The Lithosphere (Greek: Litho - Rocky) is the solid outer surface shell of the planet.
The lithosphere (from the Greek for "rocky" sphere) is the solid outermost shell of a rocky planet.
On the Earth, the lithosphere includes the crust and the uppermost layer of the mantle (the upper mantle or lower lithosphere) which is joined to the crust. The lithosphere is broken up into different plates as shown by the picture.
The distinguishing characteristic of the lithosphere is not composition, but its flow properties.
Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, while the asthenosphere accommodates strain through plastic deformation.
The lithosphere (from the Greek for "rocky" sphere) is the solid outermost shell of a rocky planet.
On the Earth, the lithosphere includes the crust and the uppermost layer of the mantle (the upper mantle or lower lithosphere) which is joined to the crust. The lithosphere is broken up into different plates as shown by the picture.
The distinguishing characteristic of the lithosphere is not composition, but its flow properties.
Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, while the asthenosphere accommodates strain through plastic deformation.
Both the crust and upper mantle float on the more plastic asthenosphere.
The crust is distinguished from the mantle
The thickness of the lithosphere varies from around 1.6 km (1 mi) at the mid-ocean ridges to approximately 130 km (80 mi) beneath older continental crust.
The thickness of the continental lithospheric plates is probably around 150 kilometers (93 mi).
As the cooling surface layer of the Earth's convection system, the lithosphere thickens over time.
It is fragmented into relatively strong pieces, called tectonic plates, which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics.
Lithosphere
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The tectonic plates of the lithosphere on Earth
Earth cutaway from core to crust, the lithosphere comprising the crust and lithospheric mantle (detail not to scale)
A lithosphere (Ancient Greek: λίθος [lithos] for "rocky", and σφαίρα [sphaira] for "sphere") is the rigid,[1] outermost shell of a terrestrial-type planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.
Contents
1 Earth's lithosphere
1.1 History of the concept
1.2 Types
1.2.1 Oceanic lithosphere
1.2.2 Subducted lithosphere
2 Mantle xenoliths
3 See also
4 References
5 Further reading
6 External links
Earth's lithosphere
Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle. The Lithosphere-Asthenosphere boundary 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.
History of the concept
The concept of the lithosphere as Earth's strong outer layer was described by A.E.H. Love in his 1911 monograph "Some problems of Geodynamics" and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term "lithosphere".[2][3][4][5] 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 Reginald Aldworth Daly in 1940 with his seminal work "Strength and Structure of the Earth."[6] 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.
Types
Different types of lithosphere
There are two types of lithosphere:
Oceanic lithosphere, which is associated with oceanic crust and exists in the ocean basins (mean density of about 2.9 grams per cubic centimeter)
Continental lithosphere, which is associated with continental crust (mean density of about 2.7 grams per cubic centimeter)
The thickness of the lithosphere is considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior.[7] The temperature at which olivine begins to deform viscously (~1000 °C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. Oceanic lithosphere is typically about 50–140 km thick [8](but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 280 km;[8] the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.
Oceanic lithosphere
Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convection[9] 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.
{\displaystyle \,h\,\sim \,2\,{\sqrt {\kappa t}}\,} \,h\,\sim \,2\,{\sqrt {\kappa t}}\,
Here, {\displaystyle h} h is the thickness of the oceanic mantle lithosphere, {\displaystyle \kappa } \kappa is the thermal diffusivity (approximately 10−6 m2/s) for silicate rocks, and {\displaystyle t} 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 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. This is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has 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 the continental lithosphere are billions of years old. 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.[10][11]
Subducted lithosphere
Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary,[12] while others "float" in the upper mantle,[13][14] while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above,[11] similar to the extent of the "tectosphere" proposed by Jordan in 1988.[15]
Mantle xenoliths
Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths[16] 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 the mantle flow that accompanies plate tectonics.[17]
Lithosphere
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
The tectonic plates of the lithosphere on Earth
Earth cutaway from core to crust, the lithosphere comprising the crust and lithospheric mantle (detail not to scale)
A lithosphere (Ancient Greek: λίθος [lithos] for "rocky", and σφαίρα [sphaira] for "sphere") is the rigid,[1] outermost shell of a terrestrial-type planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.
Contents
1 Earth's lithosphere
1.1 History of the concept
1.2 Types
1.2.1 Oceanic lithosphere
1.2.2 Subducted lithosphere
2 Mantle xenoliths
3 See also
4 References
5 Further reading
6 External links
Earth's lithosphere
Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle. The Lithosphere-Asthenosphere boundary 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.
History of the concept
The concept of the lithosphere as Earth's strong outer layer was described by A.E.H. Love in his 1911 monograph "Some problems of Geodynamics" and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term "lithosphere".[2][3][4][5] 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 Reginald Aldworth Daly in 1940 with his seminal work "Strength and Structure of the Earth."[6] 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.
Types
Different types of lithosphere
There are two types of lithosphere:
Oceanic lithosphere, which is associated with oceanic crust and exists in the ocean basins (mean density of about 2.9 grams per cubic centimeter)
Continental lithosphere, which is associated with continental crust (mean density of about 2.7 grams per cubic centimeter)
The thickness of the lithosphere is considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior.[7] The temperature at which olivine begins to deform viscously (~1000 °C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. Oceanic lithosphere is typically about 50–140 km thick [8](but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 280 km;[8] the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.
Oceanic lithosphere
Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convection[9] 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.
{\displaystyle \,h\,\sim \,2\,{\sqrt {\kappa t}}\,} \,h\,\sim \,2\,{\sqrt {\kappa t}}\,
Here, {\displaystyle h} h is the thickness of the oceanic mantle lithosphere, {\displaystyle \kappa } \kappa is the thermal diffusivity (approximately 10−6 m2/s) for silicate rocks, and {\displaystyle t} 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 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. This is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has 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 the continental lithosphere are billions of years old. 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.[10][11]
Subducted lithosphere
Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary,[12] while others "float" in the upper mantle,[13][14] while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above,[11] similar to the extent of the "tectosphere" proposed by Jordan in 1988.[15]
Mantle xenoliths
Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths[16] 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 the mantle flow that accompanies plate tectonics.[17]
Lithosphere
The lithosphere is the solid, outer part of the Earth, including the brittle upper portion of the mantle and the crust.
GRADES
4 - 12, Higher Ed
SUBJECTS
Earth science, Geology, Geography, Physical Geography
CONTENTS
3 Photographs, 2 Links, 1 Video
The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure. It is bounded by the atmosphere above and the asthenosphere (another part of the upper mantle) below.
The lithosphere is the most rigid of Earth’s layers. Although the rocks of the lithosphere are still considered elastic, they are not viscous. The asthenosphere is viscous, and the lithosphere-asthenosphere boundary (LAB)is the point where geologists and rheologists—scientists who study the flow of matter—mark the difference in ductility between the two layers of the upper mantle. Ductility measures a solid material’s ability to deform or stretch under stress. The lithosphere is far less ductile than the asthenosphere. The elasticity and ductility of the lithosphere depends on temperature, stress, and the curvature of the Earth itself.
The lithosphere is also the coolest of Earth’s layers. In fact, some definitions of the lithosphere stress its ability to conduct heat associated with the convection taking place in the plastic mantle below the lithosphere.
There are two types of lithosphere: oceanic lithosphere and continental lithosphere. Oceanic lithosphere is associated with oceanic crust, and is slightly denser than continental lithosphere. Continental lithosphere, associated with continental crust, can be much, much thicker than its oceanic cousin, stretching more than 200 kilometers (124 miles) below Earth’s surface.
Plate TectonicsThe most well-known feature associated with Earth’s lithosphere is tectonic activity. Tectonic activity describes the interaction of the huge slabs of lithosphere called tectonic plates.The lithosphere is divided into 15 major tectonic plates: the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca.Most tectonic activity takes place at the boundaries of these plates, where they may collide, tear apart, or slide against each other. The movement of tectonic plates is made possible by thermal energy (heat) from the mantle part of the lithosphere. Thermal energy makes the rocks of the lithosphere more elastic.Tectonic activity is responsible for some of Earth's most dramatic geologicevents: earthquakes, volcanoes, orogeny (mountain-building), and deep ocean trenches can all be formed by tectonic activity in the lithosphere.Tectonic activity can shape the lithosphere itself: Both oceanic and continental lithospheres are thinnest at rift valleys and mid-ocean ridges, where tectonic plates are shifting apart from one another. At these zones, the lithosphere is only as thick as the crust.How the Lithosphere Interacts with Other SpheresThe cool, brittle lithosphere is just one of five great “spheres” that shape the environment of Earth. The other spheres are the biosphere (Earth’s living things); the cryosphere (Earth’s frozen regions, including both ice and frozen soil); the hydrosphere (Earth’s liquid water); and the atmosphere (the air surrounding our planet). These spheres interact to influence such diverse elements as ocean salinity, biodiversity, and landscape.For instance, the pedosphere is part of the lithosphere made of soil and dirt. The pedosphere is created by the interaction of the lithosphere, atmosphere, cryosphere, hydrosphere, and biosphere. Enormous, hard rocks of the lithosphere may be ground down to powder by the powerful movement of a glacier (cyrosphere). Weathering and erosion caused by wind (atmosphere) or rain (hydrosphere) may also wear down rocks in the lithosphere. The organic components of the biosphere, including plant and animal remains, mix with these eroded rocks to create fertile soil—the pedosphere.The lithosphere also interacts with the atmosphere, hydrosphere, and cryosphere to influence temperature differences on Earth. Tall mountains, for example, often have dramatically lower temperatures than valleys or hills. The mountain range of the lithosphere is interacting with the lower air pressure of the atmosphere and the snowy precipitation of the hydrosphere to create a cool or even icy climate zone. A region’s climate zone, in turn, influences adaptations necessary for organisms of the region’s biosphere.
