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40-555: The Moho lies almost entirely within the lithosphere (the hard outer layer of the Earth, including the crust). Only beneath mid-ocean ridges does it define the lithosphere– asthenosphere boundary (the depth at which the mantle becomes significantly ductile). The Mohorovičić discontinuity is 5 to 10 kilometres (3–6 mi) below the ocean floor , and 20 to 90 kilometres (10–60 mi) beneath typical continental crusts, with an average of 35 kilometres (22 mi). Named after

80-475: A 5-metre (16 ft) section of the drill string twisted off and was left in the hole. Drilling was restarted in September 1986, 7,000 metres (23,000 ft) from the first hole. The third hole reached 12,262 metres (40,230 ft) in 1989. In that year, the hole depth was expected to reach 13,500 metres (44,300 ft) by the end of 1990 and 15,000 metres (49,000 ft) by 1993. In June 1990,

120-539: A breakdown occurred in the third hole at 12,262 metres (40,230 ft) of depth. The drilling of the fourth hole was started in January ;1991 from 9,653 metres (31,670 ft) of depth of third hole. The drilling of the fourth hole was stopped in April ;1992 at 11,882 metres (38,983 ft) of depth. Drilling of the fifth hole started in April 1994 from 8,278 metres (27,159 ft) of depth of

160-557: A central shaft and two off of one of those branches. In addition to being the deepest human-made hole on Earth, Kola Superdeep Borehole SG-3 was, for almost three decades, the world's longest borehole in measured depth along its bore, until surpassed in 2008 by a hydrocarbon extraction borehole in Qatar . Drilling at Kola SG-3 began on 24 May 1970 using the Uralmash -4E, a serial drilling rig used for drilling oil wells . The rig

200-540: A distinct change in material as the waves pass through the Earth, and is commonly accepted as the lower limit of the Earth's crust. The Moho is characterized by a transition zone of up to 500 meters. Ancient Moho zones are exposed above-ground in numerous ophiolites around the world. Beginning in the 1980s, geologists became aware that the Moho does not always coincide with the crust-mantle boundary defined by composition. Xenoliths (lower crust and upper mantle rock brought to

240-404: A lack of funding. The scientific team was transferred to the federal state unitary subsidiary enterprise "Kola Superdeep," downsized, and given the new task of thoroughly studying the exposed section. In 2007, the scientific team was dissolved and the equipment was transferred to a private company and partially liquidated. In 2008, the company was liquidated due to unprofitability, and the site

280-443: A large role in the fields of geology and earth science for well over a century. By observing the Moho's refractive nature and how it affects the speed of P-waves, scientists were able to theorize about the earth's composition. These early studies gave rise to modern seismology . In the early 1960s, Project Mohole was an attempt to drill to the Moho from deep-ocean regions. After initial success in establishing deep-ocean drilling,

320-508: A later date. Lithosphere A lithosphere (from Ancient Greek λίθος ( líthos )  'rocky' and σφαίρα ( sphaíra )  'sphere') is the rigid, outermost rocky shell of a terrestrial planet or natural satellite . On Earth , it is composed of the crust and the lithospheric mantle , the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on

360-753: A subduction zone cannot subduct much further than about 100 km (62 mi) before resurfacing. As a result, continental lithosphere is not recycled at subduction zones the way oceanic lithosphere is recycled. Instead, continental lithosphere is a nearly permanent feature of the Earth. Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite , lamproite , and other volcanic pipes . The histories of these xenoliths have been investigated by many methods, including analyses of abundances of isotopes of osmium and rhenium . Such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite

400-466: A third of the way through the Baltic Shield of the continental crust , estimated to be around 35 kilometres (22 mi) deep, reaching Archean rocks at the bottom. Numerous unexpected geophysical discoveries were made: In 1992, an international geophysical experiment obtained a reflection seismic crustal cross-section through the well. The Kola-92 working group consisted of researchers from

440-473: Is associated with oceanic crust (having a mean density of about 2.9 grams per cubic centimetre or 0.10 pounds per cubic inch) and exists in the ocean basins . Continental lithosphere is associated with continental crust (having a mean density of about 2.7 grams per cubic centimetre or 0.098 pounds per cubic inch) and underlies the continents and continental shelves. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle ( peridotite ) and

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480-518: Is defined by a difference in response to stress. The lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation . The thickness of the lithosphere is thus considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior. The temperature at which olivine becomes ductile (~1,000 °C or 1,830 °F)

520-411: Is denser than continental lithosphere. Young oceanic lithosphere, found at mid-ocean ridges , is no thicker than the crust, but oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. The oldest oceanic lithosphere is typically about 140 kilometres (87 mi) thick. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes

