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42-538: The Gibraltar Range is a mountain range in the Northern Tablelands region of New South Wales , Australia . The range extends off the Great Dividing Range at Bald Nob about 25 kilometres (16 mi) east northeast of Glen Innes and trends generally east northeast and north northeast for about 100 kilometres (62 mi) to the junction of Timbarra and Clarence rivers. It forms

84-531: A fold is a stack of originally planar surfaces, such as sedimentary strata , that are bent or curved ( "folded" ) 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 ,

126-421: A fold axis is called a cylindrical fold . This term has been broadened to include near-cylindrical folds. Often, the fold axis is the same as the hinge line. Minor folds are quite frequently seen in outcrop; major folds seldom are except in the more arid countries. Minor folds can, however, often provide the key to the major folds they are related to. They reflect the same shape and style, the direction in which

168-444: A hinge need to accommodate large deformations in the hinge zone. This results in voids between the layers. These voids, and especially the fact that the water pressure is lower in the voids than outside of them, act as triggers for the deposition of minerals. Over millions of years, this process is capable of gathering large quantities of trace minerals from large expanses of rock and depositing them at very concentrated sites. This may be

210-424: A mean annual rainfall of 1,146 millimetres (45.1 in) with a mean annual run-off of 624 millimetres (24.6 in) and mean annual run-off as a percentage of annual rainfall of 54 millimetres (2.1 in). The ranges have rock outcroppings and heath . The range is also home to mallee ecosystems. The area is a Northeast Forest Lands. Amalgamated ores of titanium, tin, gold, nickel, rhodium and iron are found within

252-427: A mechanism that is responsible for the veins. To summarize, when searching for veins of valuable minerals, it might be wise to look for highly folded rock, and this is the reason why the mining industry is very interested in the theory of geological folding. Anticlinal traps are formed by folding of rock. For example, if a porous sandstone unit covered with low permeability shale is folded into an anticline, it may form

294-629: A planar detachment without further fault propagation, detachment folds may form, typically of box-fold style. These generally occur above a good detachment such as in the Jura Mountains , where the detachment occurs on middle Triassic evaporites . Shear zones that approximate to simple shear typically contain minor asymmetric folds, with the direction of overturning consistent with the overall shear sense. Some of these folds have highly curved hinge-lines and are referred to as sheath folds . Folds in shear zones can be inherited, formed due to

336-541: A strong axial planar cleavage . Folds in the rock are formed about the stress field in which the rocks are located and the rheology , or method of response to stress, of the rock at the time at which the stress is applied. The rheology of the layers being folded determines characteristic features of the folds that are measured in the field. Rocks that deform more easily form many short-wavelength, high-amplitude folds. Rocks that do not deform as easily form long-wavelength, low-amplitude folds. Layers of rock that fold into

378-435: A thrust fault cuts up section from one detachment level to another. Displacement over this higher-angle ramp generates the folding. Fault propagation folds or tip-line folds are caused when displacement occurs on an existing fault without further propagation. In both reverse and normal faults this leads to folding of the overlying sequence, often in the form of a monocline . When a thrust fault continues to displace above

420-843: A variety of rock types . Most geologically young mountain ranges on the Earth's land surface are associated with either the Pacific Ring of Fire or the Alpide belt . The Pacific Ring of Fire includes the Andes of South America, extends through the North American Cordillera , the Aleutian Range , on through Kamchatka Peninsula , Japan , Taiwan , the Philippines , Papua New Guinea , to New Zealand . The Andes

462-722: Is 7,000 kilometres (4,350 mi) long and is often considered the world's longest mountain system. The Alpide belt stretches 15,000 km across southern Eurasia , from Java in Maritime Southeast Asia to the Iberian Peninsula in Western Europe , including the ranges of the Himalayas , Karakoram , Hindu Kush , Alborz , Caucasus , and the Alps . The Himalayas contain the highest mountains in

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504-504: Is accommodated by slip between the pages of the book. The fold formed by the compression of competent rock beds is called "flexure fold". Typically, folding is thought to occur by simple buckling of a planar surface and its confining volume. The volume change is accommodated by layer parallel shortening the volume, which grows in thickness . Folding under this mechanism is typical of a similar fold style, as thinned limbs are shortened horizontally and thickened hinges do so vertically. If

546-417: Is also a feature of many igneous intrusions and glacier ice. Folding of rocks must balance the deformation of layers with the conservation of volume in a rock mass. This occurs by several mechanisms. Flexural slip allows folding by creating layer-parallel slip between the layers of the folded strata, which, altogether, result in deformation. A good analogy is bending a phone book, where volume preservation

588-538: Is at work while the mountains are being uplifted until the mountains are reduced to low hills and plains. The early Cenozoic uplift of the Rocky Mountains of Colorado provides an example. As the uplift was occurring some 10,000 feet (3,000 m) of mostly Mesozoic sedimentary strata were removed by erosion over the core of the mountain range and spread as sand and clays across the Great Plains to

