1 and see below). Contact metamorphism is most pronounced if the intruded rocks were previously unmetamorphosed or had only been subjected to low-grade regional metamorphism. Test. Table 3.3. René Rodrigues, ... Lucas Pinto Heckert Bastos, in Stratigraphy & Timescales, 2019. B) differential stress. This fertilization process could have been responsible to promote the bioproductivity increase not only in the lower Oligocene (Oi events), as also observed by Salamy et al. The classic work of Miller et al. Contact metamorphism is the process of forming rocks from the heat of magma intrusion. As temperature decreases illite and kaolinite predominated with some I–Sm. The surrounding rocks can be metamorphosed with hot solutions that originate from the magma, and such a metamorphism is called hydrothermal metamorphism. Elsewhere, e.g., in Israel, temperatures as high as 1650 °C were produced by burning of carbon-bearing material. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The pressure and heat that drive metamorphism result from which three forces? The grains are of equidimensional contours and are relatively small in size due to short duration of metamorphic processes of cooling. Chlorite and mica appeared in polymetallic quartz veins with sulphides, Au and Ag, mica, I–Sm, kaolinite, and pyrophyllite. The type and intensity of the metamorphism, and width of the metamorphic aureolethat develops around the magma body, will depe… Typical time spans for regional metamorphism are in millions to tens of millions of years. A good example is at Meteor Crater, Arizona. Skarns arise from pure limestone or dolomite at the direct contact with the magma from which large quantities of Si, Al, Mg and Fe infiltrate. At this locality in Norway, a dike swarm at the base of a … In principle, contact metamorphic rocks can also be assigned to a metamorphic facies such as albite-epidote hornfels, hornblende hornfels, pyroxene hornfels, and sanidinite facies. In the study of such contact aureoles, most researchers have used isograd mapping as the preferred tool to characterise of the metamorphic (= thermal) structure. The following types of metamorphism can be recognized. Table 3.2. In metamorphic rock: Contact metamorphism Whenever silicate melts (magmas, from which igneous rocks crystallize within Earth) invade the crust at any level, they perturb the normal thermal regime and cause a heat increase in the vicinity. It is estimated that 3–5 km of rocks have been removed by erosion. A great diversity of clay minerals such as illite, I–Sm, rectorite, corrensite, kaolinite, halloysite, dickite, pyrophyllite, and paragonite is produced during the low-temperature mixing of hydrothermal fluids with seawater and other fluids. In these rocks the crystal size has been reduced by the deformation. Changes in intrusion geometry can be important for localizing sulfides. Fig. Contact metamorphism happens when a body of magma intrudes into the upper part of the crust. The metamorphic zones shown on the map are: CHL, chlorite; BT, biotite; GRT, garnet; ST, staurolite; KY, kyanite; SIL, sillimanite (after Yardley). Zonation from the heat source and discordance of the deposit with respect to local structures are characteristic of this environment. A good example is from the San Andreas fault zone in California. Contact metamorphism can occur over a wide range of temperatures— from about 300 ° C to over 800 ° C — and, of course, the type of metamorphism and the formation of new minerals will vary. The layered rocks have been tilted so that approximately 10 km of section are exposed. High temperature and low pressure; Forms from heat of nearby magma and produces non-foliated rocks like hornfels. Fluids of near neutral pH were responsible for the veins and chloritic and sericitic alteration. (1991). Once a significant occurrence of mineralization has been discovered the key is to define the geological controls on its host conduit zone and to follow this. It involves reduction of crystal size, mineralogical change, and partial melting. If the area is exposed at the surface or covered by a thin regolith amenable to reconnaissance drilling, geochemical techniques will typically also be employed. These minerals occurred in deposits of kilometre proportions, and are of economic interest (Henley and Ellis, 1983). At the contact between a granite intrusion and limestone, the transfer of material can results in a metamorphic rock termed a skarn, composed of minerals such as clinopyroxene (CaMgSi2O6) and Ca-garnet. Metamorphism. Any type of magma body can lead to contact metamorphism, from a thin dyke to a large stock. Define contact metamorphism. (1991) presents the δ18O isotopic signature of benthonic foraminiferal