Diabase ( // ) or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of English-speaking world, where sometimes the name diabase is applied to altered dolerites and basalts. Some geologists prefer the name microgabbro to avoid this confusion.
Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar.
A subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at medium to shallow depths within the crust, and has intermediate grain size and often porphyritic texture between that of volcanic rocks and plutonic rocks. Subvolcanic rocks include diabase and porphyry. Common examples of subvolcanic rocks are diabase, quartz-dolerite, micro-granite and diorite.
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.
Diabase normally has a fine but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%), and ilmenite (2%).Accessory and alteration minerals include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite. The texture is termed diabasic and is typical of diabases. This diabasic texture is also termed interstitial. The feldspar is high in anorthite (as opposed to albite), the calcium endmember of the plagioclase anorthite-albite solid solution series, most commonly labradorite.
Rock microstructure includes the texture of a rock and the small scale rock structures. The words "texture" and "microstructure" are interchangeable, with the latter preferred in modern geological literature. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, and their appearance.
A lath or slat is a thin, narrow strip of straight-grained wood used under roof shingles or tiles, on lath and plaster walls and ceilings to hold plaster, and in lattice and trellis work.
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 (from the Ancient Greek for "oblique fracture", in reference to its two cleavage angles). 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.
Diabase is usually found in smaller relatively shallow intrusive bodies such as dikes and sills. Diabase dikes occur in regions of crustal extension and often occur in dike swarms of hundreds of individual dikes or sills radiating from a single volcanic center.
A dike or dyke, in geological usage, is a sheet of rock that is formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock. A sill is a concordant intrusive sheet, meaning that a sill does not cut across preexisting rock beds. Stacking of sills builds a sill complex and a large magma chamber at high magma flux. In contrast, a dike is a discordant intrusive sheet, which does cut across older rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source. The rocks must be brittle and fracture to create the planes along which the magma intrudes the parent rock bodies, whether this occurs along preexisting planes between sedimentary or volcanic beds or weakened planes related to foliation in metamorphic rock. These planes or weakened areas allow the intrusion of a thin sheet-like body of magma paralleling the existing bedding planes, concordant fracture zone, or foliations.
A dike swarm or dyke swarm is a large geological structure consisting of a major group of parallel, linear, or radially oriented dikes intruded within continental crust. They consist of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, and are magmatic and stratigraphic. Such dike swarms may form a large igneous province and are the roots of a volcanic province.
The Palisades Sill which makes up the New Jersey Palisades on the Hudson River, near New York City, is an example of a diabase sill. The dike complexes of the British Tertiary Volcanic Province which includes Skye, Rum, Mull, and Arran of western Scotland, the Slieve Gullion region of Ireland, and extends across northern England contains many examples of dolerite dike swarms, towards the Midlands other examples include Rowley Rag. Parts of the Deccan Traps of India, formed at the end of the Cretaceous also includes dolerite.It is also abundant in large parts of Curaçao, an island off the coast of Venezuela. Another example of diabase dikes has been recognized in the Mongo area within the Guéra Massif of Chad in Central Africa.
The Palisades Sill is a Triassic, 200 Ma diabase intrusion. It extends through portions of New York and New Jersey. It is most noteworthy for The Palisades, the cliffs that rise steeply above the western bank of the Hudson River. The ideal location and accessibility of the sill, as well as its unique features, have generated much attention from nature enthusiasts, rock climbers, and geologists alike.
The Hudson River is a 315-mile (507 km) river that flows from north to south primarily through eastern New York in the United States. The river originates in the Adirondack Mountains of Upstate New York, flows southward through the Hudson Valley to the Upper New York Bay between New York City and Jersey City. It eventually drains into the Atlantic Ocean at New York Harbor. The river serves as a political boundary between the states of New Jersey and New York at its southern end. Further north, it marks local boundaries between several New York counties. The lower half of the river is a tidal estuary, deeper than the body of water into which it flows, occupying the Hudson Fjord, an inlet which formed during the most recent period of North American glaciation, estimated at 26,000 to 13,300 years ago. Tidal waters influence the Hudson's flow from as far north as the city of Troy.
