Granite Mountain is an igneous intrusion southeast of Little Rock, Arkansas. [1] Despite being named after granite, the rock at Granite Mountain is actually syenite, [2] a rock that is visually similar to granite, but contains much less quartz. The rock was formed in the Cretaceous period around 90 million years ago, after the lamproites at Prairie Creek and the later Magnet Cove complex, and before the formation of the Monroe Uplift and Jackson Dome. [3]
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 relatively small concentrations. It is considered a granitoid. Some syenites contain larger proportions of mafic components and smaller amounts of felsic material than most granites; those are classed as being of intermediate composition.
A batholith is a large mass of intrusive igneous rock, larger than 100 km2 (40 sq mi) in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite.
Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite.
The Coast Mountains are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the Coast of British Columbia south to the Fraser River. The mountain range's name derives from its proximity to the sea coast, and it is often referred to as the Coast Range. The range includes volcanic and non-volcanic mountains and the extensive ice fields of the Pacific and Boundary Ranges, and the northern end of the volcanic system known as the Cascade Volcanoes. The Coast Mountains are part of a larger mountain system called the Pacific Coast Ranges or the Pacific Mountain System, which includes the Cascade Range, the Insular Mountains, the Olympic Mountains, the Oregon Coast Range, the California Coast Ranges, the Saint Elias Mountains and the Chugach Mountains. The Coast Mountains are also part of the American Cordillera—a Spanish term for an extensive chain of mountain ranges—that consists of an almost continuous sequence of mountain ranges that form the western backbone of North America, Central America, South America and Antarctica.
The Llano Uplift is a geologically ancient, low geologic dome that is about 90 miles (140 km) in diameter and located mostly in Llano, Mason, San Saba, Gillespie, and Blanco counties, Texas. It consists of an island-like exposure of Precambrian igneous and metamorphic rocks surrounded by outcrops of Paleozoic and Cretaceous sedimentary strata. At their widest, the exposed Precambrian rocks extend about 65 miles (105 km) westward from the valley of the Colorado River and beneath a broad, gentle topographic basin drained by the Llano River. The subdued topographic basin is underlain by Precambrian rocks and bordered by a discontinuous rim of flat-topped hills. These hills are the dissected edge of the Edwards Plateau, which consist of overlying Cretaceous sedimentary strata. Within this basin and along its margin are down-faulted blocks and erosional remnants of Paleozoic strata which form prominent hills.
The St. Francois Mountains in southeast Missouri are a mountain range of Precambrian igneous mountains rising over the Ozark Plateau. This range is one of the oldest exposures of igneous rock in North America. The name of the range is spelled out as Saint Francois Mountains in official GNIS sources, but it is sometimes misspelled in use as St. Francis Mountains to match the anglicized pronunciation of both the range and St. Francois County.
Diorite is an intrusive igneous rock formed by the slow cooling underground of magma that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silica (mafic) gabbro and high-silica (felsic) granite.
Granodiorite is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar.
Borolanite is an historical petrological name for a pyroxene-melanite bearing nepheline syenite variety which contains nepheline-alkali feldspar pseudomorphs interpreted to be after leucite which occur as conspicuous white spots in the dark rock matrix. The rock occurs in the Borralan Igneous Complex or Loch Borralan Complex which is an alkalic igneous complex near Loch Borralan in northwest Scotland.
The state of Georgia is commonly divided into four geologic regions that influence the location of the state's four traditional physiographic regions. The four geologic regions include the Appalachian foreland, Blue Ridge, Piedmont, and Coastal Plain. These four geologic regions commonly share names with and typically overlap the four physiographic regions of the state: the Appalachian Plateau and adjacent Valley and Ridge; the Blue Ridge; the Piedmont and the Coastal Plain. The geologic regions of the state, established by geologists based on relationships between stratigraphic units, significantly influence the physiographic regional names used by physical geographers. Geologic regions of the state, however, do not perfectly coincide with physiographic regions of the state. Most geologic regions (terranes) in the state are separated from one another by major thrust faults that formed during the growth of the Appalachian Mountains. The Appalachian foreland, for example, is separated from the geologic Blue Ridge by the Talladega-Cartersville-Great Smoky fault. The geologic Blue Ridge is separated from the geologic Piedmont by the Brevard fault zone. The Fall Line, the surface expression of the Coastal Plain unconformity, is the geologic boundary between the Piedmont and the Coastal Plain.