The rocky lithosphere includes part of the upper mantle and crust.
Photograph by Jennifer Plourde, MyShotThe LABThe depth of the lithosphere-asthenosphere boundary (LAB) is a hot topic among geologists and rheologists. These scientists study the upper mantle’s viscosity, temperature, and grain size of its rocks and minerals. What they have found varies widely, from a thin, crust-deep boundary at mid-ocean ridges to thick, 200-meter (124-mile) boundary beneath cratons, the oldest and most stable parts of continental lithosphere.LithospheresScientists have identified many ways to define the lithosphere. The “elastic lithosphere” measures its ability to reform itself under stress. The “thermal lithosphere” measures its temperature and the thermal energy—heat—it conducts. The “seismic lithosphere” measures how lithospheric rocks move with seismic shifts and tectonic activity. The “electrical lithosphere” measures the layer’s ability to conduct electricity (much lower than the asthenosphere). Finally, the “petrologic lithosphere” measures the chemical properties of rocks in the lithosphere compared to the asthenosphere.Extraterrestrial LithospheresAll terrestrial planets have lithospheres. The lithospheres of Mercury, Venus, and Mars are much thicker and more rigid than Earth's.
Lithosphere, Rigid, rocky outer layer of the Earth, consisting of the crust and the solid outermost layer of the upper mantle. It extends to a depth of about 60 mi (100 km). It is broken into about a dozen separate, rigid blocks, or plates (see plate tectonics). Slow convection currents deep within the mantle, generated by radioactive heating of the interior, are believed to cause the lateral movements of the plates (and the continents that rest on top of them) at a rate of several inches per year.
Lithosphere
The word lithosphere is derived from the word sphere, combined with the Greek word lithos, meaning rock . The lithosphere is the solid outer section of Earth, which includes Earth's crust (the "skin" of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44–62 mi (70–100 km). This relatively cool and rigid section of Earth is believed to "float" on top of the warmer, non-rigid, and partially melted material directly below.
Earth is made up of several layers. The outermost layer is called Earth's crust. The thickness of the crust varies. Under the oceans , the crust is only about 3–5 mi (5–10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is assumed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 31–62 mi (50–100 km) below Earth's surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.
Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C), which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere , from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid asthenosphere, which seems to be in continual motion. This motion creates stress in the rigid rock layers above it, forcing the slabs or plates of the lithosphere to jostle against each other, much like ice cubes floating in a bowl of swirling water . This motion of the lithospheric plates is known as plate tectonics , and is responsible for many of the movements seen on Earth's surface today including earthquakes, certain types of volcanic activity, and continental drift.
See also Continental drift theory; Earth (planet); Earth, interior structure
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"Lithosphere." World of Earth Science. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lithosphere The upper (oceanic and continental) layer of the solid Earth, comprising all crustal rocks and the brittle part of the uppermost mantle. It is generally considered to deform by brittle fracture and if subjected to stresses of the order of 100 MPa. It comprises numerous blocks, known as tectonic plates, which have differential motions giving rise to plate tectonics. The concept was originally based on the requirement for a rigid upper layer to account for isostasy. Its rigidity is variable, but much greater than 1021P, which corresponds with the underlying asthenosphere. Its thickness is variable, from 1–2 km at mid-oceanic ridge crests, but generally increasing from 60 km near the ridge to 120–140 km beneath older oceanic crust. The thickness beneath continental crust is uncertain, probably some 300 km beneath the cratonic (see CRATON) parts of the continental crust, but the absence of the asthenosphere in these regions makes definition difficult. Compare ATMOSPHERE; and HYDROSPHERE.
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"lithosphere." A Dictionary of Earth Sciences. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lithosphere (lĬth´əsfēr´), brittle uppermost shell of the earth, broken into a number of tectonic plates. The lithosphere consists of the heavy oceanic and lighter continental crusts, and the uppermost portion of the mantle. The crust and mantle are separated by the Moho or Mohorovicic discontinuity (see earthand seismology). The thickness of the lithosphere varies from to around 1 mi (1.6 km) at the mid-ocean ridges to approximately 80 mi (130 km) beneath older oceanic crust. The thickness of the continental lithospheric plates is probably around 185 mi (300 km) but is uncertain due to the irregular presence of the Moho discontinuity. The lithosphere rests on a soft layer called the asthenosphere, over which the plates of the lithosphere glide. See plate tectonics.
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"lithosphere." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lithosphere The upper (oceanic and continental) layer of the solid Earth, comprising all crustal rocks and the brittle part of the uppermost mantle. Its thickness is variable, from 1–2 km at mid-oceanic ridge crests, but generally increasing from 60 km near the ridge to 120–140 km beneath older oceanic crust. The thickness beneath continental crust is uncertain, but is probably some 300 km in places.
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"lithosphere." A Dictionary of Ecology. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lith·o·sphere / ˈli[unvoicedth]əˌsfi(ə)r/• n. Geol. the rigid outer part of the earth, consisting of the crust and upper mantle.DERIVATIVES:lith·o·spher·ic / ˌli[unvoicedth]əˈsferik; -ˈsfi(ə)r-/ adj.
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"lithosphere." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lithosphere Solid, upper layer of the Earth which includes the crust and the uppermost mantle. Its thickness varies, but is c.60km (40mi); it extends down to a depth of c.200km (125mi). It is made up of a number of tectonic plates that move independently, giving rise to plate tectonics.
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Lithosphere
Lithosphere
The word lithosphere is derived from the word “sphere,” combined with the Greek word “lithos” which means rock. The lithosphere is the solid outer section of Earth which includes Earth’s crust (the outermost layer of rock on Earth), as well as the underlying cool, dense, and fairly rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44-62 mi (70-100 km). This relatively cool and rigid section of Earth is thought to float on top of the warmer, non-rigid, and partially melted material directly below.
Earth is made up of several layers. The outermost layer is called Earth’s crust. The thickness of Earth’s crust varies. Under the oceans the crust is only about 3-5 mi (5-10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is believed to be made up of denser material with a different chemical composition. This layer is called the upper part of the upper mantle, and varies in depth from about 31 mi (50 km) to 62 mi (100 km) below Earth’s surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.
Below the lithosphere, the temperature is thought to reach 1,832°F (1,000°C) which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone directly below the lithosphere is called the asthenosphere, from the Greek word “asthenes,” meaning “weak.” The lithosphere, including both the solid portion of the upper mantle and Earth’s crust, is carried on top of the weaker and less rigid asthenosphere, which is in continual motion. This motion creates stress in the rigid rock layers above it, and the plates of the lithosphere are forced against each other. This motion of the lithospheric plates is known as plate tectonics, and is responsible for many of the movements that we see on Earth’s surface today including earthquakes, certain types of volcanic activity, and continental drift.
See also Earth’s interior; Magma.
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"Lithosphere." The Gale Encyclopedia of Science. . Encyclopedia.com. 2 Mar. 2019 <https://www.encyclopedia.com>.
Lithosphere
Lithosphere
The word lithosphere is derived from the word "sphere," combined with the Greek word "lithos" which means rock. The lithosphere is the solid outer section of Earth which includes Earth's crust (the "skin" of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and fairly rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44-62 mi (70-100 km). This relatively cool and rigid section of Earth is believed to "float" on top of the warmer, non-rigid, and partially melted material directly below.
Earth is made up of several layers. The outermost layer is called Earth's crust. The thickness of Earth's crust varies. Under the oceans the crust is only about 3-5 mi (5-10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is believed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 31 mi (50 km) to 62 mi (100 km) below Earth's surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.
Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C) which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere , from the Greek word "asthenes," meaning "weak." The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid asthenosphere, which seems to be in continual motion . This motion creates stress in the rigid rock layers above it, and the plates of the lithosphere are forced against each other. This motion of the lithospheric plates is known as plate tectonics , and is responsible for many of the movements that we see on Earth's surface today including earthquakes, certain types of volcanic activity, and continental drift .
Introduction
The lithosphere is the solid and rigid outer layer of our planet. It includes the crust and part of the upper mantle that contains rigid rocks. Beneath this layer is the asthenosphere where the rocks in this part of the upper mantle are not rigid. The rocks can flow like a liquid or break apart similar to silly putty.
