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Geology Of Guernsey
Guernsey has a geological history stretching further back into the past than most of Europe. The majority of rock exposures on the Island may be found along the coastlines, with inland exposures scarce and usually highly weathered. There is a broad geological division between the north and south of the Island. The ''Southern Metamorphic Complex'' is elevated above the geologically younger, lower lying ''Northern Igneous Complex''. Guernsey has experienced a complex geological evolution (especially the rocks of the southern complex) with multiple phases of intrusion and deformation recognisable. Geological history Precambrian The southern part if the island is largely composed of ''Icart Gneiss''. The Icart Gneiss is an augen gneiss of granitic composition containing potassium feldspar. This was formed from a granite dated at using U-Pb dating on zircon grains. A foliated Perelle quartz diorite (also called ''Perelle Gneiss''), occurs in the centre and west of the island. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of Guernsey
Guernsey has a geological history stretching further back into the past than most of Europe. The majority of rock exposures on the Island may be found along the coastlines, with inland exposures scarce and usually highly weathered. There is a broad geological division between the north and south of the Island. The ''Southern Metamorphic Complex'' is elevated above the geologically younger, lower lying ''Northern Igneous Complex''. Guernsey has experienced a complex geological evolution (especially the rocks of the southern complex) with multiple phases of intrusion and deformation recognisable. Geological history Precambrian The southern part if the island is largely composed of ''Icart Gneiss''. The Icart Gneiss is an augen gneiss of granitic composition containing potassium feldspar. This was formed from a granite dated at using U-Pb dating on zircon grains. A foliated Perelle quartz diorite (also called ''Perelle Gneiss''), occurs in the centre and west of the island. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface. For this reason, olivine has been proposed as a good candidate for accelerated weathering to sequester carbon dioxide from the Earth's oceans and atmosphere, as part of climate change mitigation. Olivine also has many other historical uses, such as the gemstone peridot (or chrysolite), as well as industrial applications like metalworking processes. The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: ) and fayalite (Fe-endmember: ). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and fayalite (Fa) (''e.g.'', Fo70Fa30). Forsterite's melting temperature is unusually high at atmospheric pressure, almost , while ... [...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] |
Mylonite
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock. Formation Mylonites are ductilely deformed rocks formed by the accumulation of large shear strain, in ductile fault zones. There are many different views on the formation of mylonites, but it is generally agreed that crystal-plastic deformation must have occurred, and that fracturing and cataclastic flow are secondary processes in the formation of mylonites. Mechanical abrasion of grains by milling does not occur, although this was originally thought to be the process that formed mylonites, which were named from the Greek μύλος ''mylos'', meaning mill. Mylonites form at depths of no less than 4 km. There are many different mechanisms that accommodate crystal-plastic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shear Zone
In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear zone takes the form of a fracture called a fault. In the lower crust and mantle, the extreme conditions of pressure and temperature make the rock ductile. That is, the rock is capable of slowly deforming without fracture, like hot metal being worked by a blacksmith. Here the shear zone is a wider zone, in which the ductile rock has slowly flowed to accommodate the relative motion of the rock walls on either side. Because shear zones are found across a wide depth-range, a great variety of different rock types with their characteristic structures are associated with shear zones. General introduction A shear zone is a zone of strong deformation (with a high strain rate) surrounded by rocks with a lower state of finite strain. It ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lihou
Lihou () is a small tidal island located just off the west coast of the island of Guernsey, in the English Channel, between Great Britain and France. Administratively, Lihou forms part of the Parish of St. Peter's in the Bailiwick of Guernsey, and is now owned by the parliament of Guernsey (the States of Guernsey), although there have been a number of owners in the past. Since 2006, the island has been jointly managed by the Guernsey Environment Department and the Lihou Charitable Trust. In the past the island was used by locals for the collection of seaweed for use as a fertiliser, but today Lihou is mainly used for tourism, including school trips. Lihou is also an important centre for conservation, forming part of a Ramsar wetland site for the preservation of rare birds and plants as well as historic ruins of a priory and a farmhouse. Etymology In common with several nearby islands such as Jethou and Brecqhou, the name contains the Norman suffix "''-hou''" which means a sm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lihou Folds
Lihou () is a small tidal island located just off the west coast of the island of Guernsey, in the English Channel, between Great Britain and France. Administratively, Lihou forms part of the Parish of St. Peter's in the Bailiwick of Guernsey, and is now owned by the parliament of Guernsey (the States of Guernsey), although there have been a number of owners in the past. Since 2006, the island has been jointly managed by the Guernsey Environment Department and the Lihou Charitable Trust. In the past the island was used by locals for the collection of seaweed for use as a fertiliser, but today Lihou is mainly used for tourism, including school trips. Lihou is also an important centre for conservation, forming part of a Ramsar wetland site for the preservation of rare birds and plants as well as historic ruins of a priory and a farmhouse. Etymology In common with several nearby islands such as Jethou and Brecqhou, the name contains the Norman suffix "''-hou''" which means a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Level Rise
Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cryosphere in a Changing Climate .-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.) Cambridge University Press, Cambridge, UK and New York, NY, USA. https://doi.org/10.1017/9781009157964.001. This rate is accelerating, with sea levels now rising by 3.7 mm per year. Climate scientists expect further acceleration during the 21st century. Climate change heats (and therefore expands) the ocean and melts land-based ice sheets and glaciers. Between 1993 and 2018, the thermal expansion of water contributed 42% to sea level rise; melting of temperate glaciers, 21%; Greenland, 15%; and Antarctica, 8%. Over the next 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loess
Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeolian (windborne) sediment, defined as an accumulation of 20% or less of clay and a balance of roughly equal parts sand and silt (with a typical grain size from 20 to 50 micrometers), often loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. Properties Loess is homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non-stratified and often calcareous. Loess grains are angular, with little polishing or rounding, and composed of crystals of quartz, feldspar, mica and other minerals. Loess can be described as a rich, dust-like soil. Loess deposits may become very thick, more ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.58 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today, although a third epoch, the Anthropocene, has been proposed but is not yet officially recognised by the ICS). The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused. Research history In 1759 Giovanni Arduino proposed that the geological strata of northern Italy could be divided into four successive formations or "orders" ( it, quattro ordini). The term "quaternary" was introduced by Jules Desn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or 'record-groove' effect. Plagioclase is a major constituent mineral in the Earth's crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a major constituent of rock in the hig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