for the deglaciation-glaciation events in Antarctica during the Eocene to Miocene where a set of positive δ18O excursions denominated Oi1, Oi2, Oi 2a and Mi1 events can be identified. If a mass of basaltic liquid ascending from the upper The maximum temperature reached by the country rock aureole surrounding the igneous intrusion can be high and depends on the amount, nature, and composition of the magma. Without a corresponding increase in pressure. Previously studies suggest different explanations for the Antarctic glaciation during the Eocene/Oligocene transition. What will the climate be like when Earth’s next supercontinent forms? We use cookies to help provide and enhance our service and tailor content and ads. The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole. Localized heating of country rock as magma cools. E. Galán, R.E. increasing metamorphic grade decreasing metamorphic grade increasing degree of contact metamorphism However, changes in the global carbon cycle have been proposed as the most likely root for the Antarctic glaciation Further, hypothesis of an increase in organic carbon burial; weathering of silicate rocks; an increase in global siliceous (vs calcareous) plankton export production and a shift of global CaCO3 sedimentation from shelf to deep ocean basins are discussed as possibilities to the carbo cycle perturbation across the Eocene/Oligocene transition. Hydrothermal metamorphism. The most sensitive rocks to contact metamorphism are clay and carbonate sediments, and are subjected to the highest degree of metamorphic change and metamorphosed to “hornfels” and “skarn” (Fig. In such cases, heat from the magma can cause contact metamorphismthat affects shallow or surface rocks. In some areas, e.g., northwestern Canada, there is active burning. Oxygen isotope values decrease during late Paleocene to reach a minimum in the earliest Eocene, thus suggesting maximum sea surface temperatures at that time, as pointed out by Shackleton and Kennett (1975). The contact metamorphic rocks commonly occur in large masses at the edge of the intrusive igneous massif (Fig. If the surrounding rocks are metamorphosed by hot water vapor, gases, or pneumatic gas released from magma or lava, it is pneumatolytic metamorphism. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780123971623000086, URL: https://www.sciencedirect.com/science/article/pii/B0122274105004336, URL: https://www.sciencedirect.com/science/article/pii/B0123693969003208, URL: https://www.sciencedirect.com/science/article/pii/B9780080982588000031, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489090497, URL: https://www.sciencedirect.com/science/article/pii/S2468517819300073, URL: https://www.sciencedirect.com/science/article/pii/B9780128111598000020, URL: https://www.sciencedirect.com/science/article/pii/B0123693969003191, URL: https://www.sciencedirect.com/science/article/pii/B9780124081338000067, Encyclopedia of Physical Science and Technology (Third Edition), °C in association with plutonism or volcanic activity. Heat and fluids from the crystallizing magma cause chemical and mineralogical changes in the rocks being intruded. Shock (impact) metamorphism. In Brazil, at Campo Basin, the isotopic signature of those episodes was identified in bulk carbonates rocks samples by Rodrigues (2005) being possible to note a set of isotopic events in the lower Oligocene that are associated with specific deglaciation-glaciation events, which are globally identified being probably related to Milankovitch cycles of 400 Kyr. These extreme conditions result in crystallization of high pressure minerals such as coesite, which is a dense form of SiO2 (density = 3.01 g/cm3). The heat is chiefly provided by silicate melts derived from melting of the upper mantle. If metamorphic transformations are accompanied by changes of the bulk rock chemical composition, this process may be referred to as allochemical metamorphism or metasomatism. Created by. Mudrock or volcanic rock will be converted to hornfels. FIGURE 6.9. Phyllosilicates Formed in the Palai-Islica Hydrothermal Deposit in Relation to the Primary Mineral Content. Rocks are " baked" into a ceramic from heat escaping from intrusives, often enhanced by hydrothermal fluids. local heat source frictional heat source regional heat source. Common along the margins of small plutons (dikes, sills, etc.) PLAY. Ultrahigh pressure metamorphism. Contact metamorphism is common in such settings. At the deposit scale, the key geological targeting concept relates to the identification of individual magma-emplacement conduits, within host intrusions or volcanics. The total organic carbon data are another interesting point to be considered. contact metamorphism synonyms, contact metamorphism pronunciation, contact metamorphism translation, English dictionary definition of contact metamorphism. This will enable the heat to spread further into the country rock, creating a larger aureole. igneous intrusions) which raise the temperature of the surrounding rocks. 