The lithosphere is the solid and rigid outer layer of our planet. It includes the crust and part of the upper mantle that contains rigid rocks. Beneath this layer is the asthenosphere where the rocks in this part of the upper mantle are not rigid. The rocks can flow like a liquid or break apart similar to silly putty.
Two types of crustal plates
This layer of the Earth contains two very different types of crust. The continental crust contains a variety of rocks. They are igneous rocks, sedimentary rocks and metamorphic rocks that make up the rock cycle. Continental crust is lighter than oceanic crust which is made of basalt and gabbro. These rocks are derived from the upper mantle.
This layer of the Earth contains two very different types of crust. The continental crust contains a variety of rocks. They are igneous rocks, sedimentary rocks and metamorphic rocks that make up the rock cycle. Continental crust is lighter than oceanic crust which is made of basalt and gabbro. These rocks are derived from the upper mantle.
Oceanic crust
The oceanic crust is much younger because it is constantly be created at spreading zones and recycled in subduction zones. New oceanic crust forms when crustal plates separate. Molten rock from the upper mantle that has collected in magma chambers oozes onto the ocean floor forming a layer of rocks between the spreading plates. This is the newest and youngest crust on the surface of the Earth.
The oceanic crust is much younger because it is constantly be created at spreading zones and recycled in subduction zones. New oceanic crust forms when crustal plates separate. Molten rock from the upper mantle that has collected in magma chambers oozes onto the ocean floor forming a layer of rocks between the spreading plates. This is the newest and youngest crust on the surface of the Earth.
Continental crust
The lithosphere contains the continental crust that is much older than oceanic plates. Continental plates in subduction zones are not recycled because they override the oceanic plates. If continental plates meet that create a collision zone and great mountain chains like the Himalayas rise above the landscape.
The lithosphere contains the continental crust that is much older than oceanic plates. Continental plates in subduction zones are not recycled because they override the oceanic plates. If continental plates meet that create a collision zone and great mountain chains like the Himalayas rise above the landscape.
Continental plate collides with oceanic plate
When a continental plate and an oceanic plate meet the continental plate overrides the oceanic plate. As the continental plate overrides the oceanic plate it scrapes off the top layers off the oceanic plate.
When a continental plate and an oceanic plate meet the continental plate overrides the oceanic plate. As the continental plate overrides the oceanic plate it scrapes off the top layers off the oceanic plate.
San Francisco terranes
The layers that are scraped off the oceanic plates are called terranes. Seventeen of these accreted terranes have been identified in the San Francisco bay area and are related to the movement along the San Andreas Fault.
The layers that are scraped off the oceanic plates are called terranes. Seventeen of these accreted terranes have been identified in the San Francisco bay area and are related to the movement along the San Andreas Fault.
Crustal plate boundaries
Scientists use earthquakes to determine the boundaries of the crustal plates on the surface of the Earth. Earthquakes along fault lines occur frequently as plates move around the Earth.
Scientists use earthquakes to determine the boundaries of the crustal plates on the surface of the Earth. Earthquakes along fault lines occur frequently as plates move around the Earth.
Major crustal plates
The seven major plates that contain the bulk of the continents and the Pacific Ocean: African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, South American Plate and the Pacific Plate.
The seven major plates that contain the bulk of the continents and the Pacific Ocean: African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, South American Plate and the Pacific Plate.
Smaller Plates
There are also eight smaller plates that are generally shown on maps that display crust plates. These are the smaller but very important plates that have cause great earthquakes in the past.
There are also eight smaller plates that are generally shown on maps that display crust plates. These are the smaller but very important plates that have cause great earthquakes in the past.
- Arabian Plate
- Caribbean Plate
- Cocos Plate, Indian Plate
- Juan de Fuca Plate
- Nazca Plate
- Philippine Sea Plate
- Scotia Plate.
Scientists have also identified a number of micro-plates where the land is being torn apart or are subducting.
MORE PLANET EARTH LINKS
What are Northern Lights? Find out how the solar wind powered, by great storms on the Sun, create the Northern Lights.
Asthenosphere Find out why scientists say the rocks in the asthenosphere has properties like silly putty.
Polar Front Find out what happens when a cold air mass from the poles meets a warm tropical air mass!
Horse Latitudes Find out where the Horse Latitudes are located and how they got their unusual name.
Earths Crust Do you know where the youngest crust on our planet is located and how it forms?
Lithosphere The lithosphere includes oceanic crust and continental crust that make up this layer of the Earth.
Planet Earth Find out about our planet from the Earth's core to the outer reaches of our atmosphere.
Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.
The lithosphere is where we live. It is also the source of many geologic events that affect us. In this lesson, you will learn more about this important part of our planet.
What Is a Lithosphere?
The name 'lithosphere' comes from the Greek words lithos, meaning 'rocky,' and sphaeros, meaning 'sphere.'
The word is defined two ways. The first is in the context of studying the Earth as a system, a set of interrelated processes, where the word is used very broadly to identify what goes on within the solid part of the Earth; basically, everything below the ground surface. It is one of the four main components of the Earth system, along with the atmosphere, hydrosphere, and biosphere.
Geologists use the term as the name for the layer of the Earth extending from the surface to a depth of around 80 to 120 miles, depending on location, in which rocks are relatively brittle and rigid. This is the definition we will explore here.
Properties of the Lithosphere
Aside from the fact that we are living on it, the lithosphere is where many of the geologic processes that affect us originate. The movement of large pieces of the lithosphere account for the global locations of volcanoes, earthquakes, and mountain ranges, as well as the shape and location of our modern continents. Interesting, huh? Let's look at the physical characteristics of the compounds that make up the lithosphere.
The lithosphere is made up of rocks from two of the Earth's major layers. It contains all of the outer, thin shell of the planet, called the crust, and the uppermost part of the next-lower layer, the mantle. The thickness of the lithosphere varies; it's thickest below the continents and thinnest at the mid-ocean ridges, raised areas of the seafloor where new seafloor crust is formed.
The thing all of the rocks in the lithosphere have in common is the way in which they respond to forces applied to them. At the relatively low temperatures found near the Earth's surface, rocks tend to break under stress. Farther down, as temperature and pressure increase, the more likely it is that rocks will be able to accommodate stress by changing shape, or deforming, compressing, stretching, and bending, rather than breaking.
At some critical depth, the temperature will be high enough that rocks actually start behaving like a viscous fluid rather than a brittle solid. That depth is defined as the bottom of the lithosphere. Below the base of the lithosphere, rocks are hot enough that they actually deform by flowing, even though they remain solid due to the high confining pressure produced by the weight of the rocks above. That layer on which the lithosphere rests is known as the asthenosphere.
The physical connection between the lithosphere and the asthenosphere generates a considerable amount of pushing and pulling on the lithosphere as the rocks below move around. In response, the lithosphere has broken into about a dozen large pieces, called lithospheric plates, or simply plates. The movement of the plates away from, towards, and past each other is known as plate tectonics.
The lithosphere
- 1. Layers of the Earth
- 2. 4. The 6-35 km (4-21 miles) thick lithosphere. Earths crust. 3. The 2900 km (1.800 miles) thick Mantle layer formed from rapidly flowing magma. 2. The 2000 km (1,250 miles) thick outer core containing such molten heavy metals as nickel and iron.1. The 1370 km (851 miles) thick inner core, which is in acrystalline state because of the influence of heat andhigh pressure.
- 3. Lithosphere The solid part of the earth. It consists of three main layers: crust, mantle and core.
- 4. The CrustIs the outermost layer of the earth.Has a depth of about 32 to 40 km.The thinnest layer.The uppermost layer is known as the SIAL. It is composed mainly of silicon and aluminumThe bottom layer of the crust is called SIMA It is made mostly of silicon and magnesium.
- 5. Crust are further divided into two major parts: Continental crust It is about 32 kilometers thick, made mainly of granite rocks. The elevated portion of the crust. Oceanic Crust The ocean bed, it is about seven kilometers thick and made mainly of basalt.
- 6. The Mantle Located just below the crust. It is denser than crust, about 2,900 km thick. It is composed mainly of very hot, solid rocks that flow. The region between the crust and the mantle is called MOHOROVICIC DISCONTINUITY OR MOHO. Scientists have been able to confirm the differences in density between rocks of the crust and those of the mantle by studying the Moho.
- 7. The Core It is about 4,960 km deep. It is divided into: Outer core It is about 2,270 km thick Composed mainly of nickel and iron melted by intense heat. The temperature ranges from 4,000 C to 5,000 C Inner Core It is composed mainly of solid iron and nickel. The temperature is around 5,000 C to 6,000 C. The pressure is exceedingly high.
- 8. Materials of the Earth
- 9. Igneous Rocks
- 10. (1) Basalt: are dark colored, fine-grained extrusive rocks. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earths interior.
- 11. (2) Gabbro: is a dark-colored, coarse-grained intrusive igneous rock. Gabbro is very similar to basalt in its mineral make up.
