| 单词 | metamorphism |
| 例句 | On Earth, metamorphism usually happens slowly and deep underground. Earth is a geological oddball in our solar system. This is why. 2023-10-12T04:00:00Z Some form from hot water solutions, during metamorphism or weathering, or through organic processes. Physical Geology 2015-01-01T00:00:00Z Increases in temperature and pressure are the main causes of metamorphism, with fluids adding important mobilization of materials. An Introduction to Geology 2017-01-01T00:00:00Z In the Australian rocks with ancient stromatolites2, laminations are clearly visible; in the Greenland samples, however, the proposed laminations are less clear, and the degree of metamorphism is higher than that of the Australian rocks. Proposed early signs of life not set in stone 2018-10-16T04:00:00Z Menzies, O. N., Bland, P. A., Berry, F. J. & Cressey, G. A Mössbauer spectroscopy and X-ray diffraction study of ordinary chondrites: quantification of modal mineralogy and implications for redox conditions during metamorphism. Halogens in chondritic meteorites and terrestrial accretion 2017-11-28T05:00:00Z Shock metamorphism has happened often on Mars, but there’s also evidence for metamorphism that’s a bit like a cooler, gentler version of what can happen on Earth. Earth is a geological oddball in our solar system. This is why. 2023-10-12T04:00:00Z The temperature that the rock is subjected to is a key variable in controlling the type of metamorphism that takes place. Physical Geology 2015-01-01T00:00:00Z Different tectonic or geologic environments cause metamorphism, including collisions, subduction, faulting, and even impacts from space. An Introduction to Geology 2017-01-01T00:00:00Z To find more direct evidence, scientists searched for rocks untouched—or at least less altered by—metamorphism. Hints of oldest fossil life found in Greenland rocks 2016-08-31T04:00:00Z For one, he says, researchers need to settle some important debates, like whether the inclusions in Hadean zircons truly preserve original material, or if they’ve been altered, for example, during a later bout of metamorphism. Scientists may have found the earliest evidence of life on Earth 2015-10-19T04:00:00Z I know we’re in for volcanoes and earthquakes and some really wild metamorphism, accretionary wedges and the whole shebang. The Seduction of Subduction 2014-03-20T08:40:42Z For example, the growth of new minerals within a rock during metamorphism has been estimated to be about 1 mm per million years. Physical Geology 2015-01-01T00:00:00Z Metamorphic source rocks, the rocks that experience the metamorphism, are called the parent rock or protolith, from proto– meaning first, and lithos- meaning rock. An Introduction to Geology 2017-01-01T00:00:00Z Around these separate centres of intrusion are areoles of metamorphism in which the Jurassic shales have been converted into slates and phyllites. Mount Everest the Reconnaissance, 1921 2012-04-12T02:00:28.417Z Here, then, we have an example of fossilization, accomplished by reactions going on at the earth's surface, not by slow metamorphism in deeply-buried sediments. The Catholic World; Volume I, Issues 1-6 A Monthly Eclectic Magazine 2012-04-05T02:00:40.207Z The igneous rocks of the Vosges, and those of the Alps, Corsica, &c., and the subject of metamorphism occupied his attention. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 10 "David, St" to "Demidov" 2012-02-17T03:00:33.923Z The likely pattern of metamorphism in this situation is shown in cross-section in Figure 7.23a. Physical Geology 2015-01-01T00:00:00Z While not strictly a metamorphic structure, they are common around shock metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z Darwin, trained by Sedgwick, noted the contact metamorphism between the former hot molten lava and the earlier cool limestone. Darwin the Geologist 2012-02-12T23:45:00.263Z Dynamic action generates heat, but contrary to the popular notion, the heat involved in profound metamorphism is usually secondary, and the dynamic action fundamental. The Geography of the Region about Devils Lake and the Dalles of the Wisconsin 2011-11-29T03:00:17.347Z All of these rocks show more or less metamorphism either of a thermal character or due to pressure and crushing. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 3 "Gordon, Lord George" to "Grasses" 2011-11-13T03:00:13.177Z The important point is that regional metamorphism happens only at significant depths. Physical Geology 2015-01-01T00:00:00Z In the late 1800s, British geologist George Barrow mapped zones of index minerals in different metamorphic zones of an area that underwent regional metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z Many gneisses are undoubtedly sedimentary rocks that have been brought to their present state by such agents of metamorphism as heat, movement, crushing and recrystallization. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 2 "Gloss" to "Gordon, Charles George" 2011-10-31T02:00:28.703Z This result is not so different from Heim's as appears at first sight, for Heim made no allowance for unrecognized thrust faults and for the contraction incident to metamorphism. Climatic Changes Their Nature and Causes 2011-10-28T02:00:24.840Z It abounds in gaps, some of which have been caused by the destruction of strata owing to metamorphism, denudation or otherwise, others by original non-deposition, as above explained. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z Contact metamorphism takes place where a body of magma intrudes into the upper part of the crust. Physical Geology 2015-01-01T00:00:00Z When contact metamorphism occurs deeper in the Earth, metamorphism can be seen as rings of facies around the intrusion, resulting in aureoles. An Introduction to Geology 2017-01-01T00:00:00Z In a similar way the sphere of influence of metamorphism as indicated by the age of the transformed rocks in various regions has in a general way migrated from east to west across the continent. North America 2011-05-05T02:00:20.027Z These processes include the chemical reorganization of the minerals of the crust, a process which is illustrated by the metamorphism of sedimentary rocks into crystalline forms. Climatic Changes Their Nature and Causes 2011-10-28T02:00:24.840Z As the degree of metamorphism increases, the lenticles diminish in size, and the intervening crushed and foliated matrix increases in amount, until at last it may form the entire mass of the rock. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z 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. Physical Geology 2015-01-01T00:00:00Z With increasing heat and pressure, lignite turns to sub-bituminous coal, bituminous coal, and then, in a process like metamorphism, anthracite. An Introduction to Geology 2017-01-01T00:00:00Z Dynamical and chemical metamorphism may occur at less depth than purely heat metamorphism, and it may be presumed takes place in the axes of mountain ranges, even above sea-level. North America 2011-05-05T02:00:20.027Z The structure, however, which is recognized also in Bavaria and in County Galway, has proved to be due to a zonal development of serpentine during metamorphism of the ancient limestones concerned. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z Sometimes extensive metamorphism has so affected them that their original characters, including their organic contents, have been destroyed. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z The upper body, which has intruded into cool unmetamorphosed rock, has created a zone of contact metamorphism. Physical Geology 2015-01-01T00:00:00Z Grade describes the amount of metamorphism in a rock, and facies are a set of minerals that can help guide an observer to an interpretation of the metamorphic history of a rock. An Introduction to Geology 2017-01-01T00:00:00Z The rocks forming this earliest known land in the Western Hemisphere consist of crystalline schists, gneisses, and granite, which are considered by some geologists at least as having resulted from the metamorphism of sedimentary beds. North America 2011-05-05T02:00:20.027Z There is every kind of gradation in metamorphism. Geology 2011-02-20T03:00:12.660Z It is among igneous rocks that the progressive stages of metamorphism can be most easily traced. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z Contact metamorphism takes place around magma bodies in the upper part of the crust, which are also most common above convergent boundaries. Physical Geology 2015-01-01T00:00:00Z Fluids-activated metamorphism is frequently involved in creating economically important mineral deposits that are located next to igneous intrusions of magma bodies. An Introduction to Geology 2017-01-01T00:00:00Z The heat of an intruded magma affects the rocks it traverses and produces what is termed contact metamorphism. North America 2011-05-05T02:00:20.027Z Heated water would appear to have been the agent to which much of the metamorphism which affects the rocky strata must be attributed. Geology 2011-02-20T03:00:12.660Z Regional metamorphism has arisen in the heart of mountain-chains, and in any other district where the deformation of the crust has been sufficiently intense. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z What process contributes to metamorphism of oceanic crust at a spreading ridge? Physical Geology 2015-01-01T00:00:00Z Non-foliated metamorphic rocks are typically composed of just one mineral and, therefore, usually show the effects of metamorphism with recrystallization in which crystals grow together, but with no preferred direction. An Introduction to Geology 2017-01-01T00:00:00Z When the heat which produced certain phases of metamorphism is sufficiently increased, greater freedom of molecular and chemical changes occur 327 and the material acted on passes to the condition of an igneous magma. North America 2011-05-05T02:00:20.027Z We will analyze them to get a different layer of information for our samples — namely when our samples went through periods of metamorphism or orogenesis. Scientist at Work: On Last Field Day, a South Pole Detour 2011-01-12T17:17:10Z There is indeed every reason to believe that such gneisses were probably originally true granites, and that their foliation and recrystallization have been the result of metamorphism. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" 2011-09-19T02:00:10.473Z Two things that a geologist first considers when looking at a metamorphic rock are what the parent rock might have been, and what type of metamorphism has taken place. Physical Geology 2015-01-01T00:00:00Z Crystals in hornfels grow smaller with metamorphism and become so small that specialized study is required to identify them. An Introduction to Geology 2017-01-01T00:00:00Z The principal agencies which take part in contact metamorphism are heat, heated waters, pressure, and perhaps movements within the rocks. North America 2011-05-05T02:00:20.027Z The deformation and metamorphism create an overprint that masks the record of earlier events. Scientist at Work: Unraveling the History Beneath the Ice 2010-12-28T21:28:12Z Along the line of section between Luss and Ardlui important evidence is obtained of the gradual increase of metamorphism as we proceed northwards from the Highland border. Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 8 "Dubner" to "Dyeing" 2010-12-26T03:00:17.840Z Although most metamorphism involves temperatures above 150°C, some metamorphism takes place at temperatures lower than those at which the parent rock formed. Physical Geology 2015-01-01T00:00:00Z Low-grade metamorphism begins at temperatures and pressures just above sedimentary rock conditions. An Introduction to Geology 2017-01-01T00:00:00Z This regional metamorphism, as it is termed, has affected the rocks in certain instances throughout districts measuring many hundreds of square miles in surface extent, and with a vertical range of many thousands of feet. North America 2011-05-05T02:00:20.027Z The metamorphic rocks are associated with bands of epidiorite which have shared in the folding and metamorphism of the region. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 5 "Arculf" to "Armour, Philip" In the extreme north between Ardlui and the head of Glen Fyne in Argyllshire there is a large development of plutonic rocks piercing the Highland schists and producing marked contact metamorphism. Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 8 "Dubner" to "Dyeing" 2010-12-26T03:00:17.840Z The parent rock is the rock that exists before metamorphism starts. Physical Geology 2015-01-01T00:00:00Z Muscovite schist contains a slightly higher grade muscovite, indicating a greater degree of metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z In the zone of metamorphism the influence of heated percolating waters, combined with movements in the rocks, are the principal factors which lead to the concentration of mineral substances. North America 2011-05-05T02:00:20.027Z Later on he gave his attention to practical geology, to the study of ore-deposits, of rocks and metamorphism; and he was regarded as an excellent teacher. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 5 "Cosway" to "Coucy" His attention was now largely directed to the study of the artificial production of minerals, to the metamorphism of rocks, and to the genesis of igneous rocks. Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 8 "Dubner" to "Dyeing" 2010-12-26T03:00:17.840Z The critical feature of the parent rock is its mineral composition because it is the stability of minerals that counts when metamorphism takes place. Physical Geology 2015-01-01T00:00:00Z Greenschist rocks form under relatively low pressure and temperatures and represent the fringes of regional metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z The birthplace of a large variety of ores and minerals is in the zone of metamorphism. North America 2011-05-05T02:00:20.027Z On the Pacific coast metamorphism of the rocks is common, and lava-flows and tuffs occur in them. Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 3 "Destructors" to "Diameter" The deposition of ores of igneous source in the country rock into which the igneous rocks are intruded is a phase of contact metamorphism. The Economic Aspect of Geology While the rate of metamorphism is slow, the tectonic processes that lead to metamorphism are also very slow, so in most cases, the chance for metamorphic reactions to be completed is high. Physical Geology 2015-01-01T00:00:00Z Burial metamorphism commonly occurs in sedimentary basins, where rocks are buried deeply by overlying sediments. An Introduction to Geology 2017-01-01T00:00:00Z Whether the rocks below the zone of metamorphism are fused or not depends on pressure. North America 2011-05-05T02:00:20.027Z In later periods these rocks have suffered considerable movement and metamorphism, as in the Harz, Devonshire and Cornwall, and in the Belgian coalfields, where they have frequently been thrust over the younger Carboniferous rocks. Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 3 "Destructors" to "Diameter" Hence it is that the subject of contact metamorphism is of interest to economic geologists. The Economic Aspect of Geology All of the important processes of metamorphism that we are familiar with can be directly related to geological processes caused by plate tectonics. Physical Geology 2015-01-01T00:00:00Z These differences in metamorphism appear as distinct bands surrounding the intrusion, as can be seen around the Alta Stock in Little Cottonwood Canyon, Utah. An Introduction to Geology 2017-01-01T00:00:00Z The zone of metamorphism lies between a superior zone where 348 alteration by descending water is dominant, and a lower region where alteration due mainly to heat is in control. North America 2011-05-05T02:00:20.027Z The metamorphic sediments have been pierced by acid and basic igneous intrusions, partly before and partly after the folding and metamorphism of the strata. Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 2 "Baconthorpe" to "Bankruptcy" The phase of metamorphism dealing with surficial weathering, similar changes below the surface, and the formation of sediments, is called katamorphism or destructive change. The Economic Aspect of Geology Most regional metamorphism takes place within continental crust. Physical Geology 2015-01-01T00:00:00Z Along this route, the degree of metamorphism gradually increases from sedimentary parent rock to low-grade metamorphic rock, then higher-grade metamorphic rock, and eventually the igneous core. An Introduction to Geology 2017-01-01T00:00:00Z In the case of the foliated rocks motion within the mass seems to have been the predominating factor, and dynamical metamorphism is considered as important as heat metamorphism. North America 2011-05-05T02:00:20.027Z To the alteration and metamorphism of rocks by the infiltration of rain and other meteoric waters, M. De Koninck, of the Belgian Academy of Sciences, assigns the cause of many hitherto unexplained phenomena in geology. Scientific American, Volume XLIII., No. 25, December 18, 1880 A Weekly Journal of Practical Information, Art, Science, Mechanics, Chemistry, and Manufactures. The phase of metamorphism dealing with the constructive changes in rocks, due to cementation, dynamic movements, and igneous influences, is called anamorphism. The Economic Aspect of Geology Zeolites are silicate minerals that typically form during low-grade metamorphism of volcanic rocks. Physical Geology 2015-01-01T00:00:00Z Shock metamorphism produces planar deformation features, tektites, shatter cones, and quartz polymorphs. An Introduction to Geology 2017-01-01T00:00:00Z Both the upper and lower contacts, however, in certain localities, have been rendered obscure by metamorphism. North America 2011-05-05T02:00:20.027Z To the student of metamorphism the geology of this area is of very high interest. The Sunny Side of Ireland How to see it by the Great Southern and Western Railway Some geologists confine the term metamorphism to the changes involved in contact and dynamic metamorphism, and call the resulting products metamorphic rocks. The Economic Aspect of Geology As described above, regional metamorphism occurs when rocks are buried deep in the crust. Physical Geology 2015-01-01T00:00:00Z Shock metamorphism can also produce index minerals, though