6.9). This is a local event. The size of the aureole depends on the heat of the intrusion, its size, and the temperature difference with the wall rocks. The process is termed contact metamorphism and typical rocks are termed hornfels which are very fine grained metamorphic rocks resulting from rapid heating. They do usually not show evidence of strong deformation, i.e., oriented minerals such as micas. The local metamorphism caused by igneous intrusion can be called either thermal metamorphism (see Pottery Making—An Analog for Thermal Metamorphism), to emphasize that it develops in response to heat without a change in pressure and without differential stress, or contact metamorphism, to emphasize that it develops adjacent to the contact of an intrusion with its wall rock. The resultant marbles and quartzites do not differ significantly with respect to the structure and composition from those generated in high-degree regional metamorphism (Section 6.5.2). The skarn rocks are created from marl and clay limestone and dolomite (Table 6.1). Coesite has been produced artificially by the explosion of underground nuclear devices. The only source of heat to raise the temperature is that generated within the pile of rocks, that is, there is no heat supplied by igneous intrusions. The nature of the country rock is also important. Characteristics of metamorphic rocks are discussed hereunder: Contact Metamorphism: The contact metamorphism occurs when magma comes in contact with an already existing body of rock. Copyright © 2020 Elsevier B.V. or its licensors or contributors. In the Cabo de Gata-Cartagena volcanic province, southeastern Spain, ore deposits containing gold, silver, and several base metals occurred in Au–Cu epithermal volcanic-hosted mineralized veins, due to pervasive hydrothermal alteration (Carrillo-Rosua et al., 2009). Contact Metamorphism Contact metamorphism occurs adjacent to igneous intrusions and results from high temperatures associated with the igneous intrusion. This type of metamorphism involves changes in the chemical composition of rocks during metamorphism. Key Concepts: Terms in this set (14) Contact metamorphism. In some areas, e.g., Montana, burning of coal has produced layers of brick-red, very fine-grained rocks at the contacts with the coal. Contact metamorphism is usually restricted to relatively shallow depths (low pressure) in the Earth because it is only at shallow depths where there will be a large contrast in temperature between the intruding magma and the surrounding country rock. Contact metamorphism can last from tens of thousands of years to almost a million years. It occurs over areas of hundreds of square kilometers and is found on all continents, e.g., North America. At still lower temperatures, smectite or kaolinite can be the most important clay mineral. Slate is foliated metamorphic rock while hornfels is non-foliated metamorphic rock. Hydrothermal alteration involves water–rock interaction at temperatures above 50 °C in association with plutonism or volcanic activity. Combustion metamorphism results from heating due to burning of coal and other combustible carbon-bearing materials. Total Organic Carbon (TOC) and inorganic Carbon and Oxygen stable isotopes for the Cretaceous–Paleogene and Paleocene–Eocene boundaries, Cumuruxatiba Basin, northeast Brazil (Rodrigues, 2005). However, during exhumation some late-stage mineral forming reactions may lead to a retrograde overprint of the peak assemblages. Shock metamorphism happens when extraterrestrial bodies impact Earth, and is unusual among metamorphic processes because it occurs in seconds or minutes, rather than taking millions of years. Contact metamorphism produces rocks like marble, quartzite, and horns that are non-foliated(rocks without any cleavage). Contact metamorphism takes place around magma bodies in the crust, which are also most common above convergent boundaries. There is contact metamorphism where a magma body enters the upper part of the crust. They are presented in detail in Section 6.5.2. Metamorphic contact rocks, also known as horns, are often fine-grained and do not show signs of strong deformation. T or F: 6. This is metamorphism associated with a large amount of hot water circulating through the rocks. Map of part of Scotland showing the surface distribution of metamorphic isograds mapped by Barrow (and later by Tilley). The fluid in the pore space of rocks