- 12. (3) Pumice: is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lave hurtles through the air it cools and the gases escape leaving the rock full of holes. Pumice is so light that is actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes.
- 13. (3) Pumice: is a very light colored, frothy volcanic rock. Pumice isformed from lava that is full of gas. The lava is ejected and shotthrough the air during an eruption. As the lave hurtles through theair it cools and the gases escape leaving the rock full of holes.Pumice is so light that is actually floats on water. Huge pumiceblocks have been seen floating on the ocean after large eruptions.Some lava blocks are large enough to carry small animals. Pumiceis ground up and used today in soaps, abrasive cleansers, and alsoin polishes.
- 14. (4) Rhyolite: is very closely related to granite. Thedifferences is rhyolite has much finer crystals. Thesecrystals are so mall that they can not be seen by thenaked eye. Rhyolite is an extrusive igneous rock havingcooled much more rapidly than granite, giving it aglassy appearance. The minerals that make up rhyoliteare quartz, feldspar, mice, and hornblende.
- 15. (5) Granite: is an igneous rock that is composed of four minerals. These mineralsare quartz, feldspar, mica, and usually hornblende. Granite forms as magmacools far under the Earths surface. Because it hardens deep underground, itcools very slowly. This allows crystals of the four minerals to grow large enoughto be easily by the naked eye. Granite is an excellent material for buildingbridges and buildings because it can withstand thousands of pounds of pressure.It is also used for monuments because it weathers slowly. Engraving in granitecan be read for hundreds of years, making the rock more valuable. Granite isquarried in many places in the World including the United States. The state ofHew Hampshire has the nickname "Granite State" because of the amount ofgranite in the mountains of that beautiful state. The Canadian Shield of NorthAmerican contains huge outcroppings (surface rocks) of granite.
- 16. (6) Obsidian: is a very shiny natural volcanic glass. When obsidianbreaks its fractures with a distinct conchoidal fracture. Obsidian isproduced when lava cools very quickly. The lave cools so quicklythat no crystals can form. When people make glass they melt silicarocks like sand and quartz then cool it rapidly by placing it inwater. Obsidian in produced in nature in a similar way. Obsidian isusually black or a very dark green, but it can also be found in analmost clear form. Ancient people throughout the World haveused obsidian for arrowheads, knives, spearheads, and cuttingtools of all kinds. Today obsidian is used as a scalpel by doctors invery sensitive eye operations.
- 17. Metamorphic Rock:(1) White Marble: is a metamorphosed limestone or dolomite. both limestoneand dolomite have a large concentration of calcium carbonate (CaCO3). Marblehas many different sizes of crystals. Marble has many color variances due tothe impurities present at formation. Some of the different colors of marble arewhite, red, black, mottled and banded, gray, pink, and green. Marble is muchharder than its parent rock. This allows it to take a polish which makes it a goodmaterial for use as a building material, making sink tops, bathtubs, and acarving stone for artists. Today, headstones are made from marble and granitebecause both of these rocks weather very slowly and carve well with sharpedges. Marble is quarried in Vermont, Tennessee, Missouri, Georgia, andAlabama.
- 18. (2) Slate: is a fine-grained metamorphic rock with perfect cleavage that allows itto split into thin sheets. Slate usually has a light to dark brown streak. Slate isproduced by low grade metamorphism, which is caused by relatively lowtemperatures and pressures. Slate has been used by man in a variety of waysover the years. One use for slate was in the making of headstones and gravemarkers. Slate is not very hard and can be engraved easily. The problem with theslate though is its perfect cleavage. The slate headstones would crack and splitalong these cleavage planes. This in not a desirable attribute for a headstone.Slate was also used for chalk boards. The black color was good as a backgroundand the rock cleaned easily with water. Today it is not very advantageous to usethis rock because of its weight and the splitting and cracking over time.
- 19. (3) Schist: is a medium grade metamorphic rock. This means thatis has been subjected to more heat and pressure thanslate, which is a low grade metamorphic rock. The individualgrains of minerals can be seen by the naked eye. Many of theoriginal minerals have been altered into flakes. Because it hasbeen squeezed harder than slate it is often found folded andcrumpled. Schists are usually named by the main mineral fromwhich they are formed. Bitotite mica schist, hornblendeschist, garnet mica schist, and talc schist are some examples ofthis.
- 20. (4)Gneiss: is a high grade metamorphic rock. This means thatgneiss has been subjected to more heat and pressure than schist.Gneiss is coarser than schist and has distinct banding. Thisbanding has alternating layers that are composed of differentminerals. The minerals that compose gneiss are the same asgranite. Feldspar is the most important mineral that makes upgneiss along with mica and quartz. Gneiss can be formed from asedimentary rock such as sandstone or shale, or it can be formedfrom the metamorphism of the igneous rock granite. Gneiss canbe used by man as paving and building stone.
- 21. (5) Quartzite: is composed of sandstone that has beenmetamorphosed. Quartzite is much harder than theparent rock, sandstone. It forms from sandstone thathas come into contact with deeply buried magmas.Quartzite looks familiar to its parent rock. The best wayto tell quartzite from sandstone is to break the rocks.Sandstone will shatter into many individual grains ofsand while quartzite will break across the grains.
- 22. (6) Anthracite Coal: is organic sedimentary rocks formed from the build up and decay ofplant and animal material. This usually forms in swamp regions in which there is anabundant supply of growing vegetation and low amounts of oxygen. The vegetation buildsso quickly that new layers of vegetation bury the dead and decaying material very quickly.The bacteria that decay the vegetation need oxygen to survive. Because these decayinglayers are buried so fast the bacteria use up what oxygen there is available and can notfinish the decomposition of the vegetation. The overlaying layers become so heavy thatthey squeeze out the water and other compounds that aid in decay. This compressedvegetation forms coal. The longer and deeper that coal is buried makes it of higherquality. Peat is the first stage of coal formation. Lignite is the next grade of coal followedby bituminous and the highest grade, anthracite. Anthracite is actually a metamorphicrock. It forms during mountain building when compaction and friction are extremely high.This form of coal burns very hot and almost smokeless. It is used in the production of highgrade steel.
- 23. Sedimentary Rocks:(1) Limestone: is the most abundant of the non-clastic sedimentary rocks.Limestone is produced from the mineral calcite (calcium carbonate) andsediment. The main source of limestone is the limy ooze formed in the ocean.The calcium carbonate can be precipitated from ocean water or it can beformed from sea creatures that secrete lime such as algae and coral. Chalk isanother type of limestone that is made up of very small single-celledorganisms. Chalk is usually white or gray in color. Limestone can easily bedissolved by acids. If you drop vinegar on limestone it will fizz. Put a limestonerock into a plastic jar and cover it with vinegar. Cover the jar and watch thebubbling of the calcium carbonate and also the disintegration of the rock overa few days.
- 24. (2) Breccia: is formed in a very similar fashion toconglomerate. The difference between the two rocks isthat breccias rock fragments are very sharp andangular. These rock fragments have not beentransported by water, wind, or glaciers long enough tobe rounded and smoothed like in the conglomerate.The cementing agents silica, calcite (CaCO3), and ironoxides are the same as in conglomerate.
- 25. (3) Conglomerate: is a clastic sedimentary rock that forms fromthe cementing of rounded cobble and pebble sized rockfragments. Conglomerate is formed by river movement or oceanwave action. The cementing agents that fill the spaces to form thesolid rock conglomerate are silica, calcite, or iron oxides. Notice inthe photo above the rounded rock particles in the conglomerate.These rounded particles make conglomerate different frombreccia.
- 26. (4) Sandstone: is a clastic sedimentary rock that formsfrom the cementing together of sand sized grainsforming a solid rock. Quartz is the most abundantmineral that forms sandstone. Calcium carbonate, silica,or iron has been added to the water that is in contactwith the sand grains. These minerals grow crystals inthe spaces around the sand grains. As the crystals fillthe gaps the individual sand grains are now transformedinto a solid rock.
- 27. (5) Halite: is common table salt. It forms where brakish (salty)lakes or sea beds dry up. This evaporation of the water causes thesalt to precipitate forming the salt crystals. Halite frequentlyoccurs in crystal form. It is usually colorless but can be reddishbrown because of iron oxides in the water that it forms in. Halitehas perfect cleavage and a hardness o 2.5 on the Mohs hardnessscale.
- 28. Story 1: "Rock"in StoriesKate was in her career development class atCherokee Middle School. She was very interestedin the subject of earth science and wanted toknow more about Geology and the formation ofrocks through geochemical process, such as,igneous, metamorphic and sedimentary.She interviewed a scientist, Dr. Gutierrez atSouthwest Missouri State University to feed hercuriosity. They planned a journey to theSpringfield rock quarry. Kate met Dr. Gutierrez andthey traveled to the rock quarry.
