depth (erosion amount) provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] 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.

[0026] There are various methods for studying the depth (and amount) of erosion in geological bodies. Among them, thermochronology is relatively effective and can provide relatively accurate quantitative results. "Thermochronology," also known as "isotope thermochronology," is an emerging interdisciplinary discipline that combines traditional isotope chronology with other disciplines. Thermochronology provides comprehensive information on time, temperature, and spatial location, enabling precise definition of the formation of geological bodies and their subsequent thermal evolution and spatial changes. Its basic principle is to utilize the radioactive decay of isotopes and the differences in closure temperatures of different isotopic systems to date minerals. By interpreting the time and temperature information contained in these dates, it is possible to study the thermal evolution of geological bodies, such as mountain building processes, the uplift and cooling history of rock masses, the history of uplift, excavation, and erosion, and the thermal evolution of sedimentary basins. Its core concepts are the concepts of closure temperature and cooling age. Its important supporting means are (U-Th) / He, FT (fission track), Ar-Ar, U-Pb and other dating techniques and computer simulation technology of thermal evolution history.

[0027] The purpose of the present invention is to provide a large-scale erosion depth thematic mapping method, which can realize erosion depth mapping of geological bodies with large scales such as 1:50,000 and 1:200,000 and with a standard base map.

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example

[0030] As shown in FIG1 , this embodiment provides a large-scale erosion depth thematic mapping method, which includes:

[0031] S1: Create field work points and work route layout rules for the study area.

[0032] S1 specifically includes: setting the field work points according to the accuracy of thermochronological analysis, lithologic distribution characteristics, point representativeness and uniformity; and setting the work route according to the distribution of the field work points.

[0033] Program design and work preparation:

[0034] 1. Select the research work area, which is also the mapping area.

[0035] 2. After selecting the mapping work area, comprehensively collect relevant previous research results in the area and adjacent areas, including but not limited to regional geological survey reports, special research reports, mining area geological survey reports, scientific research papers, and other literature. Comprehensively analyze and organize the results of existing data to understand the tectonic position of the mapping area, regional geological structural characteristics, regional geological evolution history, and the distribution range, type, and occurrence of key geological bodies such as intrusive rocks.

[0036] 3. Prepare the working base map. Prepare a standard sheet regional geological map of the corresponding scale (1:50,000 or 1:200,000 or 1:250,000) that can cover the entire mapping area, and integrate it into the digital geological mapping system after digitization. Since the work goal is to conduct thematic mapping of erosion depth (erosion amount), this thematic mapping must be based on the previous regional geological survey work and will be based on the recognition of the correctness of the previous regional geological map of the corresponding scale (1:50,000 or 1:200,000 or 1:250,000). These standard sheet geological maps will have two uses: (1) Used as handheld geological maps (working maps) during field work, field geological surveys and site layout, wiring, etc., all use this map as the basis; (2) Used as a base map when the final erosion depth map is drawn.

[0037] 4. Prepare a topographic map (optional). Prepare a topographic map of the corresponding scale based on the scale of the planned erosion depth map. There are two sources of topographic maps: (1) purchase; (2) production. Collect and download the DEM electronic topographic map of the study area, import the data into Global Mapper to create contour lines, and export it in vector format to a MapGIS file to obtain a topographic map with contour lines. This will be used to create a base map for field work.

[0038] 5. Prepare field tools: traditional tools such as geological hammer, compass, magnifying glass; camera; GPS, handheld device; laptop computer; sample bags (of different specifications, for hand specimens, chemical samples, and large samples respectively), etc.

[0039] Specific rules for field deployment and wiring:

[0040] To conduct field work in a selected mapping research area, the first step is to set up field work points and routes. This means first laying out the points and routes, and then conducting field work according to these established points and routes. Because there were no established field point and route layout rules for large-scale erosion depth mapping, we developed these rules through exploration, practice, and innovative research.

[0041] The biggest difference between thematic mapping and regional survey mapping is that the layout and line selection of field research points do not need to follow fixed numerical grid rules. Instead, field investigation routes and observation research points must be selected according to the research purpose and the actual regional geological conditions. For thermochronological studies such as erosion depth measurement, since the related "events" have linkage and consistency within a certain area, there is no need to emphasize the mandatory nature of the investigation route and the density of field observation research points. What needs special attention is the distribution and representativeness of the points. There are points distributed in different parts of the map (center, four corners). The main issue to consider when laying out lines and points for thermochronological studies and thematic mapping is representativeness, followed by the uniformity of point distribution, and finally the density of points.

[0042] Field work points are divided into geological control points and observation (research) points. The number of points can be as many as desired, but the number should be significantly reduced compared to the number required for regional geological surveys and mapping. Based on the current analytical accuracy of low-temperature thermochronology, within a standard 1:50,000 map sheet, 15-20 valid thermochronological data points are sufficient for final mapping, corresponding to more than 40 field observation (research) points. Within a standard 1:200,000 or 1:250,000 map sheet, 25-30 valid thermochronological data points are sufficient for final mapping, corresponding to more than 60 field observation (research) points.

[0043] There is no fixed requirement for the number of routes in the design of field geological survey routes, and the basis for designing routes is the layout of the points.

[0044] In summary, the principles for field wiring and point distribution for erosion depth mapping are: setting points based on comprehensive consideration of thermochronological analysis accuracy, lithologic distribution, point representativeness, and uniformity; and setting routes based on point distribution.