630-531: Is drier, having been stripped of much of its moisture. Often, a rain shadow will affect the leeward side of a range. As a consequence, large mountain ranges, such as the Andes, compartmentalize continents into distinct climate regions . Mountain ranges are constantly subjected to erosional forces which work to tear them down. The basins adjacent to an eroding mountain range are then filled with sediments that are buried and turned into sedimentary rock . Erosion

672-425: Is relatively weak. When rock behaves as a fluid, as in the case of very weak rock such as rock salt, or any rock that is buried deeply enough, it typically shows flow folding (also called passive folding , because little resistance is offered): the strata appear shifted undistorted, assuming any shape impressed upon them by surrounding more rigid rocks. The strata simply serve as markers of the folding. Such folding

714-454: Is the midpoint of the limb. The axial surface is defined as a plane connecting all the hinge lines of stacked folded surfaces. If the axial surface is planar, it is called an axial plane and can be described in terms of strike and dip . Folds can have a fold axis . A fold axis "is the closest approximation to a straight line that when moved parallel to itself, generates the form of the fold". (Ramsay 1967). A fold that can be generated by

756-579: The Mithrim Montes and Doom Mons on Titan, and Tenzing Montes and Hillary Montes on Pluto. Some terrestrial planets other than Earth also exhibit rocky mountain ranges, such as Maxwell Montes on Venus taller than any on Earth and Tartarus Montes on Mars . Jupiter's moon Io has mountain ranges formed from tectonic processes including the Boösaule , Dorian, Hi'iaka and Euboea Montes . Fold (geology) In structural geology ,

798-473: The Ocean Ridge forms the longest continuous mountain system on Earth, with a length of 65,000 kilometres (40,400 mi). The position of mountain ranges influences climate, such as rain or snow. When air masses move up and over mountains, the air cools, producing orographic precipitation (rain or snow). As the air descends on the leeward side, it warms again (following the adiabatic lapse rate ) and

840-549: The watershed between these two rivers. Within the range is the Gibraltar Range National Park . Mines in the area have produced amalgamated ores of titanium , tin , gold , nickel , rhodium and iron . Recently, there have been forest fires or threats of forest fires in the Gibraltar Range. The Gibraltar Range is located in the northeastern part of New South Wales. The mountain range is

882-441: The accommodation of strains between neighboring faults. Fault-bend folds are caused by displacement along a non-planar fault. In non-vertical faults, the hanging-wall deforms to accommodate the mismatch across the fault as displacement progresses. Fault bend folds occur in both extensional and thrust faulting. In extension, listric faults form rollover anticlines in their hanging walls. In thrusting, ramp anticlines form whenever

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924-493: The axis of the fold. Those with limbs of relatively equal length are termed symmetrical , and those with highly unequal limbs are asymmetrical . Asymmetrical folds generally have an axis at an angle to the original unfolded surface they formed on. Vergence is calculated in a direction perpendicular to the fold axis. Folds that maintain uniform layer thickness are classed as concentric folds. Those that do not are called similar folds . Similar folds tend to display thinning of

966-412: The closures of the major folds lie, and their cleavage indicates the attitude of the axial planes of the major folds and their direction of overturning A fold can be shaped like a chevron , with planar limbs meeting at an angular axis, as cuspate with curved limbs, as circular with a curved axis, or as elliptical with unequal wavelength . Fold tightness is defined by the size of the angle between

1008-485: The east. This mass of rock was removed as the range was actively undergoing uplift. The removal of such a mass from the core of the range most likely caused further uplift as the region adjusted isostatically in response to the removed weight. Rivers are traditionally believed to be the principal cause of mountain range erosion, by cutting into bedrock and transporting sediment. Computer simulation has shown that as mountain belts change from tectonically active to inactive,

1050-409: The effects of a high-level igneous intrusion e.g. above a laccolith . The fold hinge is the line joining points of maximum curvature on a folded surface. This line may be either straight or curved. The term hinge line has also been used for this feature. A fold surface seen perpendicular to its shortening direction can be divided into hinge and limb portions; the limbs are the flanks of

1092-450: The fold's limbs (as measured tangential to the folded surface at the inflection line of each limb), called the interlimb angle. Gentle folds have an interlimb angle of between 180° and 120°, open folds range from 120° to 70°, close folds from 70° to 30°, and tight folds from 30° to 0°. Isoclines , or isoclinal folds , have an interlimb angle of between 10° and zero, with essentially parallel limbs. Not all folds are equal on both sides of

1134-409: The fold, and the limbs converge at the hinge zone. Within the hinge zone lies the hinge point, which is the point of minimum radius of curvature (maximum curvature) of the fold. The crest of the fold represents the highest point of the fold surface whereas the trough is the lowest point. The inflection point of a fold is the point on a limb at which the concavity reverses; on regular folds, this

1176-439: The folding deformation cannot be accommodated by a flexural slip or volume-change shortening (buckling), the rocks are generally removed from the path of the stress. This is achieved by pressure dissolution , a form of metamorphic process, in which rocks shorten by dissolving constituents in areas of high strain and redepositing them in areas of lower strain. Folds generated in this way include examples in migmatites and areas with

