Because geochemistry is a developing discipline with equal emphasis on theory and application, and geochemistry and other disciplines are constantly infiltrating each other, many branches of disciplines have emerged. These branches of geochemistry also have the characteristics of vigorous vitality and development. Here is a brief introduction to some main branches of geochemistry.
(1) element geochemistry
Element geochemistry is the earliest and most classic branch of geochemistry. Geochemists such as Clark of the United States and thomas lee of China started their early research work from elemental geochemistry. At present, the research contents of element geochemistry mainly include the geochemical characteristics of elements in the earth and some celestial bodies, such as nature, abundance, occurrence state, migration form, enrichment and dispersion law, evolution and cycle history.
(2) Quantum geochemistry
Quantum geochemistry is the result of the intersection of crystal chemistry, quantum chemistry (quantum mechanics), mineralogy and solid state physics in the early 1970s. It "studies chemical bonds or' electronic structure' in minerals, crystal structure and its stability, physical and chemical properties of minerals, geochemical distribution of chemical elements, phase equilibrium and element distribution, changes of crystal structure with temperature, pressure and composition (comparative crystal chemistry), thermodynamics of minerals and spectral properties of minerals. The core problem of quantum geochemistry is to study chemical bonds or' electronic structures' in minerals with quantum mechanics theory and various spectral methods. The study of quantum geochemistry includes two parts: theory and experiment. Theoretical research is to apply the theory of quantum mechanics to find the (approximate) solution of the equation of motion of quantum mechanics (Schrodinger equation) for the geochemical species studied. The experimental research is to determine the electronic structure of a species by various spectral methods (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(3) Geochemical thermodynamics
Geochemical thermodynamics is a branch of geochemistry, which applies the basic principles of thermodynamics to study the state changes of geoscience systems. It mainly studies energy and its transformation, and solves the direction and limit problems of natural processes, that is, the equilibrium problem. Its main research contents are: thermodynamics of natural hot liquid system; Mineral phase equilibrium; Thermodynamic properties of minerals; Thermodynamics of mineral solid solution; Thermodynamics of silicate melt: fluid-rock interaction: non-equilibrium nonlinear thermodynamics; Research on Computer Simulation and Modeling (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(4) Geochemical dynamics
Geochemical dynamics is a branch of geochemistry, which comes from the application of the basic principles of dynamics in the study of geochemical processes. It studies the speed and mechanism of natural processes, including the chemical dynamics of chemical reaction rate and the dynamics of physical movement, mainly referring to fluid dynamics, diffusion and dispersion (Institute of Geochemistry, Chinese Academy of Sciences, 1998). At present, geochemical literature divides chemical kinetics and kinetics into two disciplines. Kinetics or chemical kinetics studies the rate and process of chemical reaction (or reaction mechanism, which refers to the specific paths and steps that reactant molecules go through in the process of becoming product molecules). Dynamics, on the other hand, studies the rate and mechanism of macroscopic motion of an object under the action of force. In the practical research and application of earth science, both chemical kinetics and kinetics exist and should not be completely separated. Therefore, scholars at home and abroad use "geochemical process dynamics" (hereinafter referred to as geochemical dynamics) to reflect chemical dynamics and kinetic problems in geochemical research (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(5) Isotopic geochemistry
Isotopic geochemistry mainly uses geological dating and isotope tracing methods to study the formation and abundance of nuclides in the earth and cosmic materials, and tracks various geological and geochemical processes according to the decay and fractionation of these nuclides in natural processes. Isotopic geochemistry includes radioactive isotope geochemistry and stable isotope geochemistry. Radioisotope geochemistry mainly carries out geological system timing according to radioactive isotope decay and tracing analysis according to isotopic composition of radioactive product daughters. Stable isotope geochemistry mainly uses fractionation of light stable isotopes in nature to trace geological processes (Chen Daogong et al., 1994).
(6) Experimental geochemistry
Experimental geochemistry is a young branch of geochemistry, and there is no unified understanding of its definition at present. Generally speaking, experimental geochemistry is developed on the basis of experimental mineralogy and experimental petrology, which mainly involves the experimental study on the behavior and reaction mechanism of chemical elements (including isotopes and organic matter) in the process of fluid phase geochemistry (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(7) Astrochemistry
Astrochemistry, also known as space chemistry or cosmochemistry, is a new science produced by the cross-infiltration of earth science, space science and astronomy. Space chemistry studies the origin and distribution of space elements and their isotopes, as well as the chemical composition and evolution of various celestial bodies. The matter in the vast universe consists of 100 elements, more than 2000 isotopes and various chemicals from elementary particles. Astrochemistry studies the temporal and spatial distribution, existing state and evolution law of these matter layers (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(8) Rock geochemistry
Rock geochemistry is an interdisciplinary subject of modern petrology and geochemistry. According to the basic principles, experimental methods and research results of geochemistry, various petrological problems are discussed, and geological significance is derived from them (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996). The research content of rock geochemistry mainly involves the geochemical composition, function and evolution of major elements, trace elements and isotopes in igneous rocks, sedimentary rocks and metamorphic rocks. This paper studies the origin, evolution and resource and environmental effects of the earth by studying the rock origin or celestial matter of the earth.