[0045] S2: Creating field sampling rules when sampling at the field work point.

[0046] Mapping erosion depth requires analyzing geological samples to determine the amount of erosion. This requires field sampling for thermochronological analysis and other analyses. Compared to regional geological mapping and regional geochemical exploration mapping, erosion depth mapping is unique, and the field sampling rules used in previous mapping methods are no longer applicable. Through exploration, research, and practice, we have established field sampling rules for large-scale erosion depth mapping. First, we acknowledge the validity of the fundamental research findings on lithology, lithofacies, stratigraphy, and structure in regional geological maps at scales of 1:50,000, 1:200,000, and 1:250,000. Based on this, we have developed specific field sampling rules for different geological units.

[0047] Create field sampling rules for sampling at the field work points, specifically including: for intrusive rocks with an outcrop area of ​​5km 2For "stock-like rock masses" within the range of 1000 m, one thermochronological research sample shall be collected according to the surface outcrop conditions and sampling convenience; for "planar rock masses" with an elevation range of less than 400 m in the exposed range of intrusive rocks, when the "planar rock masses" are convergent rock masses, 1-2 thermochronological research samples shall be collected, and the sampling positions shall be the center of the rock mass or the highest point of the rock mass outcrop, the edge of the rock mass or the lowest point of the rock mass outcrop; when the "planar rock mass" is an elongated rock mass, 1-3 thermochronological research samples shall be collected, and the sampling positions shall be the center and both ends of the rock mass; convergent rock mass refers to rock mass in the shape of a circle, ellipse, square, etc.; for "three-dimensional rock mass" in intrusive rocks, a series of thermochronological research samples shall be collected according to the elevation difference of 300-400 m, and the sampling density shall be increased at both ends of the rock mass; the rock mass of "three-dimensional rock mass" shall be The elevation range within the exposed range is greater than 400 meters; for fault zones, control positions are set at the center and both ends of the fault zone along the fault zone, and thermochronological research samples are collected on both sides of the fault at the control positions; for shear zones, three control points are set at the center and both ends of the shear zone along the shear zone, and at least one thermochronological research sample is collected on each shear zone; for metamorphic strata, thermochronological research samples are collected according to the outcrop of metamorphic strata and the sampling rules for intrusive rocks; for sandstone and shallow metamorphic rock in sedimentary strata, lithologic control samples are collected or thermochronological research samples are collected according to the lithology and outcrop conditions and referring to the sampling rules for intrusive rocks; for continuous thermochronological profiles, 1-2 profiles with large altitude differences are selected within the map sheet, and thermochronological research samples are collected according to the preset elevation difference to make thermochronological profiles.

[0048] (1) Field sampling rules for intrusive rocks

[0049] 1. In principle, each rock mass has sample control

[0050] 2. For each lithology involved, collect a set of compositional research samples, 5-10 pieces (the specific number depends on the importance of the rock mass), each weighing 200-500 grams. If the lithology set has multiple outcrops, collect compositional research samples from each outcrop, so that the total number of samples reaches 5-10.

[0051] 3. For exposed area 5km 2 For small rock bodies (stocks) within the range, one thermochronological sample was collected taking into account the surface outcrop conditions and sampling convenience.

[0052] 4. Sampling rules for “flat rock masses”: For flat rock masses (those with elevation differences within the exposed range of less than 400 meters), different sampling rules are used to distinguish their shapes: (1) For convergent rock masses (those with round, elliptical, square, etc.), 1-2 thermochronological samples are used for control, and the sampling locations are the center of the rock mass (or the highest point of the rock mass exposure) and the edge of the rock mass (or the lowest point of the rock mass exposure); (2) For long strip rock masses, 1-3 thermochronological samples are used for control, and the sampling locations are the center and both ends of the rock mass.

[0053] 5. Sampling rules for “three-dimensional rock masses”: For three-dimensional exposed rock masses (i.e., the elevation difference within the exposed range is greater than 400 meters), in principle, a series of thermochronological research samples should be collected according to the elevation difference of 300-400 meters. The sampling density can be appropriately increased at both ends of the rock mass.

[0054] (2) Field sampling rules for fault zones

[0055] For important fault zones within the region (those that penetrate the region, form important tectonic boundaries, or have different lithologic ages on either side), control points are set along the fault zone at its center and ends, and thermochronological samples are collected on both sides of the fault at these control points. The collection of these samples can be considered in conjunction with the collection of intrusive and metamorphic rock samples.

[0056] (3) Shear zone field sampling rules

[0057] Three control points are set along the shear zone at its center and both ends (or both sides), and at least one thermochronological research sample is collected on each shear zone, and efforts are made to collect strongly deformed rock samples.

[0058] (4) Field sampling rules for metamorphic strata

[0059] For metamorphic strata, such as Pt old basement rocks and other metamorphic rocks, thermochronological research samples are collected according to their exposure conditions and referring to the sampling rules of intrusive rocks.

[0060] (5) Field sampling rules for sedimentary strata

[0061] For sandstone and shallow metamorphic rocks in sedimentary strata, generally only lithologic control samples are collected. If necessary, samples for thermochronological research may be collected based on the lithology and outcrop conditions, referring to the sampling rules for intrusive rocks.

[0062] (6) Field sampling rules for continuous thermochronological profiles

[0063] Select one or two sections with large elevation differences within the map sheet and collect thermochronological samples at a specific elevation difference (300-400 meters) to create a thermochronological profile. Note that sampling density can be appropriately increased at the low and high elevations within the profile.

