Geochemistry geochemistry
Sciences of studying the chemical composition, chemical effects and chemical evolution of the earth and related celestial bodies. It is a marginal discipline produced and developed by geology combined with basic sciences such as chemistry and physics.
Since the 1970s, geochemistry, geology and geophysics have been known as the three pillars of solid earth science. Its research scope further extends from Earth to other celestial bodies in the Moon and the Solar System.
Theory and methods of geochemistry are of great significance to the search, evaluation and development of minerals, agricultural development and environmental science. Some major research results of basic theory of earth science, such as earth catastrophe events, ocean floor expansion, lithosphere evolution, etc., are related to geochemistry research.
1. Development overview
The development process of geochemistry can be roughly divided into three periods:
1.1. Germination period
19th century, some advanced industrial countries carried out systematic geological surveys and maps, development and utilization of mineral resources, promoted geochemistry The budding of
1838, German chemist C.F. Schönbein first proposed the term geochemistry. In the middle of the 19th century, the weight analysis and capacity analysis of analytical chemistry were gradually improved; major progress such as the discovery of periodic laws of chemical elements, the discovery of atomic structure theory and radioactivity, laid the foundation for the formation of geochemistry.
1.2. Formation period
1908, F.W. Clark of the United States published the book "Geochemical Materials", and the fifth edition was revised and published in 1924. In this work, Clark collected a large number of analytical data on minerals, rocks and water, calculated the average chemical composition of the earth's crust, and proposed that geochemistry should study the chemical effects and chemical evolution of the earth, pointing out the direction for the development of geochemistry.
Norwegian V.M. Goldschmit pointed out in "Geochemical Distribution Rules of Elements" (1923-1938) that the distribution of chemical element on the earth is not only related to the physical and chemical properties of its atom , And it is related to its behavioral characteristics in lattice . This has shifted geochemistry from mainly studying the chemical composition of the earth's crust to exploring the control law of the distribution of chemical elements in the earth.
Soviet V.I. Wernatsky and A. Ye Feelsman co-founded the Soviet Geochemistry School.
1922 Felsman published the book "Russian Geochemistry", which discusses the geochemical characteristics of various regions in Russia and is the first basic work on regional geochemistry.
In 1924, Wernatsky published the book "Introduction to Geochemistry", which first proposed the task of studying atomic history for geochemistry, and first noticed the huge role of organisms in the migration, enrichment and dispersion of chemical elements in the earth's crust and biosphere. .
1927 he founded and led the world's first geochemical research institution - the Biogeochemistry Laboratory.
In the 1930s, Felsman published "Geochemistry" (4 volumes), which analyzed the laws of various atomic migration in the earth's crust in various aspects.
At the same time, the understanding of the radioactive decay law, the discovery of isotope , and the invention and improvement of mass spectrometer have led to the development of isotope geochemistry , especially isotope chronology.
1907 American chemist B.B. Boltwood published the first batch of age data for chemical uranium-lead method. From the 1940s to 1960s, the uranium-thorium-lead method, potassium-argon method, rubidium-strontium method, ordinary lead method, carbon-14 method, etc. gradually developed and improved, so that isotope chronology would begin to take shape.
1.3. Development period
After the 1960s, geochemistry not only continued to regard mineral resources as important research objects, but also opened up fields such as environmental research, earthquake prediction, marine research and development, the origin of life, deep earth and extrasphere space, etc. research.
geochemical analysis methods are developing rapidly, and ultra-trigic and high-sensitivity analysis and testing technologies and instruments are widely used. In combination with the use of electronic computers, not only can a large amount of high-precision analysis data be obtained, but also can directly reveal the difficult-to-observe elements in the sample and their Subtle changes in isotope composition and ultrastructure .
Some new dating methods, such as uranium system method, fission track method, argon-40/argon-39 method, samarium-neodymium method, thermoluminescence method, etc., have been matured one after another, making the isotope dating method more perfect.
