What Is Petrology?

Petrology is a branch of geology. It is a science that studies the distribution, occurrence, composition, structure, structure, classification, genesis, evolution, etc. of rocks.

The research content of petrology is determined with the development of the entire geological science and the needs of production. In summary, the main contents of petrological research can include the following aspects:

1. Study the characteristics of rocks, that is, the mineral composition, chemical composition, structure, structure, and rock composition of various rocks

Category naming.

2. Investigate the occurrence, age and symbiotic combinations of rock masses, the regularity of the distribution of various rocks in space and time, and determine

Their relationship to geological formations.

3 Study the relationship between rocks and mineralization and the specificity of various types of rock mineralization.

4 Study the various geological effects of rock formation, physical and chemical effects, formation environment, solve the causes, sources,

Issues such as evolution.

The first two of the above four items belong to the category of petrology and belong to the first category and are the foundation. The last two items belong to the category of petrology and are some concepts and inferred causes and hypotheses derived from the former. Only when the information obtained by studying the former is accurate and detailed, can the inferred causes, principles, and hypotheses have a reliable basis.

(I) Field Geological Methods

Mainly through field geological mapping and profile measurement, the composition, structure, structure, occurrence, age, generation sequence, symbiotic combinations of various types of rocks, lithofacies and the relationship between rock mass and minerals, and the permeability of rocks The water-tightness and the engineering mechanical properties of rocks should be described in detail. At the same time, preliminary analysis and inferences should be made. Appropriate specimens should be collected for further research in the room. Field research is extremely important. It is the basis of all research work. For this specialty, field research is even more important.

(Two) indoor research methods

The data collected in the field are used for analysis and research in the laboratory. The methods currently used are petrographic studies, petrochemical studies, and experimental petrological studies.

1. Lithofacies research mainly uses polarized light microscope, Fresnel table, electron microscope, X-ray analysis, differential thermal analysis, electronic probe and other methods to study the mineral composition, structure, and relative content of various components in detail. Provide necessary data for determining rock types, genesis, hydrology, and engineering geological properties.

2. The petrochemical method mainly uses whole rock analysis, single mineral analysis, isotope, spectral analysis, staining, etc., to study the petrochemical composition, the occurrence state of trace elements, and geochemical characteristics in order to understand the evolution law and mineralization relationship of the rock. · F

3 The experimental petrology method uses artificial high temperature and high pressure to reconstruct the mineral and rock formation process in order to understand the origin and evolution of magma and the physical and chemical conditions of metamorphic rock formation. It provides experimental basis for solving a series of complex problems concerning diagenesis and mineralization.

Petrology research should closely combine field geological observation and laboratory experimental analysis and research in order to better solve relevant petrological issues.

At first, mineralogy and petrology were indistinguishable. Later, petrology became independent from mineralogy and developed into an independent discipline. However, due to differences in petrological research content, depth, and emphasis, a series of very different branch rock disciplines have emerged. Among them, there are petrography or petrography, which is also called rock classification and description. Describe petrology; have petrology or petrogenesis, or theoretical petrology to explore the formation conditions and genesis of rocks; have high temperature and high pressure experiments and modern testing techniques as the basis for magmatism and metamorphism Experimental petrology for the simulation and testing of processes and products; others include mantle petrology, chemical petrology, etc. In contemporary petrology, the description of petrology is generally ignored, and the genesis of rocks and the synthesis of experimental data are paid attention to in order to obtain a comprehensive understanding of the generation, evolution, and spatial-temporal distribution of rocks. Petrology can better serve human society and produce greater benefits.

Igneous petrology is a discipline that studies the composition, structure, and formation conditions and evolution history of rocks mainly formed by magmatism. It uses modern experimental techniques, physical chemistry, fluid dynamics and other theories to clarify the evolutionary migration and cooling crystallization of various types of magma. Based on the regional geological distribution of magmatic rocks and the tectonic units, it summarizes the spatiotemporal distribution of natural magmatic rock combinations. law.

Sedimentary petrology is the study of the composition, structure, structure, and genesis of sediments and sedimentary rocks. Its main content includes the study of sedimentary sedimentary material composition, grain size, and bio-fossil communities; determining the sedimentary environment and source area of sediments, clarifying paleogeographical conditions and restoring paleostructures; according to the proportion of debris and matrix, according to Separation of mineral particles and organic components to classify sediments and sedimentary rocks; determine the chemical properties of water bodies and seawater depth based on the characteristics of chemical sediments.

Metamorphic petrology is a discipline that studies the metamorphism in the crust and the formation characteristics and evolution history of metamorphic rocks. The impact metamorphism of celestial meteorites also belongs to this research category.

During the crustal evolution, the interaction of the mantle and the crust caused changes in the regional heat flow and tectonic environment. A series of metamorphic rocks belonging to different metamorphic facies, metamorphic facies, and different degrees of deformation occurred. They are the records of metamorphism in nature, and are therefore the object of study on metamorphic rocks. Metamorphic petrology can be divided into two directions: metamorphic geology and metamorphic experimental petrology.

Industrial petrology is the use of silicate technology to study and develop resources related to silicate minerals, also known as process petrology.

Others include cosmic petrology, chemical petrology, experimental petrology, mantle petrology, and tectonic petrology.

