Method for analyzing sedimentary basin object source based on detrital zircon age

Abstract

The invention discloses a method for analyzing a sedimentary basin object source based on the detrital zircon age, and belongs to the field of analysis and detection, and the method comprises the following steps: S1, uniformly sampling in a known well and a potential object source area of a target layer to obtain a rock sample; s2, slicing the obtained rock sample to obtain a plurality of common slice samples and casting body slice samples, then performing component identification on slices, and analyzing identification results; s3, performing statistics on sandstone debris components of the Benxi group sample in the research area, and drawing a lithologic triangular diagram; s4, drawing a Qt-F-L diagram according to the debris component data of the research area; s5, representative samples in the research area are selected for heavy mineral analysis; s6, selecting representative samples in the research area, and measuring major elements and rare earth elements in the representative samples to analyze the material source supply condition of the research area; s7, performing U-Pb chronological characteristic analysis on the fragment zircon of the sample; and S8, performing U-Pb dating analysis on the fragment zircon of the sample.

Description

Technical Field

[0001] The present invention relates to the field of analysis and detection technology, and in particular to a method for analyzing the provenance of a sedimentary basin based on the age of detrital zircons. Background Art

[0002] The provenance area of ​​a sedimentary basin refers to the source area or parent source area of ​​the clastic materials deposited in the sedimentary basin. Sediment source analysis is to reversely infer the petrological characteristics of the parent rock in the sediment source area, as well as the climatic conditions and tectonic background at the time of deposition based on the final product of basin sedimentation. Sediment source analysis is based on two premises: one is that there is an inevitable connection between clastic rocks and parent rocks, and the other is that sedimentary rocks formed under different tectonic backgrounds have differences in composition and structure. The content of provenance analysis mainly includes the identification of ancient erosion source areas, reconstruction of ancient geomorphic features, reproduction of ancient river systems, determination of the properties of parent rocks in the provenance area, climatic conditions and tectonic background of sedimentary basins, etc. The sedimentary basin provenance analysis methods are mainly divided into: sedimentological analysis method, geochemical analysis method, isotope analysis method and geophysical analysis method.

[0003] With the diversification of modern testing technology and the continuous improvement of method levels, the types of source analysis methods are increasing day by day and becoming more mature. However, most of the current analysis methods are used in a single way, and each analysis method is mainly based on qualitative judgment, and its accuracy needs to be improved. Summary of the invention

[0004] In order to solve the technical problems existing in the above-mentioned prior art that most of the current analysis methods are used alone and each analysis method is mainly based on qualitative judgment and its accuracy needs to be improved, the present invention provides a method for analyzing sedimentary basin provenance based on detrital zircon age.

[0005] To achieve the above technical solution, the present invention provides a method for analyzing the provenance of a sedimentary basin based on detrital zircon age, comprising the steps of: S1: Determine the study area, the target layer in the study area, and the provenance area of ​​the target layer, and uniformly sample the known wells in the target layer and the potential provenance area to obtain rock samples in the study area; S2: Slice the obtained rock samples to obtain a number of common thin section samples and cast thin section samples, then identify the components of the obtained common thin section samples and cast thin section samples, and then analyze the identification results; S3: Statistical analysis of sandstone debris components of the Benxi Formation samples in the study area and draw a lithology triangle map; S4: Draw Qt-FL diagram based on the clastic component data of the study area to determine the source area information; S5: Select several representative samples in the study area for heavy mineral analysis; S6: Select representative samples in the study area and measure the major elements and rare earth elements in them to analyze the material supply in the study area; S7: Performing U-Pb geochronological characteristic analysis on the detrital zircon of the sample, wherein the U-Pb geochronological characteristic analysis of the detrital zircon comprises the following steps: S71: crushing the sample and selecting the zircon particles; S72: grinding the cleaned zircon particles to prepare samples of appropriate size and shape; S73: Cathodoluminescence (CL) imaging, LA-ICP-MS zircon U-Pb geochronology, and LA-MC-ICP-MS zircon Lu-Hf isotope analysis were performed on the samples; S74: U-Pb dating of zircon using ArF excimer laser; S75: Based on zircon U-Pb dating, in situ Lu-Hf isotope measurements of zircon are performed; S76: Analyze the cathodoluminescence photos of the study area and refer to the Th / U ratio of zircon to determine the origin of zircon; S8: Performing U-Pb dating analysis on the detrital zircon of the sample, wherein the detrital zircon U-Pb dating analysis comprises the following steps: S81: The study areas were divided into four age intervals: 2700-2300 Ma, 2300-1600 Ma, 1100-800 Ma, and 500-400 Ma according to the ages of detrital zircons; S82: Based on the zircon proportion, Th / U ratio and detrital zircon age peak data, the paleogeomorphic changes, magmatic events and geological tectonic evolution of the study area are determined.

