Lithosphere

11 Key excerpts on "Lithosphere"

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  Environmental Chemistry

  A Comprehensive Approach

  • Muhammad A. Hanif, Farwa Nadeem, Ijaz Ahmad Bhatti, Hafiz Muhammad Tauqeer(Authors)
  • 2020(Publication Date)
  • Wiley-Scrivener

    (Publisher)

  6 Lithosphere/Geosphere

  6.1 Introduction to Lithosphere/Geosphere

  The Lithosphere or geosphere is a shell of rocky planet, most rigid outer layer and solid part of the earth which constitutes crust and brittle mantle. It is found in between the atmosphere and asthenosphere from upper and lower ends, respectively. Numerous lithospheric rocks are considered elastic although they are non-viscous. However, the asthenosphere is viscous while the “Lithosphere-asthenosphere-boundary” is a point through which ductility difference is marked between two layers of upper mantle. Ductility is the ability of a solid material to stretch and deform under the highly stressful conditions. The asthenosphere is relatively more ductile than the Lithosphere. Ductility and elasticity of the Lithosphere mainly depends on the amount of stress, temperature and radius of curvature of the earth. Lithosphere is the coolest layer of the earth that contributes significantly in the conduction of heat in association with convectional processes occuring in the plastic mantle just below the Lithosphere. The two major types of Lithosphere are continental Lithosphere and oceanic Lithosphere. The continental Lithosphere is generally found in association with continental crust, whereas oceanic Lithosphere is associated with oceanic crust. Continental Lithosphere is slightly less dense than oceanic Lithosphere. However, the continental crust is much thicker than its oceanic cousin that stretches approximately 200 km or 124 miles below the surface of the earth.

  In addition to the rigid outer part of upper mantle and cooled denser underlying layer, the Lithosphere is also referred to as “skin of the rock”. This layer extends from the earth’s surface to the depth ranging from 70 km to 100 km. The Lithosphere is expected to float on the top of the non-rigid, partially melted and relatively warmer layer known as asthenosphere. The outermost layer of the earth is “crust” whose thickness varies depending upon the geographical locations. The thickness of the earth’s crust under the ocean and beneath the continents usually ranges from 5 km to 10 km and 35 km to 60 km, respectively. The “upper part of mantle” is a layer of rocky material found just beneath the earth’s crust that constitutes relatively cooler, rigid, solid and denser material having depth ranging from 50 km to 100 km below the surface of the earth. Hence, the combination of crust and upper mantle that is formed by rigid cooler rocky material is known as the Lithosphere. Below the Lithosphere, temperature is expected to be 1,000°C or 1,832°F, which is warm enough to allow the flow of rock material if pressurized sufficiently. The Lithosphere including the earth’s crust and the solid part of the upper mantle is carried “piggyback” on top of the less rigid and relatively weaker layer of asthenosphere that appears to be in continental motion. This type of movement generates stress in layers of rigid rock, resulting in the jostling of lithospheric plates or slabs just like the floating of ice cubes. Movement of lithospheric plates is known as “plate tectonics”, which is responsible for the continental drifts, volcanic activities and earthquakes.

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  Environmental Change

  The Evolving Ecosphere

  • Richard Huggett(Author)
  • 2003(Publication Date)
  • Routledge

    (Publisher)

  3Lithosphere AND BARYSPHERE

  SHAKY FOUNDATIONS: THE GEOLOGICAL ENVIRONMENT

  The layered Earth

  During the nineteenth century, the nature of the Earth’s interior was a matter of fierce and fascinating debate. All theories were hampered by a lack of evidence— the nature of rocks deep below the surface was unknown. In 1906, Richard D.Oldham observed that compressional seismic waves (P waves) slow abruptly deep within the Earth and can penetrate no further. This was strong evidence in favour of a liquid core. Three years later, Andrija Mohorovi i noticed that the velocity of seismic waves leaps from about 7.2 to 8.0 km/s at around 60 km deep. He had discovered the ‘Moho’ seismic discontinuity that marks the crust-mantle boundary. In 1926, Beno Gutenberg obtained evidence for a seismic discontinuity at the core-mantle boundary. This, the Gutenberg discontinuity, was confirmed during the 1950s when world-wide records of blasts from underground nuclear detonations were scrutinized. Subsequent studies of the Earth’s seismic properties, using seismic waves propagated by earthquakes and by controlled explosions to ‘X-ray’ the planet (a technique called seismic tomography), have revealed a series of somewhat distinct layers or concentric shells in the solid Earth (Figure 3.1 ). Each shell has different chemical and physical properties.