The City of New York, usually referred to as either New York City (NYC) or simply New York (NY), is the most populous city in the United States. With an estimated 2018 population of 8,398,748 distributed over a land area of about 302.6 square miles (784 km2), New York is also the most densely populated major city in the United States. Located at the southern tip of the state of New York, the city is the center of the New York metropolitan area, the largest metropolitan area in the world by urban landmass and one of the world's most populous megacities, with an estimated 19,979,477 people in its 2018 Metropolitan Statistical Area and 22,679,948 residents in its Combined Statistical Area. A global power city, New York City has been described as the cultural, financial, and media capital of the world, and exerts a significant impact upon commerce, entertainment, research, technology, education, politics, tourism, art, fashion, and sports. The city's fast pace has inspired the term New York minute. Home to the headquarters of the United Nations, New York is an important center for international diplomacy.
In Western Australia a 200 km long dolerite dike, the Norseman–Wiluna Beltis associated with the non-alluvial gold mining area between Norseman and Kalgoorlie, which includes the largest gold mine in Australia, the Super Pit gold mine. West of the Norseman–Wiluna Belt is the Yalgoo–Singleton Belt, where complex dolerite dike swarms obscure the volcaniclastic sediments. Large dolerite sills such as the Golden Mile Dolerite can exhibit coarse grained texture, and show a large diversity in petrography and geochemistry across the width of the sill. Early Jurassic activity resulted in the formation of dolerite intrusion on Prospect Hill in Sydney , and quarrying of basalt for roadstone and other building materials has been an important activity there for over 180 years.
Western Australia is a state occupying the entire western third of Australia. It is bounded by the Indian Ocean to the north and west, and the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Australia is Australia's largest state, with a total land area of 2,529,875 square kilometres, and the second-largest country subdivision in the world, surpassed only by Russia's Sakha Republic. The state has about 2.6 million inhabitants – around 11 percent of the national total – of whom the vast majority live in the south-west corner, 79 per cent of the population living in the Perth area, leaving the remainder of the state sparsely populated.
Gold is a chemical element with the symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium.
Norseman is a town located in the Goldfields-Esperance region of Western Australia along the Coolgardie-Esperance Highway, 726 kilometres (451 mi) east of Perth and 278 metres (912 ft) above sea level. It is also the starting point of the Eyre Highway, and the last major town in Western Australia before the South Australian border 720 kilometres (447 mi) to the east. At the 2016 census, Norseman had a population of almost 600.
In the Thuringian-Franconian-Vogtland Slate Mountains of central Germany the diabase is entirely of Devonian age.They form typical domed landscapes, especially in the Vogtland. One geotourist attraction is the Steinerne Rose near Saalburg, a natural monument, whose present shape is due to the typical weathering of lava pillows.
Germany, officially the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north and the Alps, Lake Constance and the High Rhine to the south. It borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, France to the southwest, and Luxembourg, Belgium and the Netherlands to the west.
Vogtland is a region spanning the German federal states of Bavaria, Saxony and Thuringia and north-western Bohemia in the Czech Republic. It overlaps with and is largely contained within Euregio Egrensis. The name alludes to the former leadership by the Vögte of Weida, Gera and Plauen.
Geotourism deals with the natural and built environments.
The vast areas of mafic volcanism/plutonism associated with the Jurassic breakup of Gondwanaland in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms. These include the Karoo dolerites of South Africa, the Ferrar Dolerites of Antarctica, and the largest of these, indeed the most extensive of all dolerite formations worldwide, are found in Tasmania. Here, the volume of magma which intruded into a thin veneer of Permian and Triassic rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.In Tasmania, dolerite dominates much of the landscape, particularly alpine areas.
In the Death Valley region of California, precambrian diabase intrusions metamorphosed pre-existing dolomite into economically important talc deposits.
Diabase is crushed and used as a construction aggregate for road beds, buildings, railroad beds (rail ballast), and within dams and levees.
Diabase can be cut for use as headstones and memorials; the base of the Marine Corps War Memorial is made of black diabase granite. Diabase can also be cut for use as ornamental stone for countertops, facing stone on buildings, and paving.A form of dolerite, known as bluestone, is one of the materials used in the construction of Stonehenge.
Diabase also serves as local building stone. In Tasmania, where it is one of the most common rocks found,it is used for building, for landscaping and to erect dry-stone farm walls. In northern County Down, Northern Ireland, "dolerite" is used in buildings such as Mount Stewart together with Scrabo Sandstone as both are quarried at Scrabo Hill.
