Granite is acidic (SiO 2 >66%) Magmatic rock Hit the mark Intrusive rock This is the most common kind of rock, mostly light red, light gray, gray and so on. Medium coarse-grained, fine-grained structure, Massive structure . There are also some for Variegated structure , Spherical structure Gneissy-like structure, etc. The main minerals are quartz , Potash feldspar Harmonization acidity plagioclase Secondary minerals are biotite, hornblende, and sometimes a small amount of pyroxene. The common minerals are magnetite, sphene, zircon, apatite, tourmaline, fluorite and so on. The quartz content is the most among all kinds of magmatic rocks, and its content can range from 20-50%, and a few can reach 50-60%. The content of potassium feldspar is generally more than that of plagioclase, and the proportion of the two is often two-thirds of the total amount of potassium feldspar, plagioclase accounts for one-third, and potassium feldspar is mostly light red in granite, and there are gray and gray. Off-white potassium feldspar and plagioclase are often indistinguishable from hand specimens. At this time, we should carefully observe the twin characteristics of these two feldspar, because the plagioclase Polymer twin When turning the specimen, it can be seen that there are regular light-dark polymer sheets on the plagioclase crystal, while the potassium feldspar is a cassette twin crystal, showing two half crystals with different brightness.

Granite can also be further named according to the types of dark minerals, such as dark minerals are mainly biotite, which can be called biotite granite, which is a common kind of granite. If it is biotite and Muscovite, its content is close to equal, it can be called two-mica granite, if the dark minerals are mainly hornblende, it is called hornblende granite, if the dark minerals are mainly pyroxene, it is called pyroxene granite, and almost no dark minerals can be called alasgranite. ^[1]

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Chinese name: granite
Foreign name: Granite
subject: petrology

Rock class: Acid intrusive rock
SiO2 content: > 66%
Announcement time: The year 2003 ^[5]
Publication in print: Civil Engineering Terms, Science Press

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EDITOR

Model classification of granitic rocks (Streckeisen, 1976)

The famous phrase "There are all kinds of granites", originally put forward by H. H. Read in 1933, in fact there are at least 20 proposed schemes for classifying granites (see Barbarin, 1990, 1999 for a summary; And a review of the more commonly used classification methods by Frost et al. 2001). The most common classification schemes are geochemical and/or genetic alphabetical classification schemes, such as categorizing granites into types S, I, M, A, and C (Type S is granite transformed from sedimentary rocks; Type I is magma origin; M-type is mantle origin; Type A is anhydrous granite; C is for Perilla granite); Or divided into calc alkaline, alkaline, peralkaline, peraluminum and aluminous granite; Or according to the tectonic setting is divided into "orogenic" granite (oceanic and continental volcanic arcs; Continental collision zones), "post-orogenic" granites (post-orogenic uplift or subsidence areas), and non-" orogenic "granites (continental rifts, hot spots, mid-ocean ridges, oceanic islands). ^[2]

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EDITOR

As the landmark rock of the continent, granite forms the basis of the crust in the upper part of the continent, and the formation process of granite is usually closely related to the tectonics, metamorphism and mineralization of the continent. The genesis of granite has been the subject of much debate since the 18th century, when geological science was still in its infancy. The debate on the origin of granite can be seen in the works of Gilluly (1948), Pitcher (1993), and Young (2003), which are not listed here. It should be mentioned that since Theory of plate tectonics Since its emergence in the 1960s, many explanations of granite origin have been reinterpreted in the theoretical framework of plates. In many cases, there seems to be a convergence of perceptions, but the actual debate continues.

Bowen's (1914,1922,1948) theory of crystallization differentiation of basaltic magmas is a mistake that combines the sequence of mineral crystallization with the sequence of rocks from basic to acidic magmatic rocks. Experimental results show that crystallization differentiation of basaltic magma ultimately produces only a small amount of residual granitic melt, which clearly conflicts with the fact that there are many granites in the field (Holmes, 1926; Read, 1957). The mineral reaction series can actually be applied to magmatic systems with different components. In other words, the initial crystallization from the magmatic system is not necessarily a basic rock, and the final formation is not necessarily a felsic (acidic) rock, because the properties of the rock crystallized from the melt depend on the composition of the melt rather than the order in which the minerals crystallized (Kennedy, 1933). Walton (1960) commented on Bowen's understanding as follows: "There is nothing wrong with Bowen's chemical theory or its application to the separation of basaltic magmas, which remains a fundamental principle of petrology. However, the theory of igneism rigidly binds to a single model, suggesting that most of the evolution of igneous rocks is the result of basaltic magma invading the crust to cool, crystallize, and separate, which is a bit speculative. The same chemical theory can be applied to other models."