  The crust lies above the Moho. Its thickness ranges from 3 km in parts of ocean ridges to 80 km in collisional orogenic mountain belts. Continental crust is, on average, 39 km thick. The Lithosphere is the outer shell of the solid Earth where the rocks are reasonably similar to those exposed at the surface. It includes the crust and the solid part of the upper mantle. It is the coldest part of the solid Earth. Cold rocks deform slowly, so the Lithosphere is relatively rigid, it can support large loads, and it deforms by brittle fracture. On average, the Lithosphere is about 100 km thick. Below continents it is up to 200 km thick, and beneath the oceans it is some 50 km thick. Continental Lithosphere is sometimes called the tectosphere. The differences in lithospheric thickness arise from temperature, and therefore viscosity, differences. The Lithosphere under mid-ocean ridges is warm and thin; that under subduction zones is cold and thick; that under continents is cold, buoyant, and strong.

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  Introduction to Physical Geology

  • Charles Fletcher, Dan Gibson, Kevin Ansdell(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  Above the mantle is the solid outer layer of rock that we live on, Earth’s crust. Relative to the planet’s radius, the crust is thinner than an eggshell. The crust is the outer portion of the Lithosphere, which consists of the rigid upper mantle (lower Lithosphere) and the crust (upper Lithosphere). Below the Lithosphere lies the asthenosphere, a weak and ductile layer in the upper mantle at depths between 150 km and 300 km but perhaps extending as deep as 700 km. 2[\JHQ  2  Whole Earth Earth’s Crust 2[\JHQ  2  ,URQ  )H  0DJQHVLXP  0J  6LOLFRQ  6L  6LOLFRQ  6L  $OXPLQXP  $O  ,URQ  )H  0DJQHVLXP  0J  &DOFLXP  &D  3RWDVVLXP  .  6RGLXP  1D  2WKHU   1LFNHO  1L  6XOSKXU  6  &DOFLXP  &D  $OXPLQXP  $O  2WKHU   List the five most abundant elements in the crust and Earth as a whole. Which elements appear in both lists? Expand Your Thinking—If the crust is composed of lighter compounds than the mantle, is it appropriate to refer to it as “floating” on the mantle? In general, in which direction does heat move in Earth’s interior?        'LVWDQFH NP &RQWLQHQWDO FUXVW /LWKRVSKHUH 8SSHU PDQWOH $VWKHQRVSKHUH  NP ,QQHU FRUH VROLG $VWKHQRVSKHUH  2XWHU FRUH OLTXLG 0DQWOH URFN FDSDEOH RI IORZ  NP  NP 2FHDQLF FUXVW 0DQWOH WUDQVLWLRQ ]RQH /RZHU PDQWOH ]RQH FIGURE 3.3 Evidence indicates that Earth’s interior consists of the inner core, the outer core, the mantle, and the crust. The Lithosphere consists of the crust (upper Lithosphere) and the rigid upper mantle (lower Lithosphere). The asthenosphere, also in the upper mantle, lies below the Lithosphere. 50 • CHAPTER 3 Plate Tectonics Courtesy of NASA Mashall Space Flight Center (NASA-MSFC) 3-2 The Core, Mantle, and Crust Have Distinct Chemical and Physical Features LO 3-2 List Earth’s internal layers and describe each. the field’s intensity has weakened by about 10 percent.

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  Physical Geography

  • James Petersen, Dorothy Sack, Robert Gabler(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  E A R T H ’ S P L A N E T A R Y S T R U C T U R E 357 stress (force per unit area) with little deforma- tion until a threshold limit of stress is reached. At the threshold value, elastic solids fail by fractur- ing. Behaviorally, then, this uppermost mantle and overlying crust form a single structural unit called the Lithosphere. The term Lithosphere has traditionally been used to describe the entire solid part of the Earth system (as discussed in Chapter 1 and earlier in this chapter). In recent decades, however, that term has also been used in a separate, structural sense to refer to the brittle outer shell of Earth, including the crust and the rigid, uppermost mantle layer (● Fig. 13.6). Beneath the Lithosphere lies the asthenosphere (from Greek: asthenias, without strength), a 180-kilometer (110-mi) thick layer of the upper mantle that responds to stress by deforming and flowing slowly rather than by fracturing. In other words, the asthenosphere has the characteristics of a plastic solid. Rock in the asthenosphere can flow vertically or horizontally at rates of a few centimeters per year. As material in the asthenosphere flows, it drags segments of the overlying, rigid Lithosphere along with it. This movement within the plastic asthenosphere drives tectonic forces, large-scale forces from inside Earth that break and deform the Lithosphere, sometimes resulting in earthquakes and often responsible for mountain building. Movement in the asthenosphere, in turn, is produced by thermal convection currents originating deeper in the mantle below the asthenosphere. These currents are driven by heat from decaying radioactive materials in the planet’s interior. The density of rock matter in Earth’s crust is significantly lower than that in the core and mantle, and ranges from 2.7 to 3.0 grams per cubic centimeter (0.10 to 0.11 lb/in. 3 ). The crust is also extremely thin in comparison to the diameter of the planet.

