In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, ice, air, plants and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind erosion, zoogenic erosion, anthropogenic erosion; the particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Natural rates of erosion are controlled by the action of geological weathering geomorphic drivers, such as rainfall; the rates at which such processes act control. Physical erosion proceeds fastest on steeply sloping surfaces, rates may be sensitive to some climatically-controlled properties including amounts of water supplied, wind speed, wave fetch, or atmospheric temperature.
Feedbacks are possible between rates of erosion and the amount of eroded material, carried by, for example, a river or glacier. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, which control the arrival and emplacement of material at a new location. While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the natural rate of erosion in the region. Excessive erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses.
Water and wind erosion are the two primary causes of land degradation. Intensive agriculture, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, gully erosion. Splash erosion is seen as the first and least severe stage in the soil erosion process, followed by sheet erosion rill erosion and gully erosion. In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles; the distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs.
If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope. Sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are of the order of a few centimetres or less and along-channel slopes may be quite steep; this means that rills exhibit hydraulic physics different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and flows in narrow channels during or after heavy rains or melting snow, removing soil to a considerable depth. Valley or stream erosion occurs with continued water flow along a linear feature; the erosion is both downward, deepening the valley, headward, extending the valley into the hillside, creating head cuts and steep banks.
In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain; the stream gradient becomes nearly flat, lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone
An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges. Orogeny is the primary mechanism; the word "orogeny" comes from Ancient Greek. Although it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny; the formation of an orogen can be accomplished by the tectonic processes such as oceanic subduction or continental subduction convergence of two or more continents for collisional orogeny). Orogeny produces long arcuate structures, known as orogenic belts. Orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Although orogenic belts are associated with subduction zones, subduction tectonism may be ongoing or past processes.
The subducting tectonism would consume crust, thicken lithosphere, produce earthquake and volcanoes, build island arcs in many cases. Geologists attribute the arcuate structure to the rigidity of the descending plate, island arc cusps relate to tears in the descending lithosphere; these island arcs may be added to a continental margin during an accretionary orogeny. On the other hand, subduction zones may be reworked at a time due to lithospheric rifting, leading to amphibolite to granulite facies metamorphism of the thinned orogenic crust; the processes of orogeny can take tens of millions of years and build mountains from plains or from the seabed. The topographic height of orogenic mountains is related to the principle of isostasy, that is, a balance of the downward gravitational force upon an upthrust mountain range and the buoyant upward forces exerted by the dense underlying mantle. Rock formations that undergo orogeny are deformed and undergo metamorphism. Orogenic processes may push buried rocks to the surface.
Sea-bottom and near-shore material may cover all of the orogenic area. If the orogeny is due to two continents colliding high mountains can result. An orogenic event may be studied: as a tectonic structural event, as a geographical event, as a chronological event. Orogenic events: cause distinctive structural phenomena related to tectonic activity affect rocks and crust in particular regions, happen within a specific period In general, there are two main types of orogens at convergent plate margins: accretionary orogens, which were produced by subduction of one oceanic plate beneath one continental plate to result in either continental arc magmatism or the accretion of island arc terranes to continental margins. An orogeny produces an orogen, but a range-foreland basin system is only produced on passive plate margins; the foreland basin forms ahead of the orogen due to loading and resulting flexure of the lithosphere by the developing mountain belt. A typical foreland basin is subdivided into a wedge-top basin above the active orogenic wedge, the foredeep beyond the active front, a forebulge high of flexural origin and a back-bulge area beyond, although not all of these are present in all foreland-basin systems.
The basin migrates with the orogenic front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the foreland basin are derived from the erosion of the uplifting rocks of the mountain range, although some sediments derive from the foreland; the fill of many such basins shows a change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including crustal deformation, crustal thickening, crustal thinning and crustal melting as well as magmatism and mineralization. What happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, how these properties change during orogenesis. In addition to orogeny, the orogen is subject to other processes, such as erosion; the sequence of repeated cycles of sedimentation and erosion, followed by burial and metamorphism, by crustal anatexis to form granitic batholiths and tectonic uplift to form mountain chains, is called the orogenic cycle.