[0064] (VII) Recommended sampling volumes for various types of rock samples [Note: For important samples, the sampling volume should be appropriately increased or even doubled]

[0065] 1. Intrusive rocks: ~5kg; 2. Basic rocks: >20kg; 3. Pt metamorphic rocks (gneiss, amphibolite, etc.): 5-10kg; 4. Other metamorphic rocks: as appropriate; 5. Sandstone: 5-10kg.

[0066] S3: Create field observation and recording rules applicable to thermochronological studies.

[0067] Field observation and recording are one of the basic tasks of erosion depth mapping. Based on the records of regional geological surveys, combined with the special requirements of erosion depth mapping and thermochronology research, we explored, studied, formulated and adopted the following field recording rules.

[0068] Classification and description requirements of geological points, format and content of field records:

[0069] Geological points are divided into general geological control points and observation (research) points.

[0070] 1. Geological control points: These are points along a normal geological observation route. The observations are relatively general, so descriptions can be kept relatively brief. They serve as a mnemonic aid and a prelude to the main plot. Geological control points typically only require hand specimens, or even no sampling.

[0071] 2. Observation (research) points: These are the essence of recording field geological phenomena, and most of them are our analysis and testing sampling points.

[0072] Important geological phenomena discovered, such as geological boundaries, mapping unit boundaries, unconformities, intrusive contact boundaries; outcrops of key top (bottom) structures; typical geological phenomena, such as typical fold structures, ductile shear zones, slip surfaces, etc.; important primary structures, secondary structures and their structural indicators; special geological boundaries, such as faults and thrust structures, etc., are all described as much as possible.

[0073] In particular, the focus should be on describing the relevant conditions of the field sampling points and describing in detail the conditions of the collected rock samples, such as structure, texture, weathered surface color, fresh surface color, main mineral components and their approximate content, etc.

[0074] Then, field observation and recording rules suitable for thermochronological research are created, specifically including: dividing the field work points into geological control points and geological observation points, and setting data description requirements for the geological control points and the geological observation points; setting the format and content of the field record book.

[0075] S4: Formulate mineral processing rules.

[0076] After rock samples are collected in the field, they need to be processed indoors. Through steps like sample crushing and mineral sorting, individual minerals are selected for analysis and testing such as thermochronology. Due to the specific nature of thermochronology, specific rules and requirements for mineral sorting have been established in addition to conventional procedures.

[0077] Formulate mineral processing rules, specifically including: when crushing the target minerals, pollution-free equipment must be used and cross-contamination of samples must be strictly prevented; when sorting zircon, apatite, and sphene single minerals, the crystal shape must be intact, the crushing must be completed in a short time, and the samples must be screened multiple times. High-temperature heating and baking of samples is prohibited, and the sample heating temperature must not exceed 45°C. More than 1,000 grains of each single mineral must be selected; when sorting silicate minerals, organic contamination is strictly prohibited during the sorting process, and the particle size must be 60-80 mesh, the purity must be above 99%, and the amount of each single mineral selected must reach more than 3 grams; the silicate minerals include hornblende, biotite, potassium feldspar, plagioclase, and sanidine.

[0078] 1. The first step is sample crushing. When crushing rocks, pollution-free equipment must be used to strictly prevent cross-contamination of samples.

[0079] 2. Sorting of zircon, apatite, and sphene: Ensure crystal integrity as much as possible, minimize sample crushing, and perform multiple screenings. Avoid excessive crushing at once, which may result in the breakage of large zircon or apatite particles. High-temperature heating and baking are prohibited (samples should not be heated above 45°C, and are best left to dry naturally). Ideally, select at least 1,000 grains of each mineral.

[0080] 3. Sorting of silicate minerals such as hornblende, biotite, potassium feldspar, plagioclase, and sanidine: Organic contamination is strictly prohibited during the sorting process. The particle size must be 60-80 mesh and the purity must be above 99%. In principle, the amount of each single mineral sorted must reach more than 3 grams.

[0081] S5: Apply thermochronological research methods to test and analyze the target minerals selected from each of the field work sites to obtain basic analytical data.

[0082] S5 specifically includes: performing zircon, apatite (U-Th) / He dating analysis, apatite fission track dating analysis, potassium silicate mineral Ar-Ar dating analysis, zircon U-Pb dating analysis, and whole-rock composition analysis on the target minerals selected at the field work site to obtain the basic analysis data; the basic analysis data includes the thermal chronological analysis test data and composition analysis data of the target minerals at each of the field work sites.

[0083] The fundamental analytical data required for the erosion depth mapping study is primarily thermochronological analysis and testing data, followed by compositional analysis data. After obtaining the various single minerals and other analytical test targets in step S4, a high-quality laboratory is selected to conduct the relevant analytical testing.

[0084] 1. Zircon and apatite (U-Th) / He dating. Single-grain zircon and apatite mineral (U-Th) / He dating was performed using laser heating to extract He and chemical digestion to extract U and Th. Three to five grains were analyzed per zircon sample, and five grains per apatite sample.

[0085] 2. Apatite fission track dating analysis. Fission track (FT) dating of apatite samples is performed using ICP-MS, the preferred analytical method, followed by conventional external detector methods. Conventional external detector methods require analysis of at least 30 grains per sample, while LA-ICP-MS requires analysis of at least 40 points per sample.