The Blackbird (violin) is made of black diabase.
Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.
Variolites are mafic, igneous, and typically volcanic rocks, e.g. tholeiite, basalt or komatiite, that contain centimeter-scale spherical or globular structures, called varioles, in a fine-grained matrix. These structures are lighter colored than the host rock and typically range in diameter from 0.05mm to over 5 cm. In 1648, Aldrovandi created the term variolite for aphanitic or fine-grained igneous rocks containing varioles. The weathering of varioles often cause variolites to have a pock-marked appearance. In allusion to the pock-marked appearance of weathered surfaces of variolite, this term is derived from the Latin word, variola, for smallpox.
Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive and extrusive, arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.
Ringing rocks, also known as sonorous rocks or lithophonic rocks, are rocks that resonate like a bell when struck, such as the Musical Stones of Skiddaw in the English Lake District; the stones in Ringing Rocks Park, in Upper Black Eddy, Bucks County, Pennsylvania; the Ringing Rocks of Kiandra, New South Wales; and the Bell Rock Range of Western Australia. Ringing rocks are used in idiophonic musical instruments called lithophones.
Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.
Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.
The Yilgarn Craton is a large craton that constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts. Zircon grains in the Jack Hills, Narryer Terrane have been dated at ~4.27 Ga, with one detrital zircon dated as old as 4.4 Ga.
Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano.
The Emily Ann and Maggie Hays nickel deposits are situated approximately 150 km west of the town of Norseman, Western Australia, within the Lake Johnston Greenstone Belt.
The Widgiemooltha Komatiite is a formation of komatiite in the Yilgarn Craton of Western Australia.
The High Arctic Large Igneous Province (HALIP) is a Cretaceous large igneous province in the Arctic. The region is divided into several smaller magmatic provinces. Svalbard, Franz Josef Land, Sverdrup Basin, Amerasian Basin, and northern Greenland are some of the larger divisions. Today, HALIP covers an area greater than 1,000,000 km2 (390,000 sq mi), making it one of the largest and most intense magmatic complexes on the planet. However, eroded volcanic sediments in sedimentary strata in Svalbard and Franz Josef Land suggest that an extremely large portion of HALIP volcanics have already been eroded away.
The Circum-Superior Belt is a widespread Paleoproterozoic large igneous province in the Canadian Shield of Northern, Western and Eastern Canada. It extends more than 3,400 km (2,100 mi) from northeastern Manitoba through northwestern Ontario, southern Nunavut to northern Quebec. Igneous rocks of the Circum-Superior Belt are mafic-ultramafic in composition, deposited in the Labrador Trough near Ungava Bay, the Cape Smith Belt near the southern shore of Hudson Strait and along the eastern shore of Hudson Bay in its northern portion; the Thompson and Fox River belts in the northwest and the Marquette Range Supergroup in its southern portion.
The Mackenzie Large Igneous Province (MLIP) is a major Mesoproterozoic large igneous province of the southwestern, western and northwestern Canadian Shield in Canada. It consists of a group of related igneous rocks that were formed during a massive igneous event starting about 1,270 million years ago. The large igneous province extends from the Arctic in Nunavut to near the Great Lakes in Northwestern Ontario where it meets with the smaller Matachewan dike swarm. Included in the Mackenzie Large Igneous Province are the large Muskox layered intrusion, the Coppermine River flood basalt sequence and the massive northwesterly trending Mackenzie dike swarm.
The Nipissing sills, also called the Nipissing diabase, is a large 2217– to 2210–million year old group of sills in the Superior craton of the Canadian Shield in Ontario, Canada, which intrude the Huronian Supergroup. Nipissing sills intrude all the Huronian sediments and older basement rocks in the northern margin of the Sudbury Basin; they were emplaced after the faulting and folding of Huronian rocks, and are hornblende gabbro of tholeiitic basalt composition. In the Sudbury–Elliot Lake area the Nipissing diabase is deformed; outcrops are parallel to the fold axes of the Huronian sedimentary rocks. Nipissing diabase intrusions are east-northeast trending and are no wider than 460 m (1,510 ft).
The Southern Oklahoma Aulacogen
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