50-538: The Highland Boundary Fault is a major fault zone that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic terrains: the Highlands and the Lowlands , and in most places it is recognisable as a change in topography. Where rivers cross the fault, they often pass through gorges, and
100-405: A fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between
150-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving
200-489: A fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas
250-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
300-427: A hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through the stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in
350-417: A major fault along only one of the boundaries, and these are known as half-graben. The polarity (throw direction) of the main bounding faults typically alternates along the length of the rift. The asymmetry of a half-graben strongly affects syntectonic deposition. Comparatively little sediment enters the half-graben across the main bounding fault because of footwall uplift on the drainage systems. The exception
400-484: A major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by
450-400: A manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along a decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of
500-421: A non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In
550-464: A reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of the fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on
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#1732766288602600-605: A string of negative anomalies in the north from positive ones in the south. On discovering this, Hall and Dagley concluded that the observed trend, which followed the length of the Dalradian trough, transition from positive to negative anomalies. This linear feature of magnetic anomalies has since been referred to as the Fair Head–Clew Bay line. At present, it is believed that the Highland Boundary Fault
650-422: Is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near the surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in
700-490: Is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults
750-423: Is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of the fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of
800-546: Is continuous for at least several kilometres on either side of the Highland Boundary Fault. The models generated from magnetic data suggest that the ophiolite is only slightly displaced vertically by the fault. The Old Red Sandstone is a magnafacies of red beds and lacustrine deposits from the Late Silurian to the Carboniferous . The NE segment of the Highland Boundary Fault is marked by an abrupt change in
850-544: Is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms a plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or
900-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of
950-492: Is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering , a fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing
1000-425: Is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However,
1050-762: The Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are the most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to
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#17327662886021100-549: The Southern Uplands Fault , forms the southern boundary for the Central Lowlands. The age of the Highland Boundary Fault has been inferred to be between Ordovician to middle Devonian and through several generations it has been interpreted as a graben -bounding normal fault, a major sinistral strike-slip fault , a northwest-dipping reverse fault or terrane boundary. The reason the precise nature of
1150-641: The Strathmore Basin . These garnets were linked to those in isolated Dalradian sediments in the northwest, providing evidence for post-Early Devonian (Acadian) movement to be only few tens of kilometers. In addition, the Lintrathen ignimbrite , which is present at the base of the Lower Devonian sequence was traced along the fault and it was found that the displacement was both short and lateral. The post-Acadian movements are highlighted in
1200-657: The seismic shaking and tsunami hazard to infrastructure and people in the vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
1250-488: The Highland Boundary Fault. From Loch Lomond the Highland Boundary Fault continues to Aberfoyle , then Callander , Comrie and Crieff . It then forms the northern boundary of Strathmore and reaches the North Sea immediately north of Stonehaven near the ruined Chapel of St. Mary and St. Nathalan . Aeromagnetic maps of Great Britain and Northern Ireland show that the Highland Boundary Fault can be traced from Ireland to
1300-708: The Precambrian and early Paleozoic. The oldest Dalradian rocks (the Grampian Group ) were deformed and metamorphosed around 750 Ma. The deposition of younger Dalradian sediments continued until 590 Ma, when the sediments underwent transformation to the greenschist facies during the Proterozoic and Ordovician. Modeling of gravity and magnetic data along the fault has confirmed the presence of an extensive ophiolite suite. The Dalradian metasedimentary rocks are overlain by an obducted ophiolite that
1350-587: The associated waterfalls can be a barrier to salmon migration. The fault is believed to have formed in conjunction with the Strathmore syncline to the south-east during the Acadian orogeny in a transpressive regime that caused the uplift of the Grampian block and a small sinistral movement on the Highland Boundary Fault. One of the earliest and most prominent references to the Highland Boundary Fault
1400-403: The brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when the strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of
