metaconglomerate - metamorphosed conglomerate ; marble - metamorphosed limestone ; hornfels - contact metamorphism of shale; very hard, like a brick ; . Geologic unit mapped in Maryland: Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet. Regional metamorphism refers to large-scale metamorphism, such as what happens to continental crust along convergent tectonic margins (where plates collide). Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. VALLEY, John W.1, CAVOSIE, A.J., WILDE, S.A., GRANT, M., and LIU, Dunyi, http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_39602.htm, ftp://rock.geosociety.org/pub/reposit/2002/2002034.pdf, https://en.wikipedia.org/w/index.php?title=Metaconglomerate&oldid=1007375955, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 17 February 2021, at 20:28. Dynamic metamorphism is the result of very high shear stress, such as occurs along fault zones. Mariposite is a word that has been used in many ways. What are the two textures of metamorphic rocks. When extraterrestrial objects hit Earth, the result is a shock wave. The Geology.com store offers inexpensive rock collections that can be mailed anywhere in the United States or U.S. Water within the crust is forced to rise in the area close to the source of volcanic heat, drawing in more water from further away. Thermal metamorphism in the aureole of a granite is also unlikely to result in the growth of mica in a foliation, although the growth of new minerals may overprint existing foliation(s). Supplying quality educational materials for teachers, collectors and other educational organizations since 1995. foliated metamorphic describes the texture of metamorphic rock Related questions What are some example names of foliated and un-foliated rocks? The planar fabric of a foliation typically forms at right angles to the maximum principal stress direction. [1] It is caused by shearing forces (pressures pushing different sections of the rock in different directions), or differential pressure (higher pressure from one direction than in others). It has been exposed to enough heat and pressure that most of the oxygen and hydrogen have been driven off, leaving a high-carbon material behind. When metamorphosed ocean crust is later subducted, the chlorite and serpentine are converted into new non-hydrous minerals (e.g., garnet and pyroxene) and the water that is released migrates into the overlying mantle, where it contributes to melting. That means it will take a long time to heat up, can be several hundreds of degrees cooler than the surrounding mantle. Granofels is a broad term for medium- to coarse-grained metamorphic rocks that do not exhibit any specific foliation. 2011 Richard Harwood | profharwood@icloud.com | Home. A second type of nonfoliated metamorphic rock, quartzite, is composed mostly of silicon dioxide. Phyllite is a third type of foliated metamorphic rock. With aligned minerals that are coarse enough to see, rocks that exhibit schistose foliation sparkle, because they contain micas that reflect light. The intense heat and pressure of metamorphism . Metamorphic rock that does not appear to exhibit aligned material to the naked eye may show structure at the microscopic level. The force of the collision causes rocks to be folded, broken, and stacked on each other, so not only is there the squeezing force from the collision, but from the weight of stacked rocks. The specimen shown above is about two inches (five centimeters) across. > The cement between the clasts is recrystallized, so the rock breaks across the clasts (instead of around the clasts in a sedimentary conglomerate). Introduction to Geology of the Oceans, 17a Introduction to Human Relationships with Earth Processes. Marble: A non-foliated metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Texture is divided into two groups. Want to create or adapt OER like this? There are two major types of structure - foliation and (non-foliated) massive. The pebbles in this sample are not aligned and elongated as in the metaconglomerate in Figure 10.10. Place the thick arrows in the direction of maximum stress and the thin arrows in the direction of minimum stress. If you have never seen or even heard of blueschist, that not surprising. In the example shown in Figure 7.8d, the dark bands are largely amphibole while the light-coloured bands are feldspar and quartz. Jurassic metaconglomerate bij Los Peasquitos Canyon Preserve , San Diego County, Californi . This means that the minerals in the rock are all aligned with each other. Non-foiliated - those having homogeneous or massive texture like marble. Foliation means the alignment within a metamorphic rock. The specimen shown above is about three inches across. Chapter 6. a. T. Metamorphism at ocean ridges is mainly (a) contact (b) dynamic (c) hydrothermal (d) regional. The grains form a mosaic texture. Determination of this information is not easily accomplished in this lab. Foliations typically bend or curve into a shear, which provides the same information, if it is of a scale which can be observed. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix of sand, silt, or clay. Any rock type (sedimentary, igneous or other metamorphic) can be subjected any one or any combination of the referenced agents. Foliation, as it forms generally perpendicular to the direction of principal stress, records the direction of shortening. It affects a narrow region near the fault, and rocks nearby may appear unaffected. It is composed primarily of hornblende (amphibole) and plagioclase, usually with very little quartz. The general term for the property of alignment in metamorphic rock is foliation, of which there are a number of types. Most people are surprised to learn that, so we added it to this photo collection as a surprise. This will allow the heat to extend farther into the country rock, creating a larger aureole. There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure at all. Foliated textures show a distinct planar character. Mlange matrix is foliated at the microscopic scale, where the fabric is defined both by the alignment of sheet silicates (e.g., chlorite, phengite, talc, biotite) and chain silicates (mostly amphiboles). Where the object hits, pressures and temperatures become very high in a fraction of a second. Some rocks, such as granite, do not change much at the lower metamorphic grades because their minerals are still stable up to several hundred degrees. Metamorphic differentiation, typical of gneisses, is caused by chemical and compositional banding within the metamorphic rock mass. The specimen shown above is about two inches (five centimeters) across. Figure 10.24 Metaconglomerate formed through burial metamorphism. Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. Our goal is to make science relevant and fun for everyone. Q. Slaty cleavage, schistosity, and compositional banding are all examples of ______. Observing foliation - "compositional banding", Assess foliation - foliated vs non-foliated, Compare non-foliated (massive) and foliated, (Contact Scott Brande) mailto:soskarb@gmail.com. The fractures are nested together like a stack of ice-cream cones. To the unaided eye, metamorphic changes may not be apparent at all. Usually, this is the result of some physical force and its effect on the growth of minerals. Principles of Earth Science by Katharine Solada and K. Sean Daniels is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. It is intermediate in grade between slate and schist. Labels may be used only once. Even if formed during regional metamorphism, quartzite does not tend to be foliated because quartz crystals dont align with the directional pressure. The minerals that will melt will be those that melt at lower temperatures. Heat is important in contact metamorphism, but pressure is not a key factor, so contact metamorphism produces non-foliated metamorphic rocks such as hornfels, marble, and quartzite. Non . You can help Wikipedia by expanding it. NONFOLIATED METAMORPHIC ROCKS As opposed to the foliated metamorphic rocks, the nonfoliated rocks are not distinctly layered. Metamorphism and Metamorphic Rocks, Chapter 17: Humans' Relationship to Earth Processes, Physical Geology, First University of Saskatchewan Edition, Next: 6.5 Metamorphic Facies and Index Minerals, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Houston, TX: Lunar and Planetary Institute Read full text, Physical Geology, First University of Saskatchewan Edition by Karla Panchuk is licensed under CC BY-NC-SA 4.0 Adaptation: Renumbering, Remixing, https://openpress.usask.ca/physicalgeology/. If a foliation does not match the observed plunge of a fold, it is likely associated with a different deformation event. The layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Slate, for example, is characterized by aligned flakes of mica that are too small to see. c. hydrothermal. Figure 7.7 shows an example of this effect. One kind of foliation is called gneissic banding, which looks like bands of light and dark layers. This is contact metamorphism. Most gneiss has little or no mica because it forms at temperatures higher than those under which micas are stable. Introduction to Hydrology and Glaciers, 13a. On this Wikipedia the language links are at the top of the page across from the article title. Rocks that form from regional metamorphism are likely to be foliated because of the strong directional pressure of converging plates. - Examples: quartzite derived