- 29. Kate and Dr. Gutierrez had to wear helmets to enter therock quarry due to the blasting of slabs of stone withdynamite. Kate was overwhelmed with all the differentkinds of rocks. She picked up a light whitish grey rock.Dr. Gutierrez told her the rock was composed ofCalcium Carbonate, CaC03, This type of rock is formedfrom sea creatures that secrete lime, such as algae andcoral. When they die their remains pile up on the oceanfloor and form this rock.What kind of rock would this be? What stage ofthe rock cycle is the rock found? Limestone - Sedimentary
- 30. Dr. Gutierrez informed her that the rockshe found is the parent of another kind ofrock that is much harder. This rock is madeup of different sizes of crystals and hasmany variations in color. This rock may bered, white, pink, or grey. It is used as abuilding material to make countertops and bathtubs.What kind of rock would this be? Whatstage of the rock cycle is this rock found? Marble - Metamorphic
- 31. The beginning of these rocks occurred 30meters below the Earths surface. There therock was dark colored and fined grained. Thisrock is the most widespread of this stage ofrocks. This rock is volcanic in origin and formedby rapid cooling and hardening of lava.What kind of rock would this be? Whatstage of rock cycle is this rock found? Basalt - Igneous
- 32. Story 2Whitney, a very intelligent graduate, completing hermasters in Geology decided to go on a research field classfor the summer. The instructor for this class was Dr.Playmate, a Geologist of Southwest Missouri StateUniversity.They traveled to the Rocky Mountains for their geologicalresearch. While hiking, they discovered an exposed cliffthat had been subjected to weathering.Within this cliff they found a rock that was composed ofthe minerals feldspar, mica, and quartz. This rock had abanned appearance in its layers.What kind of rock would this be? What stage of rockcycle is this rock found? Gneiss - Metamorphic
- 33. Whitney informed her classmates that thisrock can be formed from several other typesof rocks. One of these rocks forms from thecementing together of small grains. Quartz isthe most abundant mineral in this kind of rock.What kind of rock would this be? What stage ofrock cycle is this rock found? Sandstone - Sedimentary
- 34. The rock in the cliff could also be formed from acompletely different type of rock. This rock is composedof four minerals: quartz, feldspar, mica, andhornblende. This rock forms as magma cools far underthe Earths surface. Because it hardens underground, itcools slowly. This allows the crystal of the four mineralsto grow large enough to be seen by the naked eye. Thistype of rock is excellent of building bridges andmonuments because it weathers slowly.What kind of rock would this be? What stage ofrock cycle is this rock found? Granite - Igneous
- 35. Story 3:Jessica, after completing a very rough semesterat Southwest Missouri State University, decidedto take a vacation to Hawaii with her frequentflyer miles. She decided to go to the NationalVolcano Park to elevate some stress. The parkencompasses diverse environments that rangefrom seal level to the summit of the Earthsmost massive volcano, Mauna Loa at 13,677feet. After a recent volcanic eruption she took aguided tour. On this tour, she observed manydifferent types of volcanic rock.
- 36. One in particular was very light colored and lightin weight. This rock is so light that it floats onwater. It had holes all throughout the rock. Thisrock is formed when lava is ejected and shotthru the air during a volcanic eruption. As thelava flies thru the air it cools and gases escapeleaving the rock full of holes. This rock is usedtoday in soap and abrasive cleaners.What kind of rock would this be? What stage ofrock cycle is this rock found? Pumice - Igneous
- 37. They traveled on and came to a beautiful flowingstream. The guide picked up a hand full of rocksand Jessica noticed one that appeared to havemany tiny rocks inside of it. This rock wasformed by river movement and composed ofrounded cobble and pebble sized rock fragments.What kind of rock would this be? Whatstage of rock cycle is this rock found? Conglomerate - Sedimentary
- 38. After the guided tour, Jessica to take a walk onthe beach of Hawaii. As she walked, she pickedup shells and rocks from the sand. She noticedone of the rocks looked like it had been formedfrom the cementing together of small sand sizedgrains. This rock looked like sandstone, butwhen broken, the grains of sand broke into layers.What kind of rock would this be? Whatstage of rock cycle is this rock found? Quartzite - Metamorphic
- 39. Rock Name Description Rock Type Dark colored, fine grained; formed by rapid Basalt Igneous cooling and hardening of lava flow Dark colored, coarse-grained; similar to basalt Gabbro but mostly composed of the mineral Igneous plagioclase feldspar Light colored, frothy volcanic rock; formed Pumice when lava is ejected and shot through the air Igneous during an eruption; so light is can float Closely related to granite, but has very fine Rhyolite crystals; has a glassy appearance; made up of Igneous quartz, feldspar, mica and hornblende Composed of the same minerals as rhyolite; Granite forms as magma cools far under the earths Igneous surface Very shiny natural volcanic glass; produced Obsidian when lava cools very quickly so no crystals Igneous form; usually black or very dark green;
- 40. MineralsThey are naturally formed solid elementsor compounds having a crystallinestructure and possessing physical andchemical properties.They are considered as the building unitsof the Lithosphere.
- 41. The element composing the MineralsOxygen Oxygen in its combined form is the most abundant element composing minerals. It is found chemically combined with other elements forming OXIDES. Very few minerals are found to be composed of pure elements.
- 42. What is the relationship of Rocks and Minerals?Are familiar with a fruit cake? Fruit cake is a loaf of bread with nuts, raisins and glazed fruits. The fruit cake represents the rock, the nuts, raisins and glazed fruits represents the
- 43. Properties used in Identifying MineralsMINERALOGY is the science that dealswith the identification and classification ofminerals.Mineralogists subject the minerals tovarious tests to determine their properties.
- 44. Properties used in Identifying Minerals 1. Color This is the most obvious property of mineral. However, not all minerals can be identified by color for three reasons: a) Many minerals are colorless or else they have the same color. b) Impurities affect the real color of the mineral. c) Surface color tarnishesExample: Corundum is a colorless mineral. With traces ofChromium, it becomes red called (ruby) and with traces ofiron and titanium it becomes blue called ( sapphire)
- 45. 2. Luster This is the property of the mineral to reflect, refract or absorb light. Some minerals “shine’ when exposed to light while others do not. Some terms used to describe luster are: BRILLIANT, DULL, PEARLY, SILKY, EA RTHY and many more.
- 46. 3. Streak The color of the fine powder of the mineral made against a streak plate. Some minerals have streaks similar to their color. Others have streaks different from their colors. Gold is yellow, and its streak is also yellow. Pyrite (known as fool’s gold) has a greenish-black streak. Hematite is black but its streak is red.
- 47. Identifying Mineralsby StreakGold(top), platinum(middle) andcopper (bottom)have characteristicstreak colors, bestseen on a blackstreak plate.
- 48. 4. Crystal Form Minerals are usually crystalline and some minerals have enchanting crystals. Crystal form reveals the arrangement of atoms in a mineral. The atoms of each mineral are arranged in a definite geometric pattern. Each mineral had its own definite atomic arrangement which is helpful in identifying that particular mineral.
- 49. 5) Cleavage and Fracture This property reveal the structure of a mineral. Cleavage is the splitting of the mineral readily along certain planes to produce flat and smooth surfaces. Uneven breaks or cracks that form uneven surfaces are called FRACTURE.
- 50. 6. Specific Gravity This is the number that tells how many times denser the minerals is than an equal volume of water. In determining the specific gravity of a mineral. Its volume and mass are first determined. Then the density is computed using the formula: D=M/V
- 51. The resulting density is compared with the density ofwater which is equal to 1 g/cm3.For example, the density of silver is 10.6 g/cc. This isthen compared to the density of water. Thus,Specific gravity = density of silver / density of water = 10.6 g/cc / 1g/cc = 10.6Silver is 10.6 times denser than water.
- 52. Specific Gravity of Some Minerals Minerals Specific Gravity Gold 19.3 Mercury 13.6 Platinum 21.5 Silver 10.6 Copper 9.0 Zinc 7.1 Pyrite 5.2 Garnet 4.2 Diamond 3.5 Talc 2.8 Calcite 2.7 Quartz 2.6
- 53. 7. Hardness This is the resistance of a mineral to being scratched. The test for the hardness of a mineral involves the use of scale invented by Friedrich Mohs.
- 54. The Moh’s Scale of Hardness1. Talc 6. Orthoclase2. Gypsum 7. Quartz3. Calcite 8. Topaz4. Fluorite 9. Corundum5. Apatite 10. Diamond
- 55. The Forces the Construct theEarth’s Surface
- 56. Diastrophism or Crustal WarpingPertains to all the movements of the solidparts of the earth.Great forces act on the crust causing it tomove.Sometimes: the movement is so strong and sudden that we can feel the shaking of the ground. the movement may be so slow that we can not feel them, can only be detected by a seismograph.The great forces that cause the felt and unfeltmovements of the crust have been identified aspushes (compression) and pulls (tension) exerted onthe crust over long period of time.