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  Physical Geography

  Great Systems and Global Environments

  • William M. Marsh, Martin M. Kaufman(Authors)
  • 2012(Publication Date)
  • Cambridge University Press

    (Publisher)

  Notice the difference in the position of the magnetic and geographic north poles. Earth’s Internal System: Heat, Convection, Rocks, and the Planet’s Skin 422 The Uppermost Mantle: At the top of the upper mantle are two relatively thin layers, together averaging about 200 kilometers thick, which are very impor- tant to the character and behavior of the crust. The upper layer, called the litho- sphere, averages about 80 kilometers thick. It includes the crust, which forms its uppermost part. The Lithosphere is composed of solid rock that is quite rigid and, from a global perspective, it has the character of a hard rind covering the planet with the crust as its skin (replete with scars, wrinkles, and pimples). Rock density in the Lithosphere increases with depth and, like the crust, the litho- sphere is thicker under the continents and thinner under the ocean basins, as shown in Figure 17.17. The Lithosphere rests on the second layer, called the asthenosphere (also shown in Figure 17.17), a layer of softer rock about 120 kilometers thick. On seis- mographs, the asthenosphere (from the Greek word asthenes, meaning weak) appears as a shadow or low-velocity zone suggesting that the rock here is at least partially melted. Laboratory experiments simulating seismic waves in such a shadow zone reveal that the asthenosphere con- tains small amounts of liquid rock, perhaps pockets of mushy rock in a matrix of hot, solid rock. The asthenosphere is widely recognized as a critical part of Earth’s rock-moving system because it is capable of gradual flowing motion. The driving force behind the motion is heat arising from the underlying mantle and, as the asthenosphere moves, it sets the Lithosphere above it into motion. The resultant movement is the root cause of crustal deformation as the Lithosphere, partitioned into great sections or plates, shifts about on the Earth’s surface.

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  Mid-Ocean Ridges

  • Roger Searle(Author)
  • 2013(Publication Date)
  • Cambridge University Press

    (Publisher)

  3 The oceanic Lithosphere 3.1 Crust, mantle, Lithosphere and asthenosphere Traditionally, Earth scientists have divided the outer parts of the Earth into the crust and mantle. Broadly speaking these reflect a major change in chemical composition. Mantle rocks comprise a high proportion of minerals containing the elements iron and manganese, and have relatively high density ( 3300 kg m −3 ) and seismic P-wave velocity ( 8 km s −1 ); on the other hand crustal rocks, which are ultimately derived from melting (and associ- ated fractionation) of the mantle, have lower proportions of iron and manganese, higher proportions of aluminium and silicon, and consequently lower densities and velocities. The oceanic crust is generally thinner ( 8 km) and slightly denser (2800 kg m −3 ) than continental crust. An alternative way of subdividing the Earth is based not on its composition but its mechanical properties. In this classification the outermost, relatively cool, layer is one where rocks behave in a strong, brittle or elastic manner, and is termed the Lithosphere from the Greek lithos, ‘rocky’ (Dietz, 1961). Underlying this is a warmer, weak layer which, on geological timescales (1Ma), behaves as a plastic medium, and is termed the asthenosphere (from the Greek asthen¯ es, ‘weak’). The viscosity of the asthenosphere is of the order of 10 20 Pa s (Lowrie, 1997). The crust–mantle boundary, being essentially compositional, does not coincide with the Lithosphere–asthenosphere boundary, which is mechanical and usually deeper, except perhaps very near the ridge axis. The crust–mantle boundary is often referred to as the Mohoroviˇ ci´ c discontinuity or simply ‘Moho’. This is defined seismically as the depth at which the P-wave velocity first exceeds about 8 km s −1 , although a separate, ‘petrological Moho’ based on the inferred origin of the rocks is often also used (see Section 5.3.4).