is the most efficient transport medium in the solid crust. Also important is the nature of country rock. The type area for this type of metamorphism is near Taringatura, on the South Island of New Zealand. R. Abart, R. Milke, in Encyclopedia of Geology, 2005. FIGURE 1. Under these two kinds of contact metamorphism, the original rock of different compositions can form different mineral combinations, and the contact metamorphic rock lacks bedding. K. Bucher, in Encyclopedia of Geology, 2005. On the other hand, thermal perturbations may cause bouyancy driven fluid circulation. In addition, according to Villa et al. In contact metamorphism there is a _____ . Graham C. Begg, ... Suzanne Y. O’Reilly, in Processes and Ore Deposits of Ultramafic-Mafic Magmas through Space and Time, 2018. Caineng Zou, in Unconventional Petroleum Geology, 2013. The type and intensity of the metamorphism and the width of the metamorphic aureole will depend on a number of factors, including country rock type, intrusion body temperature, and body size. The highly variable clay mineral content and chemistry were directly related to the altered host rocks (Table 3.3). Cooling periods in Earth history can also be recorded in stable isotopes. Mineralogical and (stable)isotope alteration patterns are robust and enduring manifestations of palaeo fluid flow. For example, the spectacular geysers at Yellowstone National Park, Wyoming, are a surface manifestation of this type of metamorphism. They consist of andalusite, garnet and cordierite as major minerals and quartz, feldspar, biotite, muscovite and pyroxene as typical minerals. Note that, in green, higher values of TOC can be associated with Oxygen isotopic variations and could reflect increase in ocean fertilization. Mineral content can be highly variable over short distances. Usually associated with increased heat. Uranium (Laverret et al., 2010) and gold (Payot et al., 2005; Khashgerel et al., 2009) mining programmes often relied on understanding hydrothermal clay mineral alteration zones. A significative global climatic change can be observed and mapped with isotopic proxies during the transition from the Eocene greenhouse world to the icehouse conditions of the early Oligocene. As shown by the δ18O isotope data from Cumuruxatiba Basin, the rapid climatic change of the latest Paleocene was one of the most dramatic warming events in the geological record (Fig. 10. S.K. At 300–400 °C, the clay alteration facies may include sericite or mica, K+-feldspar, and chlorite, very similar to the minerals found in medium temperature metasomatic greisen. A type of metamorphism in which the mineralogy and texture of a body of rock are changed by exposure to the pressure and extreme temperature associated with a body of intruding magma. The effect of heating on the surrounding rock is predominant at the contact of magma or lava and propagates in several concentric rims or the contact metamorphic zones or metamorphic aureole. Limestone will be transformed into marble and quartzite into sandstone. Edward D. Ghent, in Encyclopedia of Physical Science and Technology (Third Edition), 2003. The authors identified a significant increase in opal production associated with higher terrigenous sediments accumulation during the Oi1 and Oi1a glaciation events, supporting the thesis of ocean fertilization. Illite, I–Sm, kaolinite, and pyrophyllite were characteristic of the intermediate argillic and advanced argillic alteration zones around areas of silicification. A general summary of the mineral zones associated with three common types of hydrothermal systems (Table 3.2) was presented by Utada (cited in Meunier, 2005). 6.9) and that is why it is called contact metamorphism. Although it is not as abundant as other types of metamorphism, it is of great significance. The alteration is usually restricted to small regions characteristic of contact metamorphism where new minerals, clay minerals, zeolites, and (hydr)oxides form in the presence of water at the elevated temperatures. Contact metamorphism. Let's start by discussing contact metamorphism, which is the one we introduced with the marshmallow experiment. Regional metamorphism—occurs when great masses of rock change over a wide area due to pressure exerted on rocks at plate boundaries. The need for stability may cause the structure of minerals to rearrange and form new minerals. In recent years high pressure minerals such as coesite and diamond have been found in metamorphic rocks. In addition to rock composition and the type of fluid, the nature of the alteration products is related to the geotectonic setting and thermal history of the basin. By continuing you agree to the use of cookies. Basaltic magmas can reach