[0006] Furthermore, in step S2, the analysis content mainly includes single mineral analysis and multi-mineral combination analysis. The single mineral analysis mainly analyzes three types of skeleton minerals, namely quartz, feldspar and rock fragments. The multi-mineral combination analysis mainly uses Dickinson's triangular diagram to analyze the mineral combination characteristics of sandstone fragments in the study area.

[0007] Furthermore, in step S5, some authigenic and secondary heavy minerals are removed, and stable heavy minerals such as zircon, tourmaline and rutile are selected to analyze the planar distribution characteristics of heavy minerals in the study area.

[0008] Further, in step S6, the main elements include: SiO2, MgO, MnO, A12O3, TiO2, Fe2O3, P2O5, K2O, NaO2 and CaO.

[0009] Furthermore, in step S71, the selected zircon particles are first processed into powder, and then the zircon particles in the sample are picked out using a heavy liquid separation method. When picking, attention should be paid to selecting particles with fewer inclusions, and particles with high transparency are given priority. The selected zircon particles are washed to remove impurities attached to the surface of the particles.

[0010] Furthermore, in step S74, the laser is focused on a sample micro-area in the sample chamber to locally melt the fragmental zircon and vaporize it. After vaporization, a carrier gas is blown through the sample chamber. At this time, the vaporized sample can flow into the plasma mass spectrometer, and finally the isotope ratio is measured using the mass spectrometer.

[0011] Furthermore, GLITTER 4.0 was used to calculate the Pb and U isotope ratios, zircon 91500 was used for calibration, and ISOPLOT 3.0 was used to compile zircon-related maps.

[0012] Furthermore, for older zircons (>1 billion years), the age value corresponding to 207Pb / 206Pb is selected, and for younger zircons (<1 billion years), the age value corresponding to 206Pb / 238U is selected.

[0013] Further, in step S75, the zircon fragments are stripped using a laser with a pulse frequency of 10 Hz. The laser beam used in the stripping process has a diameter of 44 μm and an energy density of 10 J / cm 2 , the erosion time is 50s.

[0014] Furthermore, using 176 Lu / 175 Lu = 0.02669 and 176 Yb / 172 Yb=0.5886 is used to correct the isobaric interference and obtain the sample 176 Lu / 177 Hf and 176 Hf / 177 Hf value.

[0015] In summary, the present invention has the following beneficial effects compared with the prior art: The present invention takes geological research as the main line, and according to the characteristics of sedimentation and structural evolution of the Ordos Basin, selects sandstone debris component analysis, rock debris analysis, heavy mineral analysis and paleocurrent analysis in sedimentological analysis methods, and major, trace and rare earth element analysis and isotope chronology analysis in geochemical analysis methods. On this basis, combined with the research results of previous provenance analysis, the source of the Benxi Formation in the southwest of the Yan'an gas field is analyzed. The age of the sedimentary basin clastic olivine can be accurately determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is the top structural map of the Benxi Formation; Figure 2 This is the top structural map of the Majiagou Formation; Figure 3 This is the top structural map of the Taiyuan Formation; Figure 4 A flow chart of a method for analyzing sedimentary basin provenance based on detrital zircon age provided by the present invention; Figure 5 This is the triangular distribution diagram of sandstone types of Benxi Formation samples in the study area; Figure 6 This is a graphic illustration of the distribution pattern of sandstone debris components in different source areas of the Benxi Formation in the study area. DETAILED DESCRIPTION