560-489: Is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. The lithosphere is subdivided horizontally into tectonic plates , which often include terranes accreted from other plates. The concept of the lithosphere as Earth's strong outer layer was described by the English mathematician A. E. H. Love in his 1911 monograph "Some problems of Geodynamics" and further developed by

600-734: Is the result of a scientific drilling effort to penetrate as deeply as possible into the Earth's crust conducted by the Soviet Union in the Pechengsky District of the Kola Peninsula , near the Russian border with Norway. SG (СГ) is a Russian designation for a set of superdeep ( Russian : сверхглубокая ) boreholes conceived as part of a Soviet scientific research programme of the 1960s, 1970s and 1980s. Aralsor SG-1 (in

640-439: Is the thickness of the oceanic mantle lithosphere, κ {\displaystyle \kappa } is the thermal diffusivity (approximately 1.0 × 10  m /s or 6.5 × 10  sq ft/min) for silicate rocks, and t {\displaystyle t} is the age of the given part of the lithosphere. The age is often equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge , and V

680-426: Is velocity of the lithospheric plate. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years but after this becomes increasingly denser than asthenosphere. While chemically differentiated oceanic crust is lighter than asthenosphere, thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has

720-592: The drill-ship JOIDES Resolution to sail from Colombo in Sri Lanka in late 2015 and to head for the Atlantis Bank , a promising location in the southwestern Indian Ocean on the Southwest Indian Ridge , to attempt to drill an initial bore hole to a depth of approximately 1.5 kilometres. The attempt did not even reach 1.3 km, but researchers hope to further their investigations at

760-494: The American geologist Joseph Barrell , who wrote a series of papers about the concept and introduced the term "lithosphere". The concept was based on the presence of significant gravity anomalies over continental crust, from which he inferred that there must exist a strong, solid upper layer (which he called the lithosphere) above a weaker layer which could flow (which he called the asthenosphere ). These ideas were expanded by

800-456: The Canadian geologist Reginald Aldworth Daly in 1940 with his seminal work "Strength and Structure of the Earth." They have been broadly accepted by geologists and geophysicists. These concepts of a strong lithosphere resting on a weak asthenosphere are essential to the theory of plate tectonics . The lithosphere can be divided into oceanic and continental lithosphere. Oceanic lithosphere

840-691: The Pre-Caspian Basin of west Kazakhstan ) and Biyikzhal SG-2 (in Krasnodar Krai ), both less than 6,810 metres (22,340 ft) deep, preceded Kola SG-3, which was originally intended to reach 7,000 metres (23,000 ft) deep. Drilling at Kola SG-3 began in 1970 using the Uralmash -4E , and later the Uralmash-15000 series drilling rig. A total of five 23-centimetre-diameter (9 in) boreholes were drilled, two branching from

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880-454: The basis of chemistry and mineralogy . Earth's lithosphere, which constitutes the hard and rigid outer vertical layer of the Earth, includes the crust and the lithospheric mantle (or mantle lithosphere), the uppermost part of the mantle that is not convecting. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle that is able to convect. The lithosphere–asthenosphere boundary

920-408: The continental lithosphere are billions of years old. Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2,900 kilometres (1,800 mi) to near the core-mantle boundary, while others "float" in the upper mantle. Yet others stick down into the mantle as far as 400 kilometres (250 mi) but remain "attached" to

960-403: The continental plate above, similar to the extent of the old concept of "tectosphere" revisited by Jordan in 1988. Subducting lithosphere remains rigid (as demonstrated by deep earthquakes along Wadati–Benioff zone ) to a depth of about 600 kilometres (370 mi). Continental lithosphere has a range in thickness from about 40 kilometres (25 mi) to perhaps 280 kilometres (170 mi);

1000-457: The density of the material carrying them. As a result of this information, he theorized that the second set of waves could only be caused by a sharp transition in density in the Earth's crust, which could account for such a dramatic change in wave velocity. Using velocity data from the earthquake, he was able to calculate the depth of the Moho to be approximately 54 km, which was supported by subsequent seismological studies. The Moho has played

1040-489: The depth to the Moho, since serpentinization lowers seismic wave velocities. Croatian seismologist Andrija Mohorovičić is credited with discovering and defining the Moho. In 1909, he was examining data from a local earthquake in Zagreb when he observed two distinct sets of P-waves and S-waves propagating out from the focus of the earthquake. Mohorovičić knew that waves caused by earthquakes travel at velocities proportional to

1080-437: The effect that at subduction zones, oceanic lithosphere invariably sinks underneath the overriding lithosphere, which can be oceanic or continental. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of