- 57. Direction of Forces and the Movement they Produce1. Upward forces Upward forces cause the local widespread rising or uplift of the crust. These forces are responsible for the emergence of small islands in the deep seas of the pacific. The discovery of the fossil remains of marine organisms in the rock layers of high areas indicates that these layers were pushed up from under the water of the ocean.
- 58. 2. Downward Forces Downward forces cause the local or widespread sinking or subsidence of the crust. These forces caused the disappearance of small islands in the pacific in the historic past. The fossil remains found in the rock layers reveal that there was at one time a land bridge connecting Asia and North Africa. Such a land bridge and many more have been submerge or pushed underwater by great forces.
- 59. 3. Sideward Forces Sideward forces cause the horizontal motion of the crust called thrust. Large masses of rocks slide and slip against each other into new position. Sometimes rock masses bend, tilt, or wrinkle due to these sideward forces.
- 60. Effects of DiastrophismThe movement of the crust broughtabout by the interaction of theforces described has resulted in theformation of the different surfacefeatures of the earth.
- 61. 1. FoldingFolding occurs when the crust crumples orwrinkles due to compressions or pushesfrom opposite directions.
- 62. As the crust is crumpled, the rock stratabecome tilted.
- 63. The materials of the crust are dense andrigid, but under great heat and pressure,they soften and can be deformed.The crest or upward curve of a fold iscalled anticline.The trough or downward curve is calledsyncline.
- 64. The crest may formmountains, hills or ridges and thetrough may form valley.
- 65. 2. FaultingFaulting occurs when a rock massesof the crust are pulled apart (tension)forming cracks or fractures on thecrust.The tensional forces go beyond theelastic limit of the crust that it yieldsto the stress by breaking.
- 66. Different Tensional Stress and its Effects
- 67. In some instances, parallel faults mayoccur in the crust. The area between two parallel faults may eventually sink as the downward forces act on it.The sunken area is called a graben and itmay form rift valley.The risen area is called ahorst and it may becomea plateau.
- 68. Types of Faulting
- 69. We can now conclude that throughgreat stretches of time, ocean floorshave been lifted up, high areas havebeen thruster, pushed down, pushedand pulled sideways many times.Careful observations indicate thatthese processes are still going on andaffecting the crust.Where do the forces that shapethe earth come from?
- 70. Causes of Diastrophism1. Continental Drift TheoryThis theory wasproposed by AlfredWegener, a Germanscientist in 1915.
- 71. According to him, 200 million yearsago, there was only a singlesupercontinent called Pangaea situated atthe center near the equator.
- 72. This single supercontinent broke up into pieces which drifted slowly away from each other. The pieces formed the continents of today.As the continents driftedapart, they rubbed and collidedagainst each other forming thesurface features of today.
- 73. Assignment: 1. Make at least 300 words reaction paper on the video presentation. 2. Long bond paper. 3. Hand written. 4. Follow the web site below http://www.youtube.com/watch?v=3HDb9Ijynfo&feature=related
- 74. 2. The Theory of Seafloor SpreadingIn 1920, five years after Wegener’s theory wasformulated, the existence of the mid-oceanic ridges werediscovered using an echo-sounding device like a sonar.
- 75. A break or rift was found at the middle of the ridgerunning along its length where basaltic magma wells out tothe surface.
- 76. This basaltic magma solidified forming a “new crust”.
- 77. The new crust pushes the old crust causing the ocean floor tospread.
- 78. The force according to theory caused thebreaking and drifting apart of the continents.The mid-oceanic ridges are believed to be theremnants of the continents that drifted.The ocean floor has been estimated to bespreading at the rate of 5 cm per year.This rate may seem slow, but for the past 200million years, all the existing ocean basin weregenerated through this slow movement.
- 79. An exploration using a research shipnamed Glomar Challenger drilled throughthe crust and gathered several rocksamples from both sides of the mid-oceanic ridge.
- 80. Radioactive dating techniqueproved that the rocks found fromabout the same distance from therift on both sides are of the sameage and rock type.The rocks taken near the ridgewere relatively younger thanthose further from the ridge.
- 81. If new crust is continuously beingformed, does it mean that the earth’sdiameter is expanding?Scientists explain that as a new crustis formed at the mid-oceanicridges, elsewhere on earth, the oldcrust is being destroyed at the samerate that it is created.The region where the old crust isbeing destroyed is called thesubduction zone.
- 82. Here in the subduction zone, the old crust is plungedinto high pressure and high temperatureenvironment.Thus, some of the materials melt and may migrateupward giving rise to volcanic eruptions.
- 83. http://www.youtube.com/watch?v=ep2_axAA9Mw&feature=related
- 84. 3. The Plate Tectonic TheoryThis theory proposed that theLithosphere is divided into six majorplates.
- 85. The plate may be composed of thecontinental crust on top of the oceaniccrust or may be composed of the oceaniccrust alone.
- 86. The plates are slowly, but nevertheless continually in motion. The movement of plates is believed to be caused by the convection currents in the mantle.As the magma from the lower mantle rises fromdeep within the earth and spreads laterally, theplates are set in motion.Thus, the movement of the plates generatesearthquakes, volcanic activities, as well as pushesand pulls causing the deformation of large masses ofrocks.
- 87. Thus, the movement ofthe plates generatesearthquakes, volcanicactivities, as well aspushes and pullscausing the deformationof large masses of rocks.
- 88. As the movement of the plates goeson, interaction occurs along their plateboundaries.Plate boundary is the place where two platesmeet.
- 89. The plate boundaries1. Spreading or divergent boundary An area where two plates move apart leaves a gap between them. The gap formed is immediately filled up with molten materials that wells up from the lower mantle.
- 90. The Atlantic ocean, the Great Rift Valley of Africa andthe Red Sea are believed to be formed by this type ofmovement of the plates.
- 91. 2. Colliding or convergent boundaryThis is an area where two platesmove toward each other. As the plates collide, the leading edges of one plate is bent downward allowing it to slide beneath the other. As all cases, the denser materials plunge beneath the surface.
- 92. The colliding boundary is the site where the old crust isbeing destroyed (subduction zone).The Himalayan Mountain Ranges, Andes Mountain,and the Marianas Trench are believed to be formed bythis type of plate movement.
- 93. Andes Mountain
- 94. 3. Fracture or transform boundaryThis is the area where two plates move past eachother, sliding, scraping and deforming the edges ofcontinents.
- 95. The San Andreas Fault of California is a famous example. The Pacific plate is moving towards northeast past the North American plate. Los Angeles is located on a plate situated on one side of the fault. San Francisco is located on another plate. In about 10 t0 15 million years, Los Angeles and San Francisco will be located next to each other.
What Is Lithosphere
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Every rocky planet has a lithosphere, but what is lithosphere? It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.
Oceanic lithosphere consists mainly of mafic(rich in magnesium and iron) crust and ultramafic(over 90% mafic) mantle and is denser than continental lithosphere. It thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle. It was less dense than the asthenosphere for tens of millions of years, but after this becomes increasingly denser. The gravitational instability of mature oceanic lithosphere has the effect that when tectonic plates come together, oceanic lithosphere invariably sinks underneath the overriding lithosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, so oceanic lithosphere is much younger than its continental counterpart. The oldest oceanic lithosphere is about 170 million years old compared to parts of the continental lithosphere which are billions of years old.
The continental lithosphere is also called the continental crust. It is the layer of igneous, sedimentary rock that forms the continents and the continental shelves. This layer consists mostly of granitic rock. Continental crust is also less dense than oceanic crust although it is considerably thicker(25 to 70 km versus 7-10 km). About 40% of the Earth’s surface is now covered by continental crust, but continental crust makes up about 70% of the volume of Earth’s crust. Most scientists believe that there was no continental crust originally on the Earth, but the continental crust ultimately derived from the fractional differentiation of oceanic crust over the eons. This process was primarily a result of volcanism and subduction.
We may not walk directly the lithosphere, but it shapes every topographical feature the we see. The movement of the tectonic plates has presented many different shapes for our planet over the eons and will continue to change our geography until our planet ceases to exist.
intermediate rock Igneous rock whose chemical composition lies between those of basic and acidic rocks, e.g. andesite. The limits are not fixed rigidly and a number of schemes exist that are based on modal mineralogy and the whole rock chemistry (see MODAL ANALYSIS). Compare ACID ROCK; and BASIC ROCK. See also ALKALINE ROCK.
Igneous Rocks
Igneous rocks are
formed by the cooling and hardening of molten magma. The word igneous comes
from the Latin word igneus, meaning
fire, and there are two main types of igneous rocks: intrusive and extrusive.
Intrusive igneous rock forms
within Earth’s crust; the molten
material rises, filling voids or melting overlying rocks, and eventually
hardens. Intrusive rocks are also called plutonic rocks, named after the Greek
god Pluto, god of the underworld. Extrusive igneous rocks form when the magma,
called lava once it reaches the surface, flows onto Earth’s surface. Extrusive rocks
are also known as volcanic rocks.
