Petrology is a branch of geology, which studies the distribution, occurrence, composition, structure, structure, classification, origin and evolution of rocks.
The research content of petrology is determined with the development of the whole geological science and the needs of production.To sum up, the main contents of petrology research can include the following aspects:
1. Study the characteristics of the rock itself, that is, the mineral composition, chemical composition, structure, structure and
Classification naming.
2. Study the occurrence, age and symbiotic combination of rock mass, and the distribution regularity of various rocks in space and time to determine
Their relationship with geological structure.
3. Study the relationship between rocks and mineralization and the specialization of various rocks in mineralization.
4. Study various geological processes, physical and chemical processes, generation environment of rock formation, and solve the causes, sources
Evolution.
The first two of the above four items belong to the category of petrology, which is the first and the basis. The last two items belong to the category of petrology, which are some concepts derived from the former and the causes and hypotheses deduced from the former. Only by studying the exact and detailed data obtained from the former, can the inferred causes, principles and hypotheses have a reliable basis.
research method
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（1） Field geological methods
Mainly through field geological mapping and section measurement, the composition, structure, occurrence, age, generation sequence, symbiotic association of various rocks, changes in lithofacies, relationship between rock mass and minerals, water permeability and water resistance of rocks, and engineering mechanical properties of rocks should be observed and described in detail, and preliminary analysis and inference should be made,Appropriate specimen samples should also be collected for further indoor research.Field research is extremely important. It is the basis of all research work. For this specialty, field research is more important.
（2） Indoor research methods
The data collected in the field are used for indoor analysis and research. The current methods include petrographic research, petrochemical research,Experimental petrologyResearch.
1. Petrographic research mainly uses polarizing microscope, Fraser platformelectron microscope, X-ray analysis, differential thermal analysis, electron probe and other methods are used to study the mineral composition, structure and relative content of various components of the rock in detail, so as to provide necessary data for determining the rock type, genesis, hydrology, engineering geological performance, etc.
2. The petrochemistry method mainly adopts whole rock analysis, single mineral analysis, isotope, spectral analysis, staining method, etc. to study the petrochemistry composition, occurrence state and geochemical characteristics of trace elements, so as to understand the evolution law of rocks and mineralization relationship·f
3．Experimental petrologyThe method is to artificially reconstruct the formation process of minerals and rocks by using high-temperature and high-pressure methods, so as to understand the origin and evolution of magma and the physical and chemical conditions for the formation of metamorphic rocks, and to provide experimental basis for solving a series of complex problems related to diagenesis and mineralization
In order to solve the problems related to petrology better, the field geological observation and laboratory experimental analysis should be closely combined in petrology research.
At first, mineralogy and petrology were indistinguishable. Later, petrology became independent from mineralogy and developed into an independent discipline.However, due to the differences in the research content, depth and emphasis of petrology, a series of very different branch rock disciplines have emerged, including petrology or petrography, also known as descriptive petrology, which focuses on rock classification and description;There is petrology or petrogenesis, or theoretical petrology to explore the formation conditions and genetic mechanism of rocks;Experimental petrology, based on high-temperature and high-pressure experiments and modern testing technology, simulates and tests the processes and products of magmatism and metamorphism;Others include mantle petrology, chemical petrology, etc.Contemporary petrology generally does not ignore the description of petrology, but also pays attention to the synthesis of rock genesis and experimental data, so as to gain a comprehensive understanding of the generation, evolution, space-time distribution laws of rocks, so that petrology can better serve human society and produce greater benefits.
At present, petrology is developing along the lines of magmatic petrology, sedimentary petrology andMetamorphic petrologyThe three main branches are developing in their own independent directions.Among them, magmatic petrology focuses on the composition, paragenetic association, occurrence and distribution, mineral relations, genetic mechanism of magmatic rocks, as well as the relationship between the formation, activity and evolution of magma and global tectonics. In addition, in recent years, the research content of magmatic petrology has expanded to the rocks of the upper mantle and the rocks of cosmic stars.Sedimentary petrology, focusing on the formation, migration, sedimentation and diagenesis of sedimentary materials I Composition of sedimentary rocks, sedimentary minerals, sedimentary environment, sedimentary facies.Metamorphic petrology focuses on the composition and distribution of metamorphic rocks, genesis, mineralization, protolith recovery, metamorphic facies and facies systems, and the relationship between metamorphism and tectonic activity and crustal evolution and development.[1]
Petrology Branch
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Igneous petrology is a discipline that studies the composition, structure, formation conditions and evolution history of rocks mainly formed by magmatism.It uses modern experimental technology, physical chemistryfluid dynamicsTo clarify the evolution, migration and cooling crystallization of various magmasGeotectonic unitAnd summarize the temporal and spatial distribution law of natural combination of various magmatic rocks.
Sedimentary petrology is a discipline that studies the composition, structure, structure and origin of sediments and sedimentary rocks.Its main contents include the study of material composition, grain size and biological fossil community of sediments and sedimentary rocks;Determine sedimentary environment and sediment source area, clarify paleogeographic conditions and restore paleostructure;Sediments and sedimentary rocks are classified according to the proportion of detritus and matrix, and the sorting of mineral particles and organic components;Determine the chemical properties of water body and seawater depth according to the characteristics of chemical sediment.
Metamorphic petrologyIt is a subject to study the metamorphism in the crust, the formation characteristics and evolution history of metamorphic rocks, and the impact metamorphism of celestial meteorites also belongs to this research category.