1120-560: The mantle flow that accompanies plate tectonics. The upper part of the lithosphere is a large habitat for microorganisms , with some found more than 4.8 km (3 mi) below Earth's surface. Kola Superdeep Borehole The Kola Superdeep Borehole SG-3 ( Russian : Кольская сверхглубокая скважина СГ-3 , romanized :  Kol'skaya sverkhglubokaya skvazhina SG-3 ) is the deepest human-made hole on Earth (since 1979), which attained maximum true vertical depth of 12,262 metres (40,230 ft; 7.619 mi) in 1989. It

1160-489: The oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convection in the mantle. The thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. h ∼ 2 κ t {\displaystyle h\,\sim \,2\,{\sqrt {\kappa t}}} Here, h {\displaystyle h}

1200-442: The other refracted by a high-velocity medium. The Moho marks the transition in composition between the Earth's crust and the lithospheric mantle. Immediately above the Moho, the velocities of primary seismic waves (P-waves) are consistent with those through basalt (6.7–7.2 km/s), and below they are similar to those through peridotite or dunite (7.6–8.6 km/s). This increase of approximately 1 km/s corresponds to

1240-411: The pioneering Croatian seismologist Andrija Mohorovičić , the Moho separates both the oceanic crust and continental crust from the underlying mantle. The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P-waves and S-waves , one set that followed a direct path near the Earth's surface and

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1280-479: The project suffered from political and scientific opposition, mismanagement, and cost overruns , and it was cancelled in 1966. Reaching the discontinuity by drilling remains an important scientific objective. Soviet scientists at the Kola Superdeep Borehole pursued the goal from 1970 until 1992. They reached a depth of 12,260 metres (40,220 ft), the world's deepest hole, before abandoning

1320-530: The project. One proposal considers a rock-melting radionuclide-powered capsule with a heavy tungsten needle that can propel itself down to the Moho discontinuity and explore Earth's interior near it and in the upper mantle. The Japanese project Chikyu Hakken ("Earth Discovery") also aims to explore in this general area with the drilling ship, Chikyū , built for the Integrated Ocean Drilling Program (IODP). Plans called for

1360-460: The surface by volcanic eruptions) and seismic-reflection data showed that, away from continental cratons , the transition between crust and mantle is marked by basaltic intrusions and may be up to 20 km thick. The Moho may lie well below the crust-mantle boundary and care must be used in interpreting the structure of the crust from seismic data alone. Serpentinization of mantle rock below slowly spreading mid-ocean ridges can also increase

1400-758: The third hole. Drilling was stopped in August ;1994 at 8,578 metres (28,143 ft) of depth due to lack of funds and the well itself was mothballed . The stated areas of study of the Kola Superdeep Borehole were the deep structure of the Baltic Shield , seismic discontinuities and the thermal regime in the Earth's crust, the physical and chemical composition of the deep crust and the transition from upper to lower crust, lithospheric geophysics, and to create and develop technologies for deep geophysical study. Drilling penetrated about

1440-676: The universities of Glasgow and Edinburgh in the United Kingdom, the University of Wyoming in the United States, and the University of Bergen in Norway, as well as several Russian earth science research institutions. The experiment was documented in a video recorded by Professor David Smythe, which shows the drilling deck in action during an attempt to recover a tool dropped down the hole. The drilling ended in 1995 due to

1480-605: The upper approximately 30 to 50 kilometres (19 to 31 mi) of typical continental lithosphere is crust. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity . The oldest parts of continental lithosphere underlie cratons , and the mantle lithosphere there is thicker and less dense than typical; the relatively low density of such mantle "roots of cratons" helps to stabilize these regions. Because of its relatively low density, continental lithosphere that arrives at

1520-489: Was abandoned. It is still visited by sightseers, who report that the structure over the borehole has been partially destroyed or removed. The 12,262-metre (40,230 ft) deep Kola Superdeep Borehole has been the world's deepest borehole since 1979. It was also the longest borehole in the world from 1979 to 2008. Its record length was surpassed in May ;2008 by the curved extended reach drilling bore of well BD-04A in

1560-650: Was slightly modified to be able to reach a 7,000-metre (23,000 ft) depth. In 1974, the new purpose-built Uralmash-15000 drilling rig was installed onsite, named after the new target depth, set at 15,000 metres (49,000 ft). On 6 June 1979, the world depth record then held by the Bertha Rogers hole in Washita County, Oklahoma , United States, at 9,583 metres (31,440 ft), was broken by Kola SG-3. In October 1982, Kola SG-3's first hole reached 11,662 metres (38,261 ft). The second hole

1600-428: Was started in January 1983 from a 9,300-metre (30,500 ft) depth of the first hole. In 1983, the drill passed 12,000 metres (39,000 ft) in the second hole, and drilling was stopped for about a year for numerous scientific and celebratory visits to the site. This idle period may have contributed to a breakdown after drilling resumed; on 27 September 1984, after drilling to 12,066 metres (39,587 ft),

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