Rock formation is inseparable from the geological environment at the time of formation. Rock construction is a manifestation of the geological environment. Therefore, in order to clarify the geological environment, the study of regional geology, geotectonics, tectonic geology, and stratigraphy is essential knowledge; mineralogy and geochemistry can clarify the laws of migration and change of major rock-forming minerals and elements in rocks. Combined with chemical thermodynamics and chemical reaction kinetics, it is possible to explain the possible physicochemical processes during the formation of rocks, as well as the probable rocks in which magma occurred.

Cosmic petrology can be seen as the link between petrology and astronomy, while mantle petrology can be seen as a bridge between petrology and geophysics. These two branch disciplines have expanded the time and space of petrology. The mantle, which can reach a depth of 600 kilometers, dates back to about 4 billion years, and its research results provide basic data for studying the early evolution of the Earth.

As a natural system of rock assemblage, its genesis is complex, restricted by many factors, and is closely related to crustal evolution. Effective petrological research must, on the one hand, get rid of the shackles of traditional viewpoints and liberate from the description of pure rocks; on the other hand, we must prevent the tendency of simplification and incorporate complex causes into simple causes.

Petrology is one of the basic disciplines in the field of geology, and it has a close relationship with geology and other natural sciences. Because rocks are mineral aggregates formed under certain physical and chemical conditions, to study rocks, you must have basic knowledge in the disciplines of mineralogy, crystallography, optics, physics, and chemistry. To test and analyze rocks, you also need to be familiar with or master the knowledge, techniques and equipment of various testing and analysis methods. To explore the genesis of rocks, it is necessary to simulate the formation conditions of rocks. In this way, it is necessary to understand or master the basic knowledge and technical equipment of experimental petrology and genetic mineralogy, which must have extensive physical chemistry, computational mathematics, and thermodynamics. , Fluid mechanics and other disciplines. At the same time, the research results of petrology can be widely used in mineral deposits, geochemistry, geological surveying, structural geology, environmental geology, energy geology, hydrogeology and other disciplines.

(I) The role of petrology in hydrogeology

Hydrogeology is a science that studies groundwater. Groundwater is found in the voids (pores and fissures) of the rock. The number and size of the voids are closely related to the nature of the rock. Rocks of different genetic types have different compositions, structures, and structures, and their porosity, water storage, and water permeability are also different. Therefore, to study the occurrence conditions of groundwater, petrological knowledge is required. ;:; Some deep intrusive rocks and metamorphic rocks, such as granite, gabbro, gneiss, etc., are distributed in this type of rock due to their compact structure, relatively uniform particles, small porosity, and impervious to water and water storage. It is difficult to find water in this area. Only the structural fractured zone along the fissure can find water-rich areas. In other areas, it is a poor area, and only weathered fissure water with small amount of water can be found. -In the extruded rock area, because some extruded rocks have a pore structure, the pores are often large, and some extruded rocks have columnar joints, so the permeability is good and the water storage space is large. For example, the Hannuoba basalt in northern Hebei has become a better aquifer due to the development of stomatal structures and fractures. ;! The structure of sedimentary rocks, such as the clastic rock's particle size, shape, sortability, arrangement and relationship with each other, will affect the rock's porosity, water storage and permeability. Such as coarse particles of conglomerate, sandstone, generally higher permeability. As the particles become smaller, the water permeability gradually decreases. For example, very fine-grained argillaceous rocks are often impermeable and have water-proof properties. Such rocks can communicate with the groundwater of adjacent aquifers only when they encounter cracks caused by structural changes.

Limestone, dolomite, and evaporite (gypsum, rock salt, etc.) are all relatively soluble rocks. Under appropriate conditions, they can form dissolution channels and increase their water permeability and storage space. For example, the limestone area in Zhaoqing, Guangdong, was formed by dissolution; F river.

In short, petrological research is of great significance for understanding the laws of storage, movement, and distribution of groundwater resources.

(II) The role of petrology in engineering geology

Rock is the material foundation of engineering geology (engineering foundation and surrounding rock). Except for space satellite stations, the foundations of major human engineering projects are almost inseparable from rock. The physical and mechanical properties of the rock mass and the quality of the structure play a decisive role in the success of the project. For example, when repairing underground buildings (tunnels, subways, underground power stations, underground oil depots, underground hangars, underground warships! Depots, etc.), the entire mountain is often hollowed out, and the stability of surrounding rocks must be paid attention to. Rock mass stability is closely related to the genetic type, composition, structure, structure, and combination characteristics of various rocks. For example, an underground oil depot is established in a granite area. Because the granite structure is dense and hard, the compressive strength is high, the rock mass is huge, and there is no weak rock interlayer in the middle. If it is constructed in weak and fragile rocks, the construction is difficult, the investment is large, and the cost is high. Generally speaking, the engineering mechanical properties of crystalline rocks are better than those of sedimentary rocks. However, the factors affecting the engineering mechanical properties of rock masses are various and must be studied carefully.

High dams or heavy buildings should generally be built on hard bedrocks. For example, the Sanmenxia Reservoir dam is built on diorite vermiculite, and should not be built on bedrock with weak interlayers. Weak interlayers such as chlorite schist, sericite schist, and argillaceous shale in hard bedrock can cause buildings to collapse and cause huge losses.