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0018] See also Figures 1 to 3 As shown, in order to better illustrate the method for analyzing the provenance of sedimentary basins based on the age of detrital zircons provided by the present invention, the present invention takes the sedimentary period of the target layer Benxi Formation as the late Paleozoic, which mainly experienced the Hercynian tectonic movement, and the sedimentary pattern is characterized by north-south zoning and east-west distribution. The paleo-geomorphology is characterized by high north-south, low in the middle, gentle in the north and steep in the south. Based on the drilling data of 880 completed wells and the results of stratigraphic division and comparison, combined with the regional tectonic background, the top surface structural maps of the Benxi Formation, Majiagou Formation and Taiyuan Formation in the study area were compiled.

[0019] See also Figure 4 As shown, the present invention provides a method for analyzing the provenance of a sedimentary basin based on detrital zircon age, comprising the steps of: S1: Determine the study area, the target layer in the study area, and the provenance area of ​​the target layer, and uniformly sample the known wells in the target layer and the potential provenance area to obtain rock samples in the study area; It should be noted that the provenance area is the peripheral paleo-continent of the study area, that is, in the center of the lake basin, and belongs to the intersection of the north and south provenances. The determination method is an existing technology and will not be repeated here.

[0020] S2: Slice the obtained rock samples to obtain a number of common thin section samples and cast thin section samples, then identify the components of the obtained common thin section samples and cast thin section samples, and then analyze the identification results; In order to better analyze and compare the characteristics of the sandstone components of the Benxi Formation in the study area, and thus have a clearer understanding of the provenance, sandstone components were identified on 30 ordinary thin section samples and 30 cast thin section samples of the Benxi Formation in the study area. A total of 60 sets of thin section sandstone component identification data were obtained for systematic analysis.

[0021] S3: Statistical analysis of sandstone debris components of the Benxi Formation samples in the study area and draw a lithology triangle map; The sandstone debris components of the Benxi Formation samples in the study area were statistically analyzed (Table 1 and Table 2), and the lithology triangle map was drawn ( Figure 5 ). According to the statistical results, from the perspective of plane distribution, the quartz content in the samples of the Benxi Formation in Zhidan, Ansai, Ganquan and Fuxian areas is generally greater than 90%, with no feldspar, and the rock fragment content is between 1% and 15% (average 2%). In some conglomerate samples, the rock fragment content can reach 60%. According to lithology identification, the sandstone in the study area is mainly quartz sandstone.

[0022] S4: Draw Qt-FL diagram based on the clastic component data of the study area to determine the source area information; According to the clastic component data of the study area, the source was identified using Dickinson's source analysis chart, with the main parameter minerals Qt, F, and L as the triangle Figure 3 End members are used to project points on the data of the study area to draw Qt-FL diagrams and determine the source area information.

[0023] After sorting out the data of sandstone debris components in the study area, the above-mentioned chart was used to identify its source area. The identification results can be seen Figure 6 In Qt-FL, most of the sandstone samples in the study area fall into the provenance area of ​​the re-cyclic orogenic belt. Overall, the sandstone of the Benxi Formation in the study area is mainly derived from the re-cyclic orogenic belt.

[0024] S5: Select several representative samples in the study area for heavy mineral analysis; Twelve representative samples in the study area were selected for heavy mineral analysis, and a total of 50 sets of heavy mineral data were obtained, and a systematic analysis of the heavy mineral distribution in the study area was conducted.

