Method for identifying midridge hydrothermal area in ocean based on geochemical characteristics of sediments
阅读说明：本技术 一种基于沉积物地球化学特征识别大洋中脊热液区的方法 (Method for identifying midridge hydrothermal area in ocean based on geochemical characteristics of sediments ) 是由 廖时理 陶春辉 周建平 邓显明 倪建宇 张国堙 王渊 顾春华 于 2019-12-04 设计创作，主要内容包括：本发明公开了一种基于沉积物地球化学特征识别大洋中脊热液区的方法,本发明通过对沉积物样品进行处理,获取其地球化学组成数据,并计算不同端元组成的沉积物对化学组成的贡献,获得热液来源元素的含量,估计热液来源元素的扩散距离,最后预测调查区热液活动的数量和可能产出的位置。本发明的优点是在大洋中脊热液活动探测中,可以实现活动和非活动热液区的识别,以更准确、方便的确定热液区的位置,具有便捷、高效的特点。(The invention discloses a method for identifying a hydrothermal region in an ocean based on geochemical characteristics of sediments. The method has the advantages that in the detection of the hydrothermal activity of the ridges in the ocean, the identification of the active hydrothermal area and the inactive hydrothermal area can be realized, so that the position of the hydrothermal area can be determined more accurately and conveniently, and the method has the characteristics of convenience and high efficiency.)
1. A method for identifying a midridge hydrothermal area in an ocean based on the geochemical characteristics of sediments is characterized by comprising the following steps: the method comprises the following steps:
(1) and (3) acquiring sediment samples in an investigation area, drying the sediment samples, sieving the dried sediment samples through a standard sieve, acquiring sediment samples with different grain sizes, and analyzing the geochemical composition data of the sediment samples.
(2) And analyzing the stability of the geochemical composition data of the sediments with different particle sizes to obtain the optimal analysis particle size of the sediment sample so as to remove the influence of rock debris components with larger particles on the sediment components.
(3) Analyzing the composition data of the sample of the sediment with the optimal analysis grain size in the step (2) to obtain the main end member composition of the sediment.
(4) And (4) estimating the content of hydrothermal source elements in the sediment according to the sediment main end member composition obtained in the step (3), and when the calculated value is larger than 0, considering that the sample is influenced by hydrothermal activity, and judging that a hydrothermal area exists nearby.
(5) Selecting typical hydrothermal areas of different types in the investigation area, carrying out distance analysis on the sediment sampling point and the hydrothermal area, and calculating the distance between the sediment sampling point and the hydrothermal area according to the content of hydrothermal source elements in the sediment obtained in the step (4).
(6) And (5) estimating the relationship between the content of the hydrothermal source elements and the distance according to the distance obtained in the step (5), obtaining the diffusion distance of the hydrothermal source elements in different types of hydrothermal areas, and obtaining the marked hydrothermal source elements suitable for identifying the hydrothermal areas and the number of the hydrothermal areas in the investigation area.
(7) And (4) performing buffer analysis on the sediment sampling points according to the diffusion distance of the elements for identifying the hydrothermal solution sources obtained in the step (6).
(8) The potential locations for hydrothermal activity are circled and the number of potential hydrothermal zones in the survey area is estimated.
2. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: and (2) enabling the sediment sample in the step (1) to pass through a standard sieve, wherein standard sieves of 20 meshes, 40 meshes, 60 meshes, 80 meshes, 100 meshes, 120 meshes, 160 meshes and 200 meshes are adopted.
3. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: in the step (1), the composition of the trace elements is tested by adopting ICP-MS, and the composition of the main elements is analyzed by XRF.
4. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: in the step (3), the main end member composition and the relative proportion of the main end member composition of the sediment are obtained by adopting methods such as factor analysis, principal component analysis and the like.
5. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: the hot liquid source elements in the step (4) comprise: cu, Zn, Pb, Fe, Mn, As, Co, Ni, etc.
6. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: estimating the content of hydrothermal source elements in the sediment in the step (4), and adopting an end member composition estimation method, wherein the process is as follows:
the elements of the magnesium-iron scrap source can be estimated as:
element(s)Magnesium iron scrapEither (element/Al)Mafic rock*AlGeneral of
The Ni content of the ultramagnesium iron scrap source can be calculated by the following equation:
Niultra-magnesium iron scrap＝NiGeneral of–NiMagnesium iron scrap–NiBackground deposits
Wherein the background sediment is an ocean sediment far away from the ocean center ridge;
the content of the remaining elements derived from the ultramafic scrap can be calculated by the following equation:
element(s)Ultra-magnesium iron scrapBecoming (element/Ni)Ultra-magnesium iron rock*NiUltra-magnesium iron rock
The content of the hydrothermal component can be calculated by the following equation:
element(s)Hot liquidIs elementGeneral of-element(s)Magnesium iron scrap-element(s)Ultra-magnesium iron scrap-element(s)Background deposits。
7. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: and (5) selecting different cause type hydrothermal areas including a magma control type and a structure control type.