[0086] 3. Ar-Ar dating of potassium-containing silicate minerals. We used a step-by-step heating technique to perform Ar-Ar dating of potassium-containing silicate minerals, including hornblende, biotite, muscovite, potassium feldspar, and plagioclase, separated from the samples, to obtain age spectra and isochrons.

[0087] 4. Zircon U-Pb Dating. LA-ICPMS laser plasma mass spectrometry (LA-ICPMS) was used to conduct zircon U-Pb dating on the samples. 200 targets were carefully selected for each sample, and the zircon mineral was polished to 1 / 3-1 / 2 of its original size. Cathodoluminescence (CL) photographs, as well as transmitted and reflected light photographs, were taken. Zircon dating was performed on sites with clear zoning, with no fewer than 20 valid dating points per sample. Testing included: 207Pb / 206Pb, 207Pb / 235U, 206Pb / 238U, 208Pb / 232Th isotope ratios and ages, as well as the contents of SiO2, Ti, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, Th, and U.

[0088] 5. Whole-rock composition analysis: Whole-rock samples crushed to 200 mesh are analyzed for major and trace elements, as well as isotopes such as Sr and Nd, to obtain chemical composition and isotope data for the research samples.

[0089] S6: Inputting the basic analysis data into the improved Low-T Thermo software to perform thermal evolution history simulation analysis and erosion depth calculation to obtain the erosion depth at each field work point; the improved Low-T Thermo software is based on the traditional Low-T Thermo software and adds the potassium feldspar Ar-Ar, plagioclase Ar-Ar, and amphibole Ar-Ar dating results as simulation parameters;

[0090] The basic analysis data at each of the field working points are input into the improved Low-T Thermo software to perform thermal evolution history simulation analysis and erosion depth calculation to obtain the erosion depth at each of the field working points.

[0091] The thermal history simulation and erosion calculation process are introduced using Low-T Thermo software as an example.

[0092] The main functions and uses of the "Low-T Thermo" thermochronology simulation software are as follows: (1) Low-temperature geochronological thermal history simulation (including (U-Th) / He of apatite and zircon, fission track of apatite and zircon, mica Ar-Ar, potassium feldspar Ar-Ar, plagioclase Ar-Ar, amphibole Ar-Ar, bedrock quartz optically stimulated luminescence, vitrinite reflectance, and combinations of the above methods), suitable for thermal history restoration of orogenic belts and basins; (2) Quantitative denudation calculation based on thermal history, suitable for studies on geological body denudation depth, mineral deposit preservation conditions, etc.; (3) Paleotopography simulation based on thermal history, suitable for paleogeomorphological restoration studies, etc.

[0093] In its initial version, the Ar-Ar thermochronology method used in thermal history simulations only incorporated Ar-Ar dating results from biotite. However, the Ar isotope closure temperature range for biotite, 310-345°C, differs significantly from the U-Pb closure temperature of zircon (800°C), leading to distortions in thermal history simulations for high-temperature regions. Furthermore, the Ar isotope closure temperature range for biotite differs significantly from the He closure temperature of zircon (200°C), leading to distortions in thermal history simulations for medium-temperature regions. We have modified the software to include Ar-Ar dating results from potassium feldspar, plagioclase, and hornblende as simulation parameters. This further improves the accuracy of thermal history simulations for the medium- to high-temperature range and allows for more accurate denudation depth measurements.

[0094] The improved software now includes nine different thermochronological methods for thermal history simulation. These nine methods can be selected individually or in combination. Theoretically, there are 255 possible combinations, including single method selection.

[0095] (1) Installation

[0096] Low-T Thermo is written in Mathematica and VB.NET for Microsoft Windows. Therefore, before use, you must install Mathematica 10.0 and copy Wolfram.NETLink.dll to the directory containing the main program, Low.exe. Microsoft .NET Framework 2.0 or later is also required.

[0097] (2) Program interface and usage overview

[0098] 1. A window where hot history is unfolding.

[0099] After entering Time (Ma), the corresponding Temperature (℃) and other parameters, press the "Start Modeling" button to output the age and length distribution results corresponding to the input thermal history curve.

[0100] 2. Thermochronology method selection window.

[0101] This window displays nine different thermochronology methods for thermal history simulation. You can select any of these methods, either individually or in combination. Theoretically, there are 255 possible combinations, including single method selection. The output directory is where all calculated and exported data and graphics files are stored.

[0102] 3. Input window.

[0103] After selecting different thermochronological methods, click "Next" to enter the input window and enter the corresponding experimental data and parameters. Each data input box is equivalent to a notepad, and the data can be edited at will. This is convenient for copying and pasting data from other software, and further editing can be done as needed. The specific input format can refer to the existing data format examples, and the example data can be replaced when entering. Press Enter to enter multiple lines of input. The space between data can be one space or multiple spaces, and even the Tab key can be used as a space.

[0104] For the U-Th / He method, the stopping distance for alpha particles can be selected from the Farley et al., 1996 or Ketcham, et al., 2011 models. For multiple particles, you can select "Using multiple ages one by one" to screen the hypothetical paths for each particle one by one; you can also select "Using multiple ages together" to screen the hypothetical paths for each particle together and finally take the average acceptable GOF range. "Using mean age" is used to select the average age of all particles and then screen the hypothetical paths.

[0105] "Number of grids for R" sets the number of finite difference nodes. The default is 20, and the maximum value can be set to 100. A larger value indicates a denser grid and greater accuracy, but also slower calculations. This value has a limited effect on the (U-Th) / He age simulation results; a setting of 20 is generally sufficient for most applications.