[0025] S6: Select representative samples in the study area and measure the major elements and rare earth elements in them to analyze the material supply in the study area; S7: Performing U-Pb geochronological characteristic analysis on the detrital zircon of the sample, wherein the U-Pb geochronological characteristic analysis of the detrital zircon comprises the following steps: S71: crushing the sample and selecting the zircon particles; S72: grinding the cleaned zircon particles to prepare samples of appropriate size and shape; S73: Cathodoluminescence (CL) imaging, LA-ICP-MS zircon U-Pb geochronology, and LA-MC-ICP-MS zircon Lu-Hf isotope analysis were performed on the samples; S74: U-Pb dating of zircon using ArF excimer laser; S75: Based on zircon U-Pb dating, in situ Lu-Hf isotope measurements of zircon are performed; S76: Analyze the cathodoluminescence photos of the study area and refer to the Th / U ratio of zircon to determine the origin of zircon; S8: Performing U-Pb dating analysis on the detrital zircon of the sample, wherein the detrital zircon U-Pb dating analysis comprises the following steps: S81: The study areas are divided into four age intervals according to the ages of detrital zircons: 2700-2300Ma, 2300-1600Ma, 1100-800Ma, and 500-400Ma; these four age intervals correspond to the amalgamation event of the micro-continental blocks of the North China Craton and the intense transformation and accretion event of the continental crust in the Archean, the tectonic thermal event of the Luliang Movement, the Neoproterozoic magmatic event, and the Early Paleozoic orogenic event (Caledonian Movement). Each age group will be discussed below.

[0026] S82: Based on the zircon proportion, Th / U ratio and detrital zircon age peak data, the paleogeomorphic changes, magmatic events and geological tectonic evolution of the study area are determined.

[0027] Table 1 Zircon dating sampling horizons and lithological characteristics of the Benxi Formation in the study area Table 2 Statistics of rock fragments content in the Benxi Formation in the study area As a preferred embodiment, in step S2, the analysis content mainly includes single mineral analysis and multi-mineral combination analysis. The single mineral analysis mainly analyzes three types of skeleton minerals, namely quartz, feldspar and rock fragments. The multi-mineral combination analysis mainly uses Dickinson's triangular diagram to analyze the mineral combination characteristics of sandstone debris in the study area.

[0028] As a preferred embodiment, in step S5, some authigenic and secondary heavy minerals are removed, and stable heavy minerals selected are zircon, tourmaline and rutile to analyze the planar distribution characteristics of heavy minerals in the study area.

[0029] Heavy mineral analysis is mainly aimed at sand-grade (or silt-grade) clastic sediment sources. Generally, minerals with sediment density greater than a fixed value (2.9 or 2.89) are called heavy minerals. Such as zircon, tourmaline, garnet, etc. Although the content of heavy minerals in sediments is relatively small, due to their close correlation with source rocks, they are widely used in sediment tracing, source rock composition analysis, source area structure judgment and other aspects. Table 3 shows the source rock property characteristics corresponding to the combination of heavy minerals in different parent rocks.

[0030] Table 3 Specific manifestations of heavy mineral characteristics in different parent rocks Mother rock Heavy mineral combination Acidic igneous rock Apatite, hornblende, monazite, rutile, titanite, tourmaline (pink), zircon Intermediate-basic intrusive rock Pyroxene, hornblende, blue iron ore, zircon, garnet, apatite Basic-ultrabasic intrusive rocks Olivine, common pyroxene, pyroxene, hornblende, magnetite, chrome spinel, ilmenite, chromite, spinel Granite pegmatite Cassiterite, fluorite, topaz, tourmaline (blue), wolframite, monazite, xenotime Metamorphic rocks Andalusite, corundum, kyanite, sillimanite, staurolite, topaz, fusillimanite, wollastonite, epidote, garnet, tourmaline, blueschist Sedimentary rocks Barite, hematite, leucote, rutile, (rounded) tourmaline, (rounded) zircon, (rounded) garnet Table 4 Classification of heavy mineral stability grades Due to their mineralogical characteristics and properties, heavy minerals have different abilities to resist weathering and erosion, which results in differences in stability. Based on the differences in the stability of each heavy mineral, we can further infer information such as the genesis of the sample source rock and the sedimentary environment. Based on the differences in the stability of heavy minerals, they can be divided into different grades (Table 4).