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  Essentials of Oceanography

  • Tom Garrison, Robert Ellis(Authors)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  The mantle , the layer beneath the crust, is thought to consist mainly of oxy-gen, iron, magnesium, and silicon. Most of Earth is mantle—it accounts for 68% of Earth’s mass and 83% of its volume. The outer and inner cores , which consist mainly of iron and nickel, lie beneath the mantle at Earth’s center. Chemical makeup is not the only important distinction between layers. Different conditions of temperature and pres-sure occur at different depths, and these conditions influence the physical properties of the materials. The behavior of a rock is determined by three factors: temperature, pressure, and the rate at which a deforming force (stress) is applied. Geologists have therefore devised another classification of Earth’s inte-rior based on physical rather than chemical properties. These are shown in Figure 2.3 . The Lithosphere ( lithos, “rock”)—Earth’s cool, rigid outer layer—is 70 to 200 kilometers (44–125 miles) in thickness. 6,370 km = 3,980 mi 2,900 km = 1,800 mi O u t e r c o r e Crust Inner core Mantle Figure 2.1 A cross section through Earth showing the internal layers. This representation is not to scale. © Cengage Learning Figure 2.2 Possible paths of seismic waves through Earth. Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 PLATE TECTONICS 19 Ocean water (1 g/cm 3 ) Oceanic crust (rigid) (2.9 g/cm 3 ) Lithosphere (rigid) Asthenosphere (deformable, capable of flow) 360–650 4–90 km mi Depth Upper mantle (3.3 g/cm 3 ) Lower mantle (4.5 g/cm 3 ) Continental crust (rigid) (2.7 g/cm 3 ) 220–400 3–25 70–200 CONTINENTAL OCEANIC 44–125 Figure 2.3 A cross section through Earth showing the internal layers near the surface. Note in this expanded section the relationship between Lithosphere and asthenosphere, and between crust and mantle.

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  Earth Systems and Environment

  • Amrita Pandey(Author)
  • 2019(Publication Date)
  • Delve Publishing

    (Publisher)

  Crust which is the top layer of the surface of the earth is known to be nearly 1% of the entire volume of the earth. The layers which are present beneath the crust are the tectonic plates of the earth. The crust of the surface of the earth mostly comprises of igneous, metamorphic and sedimentary rocks. The core or internal layers of the earth mostly have a steady increase in temperature and the temperature of the inner layers of the earth may have reached up to nearly 81ºC. 2.2.2. Mantle Mantle is known to be the second layer of the geosphere. The thickness of the mantle is known to be nearly 2,900 km thick and the mantle constitutes nearly 84% of the volume of the earth. Mantle comprises of silicate rocks which are rich in magnesium and iron. The mantle is known to be 2,900 km deep and it is known to get hotter in the deeper layers of the earth. The temperatures of the mantle are extremely high and the temperature of the mantle ranges between 871ºC to 4,000ºC.The crust and upper mantle of the atmosphere are either called as asthenosphere or Lithosphere. 2.2.3. Outer Core The third layer of the geosphere is known to be the outer core and the thickness of the outer core is known to be nearly 2,200 km thickness and the outer core is known to constitute nearly 15% of the volume of the earth. Iron and nickel are the metals that are present in the outer core of the earth and the temperature of the earth in the outer core may reach up to 5,000ºC. 2.2.4. Inner Core The inner most layers or the fourth layer of the surface of the geosphere is called as the inner core. The thickness of the inner core of the earth is known to be nearly 1,220 km thick and the inner core along with the outer core is known to be nearly 15% of the volume of the earth. Geosphere As a Component of Earth System 29 Iron is present in large quantities in the inner core and the temperatures of the inner core are known to be extremely high and these temperatures may be as high as 6,000ºC.