[0106] “Show modeled He age distribution” is used to set whether to display the distribution graph of He particle age versus effective uranium concentration.

[0107] For the fission track method, "Default Lo(c) constant value (μm)" is the default Lo(c) (the initial confining track length after projection correction). "Lo(c)=" is used to set the Lo(c) value using Dpar (μm). "Restore Default" restores the default setting.

[0108] For vitrinite reflectance %Ro, the calibration modes include EASY %Ro (Sweeney and Burnham, 1990), IKU %Ro (Ritter et al., 1996), and basin %Ro (Nielsen et al., 2016).

[0109] 4. Main window (thermal history inversion window).

[0110] “Ts (°C, at sea level)”: surface temperature at sea level (unit: degrees Celsius).

[0111] “Elevation (m)”: The height of the sample. The default vertical temperature gradient of the atmosphere is 6°C / km.

[0112] “Tmax(℃)”: Maximum vertical axis value. Because the vertical axis in the output thermal history simulation graph is temperature, the axis display range needs to be set.

[0113] “Duration (Ma)”: Maximum horizontal axis value. Because the horizontal axis in the output thermal history simulation diagram is time, the axis display range needs to be set.

[0114] “Paths Tried”: The number of thermal history paths searched during the inversion process, usually 10,000 (can be customized according to actual needs).

[0115] “Acceptable Fit”: Acceptable goodness of fit (GOF), usually set to 0.05. You can also set it according to actual needs.

[0116] Interval nodes: The number of nodes between two adjacent constraint boxes when the user specifies the constraint box based on actual geological conditions and other background information, for example, 3.

[0117] “Nodes when no box”: The number of nodes for each random path when there is no constraint box (for example, 10).

[0118] "Box(timemin, timemax, Tempmin, Tempmax)": If a constraint box exists, enter the time and temperature ranges for the constraint box here. Enter the minimum time value for "timemin," the maximum time value for "timemax," the minimum temperature value for "Tempmin," and the maximum temperature value for "Tempmax," in that order. Each constraint box occupies one line. Press Enter to continue multiple lines.

[0119] The "Clear All" button is used to clear all parameter inputs above.

[0120] The "Save as default" button is used to save all the parameter inputs above as the default inputs for the next simulation.

[0121] “Preview boxes distribution” previews the constraint box.

[0122] “Start Modeling”: Start inversion simulation button.

[0123] "Terminate" button to terminate the inversion simulation. When an error occurs during operation or there is no time to wait for the program to run, press this button to stop the inversion and end the simulation.

[0124] “Modeled Result”: This box is used to display the thermal history simulation results.

[0125] Default display: Default display. Select this option to display all acceptable paths. The black line is the average result of all acceptable paths.

[0126] "Traditional display": Select this option to display only the boundaries of all acceptable paths, similar to the display style of AFTSolve (Ketcham et al., 2000) and HeFTy (Ketcham, 2005). The green range represents the acceptable range (GOF ≥ Acceptable Fit). The pink range represents the high-accuracy range (GOF ≥ 0.5). If a high-accuracy range exists, the black line is the average result of all paths within the high-accuracy range; otherwise, the black line is the average result of all acceptable paths.

[0127] “Modeled He age distribution” is used to display the distribution of He grain age as a function of effective uranium concentration. The radiation damage accumulation and annealing model for apatite uses RDAAM (Flowers et al., 2009), and the radiation damage accumulation and annealing model for zircon uses ZrRDAAM (Guenthner et al., 2013).

[0128] “Modeled AFT length distribution” is used to display the length distribution of the confined tracks of apatite fission tracks.

[0129] The text box in the right column shows the age values ​​corresponding to the thermal history simulation results (i.e., black lines) of the different selected thermochronological methods.

[0130] The "Modeled Report" is used to display the detailed calculation process and report related information. When "The end" or "No Result" appears, it means the simulation is finished.

[0131] After the thermal history simulation is completed, the graphics will be output in the ".pdf" format and saved in the output directory set by the user at the beginning for subsequent editing by the user.

[0132] 5. One-dimensional peeling calculation window.

[0133] The "Temperature" button is used to select the temperature data of the thermal history curve.

[0134] The "time" button is used to select the time data of the thermal history curve.

[0135] The "Exhumation Cal" button is used to convert the thermal history curve from the temperature-time curve to the exfoliation thickness-time curve.

[0136] “Ts(at sea level)” and “Elevation(m)” are the same as those introduced above.

[0137] “Temperature Gradient” refers to the geothermal gradient.

[0138] "Turning Range" is the range for selecting the inflection point in the high-temperature segment. This is used to calibrate the starting point of the thermal history as it extends from the low-temperature segment to the high-temperature segment, or in other words, the inflection point interval between the low-temperature and high-temperature segments. If left blank, the program will search for the inflection point with the largest angle within the entire time period. If the user enters a rough time range, the resulting inflection point locations between the low-temperature and high-temperature segments will more closely resemble the actual geological conditions.

[0139] “Output interval”: The time interval for outputting the calculation results. For example, if you enter 1, it means that the erosion thickness data will be extracted every 1Ma.

[0140] 6. Two-dimensional exposure and paleotopography simulation window.

[0141] “Samples'Distance(km)” inputs the sample spacing.

[0142] “Samples'Elevation(km)” inputs the sample altitude.