In the process of crustal evolution, the interaction between the mantle and the crust caused changes in regional heat flow and tectonic environment, and a series of metamorphic rocks belonging to different metamorphic facies, metamorphic facies systems and deformation degrees occurred.They are records of metamorphism in nature, so they are alsoMetamorphic petrologyThe research object of.Metamorphic petrologyIt can also be divided into two directions: metamorphic geology and metamorphic experimental petrology.
industrial petrology It is to research and develop resources related to silicate minerals by means of silicate technology, also known asProcess petrology。
The formation of rocks is inseparable from the geological environment at the time of formation, and rock formation is a manifestation of the geological environment.Therefore, in order to clarify the geological environment, regional geologyGeotectonicsStructural geology and stratigraphy are essential knowledge;Mineralogy and geochemistry can clarify the law of migration and change of main rock forming minerals and elements in rocksChemical thermodynamicsCombined with chemical reaction kinetics, it can explain the possible physical and chemical processes in the formation of rocks, as well as the possible protolith of magma.
Cosmic petrology can be seen as the link between petrology and astronomy, while mantle petrology can be seen as the link between petrology and astronomygeophysicsAs a bridge between the two disciplines, these two sub disciplines have expanded the space and time scope of petrology research. The depth of the mantle studied can reach 600 kilometers, and the time can be traced back to about 4 billion years. Their research results provide basic data for the study of the early evolution of the Earth.
As a natural system, the genesis of rock assemblages is complex, restricted by many factors, and closely related to the crustal evolution.Effective petrological research, on the one hand, should get rid of the shackles of traditional views and liberate from the description of simple rocks;On the other hand, it is also necessary to prevent the trend of simplification and incorporate complex causes into simple cause models.
Interdisciplinary relations
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Petrology is one of the basic disciplines in the field of geology, which is closely related to geology and other natural sciences.Because rocks are mineral aggregates formed under certain physical and chemical conditions, it is necessary to have basic knowledge of mineralogy, crystallography, optics, physics and chemistry to study rocks.To test and analyze rocks, it is also necessary to be familiar with or master the knowledge, technology and equipment of various testing and analysis methods.To explore the genesis of rocks, it is necessary to simulate the formation conditions of rocks, which also needs to be understood or masteredExperimental petrologyandGenetic mineralogyBasic knowledge and technical equipment, which requires extensive knowledge of physical chemistry, computational mathematics, thermal dynamics, fluid mechanics and other disciplines.At the same time, the research results of petrology can be widely used in ore deposit science, geochemistry, geological surveying, structural geology, environmental geology, energy geology, hydrologyEngineering geologyAnd other disciplines.
Petrology application
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（1） The role of petrology in hydrogeology
Hydrogeology is a science that studies groundwater.Groundwater occurs in the pores (pores and fissures) of rocks.The number and size of voids are closely related to the nature of rocks.For rocks of different genetic types, their composition, texture and structure are different, and their porosity, water storage and permeability are also different.Therefore, to study the occurrence conditions of groundwater, you must have the knowledge of petrology.;:;Some plutonic intrusive rocks and metamorphic rocks, such as granite, gabbro, gneiss, etc., are difficult to find water in areas where such rocks are distributed because of their compact structure, uniform particles, small porosity, and difficulty in water permeability and storage. Only along structural fracture zones with relatively developed fractures can water rich sections be found, and other areas are water poor areas,Only small amount of weathered fissure water can be found-In the extrusive rock area, some extrusive rocks have pore structure, and the pores are often large. Some extrusive rocks have columnar joints, so they have good water permeability and large water storage space.For example, Hannuoba basalt in northern Hebei has become a better aquifer due to the development of pore structure and the communication with fractures.;!The structure of sedimentary rocks, such as the particle size, shape, sorting, arrangement and mutual relationship of clastic rocks, will affect the porosity, water storage and permeability of rocks.For example, conglomerate and sandstone with coarser grains have high water permeability.As the particles become smaller, the water permeability gradually decreases.For example, argillaceous rocks with very fine grains are often impermeable layers and have water resisting properties. Only when such rocks encounter cracks caused by tectonic changes can they communicate with the groundwater of adjacent aquifers.
Limestone, dolomite and evaporite (gypsum, rock salt, etc.) are all easily soluble rocks. Under appropriate conditions, they can form dissolution channels to increase their water permeability and storage space.For example, the limestone area in Zhaoqing, Guangdong, was formed due to dissolution;F River.
In a word, the study of petrology is of great significance for understanding the storage, migration and distribution of groundwater resources.
（2） The role of petrology in engineering geology
Rock is the material foundation of engineering geology (foundation and surrounding rock of the project). Except for space satellite stations, the foundation of human major engineering construction is almost inseparable from rock.The physical and mechanical properties and structure of rock mass play a decisive role in the success or failure of the project.For example, when building underground buildings (tunnels, subways, underground power stations, underground oil depots, underground aircraft hangars, underground warships, garages, etc.), the middle of the whole mountain is often hollowed out, and attention must be paid to the stability of surrounding rocks.Rock mass stabilityIt is closely related to the genetic type, composition, structure, structure and combination characteristics of various rocks.For example, to build an underground oil depot in the granite area, because the granite structure is dense and hard, with high compressive strength, huge rock mass, and no weak rock interlayer in the middle, it is not easy to collapse, and the construction is safer and the cost is lower.If it is constructed in soft and fragile rocks, it will be difficult to construct, with large investment and high cost.Generally speaking, the engineering mechanical properties of crystalline rock are better than sedimentary rock.However, there are many factors affecting the engineering mechanical properties of rock mass, which must be carefully studied.
High dams or heavy buildings should generally be built on hard bedrock. For example, the dam of Sanmenxia Reservoir is built on diorite porphyrite, and it should not be built on bedrock with weak interlayer.If the hard bedrock contains a thin layer of chlorite schist,Pinal schist , argillaceous shale and other weak intercalations can lead to building collapse, causing huge losses.