8. The method of identifying a keatite area in an ocean based on sediment geochemistry features of claim 1, wherein: in the step (8), the number of possible hot liquid areas in the investigation area is estimated by adopting the following method: when the buffer zone exists in an isolated mode, determining that the buffer zone is a hot liquid zone; when the buffer areas of the adjacent sampling positions are intersected and have obvious enrichment centers, determining that the buffer areas are hot liquid areas; two hydrothermal zones are determined when the buffers of adjacent sample locations intersect but do not have a distinct center of enrichment.
Technical Field
The invention relates to a method for identifying a hydrothermal region of a marine middle ridge, in particular to a method for identifying the hydrothermal region of the marine middle ridge by adopting geochemical characteristics of sediments.
Background
The oceanic ridge polymetallic sulfide is rich in metal elements such as Cu, Zn, Au, Ag and the like, and can form a megaton-level large deposit in a certain geological environment. In recent years, countries around the world have paid high attention to such potential resources. The hot liquid area of the ocean ridge comprises an active hot liquid area and an inactive hot liquid area. The latter is generally larger in scale and the associated biological activities are less, less environmentally protected from mining and therefore the main direction of ridge sulphide mining in future oceans. As the exploration of the episulfide in the ocean is a brand-new field, the research on the related theoretical basis and method is not mature, and the adopted technical means are relatively deficient. Currently, plume detection is mainly used internationally to identify hydrothermal activity, but the method cannot detect non-active hydrothermal regions. Therefore, a method for effectively identifying the hydrothermal region of the ocean is needed.
Disclosure of Invention
The invention provides a method for effectively identifying active and inactive hydrothermal areas according to the characteristics of ridge sulfides in the ocean, aiming at the problem that the existing mainstream tool for exploring ridge sulfides in the ocean cannot identify the inactive hydrothermal areas.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for identifying a midridge hydrothermal area in an ocean based on geochemical characteristics of sediments comprises the following steps:
(1) and (3) acquiring sediment samples in an investigation area, drying the sediment samples, sieving the dried sediment samples through a standard sieve, acquiring sediment samples with different grain sizes, and analyzing the geochemical composition data of the sediment samples.
(2) And analyzing the stability of the geochemical composition data of the sediments with different particle sizes to obtain the optimal analysis particle size of the sediment sample so as to remove the influence of rock debris components with larger particles on the sediment components.
(3) Analyzing the composition data of the sample of the sediment with the optimal analysis grain size in the step (2) to obtain the main end member composition of the sediment.
(4) And (4) estimating the content of hydrothermal source elements in the sediment according to the sediment main end member composition obtained in the step (3), and when the calculated value is larger than 0, considering that the sample is influenced by hydrothermal activity, and judging that a hydrothermal area exists nearby.
(5) And (4) selecting typical hydrothermal areas of different types in the investigation area due to different element diffusion distances of the hydrothermal areas with different cause types, performing distance analysis on the sediment sampling point and the hydrothermal area, and calculating the distance between the sediment sampling point and the hydrothermal area according to the content of hydrothermal source elements in the sediment obtained in the step (4).
(6) And (5) estimating the relationship between the content of the hydrothermal source elements and the distance according to the distance obtained in the step (5), obtaining the diffusion distance of the hydrothermal source elements in different types of hydrothermal areas, and obtaining the marked hydrothermal source elements suitable for identifying the hydrothermal areas and the number of the hydrothermal areas in the investigation area.
(7) And (4) performing buffer analysis on the sediment sampling points according to the diffusion distance of the elements for identifying the hydrothermal solution sources obtained in the step (6).
(8) The potential locations for hydrothermal activity are circled and the number of potential hydrothermal zones in the survey area is estimated.
Further, the sediment sample in the step (1) is sieved by a standard sieve, and 20 meshes, 40 meshes, 60 meshes, 80 meshes, 100 meshes, 120 meshes, 160 meshes and 200 meshes of standard sieves are adopted.
Further, in the step (1), the trace element composition is tested by ICP-MS, and the major element composition is analyzed by XRF.