1450-750: The dip of the Old Red Sandstone from around 20° to near-vertical and subsequently exposes the Old Red Sandstone basement. It is currently believed that there were two main displacement events along the Highland Boundary Fault: the Acadian, and the post-Acadian. Evidence for the Acadian displacement event is based on the geochemical study of detrital garnets in the Lower Old Red Sandstone on the Northern limb of
1500-436: The direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and the footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each
1550-411: 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 . In many rifts , the graben are asymmetric, with
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1600-456: The fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and the implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect
1650-402: The fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of the fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding
1700-440: The fault is still unknown is because there is little evidence of a continuous fault plane on the surface. More recently, seismic activities marking the fault line have been analysed to show that the 2003 Aberfoyle earthquake had a hypocentre at 4 km ( 2 + 1 ⁄ 2 mi) depth and was caused by an oblique sinistral strike-slip fault with normal movement . The fault plane was estimated to be dipping at 65° NW. To
1750-576: The fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with
1800-401: The fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into the geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in
1850-427: The fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining
1900-475: The gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of
1950-622: The north and west of the Highland Boundary Fault lie hard Precambrian and Cambrian metamorphic rocks: marine deposits metamorphosed to schists , phyllites and slates , namely the Dalradian Supergroup and the Highland Border Ophiolite suite. To the south and east are Old Red Sandstone conglomerates and sandstones: softer, sedimentary rocks of the Devonian and Carboniferous periods. Between these areas lie
2000-500: The original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to the footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other,
2050-648: The quite different rocks of the Highland Border Complex (at one time called the Highland Boundary Complex), a weakly metamorphosed sedimentary sequence of sandstones, lavas, limestones, mudstones and conglomerates. These make up a zone which is found discontinuously along the line of the fault and which is up to 1.2 kilometres ( 3 ⁄ 4 mi) in width. The Dalradian Supergroup consists of metasedimentary rocks which underwent polyphase deformation and metamorphism during
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2100-557: The region of Greenock . In these areas, the Highland Boundary Fault is seen to be dividing a northerly low area from a southerly high area. The fault is often considered a terrane boundary: the Midland Valley terrane lies to the south whilst the Southern Highlands or Grampian terrane lies to the north In 1970, Hall and Dagley identified the Highland Boundary Fault as coincident with a regional magnetic feature dividing
2150-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
2200-697: The rocks along the Highland Border suggests that rocks along both ends of the fault plane are indistinguishable from one another, with no brecciation . Aligned southwest to northeast from Lochranza on Arran, the Highland Boundary Fault bisects Bute and crosses the southeastern parts of the Cowal and Rosneath peninsulas, as it passes up the Firth of Clyde . It comes ashore near Helensburgh, then continues through Loch Lomond . The loch islands of Inchmurrin , Creinch , Torrinch , and Inchcailloch all lie on
2250-416: The size of the weathered zone and hence creates more space for groundwater . Fault zones act as aquifers and also assist groundwater transport. Graben In geology , a graben ( / ˈ ɡ r ɑː b ən / ) is a depressed block of the crust of a planet or moon, bordered by parallel normal faults . Graben is a loan word from German , meaning 'ditch' or 'trench'. The first known usage of
2300-540: The stratigraphy of the region. The Lower Old Red Sandstone is unconformably overlain by Upper Old Red Sandstone, where the Upper Old Red Sandstone is tilted close to the Highland Boundary Fault. The boundary is used as a natural barrier to prevent northwards movement of grey squirrels, thus protecting the only red squirrel population in the Highlands. Fault (geology) In geology , a fault
2350-468: The term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along
2400-420: The word in the geologic context was by Eduard Suess in 1883. The plural form is either graben or grabens . 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
2450-736: Was active during two main orogenic events associated with the Caledonian orogeny : the Grampian orogeny in the Early Ordovician and the Acadian orogeny in the Middle Devonian . The fault allowed the Midland Valley to descend as a major rift by up to 4,000 m (13,000 ft) and there was subsequent vertical movement. This earlier vertical movement was later replaced by a horizontal shear. A complementary fault,
2500-548: Was by George Barrow in 1912 ʻOn the Geology of Lower Dee-side and the Southern Highland Borderʼ, which highlights the nature of the rocks accompanying the Highland Border and describes the mineral zones associated with metamorphism. In the same publication, Barrow also outlines the ʻHighland Faultʼ and the areas where he believes there are planes of overthrust. Barrowʼs description of the structural nature of
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