[0031] As shown in Table 5, the Benxi Formation in Zhidan is dominated by rutile (average 2.10%), zircon (average 1.86%) and anatase (average 1.34%). The Ansai area is dominated by siderite (9.56%), zircon (7.01%) and rutile (5.18). The Ganquan area is dominated by anatase (11.14%), zircon (8.93%) and rutile (7.89). The Fuxian area is dominated by zircon (10.54%), followed by rutile (3.76%) and anatase (3.21).

[0032] Table 5 Heavy mineral content in the study area from Chang 10 to Chang 8 Preferably, in step S6, the main elements include: SiO2, MgO, MnO, A12O3, TiO2, Fe2O3, P2O5, K2O, NaO2 and CaO.

[0033] As a preferred method, in step S71, the selected zircon particles are first processed into powder, and the zircon particles in the sample are picked out using a heavy liquid separation method. When selecting, attention should be paid to selecting particles with fewer inclusions, and for the convenience of observation, particles with high transparency are given priority. The selected zircon particles must first be cleaned to remove impurities attached to the surface of the particles.

[0034] As a preferred embodiment, in step S74, laser focusing (laser beam spot with a diameter of 32 μm) is used to place a sample micro-area in the sample chamber to cause local melting and vaporization. After vaporization, a carrier gas (helium is used in this experiment) is blown through the sample chamber. At this time, the vaporized sample can flow into the plasma mass spectrometer, and finally the isotope ratio is measured using the mass spectrometer.

[0035] As a preference, GLITTER 4.0 was used to calculate the Pb and U isotope ratios, zircon 91500 was used for calibration, and ISOPLOT 3.0 was used to compile zircon-related maps.

[0036] As a preferred option, considering the influence of radiogenic Pb, the age value corresponding to 207Pb / 206Pb is selected for older zircons (>1 billion years), and the age value corresponding to 206Pb / 238U is selected for young zircons (<1 billion years).

[0037] As a preferred embodiment, in step S75, the experimental instrument is a Nu Plasma HR multi-receiver inductively coupled plasma mass spectrometer equipped with a 193 nm laser sampling system. A laser with a pulse frequency of 10 Hz is used for ablation. In step S75, a laser with a pulse frequency of 10 Hz is used to ablate the zircon fragments. The laser beam diameter used in the ablation process is 44 μm and the energy density is 10 J / cm 2 , the stripping time is 50s. 176 Lu / 175 Lu = 0.02669 and 176 Yb / 172 Yb=0.5886 is used to correct the isobaric interference, thus obtaining the sample 176 Lu / 177 Hf and 176 Hf / 177 Hf value. 176 The Lu decay constant is 1.867×10 -11 a, depleted mantle 176 Hf / 177 Hf value and 176 Lu / 177 The Hf values ​​are selected as 0.2832 and 0.0384; the calculation of Hf mode age (single-order mode age, T DM ) Based on the loss of the source, now 176 Hf / 177 The Hf ratio is 0.28325, 176 The Lu decay constant is 1.867×10 -11 a. Crustal (two-order) Hf model age (T DMC ) is calculated based on the average continental crust176 Lu / 177 The Hf value is assumed to be 0.011. The εHf(t) value is calculated based on zircon U-Pb ages and chondrites ( 176 Hf / 177 Hf =0.282772, 176 Lu / 177 Hf = 0.0332).