[0143] “Correspongding Temperature (℃)” inputs the ancient temperature of the sample.

[0144] The “Paleotopography” window displays the two-dimensional paleotopography simulation results, and the “Exhumation thickness” window displays the exhumation thickness simulation results.

[0145] The parameters listed are, in order, sea level surface temperature, atmospheric vertical geothermal gradient, basement temperature, basement depth, topographic wavelength, effective elastic thickness, Young's modulus, Poisson's ratio, mantle density, crustal density, thermal diffusivity, gravitational acceleration, time point, initial search height difference (>0), and initial search wavelength index. You can customize these parameters by referring to the program's default settings.

[0146] All graphics and related data displayed in the main simulation window are automatically exported to the output directory. These graphics (Figures 2-4) are saved as PDF files and can be re-edited in various vector editing software such as Adobe Illustrator and CorelDRAW. The term "Ma" in Figures 2-4 represents millions of years.

[0147] S7: Draw an erosion depth contour map of the study area according to the erosion depth at each of the field work points; use a 1:50,000 or 1:200,000 standard regional geological map of the study area as a base map, and superimpose the base map with the erosion depth contour map to obtain an erosion depth map of the study area.

[0148] S7 specifically includes: constructing a TXT document based on the point information of each field work point and the erosion depth; selecting "discrete data gridding" in MAPGIS software to process the TXT document; drawing the erosion depth contour map using the "plane contour drawing" function in MAPGIS software based on the processed TXT document; using the "image analysis" function in "image processing" in MAPGIS to vectorize the 1:50,000 or 1:200,000 standard map area geological map, and using the vectorized geological map as the base map; importing the erosion depth contour map into the corresponding area of ​​the base map to obtain the erosion depth map.

[0149] In a specific example, after obtaining the erosion depth (erosion amount) data of multiple geological points, the regional geological map with a standard scale of 1:50,000 or 1:200,000 was used as the base map, and MAPGIS software was used to draw the map. The contour map was used to represent the change of erosion depth in the study area, and the grid calculation method adopted the "King Pan-Kriging gridding method". The specific process is as follows.

[0150] Data preparation: Import the location information and erosion amount information of the corresponding sampling points into a TXT file.

[0151] Discrete Data Gridding: Use the "DTM Analysis" program within the "Spatial Analysis" window of MAPGIS software to perform gridding. Initially, use "Discrete Data Gridding" to process the TXT file above. Next, set the appropriate grid parameters (such as grid spacing) and the gridding method. This simulation uses the "Kring Pan-Kriging" gridding method.

[0152] Plane Contour Drawing: First, open the triangulation file and select the "Plane Contour Drawing" function. Next, set the plane contour drawing parameters, such as the contour segmentation parameters and smoothness. Finally, draw the plane contour map.

[0153] To vectorize a 1:50,000 or 1:200,000 standard scale regional geological map as a base map: 1. Use the "Image Analysis" function in the "Image Processing" section of MAPGIS to convert the 1:5W geological base map into a file format compatible with MAPGIS. 2. Vectorize this file, creating corresponding point, line, and surface files. 3. Vectorize the corresponding tectonic location geological map, regional granite distribution map, and other maps, and merge them into the 1:5W geological vector file.

[0154] Import erosion contour map: Import the established plane contour map into the corresponding geological base map library file for optimization (such as whether the points are covered, etc.).

[0155] Improve the mapping elements: add graphic scales, compasses, legends, connecting charts and other mapping elements outside the drawing frame; add drawing descriptions; further adjust the drawing style and color, and modify the layout of the drawing details to improve the visualization effect of the drawing.

[0156] Map output: Use the mapgif output function to output image format files.

[0157] In this example, no one, either domestically or internationally, has conducted large-scale regional geological body denudation depth mapping with standardized geological base maps, such as 1:50,000 / 1:200,000, nor has a corresponding mapping standard been established. This method explores and systematically establishes a standard for regional geological body denudation depth mapping at 1:50,000 / 1:200,000, which is original and innovative, with many highlights and advantages.

[0158] 1. Create field wiring and point distribution rules for erosion depth mapping (corresponding to "step S1"). In terms of field research point distribution and line selection, the fixed numerical grid rules used in traditional regional geological mapping are broken. According to the research purpose and the actual regional geological conditions, the field investigation route and observation research points are selected. In view of the fact that in thermochronological research, the "events" related to it have linkage and consistency within a certain area, there is no need to emphasize the mandatory nature of the investigation route and the density of field observation research points. However, it should be noted that there are points distributed in different parts of the map (center, four corners). The main issue to consider in the wiring and point distribution of erosion depth thematic mapping is representativeness, followed by the uniformity of point distribution, and finally the density of points. The field wiring and point distribution principles for erosion depth mapping determined based on this are: set points by comprehensively considering the accuracy of thermochronological analysis, lithologic distribution, and point uniformity; set routes according to the point distribution.