The debate in the 1940s (Gilluly, 1948) between the "metamorphoists" represented by H. H. Read and the "magmatism" represented by N. L. Bowen ended with the subsequent recognition of the magmatic origin of granite by more and more scholars. But where does the magma that makes up the granites come from? In Bowen's words: Whence the granites? (Where does granite come from?)

The overwhelming understanding of this problem is that granite is formed by the partial melting of rocks of different compositions in the earth's crust. This view combines two different early understandings of the origin of granite: magmatism, which holds that granite is derived from the crystallization of magma, and metamorphism, which holds that granite is a sedimentary rock rich in silicon and aluminum that has undergone dry or water-containing processes granitization Transformed into). It is suggested that granite is the result of crustal rocks through supermetamorphism (deep melting), which is of great significance for the study of the origin and chemical differentiation of the crust, because they are related to the thermal state of the crust in a specific period and the composition of the original rock, including how much granitic magma can be produced, the temperature and the amount and source of water when the granite is formed, the tectonic background and plate action process. ^[2]

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EDITOR

To properly understand the so-called "granite problem," one must first understand how geologists arrived at the conclusions that form the current theory. It is therefore necessary to set forth systematically the knowledge of ideas that have been around for a century or more. It can be seen from these accounts that many of the "new concepts" that have developed in the last twenty or thirty years are the same subjects that have been discussed and debated for the last hundred or 150 years.

In the 1930s, there was a fierce debate among geologists over which granites were magmatic and which were metamorphic or metasomatic. This dispute began as early as the era of hydrogenesis, and until the mid-nineteenth century, it was entangled in the idea that granite was deposited in an aqueous solution. Although the process of metamorphism (Layle's term) has been recognized since Hutton, its nature is not well understood. Even before the use of microscopes, much had been written about the metamorphic formation of granite. Hutton himself strongly advocated the idea of magmatic origin. According to Hutton, the characteristics of the granite unconformity intrusion stratified rocks, the coarse-grained crystalline fabric, and the diagonal granitic veins were all taken as evidence that the granite was formed by the crystallization of the "subterranean lava", which was later called "magma".

With regard to the behaviour of "magma", it has long been noted that there are many circumstances which cannot be well explained without the assumption of water. It is particularly important in the case of granite, so it is necessary here to describe in advance a problem that was revived more than a decade ago. Spllanzani (1794) may have been the first to recognize the genetic significance of the need for water to occur in molten rock. Later, Scorp (1825) discussed the existence of water in lava, while Scheerer (1862) more explicitly linked the presence of water to granite magma.

In addition, Bunsen (1861) also discussed the geology of granite, especially the genesis of granite. At the time, it was known that the crystallization temperature of quartz in the molten state was higher than that of orthoclase, and much higher than that of mica. "Antipyretics" do not accept that granite is formed by magma, and insist that if granite is indeed formed by magma, then the order of crystallization of these minerals in granite should be quartz - orthoclase - mica. It is well known that the actual crystallization sequence is exactly the opposite. So it turns out that granite can't be igneous. Bunson believed that the melting point of a mineral was not the same as the temperature at which it crystallizes from its solution in another case. On the other hand, in a further discussion, he conducted comparative work on the behavior of some chemical components in aqueous solutions.

The concept of granitization (the migration of acidic substances) dates back to Lyer's time in 1836. The debate about the genesis of granite at that time can be illustrated by the situation in the Oslo area. Leopold Von Buch surveyed the area in the early 19th century, and Charles Lyer also surveyed the area in 1837 under the direction of B. M. Keilhau. HoltedahI (1963) has commented extensively on these investigations. According to this account, von Bucher (a student of Weerner's) believed that most of the granites in this area were overlaid with fossil-bearing formations in the same form as basalt and other "dark" rocks in general, while Drammen granite was older than limestone and lay beneath it. Lyer, however, was highly skeptical of these explanations, arguing that in some places granite could be slanted over sedimentary rock, but that this was a minor feature, and that it was common for granite to extend its veins into adjacent formations, turning limestone into marble, and shale into mica schist. In essence, he adopted Hutton's concept of plutonic activity; Molten material invades the older structure violently and thrusts the overlying rock mass. However, Kelhoe did not accept these ideas, and he did not understand how such a large space could be left open for invaders to immerse themselves in the area once occupied by eruptive rock. As early as 1838, Kelhoe was probably the first to pay attention to the "spatial problem" of the emplacement of igneous bodies.