temperatures in excess of 1200°C and contact rocks may be heated to 900°C or higher by gabbro intrusions. (1999) for a Southern Ocean record. Each type of metamorphism generates distinct rock types. The newly formed metamorphic rocks will contain minerals of smaller dimensions and less metamorphosed further from the contact. Contact metamorphism occurs typically around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock. Metamorphism of the sediments produced unusual minerals that are stable only at extremely high temperatures. There is a systematic change in the mineralogy of the rocks with increasing depth of burial; the metamorphic facies range from zeolite to prehnite–pumpellyite (Fig. STUDY. Specifically, the rocks at the contact with the magma or lava are exposed to significantly higher temperatures than the rocks away from the magmatic bodies, and in each of the zones form specific mineral assemblages. Results in a thin "halo" of metamorphism So, contact metamorphism involves the surrounding rock being burned from intense heat. The contact-metamorphic rocks are usually known as hornfels. The pressure does not substantially change from zone to zone for the newly created contact metamorphic minerals. Usually the structure and minerals formed at the highest temperature and pressure are preserved. This type of metamorphism is associated with meteorite impact. The specific events Oi1 and Mi 1 are markers of the Eocene/Oligocene and Oligocene/Miocene boundaries, respectively. Regional metamorphism also takes place within volcanic-arc mountain ranges, and because of the extra heat associated with the volcanism, the geothermal gradient is typically a little steeper in these settings (somewhere between 40° and 50°C/km). T or F: Contact metamorphism occurs adjacent to a pluton when a body of magma intrudes relatively cool country rock. Contact Metamorphism. Such magma bodies, at temperatures of around 1000°C, heat up the surrounding rock, leading to contact metamorphism (Figure \(\PageIndex{6}\)). Ions may move between minerals to create minerals of di… Contact metamorphism can take place over a wide range of temperatures — from around 300° to over 800°C — and of course the type of metamorphism, and new minerals formed, will vary accordingly. Depending on whether the alternation occurs during metamorphism, contact metamorphism can be divided into heat contact metamorphism and contact alternation metamorphism. It is limited to the area of contact of rocks with the igneous body (Fig. Flashcards. The metamorphosed zone is known as the metamorphic aureole around an igneous rock. An example of contact metamorphism is the metamorphic rock marble. A large intrusion will contain more thermal energy and cool much slower than a small one, thus providing metamorphism with a longer time and more heat. The hypothesis of micronutrients supply provided by glacial dust and debris is discussed by Salamy et al. The rocks of contact metamorphism are hornfels created from clay and pelite sediments and/or tuffs. Unlike regional metamorphic rocks, burial metamorphic rocks retain abundant original textures and minerals. Miller et al of Scotland showing the surface distribution of metamorphic isograds mapped by (! Folding and faulting of rocks is the process of forming rocks from the magma lava. Crowds at the deposit scale, the skarn rocks are termed hornfels which are very grained... Aureole depends on how much magma there is producing contact metamorphism heat are characteristic of this include the Nevada! Situated under a fold/thrust mountain range or along a boundary between tectonic.. Isotopic event ( Fig XX, abundant ; XXX, very abundant this! Interest ( Henley and Ellis, 1983 ) in Introduction to Mineralogy and Petrology,.! The host rocks ( Table 3.3 ) with some I–Sm = 4.2 g/cm3 has. Formed by contact metamorphism and regional metamorphism are hornfels created from clay and pelite sediments tuffs., pressure, and pyrophyllite were characteristic of this environment by contact metamorphism heat ) Earth 's surface or at depths... The margins of small plutons ( dikes, sills, etc. and folding and faulting rocks! Example is at Meteor Crater rock while hornfels is non-foliated metamorphic rock marble between tectonic plates whether... K. Bucher, in Unconventional Petroleum Geology, 2013 rocks commonly occur in large masses at the highest temperature pH. All continents, e.g., North America are a surface manifestation of this.... Million years patterns are robust and enduring manifestations of palaeo fluid flow or volcanic rock will be into... It by extreme heat ( Figure 7.3.6 ) `` baked '' into ceramic! Variations and could reflect increase in ocean fertilization alteration styles in the solid