[0038] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for analyzing sedimentary basin provenance based on detrital zircon age, characterized in that: Includes steps: S1: Determine the study area, the target layer in the study area, and the provenance area of ​​the target layer, and uniformly sample the known wells in the target layer and the potential provenance area to obtain rock samples in the study area; S2: Slice the obtained rock samples to obtain a number of common thin section samples and cast thin section samples, then identify the components of the obtained common thin section samples and cast thin section samples, and analyze the identification results; S3: Statistical analysis of sandstone debris components of the Benxi Formation samples in the study area and draw a lithology triangle map; S4: Draw Qt-FL diagram based on the clastic component data of the study area to determine the source area information; S5: Select several representative samples in the study area for heavy mineral analysis; S6: Select representative samples in the study area and measure the major elements and rare earth elements in them to analyze the material supply in the study area; S7: Performing U-Pb geochronological characteristic analysis on the detrital zircon of the sample, wherein the U-Pb geochronological characteristic analysis of the detrital zircon comprises the following steps: S71: crushing the sample and selecting the zircon particles; S72: grinding the cleaned zircon particles to prepare samples of appropriate size and shape; S73: Cathodoluminescence (CL) imaging, LA-ICP-MS zircon U-Pb geochronology, and LA-MC-ICP-MS zircon Lu-Hf isotope analysis were performed on the samples; S74: U-Pb dating of zircon using ArF excimer laser; S75: Based on zircon U-Pb dating, in situ Lu-Hf isotope measurements of zircon are performed; S76: Analyze the cathodoluminescence photos of the study area and refer to the Th / U ratio of zircon to determine the origin of zircon; S8: Performing U-Pb dating analysis on the detrital zircon of the sample, wherein the detrital zircon U-Pb dating analysis comprises the following steps: S81: The study areas were divided into four age intervals: 2700-2300 Ma, 2300-1600 Ma, 1100-800 Ma, and 500-400 Ma according to the ages of detrital zircons; S82: Based on the zircon proportion, Th / U ratio and detrital zircon age peak data, the paleogeomorphic changes, magmatic events and geological tectonic evolution of the study area are determined.

2. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S2, the analysis content mainly includes single mineral analysis and multi-mineral combination analysis. The single mineral analysis mainly analyzes three types of skeleton minerals: quartz, feldspar, and rock fragments. The multi-mineral combination analysis mainly uses Dickinson's triangle diagram to analyze the mineral combination characteristics of sandstone fragments in the study area.

3. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S5, some authigenic and secondary heavy minerals are removed, and stable heavy minerals such as zircon, tourmaline and rutile are selected to analyze the planar distribution characteristics of heavy minerals in the study area.

4. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S6, the main elements include: SiO2, MgO, MnO, A12O3, TiO2, Fe2O3, P2O5, K2O, NaO2 and CaO.

5. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S71, the selected zircon particles are first processed into powder, and then the zircon particles in the sample are picked out using a heavy liquid separation method. When picking, attention should be paid to selecting particles with fewer inclusions, and particles with high transparency are given priority. The selected zircon particles are then washed to remove impurities attached to the surface of the particles.

6. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S74, laser focusing is used to focus the sample micro-area in the sample chamber to locally melt the fragmental zircon and vaporize it. After vaporization, a carrier gas is blown through the sample chamber. At this time, the vaporized sample can flow into the plasma mass spectrometer, and finally the isotope ratio is measured using the mass spectrometer.

7. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 6, characterized in that: GLITTER 4.0 was used to calculate the Pb and U isotope ratios, and zircon 91500 was used for calibration. ISOPLOT 3.0 was used to compile zircon-related maps.

8. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 7, characterized in that: For older zircons (>1 billion years), the age value corresponding to 207Pb / 206Pb is selected, and for younger zircons (<1 billion years), the age value corresponding to 206Pb / 238U is selected.

9. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 1, characterized in that: In step S75, the zircon fragments are stripped using a laser with a pulse frequency of 10 Hz. The laser beam used in the stripping process has a diameter of 44 μm and an energy density of 10 J / cm 2 , the erosion time is 50s.

10. The method for analyzing sedimentary basin provenance based on detrital zircon age according to claim 9, characterized in that: use 176 Lu / 175 Lu = 0.02669 and 176 Yb / 172 Yb=0.5886 is used to correct the isobaric interference and obtain the sample 176 Lu / 177 Hf and 176 Hf / 177 Hf value.

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