Further, in the step (3), the main end member composition and the relative proportion of the main end member composition of the deposit are obtained by adopting methods such as factor analysis, principal component analysis and the like.
Further, the hot liquid source elements in the step (4) comprise: cu, Zn, Pb, Fe, Mn, As, Co, Ni, etc.
Further, the content of hydrothermal source elements in the sediment is estimated in the step (4), and an end-member composition estimation method is adopted, wherein the process is as follows:
the elements of the magnesium-iron scrap source can be estimated as:
element(s)Magnesium iron scrapEither (element/Al)Mafic rock*AlGeneral of
The Ni content of the ultramagnesium iron scrap source can be calculated by the following equation:
Niultra-magnesium iron scrap＝NiGeneral of–NiMagnesium iron scrap–NiBackground deposits
Wherein the background sediment is an ocean sediment far away from the ocean center ridge;
the content of the remaining elements derived from the ultramafic scrap can be calculated by the following equation:
element(s)Ultra-magnesium iron scrapBecoming (element/Ni)Ultra-magnesium iron rock*NiUltra-magnesium iron rock
The content of the hydrothermal component can be calculated by the following equation:
element(s)Hot liquidIs elementGeneral of-element(s)Magnesium iron scrap-element(s)Ultra-magnesium iron scrap-element(s)Background deposits
Further, in the step (5), different cause type hydrothermal areas are selected, wherein the cause type hydrothermal areas comprise a magma control type and a structure control type.
Further, the number of possible hot liquid areas in the investigation area is estimated in step (8), and the following method is adopted: when the buffer zone exists in an isolated mode, determining that the buffer zone is a hot liquid zone; when the buffer areas of the adjacent sampling positions are intersected and have obvious enrichment centers, determining that the buffer areas are hot liquid areas; two hydrothermal zones are determined when the buffers of adjacent sample locations intersect but do not have a distinct center of enrichment.
The invention has the beneficial effects that: offshore exploration of ridge sulfides in the ocean is time consuming, labor consuming and costly. The implementation of the invention can realize the identification of the active and inactive hydrothermal areas of the ocean and accurately and conveniently determine the position of the hydrothermal area, thereby reducing the blindness of investigation and sampling, reducing the working cost and having the characteristics of convenience and high efficiency.
Drawings
FIG. 1 is a flow chart of a method of the present invention for identifying a hot spine area in an ocean based on sediment geochemistry characteristics;
FIG. 2 is a graphical illustration of the stability of compositional data for different sized deposits;
FIG. 3 is a schematic representation of the principal end-member composition of the deposit and its relative proportions;
FIG. 4 is a schematic diagram showing diffusion distances of Cu and Zn in a magma control type and a structure control type hydrothermal zone in an investigation region.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific examples.
Firstly, a region to be measured is determined, taking the western indian ocean center as an example, and the implementation flow of the method for identifying the ocean center hydrothermal region based on the geochemical characteristics of the sediments in the embodiment is described in detail below (as shown in fig. 1):
(1) and (4) acquiring sediment samples in the investigation area, and drying the sediment samples at 50 ℃. And respectively sieving the dried samples with 20 meshes, 40 meshes, 60 meshes, 80 meshes, 100 meshes, 120 meshes, 160 meshes and 200 meshes standard sieves, and analyzing the component compositions of the samples with the corresponding particle sizes. The trace element composition was tested by ICP-MS and the major elemental composition was analyzed by XRF.
(2) Comparing the stability of the component data of the sediment with different particle sizes obtained in the step (1) by adopting methods such as a scatter diagram and a line diagram, wherein 1-9 respectively represent 9 particle size samples with the particle sizes of >20 meshes, 20-40 meshes, 40-60 meshes, 60-80 meshes, 80-100 meshes, 100-120 meshes, 120-160 meshes, 160-200 meshes, and <200 meshes, as shown in figure 2; in the sediments with different grain diameters in the investigation region, the Cu, Zn and Fe contents in the sample with the grain diameter of more than 60 meshes are high, the stability is poor, the influence by rock debris is large, and the contents in the sample with the grain diameter of less than 60 meshes are relatively stable. Therefore, the sediment sample is set to have an optimum analysis particle size of less than 60 mesh and analyzed for geochemical characteristics.