from the metamorphism of sandstone, and marble derived from the metamorphism of limestone or dolostone. Lapis Lazuli, the famous blue gem material, is actually a metamorphic rock. The general term for the property of alignment in metamorphic rock is foliation, of which there are a number of types. In most cases, this is because they are not buried deeply, and the heat for the metamorphism comes from a body of magma that has moved into the upper part of the crust. This article related to petrology is a stub. Metamorphic rock may exhibit a variety of features related to the organization and arrangement of its component materials. The metaconglomerate formed through burial metamorphism does not display any of the foliation that has developed in the metaconglomerate in Figure 6.10. Some examples of foliated rocks include. Marble is metamorphosed limestone. Los Angeles Community College District: What Is a Foliated Metamorphic Rock? Foliated metamorphic rocks are named for their style of foliation. The surface of phyllite is typically lustrous and sometimes wrinkled. Dynamic metamorphism occurs at relatively low temperatures compared to other types of metamorphism, and consists predominantly of the physical changes that happen to a rock experiencing shear stress. The rock in the upper left of Figure 6.9 is foliated, and the microscopic structure of the same type of foliated rock is shown in the photograph beneath it. Platy minerals tend to dominate. A hard rock that is easy to carve, marble is often used to make floor tiles, columns and sculptures. Physical Geology, First University of Saskatchewan Edition by Karla Panchuk is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. Similarly, a gneiss that originated as basalt and is dominated by amphibole, is an amphibole gneiss or, more accurately, an amphibolite. The outcome of prolonged dynamic metamorphism under these conditions is a rock called mylonite, in which crystals have been stretched into thin ribbons (Figure 6.34, right). 2.1 Electrons, Protons, Neutrons, and Atoms, 4.5 Monitoring Volcanoes and Predicting Eruptions, 5.3 The Products of Weathering and Erosion, 6.3 Depositional Environments and Sedimentary Basins, 7.5 Contact Metamorphism and Hydrothermal Processes, 9.1 Understanding Earth through Seismology, 10.1 Alfred Wegener the Father of Plate Tectonics, 10.2 Global Geological Models of the Early 20th Century, 10.3 Geological Renaissance of the Mid-20th Century, 10.4 Plates, Plate Motions, and Plate-Boundary Processes, 11.5 Forecasting Earthquakes and Minimizing Damage and Casualties, 15.1 Factors That Control Slope Stability, 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting, 21.2 Western Canada during the Precambrian, Chapter 22 The Origin of Earth and the Solar System, Karla Panchuk, Department of Geological Sciences, University of Saskatchewan, 22.2 Forming Planets from the Remnants of Exploding Stars, Appendix 1 List of Geologically Important elements and the Periodic Table, Chapter 7 Metamorphism and Metamorphic Rocks. [2], The metaconglomerates of the Jack Hills of Western Australia are the source rocks for much of the detrital zircons that have been dated to be as old as 4.4 billion years.[3][4]. If the original limestone was pure calcite, then the marble will likely be white (as in Figure 7.10), but if it had various impurities, such as clay, silica, or magnesium, the marble could be marbled in appearance. Foliated - those having directional layered aspect of showing an alignment of particles like gneiss. The Origin of Earth and the Solar System, Chapter 8. Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Provide reasonable names for the following metamorphic rocks: Physical Geology by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Burial metamorphism occurs when sediments are buried deeply enough that the heat and pressure cause minerals to begin to recrystallize and new minerals to grow, but does not leave the rock with a foliated appearance. Hornfels is a fine-grained nonfoliated metamorphic rock with no specific composition. Metaconglomerate, however, breaks through the grains, as the cement has recrystallized and may be as durable as the clasts. Typical examples of metamorphic rocks include porphyroblastic schists where large, oblate minerals form an alignment either due to growth or rotation in the groundmass. 2. Foliated textures show a distinct planar character. Where slate is typically planar, phyllite can form in wavy layers. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks. The cement matrix of conglomerate is not as durable as the grains, and hence when broken, conglomerate breaks around the grains. Seeing and handling the rocks will help you understand their composition and texture much better than reading about them on a website or in a book. When a rock is acted upon by pressure that is not the same in all directions, or by shear stress (forces acting to smear the rock), minerals can become elongated in the direction perpendicular to the main stress. Partial melting occurs when the temperature on a rock is high enough to melt only some of the minerals in the rock. The larger size gives the foliation a slighly shiny appearance. b. Hutton. Foliated metamorphic rocks exhibit layers or stripes caused by the elongation and alignment of minerals in the rock as it undergoes metamorphism. This means that slate breaks into thin layers, which have economic value as tiles and blackboards. This is probably because nonfoliated rocks were exposed to high temperature conditions, but not to high directional pressure conditions. Samantha Fowler; Rebecca Roush; and James Wise, 1.2 Navigating Scientific Figures and Maps, 2.2 Forming Planets from the Remnants of Exploding Stars, 5.2 Chemical and Biochemical Sedimentary Rocks, 5.4 Depositional Environments and Sedimentary Basins, 6.4 Types of Metamorphism and Where They Occur, 6.5 Metamorphic Facies and Index Minerals, 6.6 Metamorphic Hydrothermal Processes and Metasomatism, 7.1 Alfred Wegener's Arguments for Plate Tectonics, 7.2 Global Geological Models of the Early 20th Century, 7.3 Geological Renaissance of the Mid-20th Century, 7.4 Plates, Plate Motions, and Plate-Boundary Processes, 8.2 Materials Produced by Volcanic Eruptions, 8.7 Monitoring Volcanoes and Predicting Eruptions, 9.5 Forecasting Earthquakes and Minimizing Impacts, 10a. The protolith for quartzite is quartz, and because quartz is stable under high pressure and high temperatures, metamorphism of this rock simply causes the reorganization of its crystals. . The mineral alignment in the metamorphic rock called slate is what causes it to break into flat pieces (Figure 10.12, left), and is why slate has been used as a roofing material (Figure 10.12, right). Regional metamorphism also takes place in this setting, and because of the extra heat associated with the magmatic activity, the geothermal gradient is typically steeper in these settings (between ~40 and 50 C/km). The specimen shown above is about two inches (five centimeters) across. of rock masses in, for example, tunnel, foundation, or slope construction. If a rock is buried to a great depth and encounters temperatures that are close to its melting point, it will partially melt. Phyllite is a foliated metamorphic rock that is made up mainly of very fine-grained mica. A rock that is dominated by aligned crystals of amphibole. Weakly foliated: Any material: Hard, fine-grained rock: Metaconglomerate: Weakly foliated: Quartz-rich conglomerate: Strongly stretched pebbles: Amphibolite: Weakly foliated: Mafic volcanic rocks: Coarse-grained: Examples of metamorphic rock: Index Reference Lutgens and Tarbuck Ch 7 . Schistose foliation is composed of larger minerals which are visible to the unaided eye. Slate tends to break into flat sheets. This forms planes of weakness, and when these rocks break, they tend to break along surfaces that parallel the orientation of the aligned minerals (Figure 10.11). . However, compositional banding can be the result of nucleation processes which cause chemical and mineralogical differentiation into bands. Contact metamorphic aureoles are typically quite small, from just a few centimeters around small dykes and sills, to as much as 100 m around a large stock. As already noted, slate is formed from the low-grade metamorphism of shale, and has microscopic clay and mica crystals that have grown perpendicular to the stress. It is composed primarily of calcium carbonate. One derived from shale may be a muscovite-biotite schist, or just a mica schist, or if there are garnets present it might be mica-garnet schist. The pebbles have developed "wings" to varying degrees (e.g., white dashed ellipse). Examples of foliated rocks include: gneiss, phyllite, schist, and slate. Any type of magma body can lead to contact metamorphism, from a thin dyke to a large stock. Alignment of tabular minerals in metamorphic rocks, igneous rocks and intrusive rocks may form a foliation. If the hornfels formed in a situation without directed pressure, then these minerals would be randomly orientated, not foliated as they would be if formed with directed pressure. Click on image to see enlarged photo. The pattern of aligned crystals that results is called foliation. Gneissic banding is the easiest of the foliations to recognize. This is a megascopic version of what may occur around porphyroblasts. Shocked quartz (Figure 6.32 left) refers to quartz crystals that display damage in the form of parallel lines throughout a crystal. Essentially, the minerals are randomly oriented. Foliated metamorphic rocks have elongated crystals that are oriented in a preferred direction. Study Tip. In this treatment, we'll describe metamorphic rock that does not show visible alignment of materials as massive. Following such a methodology allows eventual correlations in style, metamorphic grade, and intensity throughout a region, relationship to faults, shears, structures and mineral assemblages. The Himalaya range is an example of where regional metamorphism is happening because two continents are colliding (Figure 6.25). As a rock heats up, the minerals that melt at the lowest temperatures will melt first. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix of sand, silt, or clay. The rock in Figure 10.10 had a quartz-rich conglomerate as a parent rock. At subduction zones, where ocean lithosphere is forced down into the hot mantle, there is a unique combination of relatively low temperatures and very high pressures. Squeezing and heating alone (as shown in Figure 7.5) and squeezing, heating, and formation of new minerals (as shown in Figure 7.6) can contribute to foliation, but most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress (Figure 7.6). In geology, cleavage refers to the tendency of a rock to break parallel to the alignment of the tiny mica minerals it is composed of. Examples include the bands in gneiss (gneissic banding), a preferred orientation of planar large mica flakes in schist (schistosity), the preferred orientation of small mica flakes in phyllite (with its planes having a silky sheen, called phylitic luster the Greek word, phyllon, also means "leaf"), the extremely fine grained preferred orientation of clay flakes in slate (called "slaty cleavage"), and the layers of flattened, smeared, pancake-like clasts in metaconglomerate.[1]. EARTH SCIENCE LAB Metamorphic Sample #1: Identify the Texture, Foliation, Composition, Parent Rock and Rock Type Metamorphic Rock Identification Chart FOLIATION COMPOSITION PARENT ROCK ROCK NAME TEXTURE Oslaty O mica Mudstone O phyllitic O quartz, mica, chlorite O Mudstone O Foliated Omica, quartz O Slate O schistose amphibole, plagioclase O It forms from sediments deposited in marine environments where organisms such as diatoms (single-celled algae that secrete a hard shell composed of silicon dioxide) are abundant in the water. Phyllite Rock Type: Metamorphic - A low to intermediate grade metamorphic rock produced from the metamorphism of shale. Thus, they are not always 'planar' in the strictest sense and may violate the rule of being perpendicular to the regional stress field, due to local influences. These rocks are all foliated because of the strong compressing force of the converging plates. A fourth type of foliated metamorphic rock is called slate. The quartz crystals were subjected to the same stress as the mica crystals, but because quartz grows in blocky shapes rather than elongated ones, the crystals could not be aligned in any one direction. This is because mariposite is an ore of gold. Foliation may be formed by realignment of micas and clays via physical rotation of the minerals within the rock. The parent rock that undergoes metamorphism is called the protolith. Generally, the acute intersection angle shows the direction of transport. Quartz has a hardness of 7, which makes it difficult to scratch. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. If you happen to be in the market for stone countertops and are concerned about getting a natural product, it is best to ask lots of questions. Some types of metamorphic rocks, such as quartzite and marble, which also form in directed-pressure situations, do not necessarily exhibit foliation because their minerals (quartz and calcite respectively) do not tend to show alignment (see Figure 7.12). This is not always the case, however. Image copyright iStockPhoto / RobertKacpura. Most sandstone contains some clay minerals and may also include other minerals such as feldspar or fragments of rock, so most quartzite has some impurities with the quartz. Metamorphic rocks can be foliated, displaying banding or lamellar texture, or non-foliated. It has a bright, lustrous appearance and breaks with a semi-conchoidal fracture. Foliation. Granite may form foliation due to frictional drag on viscous magma by the wall rocks. Hornfels is a rock that was "baked" while near a heat source such as a magma chamber, sill, or dike. The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well. The classification of metamorphic rocks is based on the minerals that are present and the temperature and pressure at which these minerals form. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. Most of the blueschist that forms in subduction zones continues to be subducted. Contrast the rock known commercially as Black Marinace Gold Granite (Figure 6.24)but which is in fact a metaconglomeratewith the metaconglomerate in Figure 6.10. A large intrusion will contain more thermal energy and will cool much more slowly than a small one, and therefore will provide a longer time and more heat for metamorphism. This typically follows the same principle as mica growth, perpendicular to the principal stress. Therefore, a simplified system is used based on texture and composition. It is a low-grade metamorphic rock that splits into thin pieces. Metamorphism and Metamorphic Rocks, Chapter 13. The growth of platy minerals, typically of the mica group, is usually a result of prograde metamorphic reactions during deformation. Anthracite is the highest rank of coal. The rock also has a strong slaty foliation, which is horizontal in this view, and has developed because the rock was being squeezed during metamorphism. At an oceanic spreading ridge, recently formed oceanic crust of gabbro and basalt is slowly moving away from the plate boundary (Figure 6.26). This is illustrated in Figure 7.6, where the parent rock is shale, with bedding as shown. It is a soft, dense, heat-resistant rock that has a high specific heat capacity. There are two basic types of metamorphic rocks. Under these conditions, higher grades of metamorphism can take place closer to surface than is the case in other areas. The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are slate, phyllite, schist, and gneiss (Figure 7.8). A fine-grained rock that splits into wavy sheets. The mica crystals are consistently parallel to one another. It is composed of alternating bands of dark and light minerals. Contact metamorphism happens when a body of magma intrudes into the upper part of the crust. A mineral may be a single element such . It is dominated by quartz, and in many cases, the original quartz grains of the sandstone are welded together with additional silica. Metamorphic differentiation can be present at angles to protolith compositional banding. Territories. Usually, this is the result of some physical force and its effect on the growth of minerals. Thus, aureoles that form around wet intrusions tend to be larger than those forming around their dry counterparts. is another name for dynamothermal metamorphism. Think of foliated rocks as something that is foiled. Rich in talc, soapstones feel greasy, like soap. METACONGLOMERATE The parent rock for metaconglomerate is the sedimentary rock . Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. Polymict metaconglomeraat, . When describing a foliation it is useful to note. There are many other types of specific nonfoliated metamorphic rocks, such as greenstone, eclogites and serpentines. . Anthracite coal is generally shiny in appearance and breaks with a conchoidal fracture (broken glass also shows this type of fracture). Differential stress has caused quartz pebbles within the rock to become elongated, and it has also caused wings to form around some of the pebbles (see the pebble in the dashed ellipse). Introduction to Hydrology and Shorelines, 14a. Learn how BCcampus supports open education and how you can access Pressbooks. Crenulation cleavage and oblique foliation are particular types of foliation. As we're confining our observation to samples without visual aids, we may be subject to some error of identification. . Further identification of non-foliated rocks is dependent on the composition of the minerals or components in the rock. Foliation Often, retrograde metamorphism will not form a foliation because the unroofing of a metamorphic belt is not accompanied by significant compressive stress. Any rock that contains more than one kind of mineral can be the protolith for gneiss, which is the name for a metamorphic rock that exhibits gneissic banding. Labels may be used only once. Essentials of Geology, 3rd Ed, Stephen Marshak. Metaconglomerate & Metabreccia > Metaconglomerate and metabreccia are variably metamorphosed conglomerates and breccias that may or may not be foliated. The figure below shows a metaconglomerate. An example of this is shown in Figure 7.12. Considering that the normal geothermal gradient (the rate of increase in temperature with depth) is around 30C per kilometer in the crust, rock buried to 9 km below sea level in this situation could be close to 18 km below the surface of the ground, and it is reasonable to expect temperatures up to 500C. 1. Hornfels is another non-foliated metamorphic rock that normally forms during contact metamorphism of fine-grained rocks like mudstone or volcanic rock (Figure 7.13).
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