What is petrology in geology


Petrology, [from Greek petra = stone], Geology, Sub-discipline of geosciences that deals with occurrence, mineral composition, structure, chemical composition and formation of rocks. Since rocks represent the essential components of the earth and since they themselves consist of a mixture of minerals, petrology has close relationships with the neighboring subjects of geology and mineralogy. According to the traditional subdivision of rocks according to their genesis into igneous (igneous rocks), metamorphic (metamorphic rocks) and sedimentary rocks, this three-way division has also become common in petrology. In addition, the following methodological sub-areas of petrology can be distinguished: a) Petrography: It deals with the natural occurrence, description and classification of rocks; b) Petrogenesis: It tries to clarify the history of the formation of the rocks; c) chemical petrology (geochemistry): it studies the chemical composition (elements and isotopes) of rocks; d) Petrophysics: It investigates the physical properties of rocks and therefore has many points of contact with e) technical (or applied) rock science, which deals with the diverse possible uses of loose and solid rock in technology and industry; f) Experimental petrology: This area, which has grown in importance in recent decades, tries to clarify the rock-forming processes occurring in the earth by means of laboratory experiments in which the natural conditions are reproduced; g) Theoretical petrology: It tries to contribute to the modeling and clarification of the rock-forming processes on and within the earth through the application of physical and chemical laws (such as thermodynamics or kinetics).

Petrology has existed as an independent field of research since the second half of the 18th century. While initially the dispute between Neptunists (Neptunism), who were of the opinion that all rocks must have been formed by deposits from a sea, and plutonists (Plutonism), who also believed that rocks could be formed from a melt, dominated the scientific discussion , not least through the introduction of the microscopic investigation method from around 1860, a wealth of new knowledge resulted, which led to a systematic description and classification of the rocks into the three genetic groups (magmatites, metamorphic rocks and sedimentary rocks) that are still in use today. Since the beginning of the 20th century, chemical and experimental methods of investigation have become increasingly important. Particularly noteworthy in this context is the establishment of the ›Geophysical Laboratory‹ in Washington (USA) in 1904, which played a leading role in the development of new experimental techniques and their application to petrological issues. Especially since the end of the Second World War, advances in analytical methods (e.g. isotope geochemistry) and in experimental procedures (e.g. the punch-cylinder press) have contributed to a better understanding of the complex processes involved in rock formation. In connection with the new global theory of plate tectonics developed between 1960 and 1970, it is now possible to describe and understand most of the rock-forming processes occurring on and in the earth. The following compilation shows a few selected examples of current research focuses in which petrologists play a major role: a) in sedimentology, the reconstruction of climatic events and environmental conditions since the last ice age with the help of lake sediments or marine deposits; b) in igneous petrology, the study of volcanic activities along converging plate boundaries; An important question is what influence differently composed fluids have on the formation and rise of basaltic or andesitic melts; c) In metamorphic petrology, the answer to the question of how pressure-temperature-time paths (P-T-t paths) can be derived from metamorphic rocks and used for the reconstruction of geodynamic processes, e.g. in the case of continent-continent collisions. Other current topics are, for example, the experimental investigations into questions of phase transformations in the deeper mantle and the structure, composition and magnetism of the earth's core or research into the mineralization processes that take place when hydrothermal solutions escape at the deep sea floor. [MS]