they are typically only found via microscopic analysis. An Introduction to Geology 2017-01-01T00:00:00Z An important result of metamorphism is the production of new minerals in the rocks acted on. North America 2011-05-05T02:00:20.027Z This final stage is macroscopically nothing more than a siliceous slate or schist, and is barely distinguishable from the end products of similar metamorphism in the more feldspathic schists and the Loudoun sandy slates. History and Comprehensive Description of Loudoun County, Virginia Looked at broadly, the deposition of ores at igneous contacts under contact metamorphism is a mere incident in the much more widespread and extensive alterations of this kind. The Economic Aspect of Geology Why does contact metamorphism not normally take place at significant depth in the crust? Physical Geology 2015-01-01T00:00:00Z The zircon grains were incorporated into metasedimentary host rocks, sedimentary rocks showing signs of having undergone partial metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z More than one epoch of metamorphism has perhaps occurred, and the entire record now accessible is exceedingly complicated. North America 2011-05-05T02:00:20.027Z The metamorphism of the igneous rocks is regional in nature and has the same increase from west to east as the sediments. History and Comprehensive Description of Loudoun County, Virginia Corundum is a product of contact metamorphism and also a result of direct crystallization from molten magma. The Economic Aspect of Geology What is the role of magmatic fluids in metamorphism that takes place adjacent to a pluton? Physical Geology 2015-01-01T00:00:00Z The host rocks were not very old but the embedded zircon grains were created 4.4 billion years ago and survived the subsequent processes of weathering, erosion, deposition, and metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z In the case of intense contact metamorphism, the altered rock assumes a new form, and may exhibit a crystalline and foliated or schistose structure. North America 2011-05-05T02:00:20.027Z The Weverton sandstone has suffered less from metamorphism than any of the sediments. History and Comprehensive Description of Loudoun County, Virginia Garnets result mainly from contact metamorphism, and commonly occur either in schists and gneisses or in marble. The Economic Aspect of Geology When radiometric techniques are applied to metamorphic rocks, the results normally tell us the date of metamorphism, not the date when the parent rock formed. Physical Geology 2015-01-01T00:00:00Z Dating a mineral within the granite would give the crystallization age of the rock while dating the gneiss might reflect the timing of metamorphism. An Introduction to Geology 2017-01-01T00:00:00Z The appearance of these materials at the surface indicates the removal by denudation and the extreme metamorphism of much sedimentary deposit. The Birth-Time of the World and Other Scientific Essays The obscure process of this metamorphism, and the action if produces, must therefore compose the third class of the fundamental forms of rock. COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 This is called contact metamorphism or thermal metamorphism. The Economic Aspect of Geology This type of information is critical to our understanding of plate tectonics, earthquakes, the formation of mountains, metamorphism, and Earth resources. Physical Geology 2015-01-01T00:00:00Z Metamorphic rocks are crystalline, but the processes of metamorphism may reset the clock and derived ages may represent a smear of different metamorphic events rather than the age of original crystallization. An Introduction to Geology 2017-01-01T00:00:00Z The principal cause of this common phenomenon is what is known as "metamorphism"—that is, the subjection of the rock to a sufficient amount of heat to cause a rearrangement of its particles. The Ancient Life History of the Earth A Comprehensive Outline of the Principles and Leading Facts of Palæontological Science There are certain parts in most countries, and particularly in Ireland, where masses of vegetation have undergone a still further stage in metamorphism, namely, in the well-known and famous peat-bogs. The Story of a Piece of Coal What It Is, Whence It Comes, and Whither It Goes The processes are even more effective when acting in connection with the more intense metamorphism described under the next heading. The Economic Aspect of Geology And, as we’ll see in Chapter 7, the heat of a body of magma can lead to metamorphism of the country rock. Physical Geology 2015-01-01T00:00:00Z Heat as