(9) Regional geochemistry
The advocator of regional geochemistry is Felsmann. Felsmann believes that the task of regional geochemistry is to study the temporal and spatial distribution, distribution, migration and concentration law of chemical elements in a certain area. Modern regional geochemistry is a branch of geochemistry (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996). Taking the regional lithosphere, a subsystem of the global lithosphere, as the object, the chemical composition, chemical action and chemical evolution of this subsystem are comprehensively studied.
(10) tectonic geochemistry
The idea of tectonic geochemistry sprouted in the19th century (H.C.Sorby), and its theoretical basis was laid by W.C.Fyfe and Chen in the 1960s. Structural geochemistry is an interdisciplinary subject of structural geology and geochemistry, which studies the geochemical processes such as the occurrence, distribution, migration, dispersion and enrichment of elements in the earth (mainly the crust) in fluids and solid rocks under tectonic action. Chen Zai 1976 and 1984 pointed out many times: "Tectonic geochemistry is a discipline between tectonic geology and geochemistry, which studies the relationship between various geological structures and the distribution, migration, dispersion and enrichment of chemical elements in the crust. Its main task is to study the relationship between geological structure and geochemical process, that is, the relationship between movement and matter in time, space and genesis, and to study formation and deformation, structure and transformation in a unified way "(Wu, 1998).
(1 1) deep geochemistry
Deep geochemistry is also called deep earth material science. This subject mainly studies the chemical composition, chemical action and chemical evolution of the deep earth (especially the mantle and core). This aspect includes theoretical research and experimental research. Theoretical research mainly uses the basic principles of geology, geochemistry, geophysics, petrology, mineralogy and structural geology to construct the deep earth model. The experimental research mainly depends on the development of diamond pressure chamber and large chamber experimental technology, static ultra-high pressure experimental technology and ultra-deep drilling technology. Its research contents are as follows: ① Study on the physical and chemical properties of deep earth materials; ② Study the physical and chemical properties of the earth's interior; ③ Research on Earth Evolution and Geodynamics (Xie et al., 1997).
(12) Ore deposit geochemistry
Mineral deposit geochemistry is a frontier discipline combining mineral deposit science and geochemistry, which mainly studies mineral resources. It mainly uses geochemical theories and methods to study mineral deposits. On the one hand, deposit geochemistry contains and inherits the theories and research methods of classical deposit science and geochemistry, and at the same time introduces some theoretical knowledge and research methods of mathematics, physics and chemistry outside the field of geosciences. Ore deposit geochemistry should not only study the chemical composition, chemical action and chemical evolution of the deposit itself, but also study the mineralization process of the deposit formation and its preservation and evolution after formation (Li Chaoyang, 1999).
(13) exploration geochemistry
Exploration geochemistry is a new applied discipline developed from geochemical prospecting. The definition of geochemical prospecting in western countries is: "Geochemical prospecting is any mineral exploration method based on systematic determination of one or more chemical properties of natural substances" (H.E.Hawkes et al., 1962). Scholars in the former Soviet Union thought: "Geochemical prospecting is a prospecting method to find ore deposits based on microscopic dispersion halo of minerals in bedrock and overburden, groundwater and surface water flow, plants, soil and gas" (вч. Krasnikov, 1955). In the early days, geochemistry produced an applied discipline aimed at mineral exploration, called geochemical prospecting. Later, geochemical prospecting has made great progress in theory, method and technology, especially in the application field, which has expanded from simple prospecting geochemistry to environmental geochemistry, engineering geochemistry, agricultural geochemistry and other fields. Therefore, the term geochemical prospecting has been gradually replaced by exploration geochemistry.