1218-471: 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

1260-548: The limbs and thickening of the hinge zone. Concentric folds are caused by warping from active buckling of the layers, whereas similar folds usually form by some form of shear flow where the layers are not mechanically active. Ramsay has proposed a classification scheme for folds that often is used to describe folds in profile based upon the curvature of the inner and outer lines of a fold and the behavior of dip isogons . that is, lines connecting points of equal dip on adjacent folded surfaces: (A homocline involves strata dipping in

1302-609: The mechanical layering and the contrast in properties between the layers. If the layering does begin to fold, the fold style is also dependent on these properties. Isolated thick competent layers in a less competent matrix control the folding and typically generate classic rounded buckle folds accommodated by deformation in the matrix. In the case of regular alternations of layers of contrasting properties, such as sandstone-shale sequences, kink-bands, box-folds and chevron folds are normally produced. Many folds are directly related to faults, associated with their propagation, displacement and

Gibraltar Range - Misplaced Pages Continue

1344-618: The mountains. In 1890s and 1900s, an area of the mountain range had been reserved for forestry. Construction of the first "sealed road" over the mountain range began in 1960. It allowed the first bicycle race from the town of Grafton on the East Coast to the town of Inverell on the Northern Tablelands. In 2002, forest fires were burning in the Gibraltar Ranges. In late 2007, two prison escapees were last spotted near

1386-540: The orientation of pre-shearing layering or formed due to instability within the shear flow. Recently deposited sediments are normally mechanically weak and prone to remobilization before they become lithified, leading to folding. To distinguish them from folds of tectonic origin, such structures are called synsedimentary (formed during sedimentation). Slump folding: When slumps form in poorly consolidated sediments, they commonly undergo folding, particularly at their leading edges, during their emplacement. The asymmetry of

1428-620: The range date to the Late Permian (Lopingian) Epoch, with granite in the range dating to the Permo- Triassic . In the range are volcanic intrusions. They can be seen in "intrusive and extrusive igneous rocks which clearly pre-date the Great Escarpment ." The Gibraltar Range receives much rain. There is a surface water measurement station found in the range at Dandahra Creek that was opened on 10 May 1972. The area has

1470-463: The range. Thickly forested highland areas cover part of the mountains, and there are isolated populations of Waratah . The rufous scrub-bird lives in the Gibraltar Range, although its population was slightly reduced due to a fire in 2002. The mountain range is also home to the Parma wallaby . During the 1850s, European fruit trees flourished at the base of the range. In the 1850s, there were mines in

1512-556: The ranges and the police were looking for them. In October 2009, parts of the Gibraltar Range were closed because of the potential for bushfires. Mountain range Mountain ranges are usually segmented by highlands or mountain passes and valleys . Individual mountains within the same mountain range do not necessarily have the same geologic structure or petrology . They may be a mix of different orogenic expressions and terranes , for example thrust sheets , uplifted blocks , fold mountains, and volcanic landforms resulting in

1554-627: The rate of erosion drops because there are fewer abrasive particles in the water and fewer landslides. Mountains on other planets and natural satellites of the Solar System, including the Moon , are often isolated and formed mainly by processes such as impacts, though there are examples of mountain ranges (or "Montes") somewhat similar to those on Earth. Saturn 's moon Titan and Pluto , in particular, exhibit large mountain ranges in chains composed mainly of ices rather than rock. Examples include

1596-400: The same direction, though not necessarily any folding.) Folds appear on all scales, in all rock types , at all levels in the crust . They arise from a variety of causes. When a sequence of layered rocks is shortened parallel to its layering, this deformation may be accommodated in a number of ways, homogeneous shortening, reverse faulting or folding. The response depends on the thickness of

1638-723: The site of the Gibraltar Range National Park, one of the Gondwana Rainforests of Australia . The mountains are found in the Clarence Valley Council area. The range is inland of Grafton . The Gwydir Highway runs through the range and its national park. The Gibraltar Range is defined by its high ridges and steep valleys that intersect plateaus . They were created in the middle of the Palaeozoic Era. Volcanoes found in

1680-420: The slump folds can be used to determine paleoslope directions in sequences of sedimentary rocks. Dewatering: Rapid dewatering of sandy sediments, possibly triggered by seismic activity, can cause convolute bedding. Compaction: Folds can be generated in a younger sequence by differential compaction over older structures such as fault blocks and reefs . The emplacement of igneous intrusions tends to deform

1722-430: The surrounding country rock . In the case of high-level intrusions, near the Earth's surface, this deformation is concentrated above the intrusion and often takes the form of folding, as with the upper surface of a laccolith . The compliance of rock layers is referred to as competence : a competent layer or bed of rock can withstand an applied load without collapsing and is relatively strong, while an incompetent layer

Gibraltar Range - Misplaced Pages Continue

1764-543: The world, including Mount Everest , which is 8,848 metres (29,029 ft) high. Mountain ranges outside these two systems include the Arctic Cordillera , Appalachians , Great Dividing Range , East Siberians , Altais , Scandinavians , Qinling , Western Ghats , Vindhyas , Byrrangas , and the Annamite Range . If the definition of a mountain range is stretched to include underwater mountains, then

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