an agent in volcanic phenomena, igneous eruptions, metamorphism, veins, etc. The Atlantic Monthly, Volume 11, No. 66, April, 1863 Anterior to the Cambrian is the great series of the Laurentian, which, owing to the metamorphism to which it has been subjected, has so far yielded but the singular Eozoön. The Ancient Life History of the Earth A Comprehensive Outline of the Principles and Leading Facts of Palæontological Science At Porton, east of Truxillo, the same metamorphism which has changed the ridge of sandstone to a hard quartzite has also changed the ordinary bituminous coal into an anthracite, which is here vertical in position. The Story of a Piece of Coal What It Is, Whence It Comes, and Whither It Goes This process may be called contact metamorphism, but in so far as it results in mashing of the rocks it is closely allied to dynamic metamorphism. The Economic Aspect of Geology 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. Physical Geology 2015-01-01T00:00:00Z Under the head of Heat as an Agent, we have, as might be expected, interesting and valuable matter upon volcanic phenomena, and those of metamorphism. The Atlantic Monthly, Volume 11, No. 66, April, 1863 The rock has probably been derived by dynamic metamorphism, from a coarse igneous rock like a gabbro. The Long Labrador Trail In this rock the planes of deposition are distinctly preserved, and the metamorphism is evidently due to the proximity of volcanic rocks. The Exploring Expedition to the Rocky Mountains, Oregon and California To which is Added a Description of the Physical Geography of California, with Recent Notices of the Gold Region from the Latest and Most Authentic Sources Dynamic and contact metamorphism may in some cases produce rocks identical in appearance with those produced by ordinary processes of cementation and recrystallization without movement. The Economic Aspect of Geology 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. Physical Geology 2015-01-01T00:00:00Z His studies of metamorphism will long do him honor. Scientific American Supplement, No. 299, September 24, 1881 The rock has undergone complete metamorphism and its origin is unknown. The Long Labrador Trail Early stages of metamorphism are seen in SLATE. The Elements of Geology While segregation of materials is characteristic of the surficial products of weathering, the opposite tendency, of mixing and aggregation, is the rule under dynamic metamorphism, notwithstanding the minor segregation above noted. The Economic Aspect of Geology 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. Physical Geology 2015-01-01T00:00:00Z Such facts may induce us to consider whether many granites and other rocks of that class may not sometimes represent merely the extreme of a similar slow metamorphism. The Student's Elements of Geology The rock has been derived by dynamic metamorphism from a basic igneous rock. The Long Labrador Trail All gradations between it and phyllite may be traced, and in many cases we may prove it due to the metamorphism of slates and shales. The Elements of Geology Dynamic metamorphism is for the most part unfavorable to the development of mineral products. The Economic Aspect of Geology Even if formed during regional metamorphism, quartzite does not tend to be foliated because quartz crystals don’t align with the directional pressure. Physical Geology 2015-01-01T00:00:00Z Hydrothermal action producing metamorphism. — in formation of granite. — forming granite veins. The Student's Elements of Geology The process, called metamorphism, took place in the depths of the earth, where the heat is greater than at the surface. An Introduction to Chemical Science Suggest how rocks now in process of metamorphism may sometimes be exposed to view. The Elements of Geology Rocks are not permanent in their condition, but at practically all times and places are undergoing some kind of metamorphism which tends to adapt them to their environment. The Economic Aspect of Geology On the other hand, any clay present in the original sandstone is likely to be converted to mica during metamorphism, and any such mica is likely to align with the directional pressure. Physical Geology 2015-01-01T00:00:00Z Sorby, Mr., on action of water in metamorphism. —, on glass cavities in quartz. —, on mechanical theory of cleavage. —, on ripple-marks in mica schist. The Student's Elements of Geology Chapter VI.