Igneous rocks are
classified according to their texture and mineral or chemical content. The
texture of the rock is determined by the rate of cooling. The slower the rock
cools, the larger the crystals form. Because the magma chamber is well
insulated by the surrounding country rock, intrusive rocks cool very slowly and
can form large, well developed crystals. Rapid cooling results in smaller,
often microscopic, grains. Some extrusive rocks produced in explosive volcanic
eruptions solidify in the air before they hit the ground. Sometimes the rock
mass starts to cool slowly, forming large crystals, and then finishes cooling
rapidly, resulting in rocks that have larger crystals surrounded by a
fine-grained matrix. This is known as a porphyritic texture. Other extrusive rocks
cool before the chemical constituents of the melt are able to arrange
themselves into any crystalline form. These are said to have glassy texture and
include the rocks obsidian and pumice.
The
chemistry of the magma determines the minerals that will crystallize and their
relative abundance in the rocks that form. Light-colored igneous rocks are
likely to contain high proportions of light colored minerals, such as quartz
and feldspars and are called felsic. Dark rocks will contain iron and magnesium-rich
minerals like pyroxene and olivine and are known as mafic rocks. Those rocks
with a color falling between the two are said to have an intermediate
composition. The sequence of crystallization as temperatures decrease is
represented by Bowen’s reaction series.
Once the composition and
texture of the rock are determined, they are combined to establish the name of
the rock. For example, a coarse-grained, felsic rock is called granite and a
fine-grained felsic rock is called rhyo-lite. These two rocks are composed of
the same minerals, but the slow cooling history of the granite has allowed its
crystals to grow larger. These are some of the most familiar igneous rocks
because continental portions of the crust are built largely of rock that is
similar in composition to these felsic rocks. Coarse-grained and fine-grained
mafic rocks are called gabbro and basalt, respectively. Each of these is easily
recognized by their dark color. In general, oceanic crustal plates are
primarily mafic in chemistry. Diorite and andesite are the respective names for
coarse-and fine-grained rocks of intermediate composition. While geologists
sometimes use more detailed classification systems, this basic method is used
for preliminary differentiation of crystalline igneous rocks.
Certain igneous rocks are
named on the basis of particular features. Fragmental rocks like tuff and
volcanic breccia are named on the basis of the size of particles of volcanic
material ejected during an eruption. Tuff is composed of fine particles of volcanic
ash, whereas breccia includes larger pieces of broken rock. Obsidian, pumice,
and scoria have a non-crystalline, glassy texture that can be distinguished on
the basis of the quantity of trapped gas. Obsidian contains no such gas, but
pumice has so many gas bubbles that it will float on water. Scoria is produced
by the cooling of frothy mafic lava.
Earth’s tectonic plates are
continually shifting and altered by earthquakes and volcanoes. As old plates
are drawn downward into the mantle, rock is recycled through melting. New
igneous material is continually added to the crust along plate margins and
other locations through igneous intrusions and volcanic activity. Igneous rocks
represent both the ancient history of the formation of the earth and
modern episodes of regeneration. Associated igneous processes are evidence of
the continuing activity of Earth’s interior and the form
and composition of each of the igneous rocks give clues as to the conditions
and processes under which they formed.
Igneous rocks are formed by the cooling and
hardening of molten material called magma.
The word igneous comes from the Latin word igneus,
meaning fire. There are two types of igneous rocks: intrusive and extrusive.
Intrusive igneous rock forms within Earth's crust; the molten material rises,
filling voids in the crust, and eventually hardens. Intrusive rocks are also
called plutonic rocks, named after the Greek god Pluto ,
god of the underworld. Extrusive igneous rocks form when the magma, called lava
once it reaches the surface, pours out onto the earth's surface. Extrusive
rocks are also known as volcanic rocks.
Igneous rocks are
classified according to their texture and mineral or chemical content. The
texture of the rock is determined by the rate of
cooling. The slower the rock cools, the larger the crystals form. Because the
magma chamber is well insulated by the surrounding country rock, intrusive
rocks cool very slowly and can form large, well developed crystals. Rapid
cooling results in smaller, often microscopic, grains. Some extrusive rocks
solidify in the air, before they hit the ground. Sometimes the rock mass starts
to cool slowly, forming large crystals, and then finishes cooling rapidly,
resulting in rocks that have larger crystals surrounded by a fine-grained matrix . This is known as a porphyritic
texture. Other extrusive rocks cool before the chemical constituents of the
melt are able to arrange themselves into any crystalline form. These are said
to have glassy texture and include the rocks obsidian and pumice.
The chemistry of the magma determines the minerals that
will crystallize and their relative abundance in the rocks that form.
Light-colored igneous rocks are likely to contain high proportions of light
colored minerals, such as quartz and feldspars and are called felsic. Dark
rocks will contain iron and
magnesium-rich minerals like pyroxene and olivine and are known as mafic rocks.
Those rocks with a color falling
between the two are said to have an intermediate composition.
Once the basic composition and
texture of the rock are determined, they are combined to establish the name of
the rock. For example, a coarse-grained, felsic rock is called granite and a
fine-grained felsic rock is called rhyolite. These two rocks are composed of
the same minerals, but the slow cooling history of the granite has allowed its
crystals to grow larger. These are some of the most familiar igneous rocks
because continental portions of the crust are built largely of rock that is
similar in composition to these felsic rocks. Coarse-grained and fine-grained
mafic rocks are called gabbro and basalt, respectively. Each of these is easily
recognized by their dark color. In general, oceanic crustal plates are
primarily mafic in chemistry. Diorite and andesite are the respective names for
coarse- and fine-grained rocks of intermediate composition. While geologists
sometimes use more detailed classification systems, this basic method is used
for preliminary differentiation of crystalline igneous rocks.
Certain igneous rocks are
named on the basis of particular features. Fragmental rocks like tuff and
volcanic
breccia are named on the basis of the size of particles of volcanic material ejected during an eruption. Tuff is composed of fine particles of volcanic ash, while breccia includes larger pieces. Obsidian, pumice, and often scoria have a non-crystalline, glassy texture that can be distinguished on the basis of the quantity of trapped gas. Obsidian contains no such gas and pumice has so many gas bubbles that it will sometimes actually float on water .
breccia are named on the basis of the size of particles of volcanic material ejected during an eruption. Tuff is composed of fine particles of volcanic ash, while breccia includes larger pieces. Obsidian, pumice, and often scoria have a non-crystalline, glassy texture that can be distinguished on the basis of the quantity of trapped gas. Obsidian contains no such gas and pumice has so many gas bubbles that it will sometimes actually float on water .
Earth's crustal plates are
continually shifting, being torn open by faults, and altered by earthquakes and
volcanoes. As old plates are drawn downward into the mantle, old rock material
is recycled through melting. New igneous material is continually added to the
crust along plate margins and other locations through igneous intrusions and
volcanic activity. Igneous rocks represent both the ancient history of the
formation of the earth and
modern episodes of regeneration. Associated igneous processes are evidence of
the continuing activity of Earth's
interior and the form and composition of each of the igneous rocks
give clues as to the conditions and processes under which they formed.
The first
rocks on Earth were
igneous rocks. Igneous rocks are
formed by the cooling and hardening of molten material called magma . The word igneous comes from the
Latin word ignis, meaning fire.
There are two types of igneous rocks: intrusive and extrusive. Intrusive
igneous rocks form within Earth's crust ;
the molten material rises, filling any available crevices, into the crust, and
eventually hardens. These rocks are not visible until the earth above
them has eroded away. Intrusive rocks are also called plutonic rocks, named
after the Greek god Pluto, god of the underworld. A good example of intrusive
igneous rock is granite . Extrusive igneous rocks form
when the magma or molten rock pours out onto the earth's surface or erupts at
the earth's surface from a volcano .
Extrusive rocks are also called volcanic rocks. Basalt ,
formed from hardened lava , is
the most common extrusive rock. Obsidian ,
a black glassy rock, is also an extrusive rock.
Igneous rocks are classified
according to their texture and mineral or chemical content. The texture of the
rock is determined by the rate of cooling. The slower the cooling, the larger
the crystal. Intrusive rock can take one million years or more to cool. Fast
cooling results in smaller, often microscopic, grains. Some extrusive rocks
solidify in the air, before they hit the ground. Sometimes the rock mass starts
to cool slowly, forming larger crystals ,
and then finishes cooling rapidly, resulting in rocks that have crystals
surrounded by a fine, grainy rock mass. This is known as a porphyritic texture.
Most of Earth's minerals are
made up of a combination of up to ten elements. Over 99% of Earth's crust
consists of only eight elements (oxygen , silicon , aluminum , iron , calcium, sodium, potassium, and
magnesium). Most igneous rocks contain two or more minerals, which is why some
rocks have more than one color. For example, the most common minerals in
granite are quartz (white or
gray), feldspar (white or pinks
of varying shades), and mica (black). The amount of a specific element in a
mineral can determine a color or intensity of color. Because of the way granite
is formed, the different composition of minerals is easy to see. It is difficult
to see the distinct composition of some extrusive rocks, like obsidian, due to
their extremely fine texture. Igneous rocks contain mostly silicate minerals
and are sometimes classified according to their silica content. Silica (SiO2) is
a white or colorless mineral compound. Rocks containing a high amount of
silica, usually more than 50%, are considered acidic (sometimes the term felsic is used), and those with a low
amount of silica are considered basic (or mafic ).