(14) low temperature geochemistry
Low temperature geochemistry mainly studies the geochemical process and evolution below 200℃ in nature, including the geochemical behavior of extraction, activation, migration and enrichment of minerals at room temperature and below zero degrees Celsius. In the past, the field of low-temperature geochemistry was in a weak state for a long time, mainly because: ① most of the past geochemical experiments were carried out under the condition of medium and high temperature; ② The previous data of diagenesis and mineralization temperature measurement were not sufficient and perfect; For a long time, people's understanding of element activity is one-sided, and they have not realized the strong geochemical activity of elements at low temperature. ④ Some low-temperature metasomatism used to be mistaken for the products of high temperature and high-temperature fluid. Since 1990s, under the initiative of Tu Guangchi, China has carried out low-temperature geochemical research. At present, the experimental research system of low-temperature geochemistry has been established and perfected. The geochemical characteristics of some low-temperature deposits and mineralized horizons in China have been summarized, the low-temperature geochemical behaviors of gold, silver, platinum group metals, rare earth elements and some dispersed elements and the low-temperature mineralization of some nonmetals have been studied, the migration and enrichment process of ore-forming elements in low-grade metamorphism and buried metamorphism of mineralization has been analyzed, the migration and precipitation experiments of some ore-forming elements under low-temperature conditions have been carried out, and the water-rock interaction model in low-temperature open system has been established.
(15) organic geochemistry
In the early 1920s, B.и Wernatsky published the Biosphere and other works, and built the world's first "living laboratory" of organic geochemistry, marking the germination of organic geochemistry. After that, with the development of petroleum geology and petroleum industry, due to the development and mutual penetration of geology, sedimentology, biology, organic chemistry, petroleum geology and other disciplines, organic geochemistry has made great progress. It is defined as: organic geochemistry mainly studies the composition, structure and properties of naturally occurring organic matter, their distribution, transformation and their role in geological processes (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
It is worth pointing out that biogeochemistry, another branch of geochemistry, is related to organic geochemistry. So it is not listed separately. It can be considered that biogeochemistry sprouted in the early 1920s. It is to study the geochemical process in the biosphere in which biological organisms participate, reveal the correlation between organisms and their environment in chemical element composition, find out the geochemical province and its relationship with endemic diseases, and focus on the influence of biological and human activities on the geochemical cycle of carbon, nitrogen, phosphorus and sulfur (National Natural Science Foundation, 1996).
(16) environmental geochemistry
Environmental geochemistry studies the relationship between human activities and geochemical environment, which is a new frontier subject arising from the mutual infiltration of geochemistry and environmental science. Based on geology and from the viewpoint of the integrity and interdependence of the earth's environment, this paper comprehensively studies the geochemical behaviors of chemical elements in the earth-water-gas-biology-human environmental system, reveals the changing laws of regional and global environmental systems under the interference of human activities, and serves the development and utilization of resources, environmental quality control and human survival and health (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(17) fluid geochemistry
In recent ten years, through the direct detection and observation of fluid inclusions in the earth from volcanoes, earthquakes, submarine hydrothermal fluids, ultra-deep drilling, abiogenic natural gas, rocks and minerals, as well as the field and indoor experimental research on fluid-rock interaction, many important discoveries and cognitive leaps have been made, and the research system of fluid geochemistry has been improved (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996). More and more attention has been paid to the study of fluid geochemistry. For example, 1993 and 1997 held two international academic conferences on "Earth Fluid"; 1996, "Fluid Geochemistry" started as a postgraduate course in Chengdu University of Technology; 1997 "Fluid Geology and Metallogenic Effectiveness" is listed as the pre-selected project of the national climbing plan, and so on. Fluid geochemistry mainly studies the laws of formation, migration and location (transformation, evolution, unloading and storage, etc.). ), focusing on the geochemical laws, principles and effects in the process of fluid geology.
(18) gas geochemistry
Gas geochemistry mainly studies the geochemical characteristics, genetic types, migration and accumulation laws of various gases in nature, and their geochemical dynamic processes and geological significance (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).
(19) agricultural geochemistry
Agricultural geochemistry mainly studies the distribution of elements in soil, the geochemical process of soil formation, the utilization and improvement of soil, agricultural pollution and its prevention, and the relationship between soil geochemical environment and the output and quality of agricultural products (especially grain). It is of great economic significance under the severe situation of population explosion, reduction of cultivated land and decline of land carrying capacity (National Natural Science Foundation of China, 1996).
(20) Marine geochemistry
Marine geochemistry in a narrow sense refers to submarine geochemistry. Until the 1960s, it was in the stage of data accumulation. After the 1960s, with a series of events, such as large-scale survey of manganese nodules in the ocean, discovery of sulfide in submarine hot water, deep-sea drilling and international ocean survey, the rapid development of marine geochemistry was promoted (National Natural Science Foundation of China, 1996). Modern marine geochemistry is defined as the study of various geochemical processes in the marine environment, as well as the behavior laws and natural evolution history of chemical elements in these processes (Ouyang Ziyuan, Ni Jizhong, Xiang, 1996).