Kelhoe proposed his "transmutations" theory to replace this idea. The view of this argument is that the early rock mass was transformed into granite and syenite by a slow and steady process. Kelhoe called this process "granitification." He also claims to have found an example of sedimentary rock turning into granite; For this change he did not take into account either the connection with deep phenomena or the temperature increase involved.

However, Kjerulf (1855,1879) argued that Oslo's granite was igneous. He acknowledged the spatial problems raised by Kelhoe, but argued that the searing intrusion had devoured the previously sedimentary rocks. Therefore, the concept of "assimilation" is introduced in the petrology of igneous rocks. A few decades later, Michel-Levv (1894), probably not yet aware of Kaiselulf's work, cited the concepts of metasomatism and assimilation when describing the genesis of granite in France. At the end of the nineteenth century, the concept that granite was formed by metamorphism and metasomatism was quite prevalent in France. Those educated in France and England, such as the Norwegian Kekirulf, favored the magmatic-igneous view.

In Finland, Sederholm (1893) originally opposed the views of the Canadian A. C. Lawson, who had argued that the invasion Primitive crust The oldest granites, among the oldest sedimentary rocks, were formed by remelting of the oldest sediments at the bottom. Cederholm (1892) argued that the porphyry is a true magmatic rock, and that magma can be filled into graben-like depressions during periods of strong vertical movement, during which the porphyry is invaded in large scale. Sederholm later developed his own concepts of regeneration and deep melting for some other granites, which were in part consistent with those formulated by Lawson in Canada. T/gerstedt (1893) published a slightly different concept when describing some of the migmatites of southern Finland (later called migmatites). He suggested that the rocks were formed when granitic material penetrated into a metamorphic deposit called neiss. This granitic material contains a considerable amount of water, the presence of which accelerates the process and causes the granitic material to form small veins into the gneiss. So he again mentioned the existence of water to explain the formation of narrow resistance and long distance aplitic veins; There is considerable difficulty in explaining their formation in any other way.

It is generally believed that granite generally forms huge batholith. In fact, very little of these batholith is granite, and most of it is mountain granoblende, steep rock and rock Quartz diorite Composed of. Some granites, however, are thought to form lappes, basins, or domes.

The determination of the occurrence of granite is an important problem, and the terms used to describe the occurrence have genetic implications in the eyes of those who use them. According to Gil-bert (1877), the mantle is the result of the ascending movement of magma, while the meaning of a rock basin is the passive displacement of magma into the space formed by the collapse of the chassis. The term batholith was recommended by Suess (1895); It is difficult to infer the immersion desert pattern of a batholith. Hughes himself likened the process of magma rising through the earth's crust to "the process of forcing a board through with hot tongs." Nevertheless, this vivid metaphor is by no means an explanation (Levinson-Liesinger). Kekirulf (1855) and Michel-Levy argued that rock mass is formed by the gradual assimilation of magma into the surrounding rock, and the rate of magma rise depends on the rate of magma digestion of the surrounding rock and roof. Later, in 1923, Cloos suggested that many of the plutons that had been assumed to be rocks were in fact large intrusive sills, and that the difficult spatial problem of sill emplacement was no longer a problem. In dome structures, there is often a granitic core surrounded by gneiss. The Finnish geologist Gadolin (1858) was the first to describe the structure of the dome north of Lake Ladoga in Pusunsaari. According to his opinion, the dome structure is the intrusion of gneiss formation under the granite rock mass mountain, the upper contact Angle is slow, the downward Angle gradually increases, and the intrusion construction remains gentle and the outward slope decreases from the core. In 1951, Escora gave the following explanation of the dome: "As summarized in my 1949 paper, it has been shown that granitization, with the addition of large quantities of potassium and the increase in volume, has specifically altered the edges of the rock mass, allowing ancient intrusions to rise and Pierce the dome." ^[3]