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  Plate Tectonics

  • Kent C. Condie, Kent C. Condie(Authors)
  • 1997(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  For the oceanic Lithosphere, where thickness is controlled by cooling, it can be defined as the outer shell of the Earth with a conductive temperature gradi-ent overlying the convecting adiabatic interior (White, 1988). This is known as the thermal Lithosphere. Thus, asthenosphere can be converted to oceanic Lithosphere simply by cooling. The progressive thickening of the oceanic Lithosphere continues until about 70 My, and afterwards it remains relatively constant in thickness until subduction (Figure 4.7). Convective erosion at the base of the oceanic Lithosphere may be responsible for main-taining this constant depth. The thickness of the rigid part of the outer layer of the Earth that readily bends under a load, known as the elastic Lithosphere, is less than that of the thermal Lithosphere. The base of the oceanic elastic Lithosphere varies with composition and temperature, increasing from about 2 km at ocean ridges to 50 km just before subduction. It corresponds roughly to the 500-600 °C isotherm. In continental Lithosphere. 120 Plate Tectonics and Crustal Evolution Figure 4.12 S-wave velocity distribution in the upper mantle along a great circle passing through Hawaii and Iceland. Darker shades indicate faster velocities. Map shows location of great circle and major hotspots (black dots). From Zhang and Tanimoto (1993). Depth (km) shown on vertical axis. s%»'>-fesj the elastic thickness is less than crustal thickness, by 10-15 km. often Thickness of continental Lithosphere The thermal continental Lithosphere varies considerably in thickness depending on its age and mechanism of formation. Shear-wave tomographic studies of the upper mantle have been most definitive in estimating thickness of continental Lithosphere (Grand, 1987; Polet and Ander-son, 1995). Most post-Archean Lithosphere is 100-200 km thick, while Lithosphere beneath Archean shields is commonly > 300 km thick. Rheological models suggest thicknesses in these same ranges (Ranalli, 1991).

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  A Continent Revealed

  The European Geotraverse, Structure and Dynamic Evolution

  • D. J. Blundell, R. Freeman, Stephan Mueller(Authors)
  • 1992(Publication Date)
  • Cambridge University Press

    (Publisher)

  Initially the mechanical behaviour of the upper part of the Lithosphere was described in terms of a uniform elastic plate with a thickness defined by an isotherm of 300-600°C based on studies of the flexure and intraplate seismicity in oceans. Hence the elastic part of the Lithosphere was found to correspond roughly to the upper half of the total thermally defined Lithosphere, displaying an increase in the effective elastic thickness (EET) with thermal age. For continental Lithosphere, which has undergone repeated deformation with often complicated loading scenarios, flexural studies are not as straightforward as the studies that have been carried out for oceanic Lithosphere. All these investigations have shown, however, that the Lithosphere is capable of supporting significant tectonic stresses over long geological time scales over a temperature range that is lower than half the melting point (which corresponds to temperatures at the base of the Lithosphere estimated in the range 1200-1400 °C). The concept of a uniform elastic plate has been quite useful as a first order description of the thickness of that part of the Lithosphere which has the potential to accumulate tectonic stress. For an actual comparison of stresses in the Lithosphere (Zoback et al. 1989) with EUROPE'S Lithosphere - PHYSICAL PROPERTIES Uniform Elastic Plate Analogue | Depth Dependent Rheology | 300° - 600 c 25- f 50H 75- 100 Ma old oceanic Lithosphere 100 -Strength- -MSL- Thermally defined Lithosphere 1300° Figure 4-7. Panel illustrating for 100 Ma old oceanic Lithosphere the relationship between thermal Lithosphere (defined by the 1300°C isotherm), the effective elastic thickness, EET, and the mechanically strong part of the Lithosphere, MSL, with a brittle/ductile rheology and a finite depth-dependent strength, rapidly decreasing at temperatures around 750-800°C.

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  The Solid Earth

  An Introduction to Global Geophysics

  • C. M. R. Fowler(Author)
  • 2004(Publication Date)
  • Cambridge University Press

    (Publisher)

  Chapter 10 The continental Lithosphere 10.1 Introduction 10.1.1 Complex continents We have seen something of the general simplicity of the Earth’s internal structure and the detailed complexity of the motions of tectonic plates and convective systems. The clues to this simplicity and complexity come from the oceans, the study of whose structures has led to an understanding of the plates, of the mantle beneath and, to some extent, of the core, via its magnetic properties. Although complex details must be sorted out and theories may change slightly, we can now be reasonably confident that the oceans are understood in their broad structure. In contrast, the continents are not understood at all well. Yet we need to understand the continents because in their geological record lies most of the history of the Earth and its tectonic plates, from the time that continental material first formed over 4400 Ma ago (see Section 6.10). The oldest oceanic crust is only about 160 Ma old, so the oceanic regions can yield no earlier information. In the broadest terms, the continents are built around ancient crystalline crust, flanked by younger material representing many events of mountain building, collision, rifting and plate convergence and subsidence. Figure 3.30 shows the recent motions of the plates, illustrating how continents have collided and been torn asunder. A major problem in the geological and geophysical study of continents is that we can observe only what is exposed at or near the surface. To extend that knowledge to tens of kilometres deep, let alone to hundreds of kilometres, demands conjecture that cannot be tested directly. Oil and mineral exploration companies have developed sophisticated techniques for surveying the upper few kilometres of the crust in search of deposits and have significantly advanced our knowledge of sedimentation, oil maturation and ore genesis.

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