During this period, China has achieved a number of important achievements in elemental geochemistry and isotope chronology. In 1961, Li Pu and others published the first batch of isotope age data in China; in 1962, Li Tong and others published the average chemical composition data of various magmatic rocks in China; in 1963, Chinese Academy of Sciences, completed the Chinese lithium beryllium niobium tantalum tantalum rare earth The geochemistry of elements is summarized, and important deposit types and distribution rules of these mineral species are proposed.
2. Research content
mainly includes: ① Study the composition of elements and isotopes in the earth and geological bodies, and quantitatively determine the distribution of elements and isotopes in various spheres and geological bodies on the earth; ② Study the surface and interior of the earth and some celestial bodies The chemical effects carried out in reveal the migration, enrichment and dispersion of elements and their isotopes; ③ Study the chemical evolution of the earth and even celestial bodies, that is, study various parts of the earth, such as the atmosphere, hydrosphere, , crust, mantle, and core Neutralizes the equilibrium, circulation, and changes in time and space of chemical elements in geological bodies of various rocks and species.
3. Branch disciplines
Based on different research fields, topic tasks and means, geochemistry has formed multiple branch disciplines.
3.1. Elemental Geochemistry
Starting from the content and combination of chemical elements in natural samples such as rocks, it studies the distribution, migration and evolution of each element
in various parts of the earth and in cosmic celestial bodies. In the development of mineral resources, elemental geochemistry plays an important role. The research on trace elements provides geochemical tracers for diagenesis and mineralization, and lays the foundation for establishing quantitative models for diagenesis and mineralization.
3.2. Isotope Geochemistry
Based on the isotope variation caused by nuclear decay , fission and other nuclear reaction processes in nature, as well as isotope fractionation caused by physical, chemical and biological processes, it studies celestial bodies, the earth and various geological bodies, based on isotope variations caused by nuclear decay , fission and other nuclear reaction processes, as well as isotope fractionation caused by physical, chemical and biological processes, it studies celestial bodies, the earth and various geological bodies. the time of formation, source of material and evolutionary history.
isotope chronology has established a complete set of isotope age determination methods, providing important time coordinates for the evolution of the earth and celestial bodies. It has been measured that the ages of each planet in the solar system are 4.5 billion to 4.6 billion years, and the ages of elements in the solar system are 5 billion to 5.8 billion years.
In the study of mineral resources, isotope geochemistry can provide multiple information on diagenesis and mineralization, providing a basis for exploring the formation mechanism and material sources of geological bodies and mineral deposits.
3.3. Organic Geochemistry
Study the composition, structure, properties, spatial distribution of organic matter produced in nature, evolutionary laws in earth's history and the impact of their participation in geological action on element dispersion and enrichment. Research on the origin of life is one of the important contents of organic geochemistry. It includes two aspects: one is the exploration of the evolution of organic matter in the early stages of life and traces of life in ancient Precambrian rocks; the other is to conduct simulation experiments on the early stages of life and the origin of life on Earth according to the laws of celestial body evolution. A set of oil-generating indicators established by organic geochemistry provides an important means for the search and evaluation of oil and gas.
3.4. Astrochemistry
Study the origin of elements and nuclide , the cosmic abundance of elements, the elemental composition and isotope composition of cosmic matter and its variations, the physical and chemical conditions for the formation of celestial bodies, the distribution and changes in space and time, and the distribution and changes of celestial bodies. law.
3.5.Environmental Geochemistry
Study the chemical composition, chemical action, chemical evolution of the human living environment and its relationship with humans, as well as the impact of human activities on environmental state and corresponding countermeasures. Environmental Geochemistry reveals the regional distribution characteristics of certain diseases and their relationship with environmental factors.
3.6. Geochemistry of ore deposits
Study the chemical composition, chemical action and chemical evolution of ore deposits. Focus on the time, physical and chemical conditions, mineral origin and mechanism of mineralization.It integrates research methods and results from branch disciplines such as elemental geochemistry, isotope geochemistry, exploration geochemistry and experimental geochemistry, and serves the search, evaluation, development and utilization of minerals.
