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Llano Uplift
The Llano Uplift is a geologically ancient, low geologic dome that is about 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 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.Barnes, V.E., Bell, W.C., Clabaugh, S.E., Cloud, P.E., Jr., Young, K., and McGehee, R.V., 1962. ''Field ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five major unincorporated territories, nine United States Minor Outlying Islands, Minor Outlying Islands, and 326 Indian reservations. The United States is also in Compact of Free Association, free association with three Oceania, Pacific Island Sovereign state, sovereign states: the Federated States of Micronesia, the Marshall Islands, and the Palau, Republic of Palau. It is the world's List of countries and dependencies by area, third-largest country by both land and total area. It shares land borders Canada–United States border, with Canada to its north and Mexico–United States border, with Mexico to its south and has maritime borders with the Bahamas, Cuba, Russia, and other nations. With a population of over 333 m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as either '' bedding surfaces'' or ''bedding planes''.Salvador, A. ed., 1994. ''International stratigraphic guide: a guide to stratigraphic classification, terminology, and procedure. 2nd ed.'' Boulder, Colorado, The Geological Society of America, Inc., 215 pp. . Prior to the publication of the International Stratigraphic Guide, older publications have defined a stratum as either being either equivalent to a single bed or composed of a number of beds; as a layer greater than 1 cm in thickness and constituting a part of a bed; or a general term that includes both ''bed'' and '' lamina''.Neuendorf, K.K.E., Mehl, Jr., J.P., and Jackson, J.A. , eds., 2005. ''Glossary of Geology'' 5th ed. Alexandria, Virginia, American Geological Institute. 779 pp. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basement (geology)
In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". Crustal rocks are modified several times before they become basement, and these transitions alter their composition. Continental crust Basement rock is the thick foundation of ancient, and oldest, metamorphic and igneous rock that forms the crust of continents, often in the form of granite. Basement rock is contrasted to overlying sedimentary rocks which are laid down on top of the basement rocks after the continent was formed, such as s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basement High
In geology, a basement high is a portion of the basement in a sedimentary basin that is higher than its surroundings. Commonly, structures referred to as basement highs are hidden by the sedimentary fill of the basin. Usually basement highs are elongated features of tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ... origin. {{geology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Structural Geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation ( strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometries. This understanding of the dynamics of the stress field can be linked to important events in the geologic past; a common goal is to understand the structural evolution of a particular area with respect to regionally widespread patterns of rock deformation (e.g., mountain building, rifting) due to plate tectonics. Use and importance The study of geologic structures has been of prime importance in economic geology, both petroleum geology and mining geology. Folded and faulted rock strata commonly form traps that accumulate and concentrate fluids such as petroleum and natural gas. Sim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geologic Map
A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features. Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Symbols Lithologies Rock units are typically represented by colors. Instead of (or in addition to) colors, certain symbols can be used. Different geologic mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of dif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Llano Uplift Geologic Map V1
''Llano'' is the Spanish word for plain. It may refer to: * Llano, California * Llano Estacado, a region in northwest Texas and eastern New Mexico * Llano, Texas, a small city in Llano County, Texas * Llano County, Texas * Llano River, a Texas river * Llano Uplift, a geologic dome exposing Precambrian rocks in Central Texas. * Gonzalo Queipo de Llano, a Spanish army-officer serving during the Spanish Civil War * The Llanos, a plain in north-western South America ** ''Llanero'', a person from the Llanos * The Llano, a magical song from Piers Anthony's ''Incarnations of Immortality'' series * The codename for the first AMD Accelerated Processing Unit microprocessor See also * ''Llanito'', the local language of Gibraltar. * Llanite, a variety of rhyolite 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 grou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Llanite
Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals. Llanite comes from a hypabyssal porphyritic rhyolite dike that intrudes Precambrian metamorphics in the Llano Uplift of central Texas. Published radiometric dating on this llanite indicates that it's 1.106 billion years old (late Mesoproterozoic). The quartz crystals found in llanite are blue hexagonal bipyramids. The unusual blue coloration of the quartz is thought to be due to ilmenite inclusions. It is named after Llano County, Texas, the only place where it is found. However, the geology of North-East Africa is very similar to that of Texas. Many of the minerals and fossils found are only found in these two locations on the whole planet. (geologists have identified other locations where similar types of rock may be found).Re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Granite Mountain (Texas)
Granite Mountain is a solid dome, also known as a bornhardt, of pink granite (pink granite is also known as Sunset Red) rising over 860 feet one mile west of Marble Falls, Texas. Since quarry operations began in the late 19th century, the distinctive pink-red colored rock has been used in the construction of the Texas State Capitol in Austin, Texas, and also for the construction of the Galveston Seawall. In 1882, three businessmen and the owners of Granite Mountain, G. W. Lacy (of the Lacy Lans Ranch), N. L. Norton and W. H. Westfall, donated the amount of granite necessary to build the Texas State Capitol. The mountain no longer looks like a geographic feature because of the heavy mining, which has fully covered its surface. A similar but much larger area known as Enchanted Rock State Natural Area can be seen in its undisturbed state west of Marble Falls near Fredericksburg, Texas. See also * Llano Uplift * Geology of Texas Texas contains a wide variety of geologic setting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enchanted Rock
Enchanted Rock is a pink granite mountain located in the Llano Uplift about north of Fredericksburg, Texas and south of Llano, Texas, United States. Enchanted Rock State Natural Area, which includes Enchanted Rock and surrounding land, spans the border between Gillespie and Llano counties, south of the Llano River. Enchanted Rock covers roughly and rises around above the surrounding terrain to an elevation of above sea level. It is the largest pink granite monadnock in the United States. Enchanted Rock State Natural Area, a part of the Texas state park system, includes . In 1936, the area was designated a Recorded Texas Historic Landmark. In 1971, Enchanted Rock was designated as a National Natural Landmark by the National Park Service. Enchanted Rock was rated in 2017 as the best campsite in Texas in a 50-state survey. Geology The prominent granite dome is visible for many miles in the surrounding basin of the Llano Uplift. The weathered dome, standing above the sur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Granite Dome
Granite domes are domical hills composed of granite with bare rock exposed over most of the surface. Generally, domical features such as these are known as bornhardts. Bornhardts can form in any type of plutonic rock but are typically composed of granite and granitic gneiss. As granitic plutons cool kilometers below the Earth's surface, minerals in the rock crystallize under uniform confining pressure. Erosion brings the rock closer to Earth's surface and the pressure from above the rock decreases; as a result the rock fractures. These fractures are known as exfoliation joints, or sheet fractures, and form in onionlike patterns that are parallel to the land surface. These sheets of rock peel off the exposed surface and in certain conditions develop domical structures. Additional theories on the origin of granite domes involve scarp-retreat and tectonic uplift. Sheet fractures Sheet fractures are arcuate fractures defining slabs of rock that range from 0.5 to 10 meters thic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graben
In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic context by Eduard Suess in 1883. The plural form is either ''graben'' or ''grabens''. Formation A graben is a valley with a distinct escarpment on each side caused by the displacement of a block of land downward. Graben often occur side by side with horsts. Horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of the footwall is upward. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between graben; the bounding faults of a horst typically dip away from the center line of the horst. Single or multiple graben can produce a rift valley. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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