The geology of Hong Kong is dominated by igneous rocks formed during a major volcanic eruption period in the Mesozoic era. It made up 85% of Hong Kong's land surface and the remaining 15% are mostly sedimentary rocks located in the northeast New Territories. There are also a very small percentage of metamorphic rocks in the New Territories, formed by deformation of pre-existing sedimentary rocks (metamorphism).
Shonkinite is an intrusive igneous rock found in few places in the world. It is unique in having low silica, feldspathoid minerals, and large blocky crystals of black augite. It makes up much of the hard dark grey rock comprising certain mountains and buttes in Montana that are remnants of laccoliths and stocks, such as the Highwood mountains.
Quartzolite or silexite is an intrusive igneous rock, in which the mineral quartz is more than 90% of the rock's felsic mineral content, with feldspar at up to 10%. Typically, quartz forms more than 60% of the rock, the rest being mostly feldspar although minor amounts of mica or amphibole may also be present. Quartzolite occurs as dykes, sills, veins, bosses and segregation masses; it is also found in association with greisen and pegmatite. Quartzolite is an extremely rare type of rock. No extrusive rock equivalent of quartzolite is known.
Midnight Volcano is believed to be a buried extinct volcano in southern Humphreys County, Mississippi. It is named after the nearby town of Midnight, Mississippi. During the time it was active, Midnight Volcano may have been a volcanic island in the Mississippi Embayment.
The geology of Arkansas includes deep 1.4 billion year old igneous crystalline basement rock from the Proterozoic known only from boreholes, overlain by extensive sedimentary rocks and some volcanic rocks. The region was a shallow marine, riverine and coastal environment for much of the early Paleozoic as multi-cellular life became commonplace. At the end of the Paleozoic in the Permian the region experienced coal formation and extensive faulting and uplift related to the Ouachita orogeny mountain building event. Extensive erosion of new highlands created a mixture of continental and marine sediments and much of the state remained flooded even into the last 66 million years of the Cenozoic. In recent Pleistocene and Holocene time, glacial sediments poured into the region from the north, down major rivers, forming dunes and sedimentary ridges. Today, Arkansas has an active oil and gas industry, although hydraulic fracturing related earthquake swarms have limited extraction. Mining industries in the state also produce brines, sand, gravel and other industrial minerals.
The geology of Virginia began to form 1.8 billion years ago and potentially even earlier. The oldest rocks in the state were metamorphosed during the Grenville orogeny, a mountain building event beginning 1.2 billion years ago in the Proterozoic, which obscured older rocks. Throughout the Proterozoic and Paleozoic, Virginia experienced igneous intrusions, carbonate and sandstone deposition, and a series of other mountain building events which defined the terrain of the inland parts of the state. The closing of the Iapetus Ocean, to form the supercontinent Pangaea added additional small landmasses, some of which are now hidden beneath thick Atlantic Coastal Plain sediments. The region subsequently experienced the rifting open of the Atlantic Ocean in the Mesozoic, the development of the Coastal Plain, isolated volcanism and a series of marine transgressions that flooded much of the area. Virginia has extensive coal, deposits of oil and natural gas, as well as deposits of other minerals and metals, including vermiculite, kyanite and uranium.
The geology of Bosnia & Herzegovina is the study of rocks, minerals, water, landforms and geologic history in the country. The oldest rocks exposed at or near the surface date to the Paleozoic and the Precambrian geologic history of the region remains poorly understood. Complex assemblages of flysch, ophiolite, mélange and igneous plutons together with thick sedimentary units are a defining characteristic of the Dinaric Alps, also known as the Dinaride Mountains, which dominate much of the country's landscape.
The geology of Alaska includes Precambrian igneous and metamorphic rocks formed in offshore terranes and added to the western margin of North America from the Paleozoic through modern times. The region was submerged for much of the Paleozoic and Mesozoic and formed extensive oil and gas reserves due to tectonic activity in the Arctic Ocean. Alaska was largely ice free during the Pleistocene, allowing humans to migrate into the Americas.
The geology of Montana includes thick sequences of Paleozoic, Mesozoic and Cenozoic sedimentary rocks overlying ancient Archean and Proterozoic crystalline basement rock. Eastern Montana has considerable oil and gas resources, while the uplifted Rocky Mountains in the west, which resulted from the Laramide orogeny and other tectonic events have locations with metal ore.
The geology of Brazil includes very ancient craton basement rock from the Precambrian overlain by sedimentary rocks and intruded by igneous activity, as well as impacted by the rifting of the Atlantic Ocean.
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