For example, the Caledonian Orogeny refers to a series of tectonic events due to the continental collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana in the Early Paleozoic. The Caledonian Orogen resulted from these events and various others that are part of its peculiar orogenic cycle. In summary, an orogeny is an episode of deformation and magmatism at convergent plate margins, during which many geological processes play a role at convergent plate margins; every orogeny has its own orogenic cycle, but composite orogenesis is common at convergent plate margins. Erosion represents a subsequent phase of the orogenic cycle. Erosion removes much of the mountains
Granite is a common type of felsic intrusive igneous rock, granular and phaneritic in texture. Granites can be predominantly white, pink, or gray depending on their mineralogy; the word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Speaking, granite is an igneous rock with between 20% and 60% quartz by volume, at least 35% of the total feldspar consisting of alkali feldspar, although the term "granite" is used to refer to a wider range of coarse-grained igneous rocks containing quartz and feldspar; the term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks consist of feldspar, quartz and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole peppering the lighter color minerals; some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic.
A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids; the extrusive igneous rock equivalent of granite is rhyolite. Granite is nearly always massive and tough; these properties have made granite a widespread construction stone throughout human history. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength lies above 200 MPa, its viscosity near STP is 3–6·1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. Granite is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz, alkali feldspar and plagioclase feldspar on the A-Q-P half of the diagram.
True granite contains both alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite; when a granitoid contains less than 10% orthoclase, it is called tonalite. A granite containing both muscovite and biotite micas is called two-mica granite. Two-mica granites are high in potassium and low in plagioclase, are S-type granites or A-type granites. A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: Granite containing rock is distributed throughout the continental crust. Much of it was intruded during the Precambrian age. Outcrops of granite tend to form rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite occurs as small, less than 100 km2 stock masses and in batholiths that are associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are associated with the margins of granitic intrusions.
In some locations coarse-grained pegmatite masses occur with granite. Granite is more common in continental crust than in oceanic crust, they are crystallized from felsic melts which are less dense than mafic rocks and thus tend to ascend toward the surface. In contrast, mafic rocks, either basalts or gabbros, once metamorphosed at eclogite facies, tend to sink into the mantle beneath the Moho. Granitoids have crystallized from felsic magmas that have compositions near a eutectic point. Magmas are composed of minerals in variable abundances. Traditionally, magmatic minerals are crystallized from the melts that have separated from their parental rocks and thus are evolved because of igneous differentiation. If a granite has a cooling process, it has the potential to form larger crystals. There are peritectic and residual minerals in granitic magmas. Peritectic minerals are generated through peritectic reactions, whereas residual minerals are inherited from parental rocks. In either case, magmas will evolve to the eutectic for crystallization upon cooling.
Anatectic melts are produced by peritectic reactions, but they are much less evolved than magmatic melts because they have not separated from their parental rocks. The composition of anatectic melts may change toward the magmatic melts through high-degree fractional crystallization. Fractional crystallisation serves to reduce a melt in iron, titanium and sodium, enrich the melt in potassium and silicon – alkali feldspar and quartz, are two of the defining constituents of granite; this process operates regardless of the origin of parental magmas to granites, regardless of their chemistry. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was; the final texture and composition of a granite are distinctive as to its parental rock. For instance, a granite, derived from partial melting of meta
Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in small concentrations. Some syenites contain larger proportions of mafic components and smaller amounts of felsic material than most granites; the volcanic equivalent of syenite is trachyte. The feldspar component of syenite is predominantly alkaline in character. Plagioclase feldspars may be present in small proportions, less than 10%; such feldspars are interleaved as perthitic components of the rock. When ferromagnesian minerals are present in syenite at all, they occur in the form of hornblende and clinopyroxene. Biotite is rare, because in a syenite magma the formation of feldspar consumes nearly all the aluminium, however less Al rich phyllosilicates may be included such as annite. Other common accessory minerals are apatite, titanite and opaques. Most syenites are either peralkaline with high proportions of alkali elements relative to aluminum, or peraluminous with a higher concentration of aluminum relative to alkali and earth-alkali elements.