—Perhaps some facts on metamorphism, but chiefly on the layers in mica-slate, etc., being analogous to cleavage. More Letters of Charles Darwin — Volume 2 We may contrast with metamorphism the action of external agencies in weathering, which render rocks less coherent by dissolving their soluble parts and breaking down their crystalline grains. The Elements of Geology Contact metamorphism along both the quartz-porphyry and the diorite contacts was practically lacking. The Economic Aspect of Geology The quartz crystals show no alignment, but the micas are all aligned, indicating that there was directional pressure during regional metamorphism of this rock. Physical Geology 2015-01-01T00:00:00Z Water, denuding power of running. —, action of, in metamorphism. The Student's Elements of Geology The metamorphism is more striking in the first change than in the second. A journey in other worlds A romance of the future All these theories agree that the present foliated condition of these rocks is due to the intense metamorphism which they have suffered. The Elements of Geology The emery of Greece and Turkey occurs as lenses or pockets in crystalline limestones, and is the result of contact metamorphism by intrusive granites. The Economic Aspect of Geology Figure 7.16 b: Regional metamorphism of oceanic crustal rock on either side of a spreading ridge. Physical Geology 2015-01-01T00:00:00Z That this pure carbon may have been of organic origin before metamorphism has naturally been conjectured. The Student's Elements of Geology Most regional metamorphism takes place beneath mountain ranges because the crust becomes thickened and rocks are pushed down to great depths. Physical Geology 2015-01-01T00:00:00Z It is known to be produced in some cases by the metamorphism of coal, which itself is formed of decomposed vegetal tissues. The Elements of Geology Amorphous graphite is formed in many places where coal and other carbonaceous materials have undergone extreme metamorphism. The Economic Aspect of Geology Figure 7.17 c: Regional metamorphism of oceanic crust at a subduction zone. Physical Geology 2015-01-01T00:00:00Z The materials of such strata, if they underwent metamorphism, would be subject to chemical laws, simple and uniform in their action, the same in every climate, and wholly undisturbed by mechanical and organic causes. The Student's Elements of Geology As we’ve discussed in the context of metamorphism, Earth’s internal temperature increases with depth. Physical Geology 2015-01-01T00:00:00Z In contact metamorphism, thin sheets of molten rock produce less effect than thicker ones. The Elements of Geology The origin of the ores is obscured by later shearing and metamorphism, but it seems best explained by replacement of the limestone by heated solutions coming from the granitic mass. The Economic Aspect of Geology Figure 7.20 Types of metamorphism shown in the context of depth and temperature under different conditions. Physical Geology 2015-01-01T00:00:00Z Neither, with the exception of the Brazilian ores, have they undergone any deep-seated metamorphism. The Economic Aspect of Geology Certain kinds of metamorphism are suggestive of the nature of the mineral deposits with which they are associated. The Economic Aspect of Geology The pre-Cambrian rocks are of very great economic importance, because of their extensive metamorphism and the enormous masses of igneous rock which they involve. The Elements of Geology Pegmatites which have been subjected to dynamic metamorphism are often not available as a source of mica, because of the distortion of the mica sheets. The Economic Aspect of Geology Figure 7.25 Depiction of metamorphism and alteration around a pluton in the upper crust. Physical Geology 2015-01-01T00:00:00Z The presence of metamorphism indicating high temperatures and pressures to some extent limits the kinds of minerals which one may expect to find. The Economic Aspect of Geology Sapphire, ruby, emerald, and tourmaline result also from contact metamorphism of sediments in the vicinity of igneous rocks. The Economic Aspect of Geology Talc and slate are almost the only mineral products which owe their value principally to dynamic metamorphism. The Economic Aspect of Geology Metalliferous mineral lands are considered in relation to general geology, country rock, intrusions and metamorphism, structure, outcrops and float of lodes, prospects and mines, samples, and history of the region. The Economic Aspect of Geology Oceanic crustal rock can be metamorphosed near the spreading ridge where it was formed, but most other regional metamorphism takes place in areas where mountain ranges have formed, which are most common at convergent boundaries. Physical Geology 2015-01-01T00:00:00Z |
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