[0159] 2. Create field sampling rules for erosion depth mapping (corresponding to "step S2"). For intrusive rocks of different occurrences, sampling rules such as "stock-shaped rock mass", "plane rock mass", and "three-dimensional rock mass" were established respectively; for important fault zones in the region (penetrating through the region, or important structural boundaries, or the rock lithology ages on both sides are different), control points are set along the fault zone at its center and both ends, and thermochronological research samples are collected on both sides of the fault at the control point; for shear zones, three control points are set along the shear zone at its center and both ends (or both sides), and at least one thermochronological research sample is collected on each shear zone, and efforts are made to collect strongly deformed rock samples; for metamorphic strata, such as the old basement of the Proterozoic For rocks and other metamorphic rocks, refer to the sampling rules for intrusive rocks and collect samples for thermochronological research. For sandstones and shallow metamorphic rocks in sedimentary strata, significantly thin out lines and points based on the 1:50,000 / 1:200,000 / 1:250,000 regional survey and mapping specifications. If necessary, collect samples for thermochronological research. Set up continuous thermochronological profiles: select 1-2 profiles with large altitude differences within the map sheet, and collect thermochronological samples at a certain elevation difference (300-400 meters). Note that the sampling density can be appropriately increased at the low and high ends of the profile to make thermochronological profiles. For rocks of different lithologies, provide reasonable sampling volume recommendations.

[0160] 3. Establish field observation and recording rules suitable for thermochronological research (corresponding to "step S3"), streamline the traditional regional survey and mapping record content, and especially add sample description content, field photography record content of sampling points, etc.

[0161] 4. Established mineral processing rules (corresponding to "Step S4"). After collecting rock samples in the field, the next important task is to separate the individual minerals for thermochronological analysis and testing. Due to the particularity of thermochronological analysis, there are also special requirements for single mineral separation. Based on the conventional process, special mineral processing specifications for zircon, apatite, sphene, etc. have been formulated: ensure the integrity of the crystal shape as much as possible, the sample crushing time should be short, and multiple screenings should be carried out. Avoid crushing too finely at one time, which may cause large particles of zircon or apatite to be broken. Do not heat or bake at high temperatures! (The sample heating temperature must not exceed 45°C! It is best to dry it naturally).

[0162] 5. For the different thermal evolution temperature stages experienced by the rock, the basic data are obtained by using the thermochronological research methods corresponding to the temperature range (corresponding to "step S5"): (1) The magmatic activity stage and the high-temperature cooling stage of the rock mass (high-temperature thermal evolution processes such as magma crystallization-emplacement-in situ cooling) are studied by using high-temperature thermochronological methods such as zircon U-Pb isotope dating and amphibole and sanguinis Ar-Ar dating; (2) The uplift and erosion process of the rock mass is mainly studied by using medium-low temperature thermochronological methods such as biotite, muscovite, plagioclase and low activation energy potassium feldspar Ar-Ar dating, zircon, apatite fission track dating and (U-Th) / He dating.

[0163] 6. Use Low-T Thermo software to perform thermal history simulation analysis and erosion calculation (corresponding to "step S6")

[0164] When conducting thermal history simulation research, we use the "Low-T Thermo" thermochronology simulation software, whose main functions and uses are: (1) Multi-method low-temperature chronology thermal history simulation, which can use methods including U-Th / He of apatite and zircon, fission track of apatite and zircon, mica Ar-Ar, hornblende Ar-Ar, bedrock quartz luminescence, vitrinite reflectance and the combination of the above methods to perform low-temperature chronology thermal history simulation. There are a total of nine different thermochronology methods for thermal history simulation. These nine methods can be selected arbitrarily, including single selection or multiple selection. Theoretically, there are 255 combination modes; (2) Calculation of quantitative erosion amount in different time periods based on thermal history, which is suitable for research on erosion depth of geological bodies, preservation conditions of ore deposits, etc.; (3) Paleotopography simulation based on thermal history, which is suitable for paleogeomorphological restoration research, etc.; (4) The thermal evolution history curve can be displayed in reverse, and the calculation results of erosion depth (erosion amount) can be directly output, which can be displayed in numbers and graphics respectively. In its initial version, the Ar-Ar thermochronology method used in thermal history simulations only incorporated Ar-Ar dating results from biotite. However, because the Ar isotope closure temperature range for biotite is 310-345°C, which differs significantly from the U-Pb closure temperature of zircon (800°C), this can easily lead to distortions in thermal history simulations for high-temperature regions. Furthermore, the Ar isotope closure temperature range for biotite differs significantly from the He closure temperature of zircon (200°C), which can easily lead to distortions in thermal history simulations for medium-temperature regions. We have modified the software to include Ar-Ar dating results from potassium feldspar, plagioclase, and hornblende as simulation parameters. This further improves the accuracy of thermal history simulations for medium- to high-temperature regions and helps to obtain more accurate denudation depth values.

[0165] 7. The final map has several advantages (corresponding to "step S7"): (1) The standard regional geological map is vectorized and used as a base map for mapping. The plane contour map is imported into the corresponding geological base map, and the two are superimposed to form an erosion depth map. The map thus prepared has geological elements such as geological body distribution, structure, lithology, etc. that are completely consistent with the regional geological map of the relevant scale, making it convenient to use the erosion depth map to carry out regional geological research and mineral exploration. However, the base map used by the predecessors was arbitrary, inconvenient to use, and had limited application value; (2) The density of points used for the final map is high, and the compiled erosion depth map is more accurate; (3) The map has a large scale and can more accurately display the regional erosion history. However, the erosion depth map compiled by the predecessors has a small scale and is only suitable for expressing large-scale macro phenomena and has no application value for regional research; (4) The use of contour lines to represent the erosion depth allows users to quickly and easily understand the degree of erosion and the changes in erosion depth in the study area.

