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Shear Zones
image:boudin_vein.jpg, Boudinaged quartz vein (with strain fringe) showing ''Fault (geology), sinistral shear sense'', Starlight Pit, Fortnum Gold Mine, Western Australia In geology, shear is the response of a rock to Deformation (engineering), deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or List of rock textures, rock texture and Fault (geology), fault mechanics. The process of shearing occurs within brittle, brittle-ductile, and ductile rocks. Within purely brittle rocks, compressive stress results in Fracture (geology), fracturing and simple Fault (geology), faulting. Rocks Rocks typical of shear zones include mylonite, cataclasite, Tectonite, S-tectonite and Tectonite, L-tectonite, pseudotachylite, certain breccias and highly Foliation (geology), foliated versions of the w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boudin Vein
Boudin () are various kinds of sausage in French, Luxembourgish, Belgian, Swiss, Québécois, Acadian, Aostan, Louisiana Creole, and Cajun cuisine. Etymology The Anglo-Norman word meant 'sausage', 'blood sausage' or 'entrails' in general. Its origin is unclear. It has been traced both to Romance and to Germanic roots, but there is not good evidence for either (cf. boudin. The English word "pudding" probably comes from . Types * '' ball'': A Cajun variation on . Instead of the filling being stuffed into pork casings, it is rolled into a ball, battered, and deep-fried. * : Originally, a white sausage made of pork without the blood. Variants include: ** French/Belgian boudin blanc, with milk. Generally sautéed or grilled. ** Cajun boudin blanc, made from a pork and rice mixture (much like dirty rice) in pork casings. Often includes pork liver and heart. Generally simmered or braised, although it may also be grilled. ** (): a traditional French , which may only conta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Breccia
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia. A megabreccia is a breccia composed of very large rock fragments, sometimes kilometers across, which can be formed by landslides, impact events, or caldera collapse. Types Breccia is composed of coarse rock fragments held together by cement or a fine-grained matrix. Like conglomerate, breccia contains at least 30 percent of gravel-sized particles (particles over 2mm in size), but it is distinguished from conglomerate because the rock fragments have sharp edges that have not been worn down. These indicate that the gravel was deposited very close to its source area, since otherwise th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Geological Institute
The American Geosciences Institute (AGI) is a nonprofit federation of about 50 geoscientific and professional organizations that represents geologists, geophysicists, and other earth scientists. The organization was founded in 1948. The name of the organization was changed from the American Geological Institute on October 1, 2011. The organization's offices are in Alexandria, Virginia. About AGI's monthly magazine ''Geotimes'' became ''EARTH Magazine'' on September 1, 2008, with an increased focus on public communication of geoscience research. As of April 1, 2019, ''EARTH Magazine'' suspended publication and has been folded into ''Nautilus'' magazine. Since 1966, AGI has produced GeoRef, a literature database for those studying the earth sciences. AGI operates the Center for Geosciences and Society. Mission The stated mission of AGI is to “represent and serve the geoscience community by providing collaborative leadership and information to connect Earth, science, and peopl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metasomatism
Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid. Synonyms to the word metasomatism are metasomatose and metasomatic process. The word metasomatose can also be used as a name for specific varieties of metasomatism (for example '' Mg-metasomatose'' and '' Na-metasomatose''). Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact metamorphic aureole adjacent to an intrusive rock mass. In the metamorphic environment, metasomatism is created by mass ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface. Various forms of metamorphism exist, including regional, contact, hydrothermal, shock, and dynamic metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent to which reactive fluids are involved. Metamorphism occurring at increasing pressure and temperature conditions is known as ''prograde metamorphism'', while decreasing temperature and pressure characterize ''retrograde metamorphism''. Metamorphic petrology is the study of metamorphism. Metamorphic petrologists re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orogeny
Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere ( crust and uppermost mantle). A synorogenic process or event is one that occurs during an orogeny. 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 f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrothermal Circulation
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press. and θέρμη, ''heat'' ). Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near volcanic activity, but can occur in the shallow to mid crust along deeply penetrating fault irregularities or in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism. Seafloor hydrothermal circulation Hydrothermal circulation in the oceans is the passage of the water through mid-oceanic ridge systems. The term includes both the circulation of the well-known, high-temperature vent waters near the ridge crests, and the much-lower-temperature, diffuse flow of water through sedim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
En Echelon Veins
In structural geology, en échelon veins, "en échelon gash fractures" or "Tiger Stripes" are structures within rock caused by noncoaxial shear. En echelon veins can be parallel or subparallel, closely-spaced, overlapping or step-like minor structural features in rock. These step-like features can be faults, or tension fractures, that are oblique to the overall structural trend. They originate as tension fractures that are parallel to the major stress orientation, σ1, in a shear zone. They are subsequently filled by precipitation of a mineral, typically quartz or calcite. As soon as they form, they begin to rotate in the shear zone. Subsequent growth of the fracture therefore causes the vein to take on a sigmoidal shape. They can be used to determine the incremental kinematics Kinematics is a subfield of physics, developed in classical mechanics, that describes the Motion (physics), motion of points, Physical object, bodies (objects), and systems of bodies (groups of object ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fold (geology)
In structural geology, a fold is a stack of originally planar surfaces, such as sedimentary strata, that are bent or curved during permanent deformation. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur as single isolated folds or in periodic sets (known as ''fold trains''). Synsedimentary folds are those formed during sedimentary deposition. Folds form under varied conditions of stress, pore pressure, and temperature gradient, as evidenced by their presence in soft sediments, the full spectrum of metamorphic rocks, and even as primary flow structures in some igneous rocks. A set of folds distributed on a regional scale constitutes a fold belt, a common feature of orogenic zones. Folds are commonly formed by shortening of existing layers, but may also be formed as a result of displacement on a non-planar fault (''fault bend fold''), at the tip of a propagating fault (''fault propagation fold''), by differential compaction or due to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Foliation (geology)
Foliation in geology refers to repetitive layering in metamorphic rocks.Marshak, Stephen, ''Essentials of Geology,'' W. W. Norton 3rd Ed, 2009 Each layer can be as thin as a sheet of paper, or over a meter in thickness. The word comes from the Latin ''folium'', meaning "leaf", and refers to the sheet-like planar structure. 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). The layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Nonfoliated metamorphic rocks are typically formed in the absence of significant differential pressure or shear. Foliation is common in rocks affected by the regional metamorphic compression typical of areas of mountain belt formation (orogenic belts). More technically, foliation is any penetrative planar fabric present in metamorphic rocks. Rocks exhibiting foliat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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