(3) According to the component data of the sediment sample with the optimal analysis particle size obtained in the step (2), the main end member composition and the relative proportion of the main end member composition of the sediment are obtained by adopting analysis methods such as factor analysis, principal component analysis and the like, as shown in the attached
(4) And (4) estimating the content of hot liquid source elements in the sediment by adopting the following method according to the sediment end member composition obtained in the step (3):
the main components of the sediment in the investigation region are wind dust, in-situ rock debris (mafic rock and ultramafic rock), hydrothermal sediment, iron-manganese oxide, calcareous sediment and the like. The calcareous deposit content was obtained directly by testing. The wind dust content of the ridges in the ocean is negligible, so elemental aluminum (Al) is mainly derived from in-situ rock debris. Al in mafic rock2O3The content is about 15 percent generally, and Al in the ultrabasic rock2O3The content is typically around 1.5%, so it can be assumed that the Al in the deposit is derived from the magnesium-iron scrap. Thus, the elements of the magnesium-iron scrap source can be estimated as:
element(s)Magnesium iron scrapEither (element/Al)Mafic rock*AlGeneral of
According to the published data, the content of chromium (Cr) and nickel (Ni) elements in the ultramafic rock is about 1700ppm and 1500ppm, and the content of Cr and Ni elements in the mafic rock is less than 100 ppm. The ferrimanganic oxide also contains a small amount of Cr and Ni, but considering that the end member component obtained in step (3) is only 10% of the total amount (fig. 3), it can be assumed that Cr and Ni in the deposit are mainly derived from mafic and ultramafic fragments. Therefore, the Ni content of the ultramafic scrap source can be calculated by the following equation:
Niultra-magnesium iron scrap＝NiGeneral of–NiMagnesium iron scrap–NiBackground deposits
Wherein the background sediment is an ocean sediment away from the ocean center ridge.
The content of the remaining elements derived from the ultramafic scrap can then be calculated by the following equation:
element(s)Ultra-magnesium iron scrapBecoming (element/Ni)Ultra-magnesium iron rock*NiUltra-magnesium iron rock
Ferrimanganic oxide in the ridges of the ocean is generally considered to be a neutral plume source, which is considered a hot liquid product in the present process. Thus, the amount of elements remaining in the total amount can be considered a source of hydrothermal fluid. The amount of the hot liquid component can therefore be inferred by the formula, which is calculated as follows:
element(s)Hot liquidIs elementGeneral of-element(s)Magnesium iron scrap-element(s)Ultra-magnesium iron scrap-element(s)Background deposits
When the calculated value is greater than 0, the sample is considered to be affected by hydrothermal activity, and a hydrothermal region is determined to exist in the vicinity.
(5) The investigation region mainly comprises a magma control type hydrothermal region and a structure control type hydrothermal region, two typical hydrothermal regions (two typical hydrothermal regions of Longman 2605050and bridge cut-off are selected for the western south Indian ridge) are selected according to the content of hydrothermal source elements in the sediment obtained in the step (4), and the distance between a sediment sampling point and the hydrothermal regions is calculated.
(6) And (5) estimating the relationship between the content of the hydrothermal source elements and the distance according to the distance obtained in the step (5), and obtaining the diffusion distance of the hydrothermal source elements such as Cu, Zn and the like in the magma control type hydrothermal zone and the structure control type hydrothermal zone, as shown in the attached figure 4. According to the analysis results, the diffusion distances of Cu and Zn in the magma control type hydrothermal region are respectively (Zn: 1.5-2 km; Cu: 1.0-1.5 km), and the diffusion distances of the structure control type hydrothermal region are respectively (Zn: 2 km; Cu: 5-6 km), which shows that the diffusion distance difference of Cu in the two types of hydrothermal regions is larger, the diffusion distance of Zn is more stable, and the diffusion distance is smaller. Therefore, Zn is more suitable for defining the position of the hydrothermal area, and Zn is used as an element for marking the hydrothermal source.
(7) And (5) taking the diffusion distance 2km of the Zn element obtained in the step (6) as the radius of a buffer area, and carrying out buffer area analysis on the sediment sampling point.
(8) According to the spatial distribution characteristics of the Zn element diffusion buffer zone obtained in the step (6) and the step (7), the following method is adopted to identify the possible number of hydrothermal zones: when the buffer zone exists in an isolated mode, determining that the buffer zone is a hot liquid zone; when the buffer areas of the adjacent sampling positions are intersected and have obvious enrichment centers, determining that the buffer areas are hot liquid areas; two hydrothermal zones are determined when the buffers of adjacent sample locations intersect but do not have a distinct center of enrichment.
The foregoing is a more detailed description of the present invention in connection with specific preferred embodiments thereof, and it is not intended that the invention be limited to the specific embodiments thereof. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the scope of the invention.
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