[0166] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A large-scale erosion depth thematic mapping method, characterized in that: The large-scale erosion depth thematic mapping method comprises: Creating rules for the layout and routing of field work points and work routes in the study area and creating field sampling rules when sampling at the field work points; Create field observation and recording rules applicable to thermochronological studies and develop mineral processing rules; Applying thermochronological research methods to test and analyze the target minerals selected from each field work point to obtain basic analysis data; The basic analysis data is input into the improved Low-T Thermo software for thermal evolution history simulation analysis and erosion depth calculation, and the erosion depth at each field work point is obtained; the improved Low-T Thermo software is based on the traditional Low-T Thermo software and adds the potassium feldspar Ar-Ar, plagioclase Ar-Ar and amphibole Ar-Ar dating results as simulation parameters; An erosion depth contour map of the study area is drawn according to the erosion depth at each of the field work points; a 1:50,000 or 1:200,000 standard regional geological map of the study area is used as a base map, and the base map and the erosion depth contour map are superimposed to obtain an erosion depth map of the study area.

2. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Create the layout and routing rules for field work points and work routes in the study area, including: The field work points are set according to the accuracy of thermochronological analysis, lithological distribution characteristics, point representativeness and uniformity; The work route is set according to the distribution of the field work points.

3. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Create a field sampling rule for sampling at the field work point, specifically including: For intrusive rocks with an outcrop area of ​​5km 2 For the "stock-like rock mass" within 1000 m2, one sample for thermochronological research shall be collected according to the surface outcrop conditions and sampling convenience; For "plane rock mass" with an elevation range of less than 400 meters within the exposed range of intrusive rocks, when the "plane rock mass" is a convergent morphology rock mass, collect 1-2 thermochronological research samples, and the sampling positions are the center of the rock mass or the highest point of the rock mass exposure, the edge of the rock mass or the lowest point of the rock mass exposure; when the "plane rock mass" is a long strip rock mass, collect 1-3 thermochronological research samples, and the sampling positions are the center and both ends of the rock mass; For the "three-dimensional rock mass" in the intrusive rock, a series of thermochronological research samples were collected according to the elevation difference of 300-400 meters, and the sampling density was increased at both ends of the rock mass; the elevation difference within the exposed range of the "three-dimensional rock mass" was greater than 400 meters; For the fault zone, control positions are set at the center and both ends of the fault zone, and thermochronological research samples are collected on both sides of the fault at the control positions; For shear zones, three control points were set along the shear zone at the center and both ends of the shear zone, and at least one thermochronological research sample was collected on each shear zone; For metamorphic strata, samples for thermochronological research are collected according to the outcrop of metamorphic strata and the sampling rules for intrusive rocks; For sandstone and shallow metamorphic rock in sedimentary strata, collect lithology control samples or collect thermochronology research samples according to lithology and outcrop conditions and in accordance with the sampling rules for intrusive rocks; For continuous thermochronological profiles, select 1-2 profiles with large elevation differences within the map, collect thermochronological research samples according to the preset elevation difference, and make thermochronological profiles.

4. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Create field observation and recording rules for thermochronology studies, including: Divide the field work points into geological control points and geological observation points, and set data description requirements for the geological control points and the geological observation points; Set the format and content of the field notebook.

5. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Formulate mineral processing rules, including: When crushing the target minerals, pollution-free equipment must be used to strictly prevent cross-contamination of samples; When sorting zircon, apatite and titanite single minerals, the crystal shape must be intact, the sample must be crushed in a short time, and it must be screened multiple times. It is forbidden to heat and bake the sample at high temperature. The sample heating temperature must not exceed 45°C. Each single mineral requires more than 1,000 grains to be selected; When separating silicate minerals, organic contamination is strictly prohibited during the separation process. The particle size is required to be 60-80 mesh, the purity is more than 99%, and the amount of each single mineral separated is required to reach more than 3 grams; the silicate minerals include amphibole, biotite, potassium feldspar, plagioclase and sanudite.

6. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Thermochronology research methods are used to test and analyze the target minerals selected from each field work point to obtain basic analysis data, including: The target minerals selected at the field work sites are subjected to zircon, apatite (U-Th) / He dating analysis, apatite fission track dating analysis, potassium silicate mineral Ar-Ar dating analysis, zircon U-Pb dating analysis, and whole-rock composition analysis to obtain the basic analysis data; the basic analysis data include thermochronological analysis test data and composition analysis data of the target minerals at each of the field work sites.

7. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: The basic analysis data at each of the field working points is input into the improved Low-T Thermo software to perform thermal evolution history simulation analysis and erosion depth calculation to obtain the erosion depth at each of the field working points.

8. The large-scale erosion depth thematic mapping method according to claim 1 is characterized in that: Draw an erosion depth contour map of the study area according to the erosion depth at each field work point; use a 1:50,000 or 1:200,000 standard regional geological map of the study area as a base map, and superimpose the base map with the erosion depth contour map to obtain an erosion depth map of the study area, specifically including: Constructing a TXT document based on the location information of each field work location and the erosion depth; In MAPGIS software, "discrete data gridding" is selected to process the TXT document; According to the processed TXT document, the "plane contour drawing" function in MAPGIS software is used to draw the erosion depth contour map; Use the "Image Analysis" function in the "Image Processing" of MAPGIS to vectorize the 1:50,000 or 1:200,000 standard regional geological map, and use the vectorized geological map as the base map; The erosion depth contour map is imported into the corresponding area of ​​the base map to obtain the erosion depth map.

Images