Syenites are products of alkaline igneous activity formed in thick continental crustal areas, or in Cordilleran subduction zones. To produce a syenite, it is necessary to melt a granitic or igneous protolith to a low degree of partial melting; this is required because potassium is an incompatible element and tends to enter a melt first, whereas higher degrees of partial melting will liberate more calcium and sodium, which produce plagioclase, hence a granite, adamellite or tonalite. At low degrees of partial melting a silica undersaturated melt is produced, forming a nepheline syenite, where orthoclase is replaced by a feldspathoid such as leucite, nepheline or analcime. Conversely in certain conditions, large volumes of anorthite crystals may precipitate from molten magma in a cumulate process as it cools; this leaves a drastically reduced concentration of silica in the remainder of the melt. The segregation of the silica from the melt leaves it in a state. Syenite is not a common rock. Regions where it occurs in significant quantities include the following.
In the Kola Peninsula of Russia two giant nepheline syenite bodies exists making up the Lovozero Massif and the Khibiny Mountains. These syenites are part of the Kola Alkaline Province. In North America syenite occurs in Montana. Regions in New England have sizable amounts, in New York syenite gneisses occur; the "great syenite dyke" extends from Hanging Rock, South Carolina through Taxahaw, South Carolina to the Brewer and Edgeworth mine in Chesterfield, South Carolina. Syenite clasts containing fluorescent sodalite were found on a beach in Michigan in 2017, their discoverer Erik Rintamaki finding that they glowed under ultraviolet light and naming them "Yooperlite". Rintamaki's discovery was made public and verified in May 2018. In Europe syenite may be found in parts of Switzerland, Norway, Portugal, in Plovdiv, Bulgaria and in Ditrău, Romania. In Africa there are syenite formations in Aswan, in Malawi in the Mulanje Mountain Forest Reserve. Syenite rock was used to make the Quay with Sphinxes.
In Australia syenite occurs as small intrusive bodies in nearly every state. In New South Wales, a large syenite intruded during the breakup of Gondwana in the Cretaceous. Instead of the usual rock syenite, some of the more important events in New England, Montana, New York, Germany, Plovdiv, Bulgaria and Romania; the Malvern Hills, on the border between the counties of Herefordshire and Worcestershire United Kingdom are formed of syenite. Paatusoq and Kangerluluk fjords in southeastern Greenland, where a bay within the latter and a headland are named after the rock; the term syenite was applied to hornblende granite like that of Syene in Egypt, from which the name is derived. Episyenite is a term used in petrology to describe the depletion of silicon dioxide in rock rich in silicon dioxide. A process that results in depletion is termed episyenitization; the term refers only to the macroscopic effect of relative depletion in a rock. Many different metamorphic processes can lead to episyenitization.
For example: chemical components in a stagnant melt can diffuse under the influence of chemical potential gradients that cause their segregation from low- SiO2 components when the melt begins to solidify a SiO2-undersaturated fluid may dissolve quartz from rock and remove it by advection, thus leaving the parent rock depleted of silica. A marginally molten rock mass may retain its unmolten silica-rich components, while the molten, silica-depleted fluid cools to form a syenite. on beginning to cool, a molten silica-rich melt might precipitate its silica-containing components, leaving the silica-depleted melt to form a syenite afterwards. List of rock types E. Wm. Heinrich. Microscopic Petrography, McGraw-Hill, 1956
Quartz diorite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less potassium feldspar. Quartz is present at between 20 % of the rock. Biotite and pyroxenes are common dark accessory minerals. Williams, Howel.
Feldspars are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are present in many types of metamorphic rock. Rock formed entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are found in many types of sedimentary rocks; the name feldspar derives from the German Feldspat, a compound of the words Feld, "field", Spat meaning "a rock that does not contain ore". The change from Spat to -spar was influenced by the English word spar, meaning a non-opaque mineral with good cleavage. Feldspathic refers to materials; the alternate spelling, has fallen out of use. This group of minerals consists of tectosilicates. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: potassium feldspar endmember KAlSi3O8, albite endmember NaAlSi3O8, anorthite endmember CaAl2Si2O8. Solid solutions between K-feldspar and albite are called "alkali feldspar".
Solid solutions between albite and anorthite are called "plagioclase", or more properly "plagioclase feldspar". Only limited solid solution occurs between K-feldspar and anorthite, in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Albite is considered both alkali feldspar. Alkali feldspars are grouped into two types: those containing potassium in combination with sodium, aluminum, or silicon; the first of these include: orthoclase KAlSi3O8, sanidine AlSi3O8, microcline KAlSi3O8, anorthoclase AlSi3O8. Potassium and sodium feldspars are not miscible in the melt at low temperatures, therefore intermediate compositions of the alkali feldspars occur only in higher temperature environments. Sanidine is stable at the highest temperatures, microcline at the lowest. Perthite is a typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition; the perthitic textures in the alkali feldspars of many granites can be seen with the naked eye.
Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are considered alkali feldspars. Barium feldspars form as the result of the substitution of barium for potassium in the mineral structure; the barium feldspars are monoclinic and include the following: celsian BaAl2Si2O8, hyalophane 4O8. The plagioclase feldspars are triclinic; the plagioclase series follows: albite NaAlSi3O8, oligoclase AlSi2O8, andesine NaAlSi3O8—CaAl2Si2O8, labradorite AlSi2O8, bytownite AlSi2O8, anorthite CaAl2Si2O8. Intermediate compositions of plagioclase feldspar may exsolve to two feldspars of contrasting composition during cooling, but diffusion is much slower than in alkali feldspar, the resulting two-feldspar intergrowths are too fine-grained to be visible with optical microscopes; the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to fine-grained exsolution lamellae.
The specific gravity in the plagioclase series increases from albite to anorthite. Chemical weathering of feldspars results in the formation of clay minerals such as illite and kaolinite. About 20 million tonnes of feldspar were produced in 2010 by three countries: Italy and China. Feldspar is a common raw material used in glassmaking, to some extent as a filler and extender in paint and rubber. In glassmaking, alumina from feldspar improves product hardness and resistance to chemical corrosion. In ceramics, the alkalis in feldspar act as a flux. Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fiber. Ceramics and other uses, such as fillers, accounted for the remainder. In earth sciences and archaeology, feldspars are used for K-Ar dating, argon-argon dating, luminescence dating. In October 2012, the Mars Curiosity rover analyzed a rock that turned out to have a high feldspar content.
List of minerals – A list of minerals for which there are articles on Wikipedia List of countries by feldspar production This article incorporates public domain material from the United States Geological Survey document: "Feldspar and nepheline syenite". Bonewitz, Ronald Louis. Rock and Gem. New York: DK Publishing. ISBN 978-0-7566-3342-4. Media related to Feldspar at Wikimedia Commons
Granodiorite is a phaneritic-textured intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. According to the QAPF diagram, granodiorite has a greater than 20% quartz by volume, between 65% to 90% of the feldspar is plagioclase. A greater amount of plagioclase would designate the rock as tonalite. Granodiorite is felsic to intermediate in composition, it is the intrusive igneous equivalent of the extrusive igneous dacite. It contains a large amount of sodium and calcium rich plagioclase, potassium feldspar and minor amounts of muscovite mica as the lighter colored mineral components. Biotite and amphiboles in the form of hornblende are more abundant in granodiorite than in granite, giving it a more distinct two-toned or overall darker appearance. Mica may be present in well-formed hexagonal crystals, hornblende may appear as needle-like crystals. Minor amounts of oxide minerals such as magnetite and ulvöspinel, as well as some sulfide minerals may be present.
On average, the upper continental crust has the same composition as granodiorite. Granodiorite is a plutonic igneous rock, formed by intrusion of silica-rich magma, which cools in batholiths or stocks below the Earth's surface, it is only exposed at the surface after uplift and erosion have occurred. The name comes from two related rocks to which granodiorite is an intermediate: diorite; the gran- root comes from the Latin grānum for "grain", an English language derivative. Diorite is named after the contrasting colors of the rock. Plymouth Rock is a glacial erratic boulder of granodiorite; the Sierra Nevada mountains contain large sections of granodiorite. Granodiorite was quarried at Mons Claudianus in the Red Sea Governorate in eastern Egypt from the 1st century AD to the mid-3rd century AD. Much of the quarried stone was transported to Rome for use in major projects such as the Pantheon and Hadrian's Villa. Additionally, granodiorite was used for the Rosetta Stone. Granodiorite is most used as crushed stone for road building.
It is used as construction material, building facade, paving, as an ornamental stone. The Rosetta Stone is a stele made from granodiorite; the portico columns of the Pantheon in Rome are formed from single shafts of granodiorite, each 12 metres tall by 1.5 metres in diameter. List of rock types This article incorporates public domain material from the United States Geological Survey document: "Granodiorite definition".. Media related to Granodiorite at Wikimedia Commons