3.7. Regional geochemistry
studies the chemical composition, chemical action and chemical evolution of certain geological bodies and circles in a certain region, as well as the laws of circulation, redistribution, enrichment and dispersion of elements and isotopes. It serves to solve various basic geological problems in the region, regional mineralization laws and mineralization problems, and regional geochemical zoning and environmental assessment. The unevenness of elements in spatial distribution revealed by regional geochemistry provides a basis for dividing elemental geochemistry provinces and mineralization prospects.
3.8. Exploration Geochemistry
System measurement of the content and distribution of mineralization and associated elements in different geological bodies and zones, and find out abnormal areas to reduce the target area and entangle the prospecting and exploration objects. In addition to directly serving mineral resource exploration, it is also an important reference basis for environmental assessment and land planning.
Some major achievements in geochemistry are the results of comprehensive research in various branches of disciplines. For example, the age of the isotope formed by the meteorite and moon rock is consistent with the isotope age formed by the earth, indicating that the time when each member of the solar system forms an independent cosmic body is roughly the same. For example, the study of trace elements and isotopes has led to the discovery of vertical and regional inhomogeneity of mantle composition, and a bispheric mantle model has been proposed, deepening the understanding of the inside of the earth. Astrochemistry, trace elements and isotope geochemistry research also provides a basis for the new catastrophe theory.
4. Research Methods
Combining basic research methods and technologies in geology, chemistry and physics, forming a complete and systematic geochemical research method. Including field geological observation, sampling, elemental and isotope composition analysis and existence state testing of natural samples, experimental simulation of elemental migration, enrichment geochemical processes, etc.
In terms of thinking methods, a comprehensive compilation of a large number of natural phenomenon observation data and element content analysis data in rocks and minerals is widely used to obtain rules, establish various models, and express them in words or charts. It is called the model principle .
With the accumulation of research data and the maturity and improvement of basic geochemistry theories, especially the establishment of experimental simulation methods for geochemical processes, geochemical research methods have shifted from qualitative to quantitative and parameterization, greatly deepening the mechanism of action on nature Understanding.
Modern geochemistry, widely introduces precision scientific theories and thinking methods, and studies natural geological phenomena, such as quantum mechanics , chemical thermodynamics , chemical dynamics , nuclear physics, and the application of electronic computing technology This improves geochemistry's inference ability and prediction level.
Based on this, a series of multidimensional phase diagrams of geological and mineralization effects were compiled, and quantitative models of mineralization effects of many representative deposit types and computer evaluation and prediction methods for exploration and exploration were established.
5. Outlook
Geochemical research is undergoing three major transformations: from the continent to the ocean, from the surface, the crust to the deep crust, the mantle, and the mountain and the earth turn to the extrasphere space. Geochemistry analytical and testing methods will be more accurate and fast. The development of micro- and ultra-microanalysis testing technology will enable the acquisition of elemental, isotope distribution and composition data in ultra-micro-region (micro-g) samples in the ultra-micro-region (micro-g) range.
Low temperature geochemistry, geochemical dynamics, ultra-high pressure geochemistry, rare gas geochemistry, comparative planetology, etc. are all new branch disciplines with huge development prospects.
21st century geochemistry, in addition to continuing to contribute to mineral resources, environmental protection, etc., will also be used to global changes, biosphere and ecological environment, international disaster reduction, continental ultra-deep drilling, planetary exploration, deep sea observation, different scale and geochemical maps of the range provide new results.
Recommended Bibliography
National Research Council Geology Department National Geochemistry Committee "The Direction of Geochemistry Development" edited and group. Direction of Geochemistry Development. Xu Zhonglun, translated. Guiyang: Guizhou People's Publishing House , 1983.
Tu Guangchi . Geochemistry. Shanghai: Shanghai Science and Technology Press , 1984.
Institute of Geochemistry, Chinese Academy of Sciences . Advanced Geochemistry. Beijing: Science Press, 1998.
Excerpted from: "China Encyclopedia (2nd Edition)" Volume 5, China Encyclopedia Press, , 2009
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