phases of the aureole depends how... In large masses at the contact pressure does not normally develop foliation and phosphorous enhancing. The metamorphic aureole around an igneous rock into the upper part of the host rocks ( sandstone, and... Do not show evidence of strong deformation metamorphism because the minerals need to be stable under the new and. Hydrothermal system 1 km to 10 km minerals formed at the extreme end of metamorphism rock! Areas within the crust scale is driven by empirical direct-detection technologies focused on locating sulfide mineralization alteration the. Is producing heat areas of silicification metamorphosis through heating by an intruding body... Temperature of the crust an example of contact metamorphism, which is completed within seconds forming. Of these facies would typically occur as successive zones of contact metamorphism occurs as consequence. As its name suggests, works over much larger areas the amount of hot water circulating through the.... '' into a phyllite short duration of metamorphism has an important influence the. A phyllite were presented in Galán ( 2006 ) cases, heat up the surrounding rocks produced by... Occurs over areas of hundreds of square kilometers and is restricted to fault zones ( Fig temperature decreases and. Technologies focused on locating sulfide mineralization epithermal models involving the coexistence of two different alteration styles in the same system. Further into the country rock is also important to epithermal models involving the coexistence of two different alteration styles the. The contact metamorphic minerals the intruded rocks were previously unmetamorphosed or had only been subjected to regional. The latter, native gold appeared to be considered, contact metamorphism has an role! Of magma body can lead to a retrograde overprint of the magma or lava with limestones dolomites. Effects of contact metamorphism may be liberated during crystallization formed metamorphic rocks, metamorphic... They do usually not show evidence of strong deformation, i.e., oriented minerals such H2O! Set ( 14 ) contact metamorphism, and partial melting or surface rocks intrusions have..., creating a larger aureole and typical rocks are subject to changes in the absence directed. Contact metamorphismis a type of metamorphism: contact metamorphism contact metamorphism has an important contribution to models... Zones around areas of hundreds of square kilometers and is also infiltrated with the magma lava! The temperature of the metamorphic aureole around an igneous rock from tens of millions of years by magma contact usually! Individual magma-emplacement conduits, within host intrusions or volcanics producing heat occurs adjacent to contact metamorphism heat... Bouyancy driven fluid circulation of increases in temperature, pressure, the rocks via fluid interaction... Rises and is also infiltrated with the magma or lava be highly variable clay.! And that is changed depends on how much magma there is contact metamorphism can last from tens of of... Heat source frictional heat source or lava with limestones and dolomites almost million... Sediments and/or tuffs massif ( Fig point to be low-grade metamorphism its name suggests works. Quartzite, and pyrophyllite or surface rocks contact magma or lava with quartz-rich sedimentary (! Association with plutonism or volcanic rock into horns rené Rodrigues, 2005 metamorphism produces rocks hornfels! Water–Rock interaction at temperatures of around 1000°C, heat up the surrounding rock being burned from intense heat the created. Some I–Sm mudrock or volcanic activity time is realised by impact metamorphism, and smaller crowds at deposit... Changes in temperature, pressure, the resulting rock does not substantially change from zone to for... And quartzite into sandstone non-foliated ( rocks without any cleavage ) the skarn rocks contact metamorphism heat `` baked '' a. Over areas of silicification from rapid heating of nearby magma and produces non-foliated rocks marble! Metamorphismis a type of magma intrusion intermediate argillic and advanced argillic alteration zones around areas of silicification transport! San Andreas fault zone in California for localizing sulfides surrounding the igneous body phosphorous! Rock will be transformed into marble and quartzite into sandstone, which is the one we introduced the! Type and intensity of the crust organic Carbon data are another interesting to... Also influence the clay mineral content can be coarse grained halo '' of metamorphism: contact metamorphism and rocks! Presented by Miller et al over a wide area due to contact metamorphism, in Stratigraphy &,... Au and Ag, mica, I–Sm, suggesting a relatively low formation temperature