Acidic rocks are light in color and basic rocks are dark in color.
Essentially, Earth's
continents are slabs of granite sitting on top of molten rock. The crustal
plates of Earth are continually shifting, being torn open by faults, and
altered by earthquakes and volcanoes. New igneous material is continually added
to the crust, while old crust falls back into the earth, sometimes deep enough
to be remelted. Igneous rocks are the source of many important minerals, metals , and building materials.
spilite A low-grade metamorphic rock composed of albite, chlorite, actinolite, sphene, and calcite, with or without epidote, prehnite, and laumonite, and formed by sea-floor metasomatism of mid-oceanic-ridge basalts. Sea water circulating through the oceanic crust is heated by the cooling basalt dykes and lavas and reacts with them, introducing sodium and water into
the rock system and converting the basalt mineral assemblage into a typical spilite assemblage.
Basic Rock
basic rock Rock with a
relatively high concentration of iron, magnesium, and calcium, and with 45–53%
of silica by weight. Examples include gabbro, which is a coarse-grained basic intrusive rock, and basalt, which is a fine-grained basic volcanic (extrusive) rock. Compare ACID ROCK; and INTERMEDIATE ROCK. See also ALKALINE ROCK.
basic rock Rock that has
a relatively high concentration of iron, magnesium, and calcium, and with 45–53
per cent of silica by weight. Examples include gabbro, which is a
coarse-grained basic intrusive rock, and basalt, which is a fine-grained basic
volcanic (extrusive) rock. See also alkaline rock. Compare acid rock and intermediate rock.
Intermediate Rock
intermediate rock Igneous rock whose chemical composition lies between those of basicand acidic rocks, e.g. andesite. The limits are not fixed rigidly and a number of schemes
exist that are based on modal mineralogy and the whole rock chemistry (see MODAL ANALYSIS). Compare ACID ROCK; and BASIC ROCK. See also ALKALINE ROCK.
Rock
To the geologist, the
term rock means a naturally occurring aggregate of minerals that
may include some organic solids (e.g., fossils ) and/or glass .
Rocks are generally subdivided into three large classes: igneous, sedimentary,
and metamorphic. These classes relate to common origin, or genesis. Igneous rocks form from cooling
liquid rock or related volcanic eruptive processes. Sedimentary rocks form
from compaction and cementation of sediments. Metamorphic rocks develop due to
solid-state, chemical and physical changes in pre-existing rock because of
elevated temperature , pressure, or chemically active fluids.
With igneous rocks, the aggregate of minerals
comprising these rocks forms upon cooling and crystallization of liquid rock.
As crystals form in the liquid rock, they become
interconnected to one another like jigsaw puzzle pieces. After total
crystallization of the liquid, a hard, dense igneous rock is the result. Also,
some volcanic lavas, when extruded on the surface and cooled instantaneously,
will form a natural glass. Glass is a mass of disordered atoms, which are
frozen in place due to sudden cooling, and is not a crystalline material like a
mineral. Glass composes part of many extrusive igneous rocks (e.g., lavaflows)
and pyroclastic igneous rocks. Alternatively, some igneous rocks are formed
from volcanic processes, such as violent volcanic eruption. Violent eruptions
eject molten, partially molten, and non-molten igneous rock, which then falls
in the vicinity of the eruption. The fallen material may solidify into a hard
mass, called pyroclastic igneous rock. The texture of igneous rocks (defined as
the size of crystals in the rock) is strongly related to cooling rate of the
original liquid. Rapid cooling of liquid rock promotes formation of small
crystals, usually too small to see with the unaided eye. Rocks with this
cooling history are called fine-textured igneous rocks. Slow cooling (which
usually occurs deep underground) promotes formation of large crystals. Rocks
with this cooling history are referred to as coarse-textured igneous rocks.
The mineral composition of igneous rocks falls
roughly into four groups: silicic , intermediate, mafic ,
and ultramafic. These groups are distinguished by the amount of silica (SiO4), iron (Fe), and magnesium (Mg) in the
constituent minerals. Mineral composition of liquid rock is related to place of
origin within the body of the earth. Generally speaking, liquids from
greater depths within the earth contain more Fe and Mg and less SiO4 than those from shallow depths.
In sedimentary rocks, the type of sediment
that is compacted and cemented together determines the rock's main
characteristics. Sedimentary rocks composed of sediment that has been broken
into pieces (i.e., clastic sediment), such as gravel, sand ,
silt, and clay , are clastic sedimentary rocks (e.g.,
conglomerate, sandstone , siltstone, and shale, respectively).
Sedimentary rocks composed of sediment that is chemically derived (i.e.,
chemical sediment), such as dissolved elements like calcium (Ca), sodium (Na),
iron (Fe), and silicon (Si), are chemical sedimentary rocks.
Examples of chemical sedimentary rocks are limestone (composed
of calcium carbonate), rock salt (composed
of sodium chloride), rock gypsum (composed
of calcium sulfate), ironstones (composed of iron oxides), and chert (composed
of hydrated silica). Biochemical sedimentary rocks are a special kind of
chemical sedimentary rock wherein the constituent
particles were formed by organisms (typically as organic hard parts, such as
shells), which then became sedimentary particles. Examples of this special kind
of sedimentary rock include chalk,
fossiliferous limestone, and coquina. Sedimentary rocks are formed from
sediment in two stages: compaction and cementation. Compaction occurs when
sediments pile up to sufficient thickness that overlying mass squeezes
out water and closes much open space .
Cementation occurs when water flowing through the
compacted sediment deposits mineral crystals
upon particles thus binding them together. The main cement minerals are calcite
(CaCO3), hematite (Fe2O3), and quartz (SiO2).
With metamorphic rocks, the nature of the
pre-existing rock (protolith) determines in large part the characteristics of
the ultimate metamorphic rock . Regardless of protolith,
however, almost all metamorphic rocks are harder and more
dense than their protoliths. A protolith with flat or elongate mineral crystals
(e.g., micas or amphiboles) will yield a metamorphic rock with preferentially
aligned minerals (due to directed pressure). Such metamorphic rocks are called
foliated metamorphic rocks (e.g., slate and schist ).
Non-foliated metamorphic rocks (e.g., marble and quartzite)
come from protoliths that have mainly equidimensional mineral crystals (e.g.,
calcite and quartz, respectively). For example, a protolith shale will yield a
foliated metamorphic rock, and a protolith limestone will yield marble, a
non-foliated metamorphic rock. Metamorphic rocks possess distinctive grades or
levels of metamorphic change from minimal to a maximum near total melting .
Low-grade metamorphic rocks generally have fine-textured crystals and
low-temperature indicator minerals like the mica chlorite. High-grade
metamorphic rocks generally have coarse-textured crystals and very distinctive
foliation, plus high-temperature indicator minerals like the silicate mineral staurolite.
Rock is a brittle natural solid found mainly
in the outer reaches of Earth's crust and upper
mantle. Material that would be brittle rock at such shallow depths becomes to
one degree or another rather plastic within the body of the earth. The term
"rock" is not generally applied to such non-brittle internal Earth
materials. Therefore, rock is a concept related to the outer shell of the
earth. The term rock may also be properly applied to brittle natural solids
found on the surfaces of other planets and satellites in our solar system . Meteorites are rock.
Naturally occurring ice (e.g., brittle water ice in a glacier,
H2O) is also a rock, although we do not normally
think of ice this way.
Rock has been an important natural resource
for people from early in human evolution . Rocks' properties
are the key to their specific usefulness, now as in the past. Hard, dense rocks
that could be chipped into implements and weapons were among the first useful
possessions of people. Fine-textured and glassy rocks were particularly handy
for these applications. Later on, rock as building stone and pavement material
became very important, and this continues today in our modern world. All of
Earth's natural mineral wealth, fossil energy resources, and most groundwater are
contained within rocks of the earth's crust.
See also Lithification; Metamorphism
World of Earth Science
Rock
Views 3,639,256Updated Dec
01 2019
rock A consolidated or unconsolidated aggregate of minerals or organic matter. The minerals may be all of one
type, in which case the rock is ‘monomineralic’, or of many types, in which
case it is ‘polymineralic’. The aggregate of minerals can form by: (a)
accretion or precipitation of grains during Earth surface processes, to give sedimentary rocks; (b) crystallization
of magma to give igneous rocks; and (c)
solid-state recrystallization in response to changes
in external conditions (e.g. pressure and temperature) to give metamorphic rocks. The grain relationships (textures) of these three rock types contrast.
Sedimentary rocks are characterized by one of the following: (i) rounded or
angular grains held together by an intergrain precipitate or a fine intergrain
mud; (ii) fine aggregates of clay minerals displaying a preferred
orientation of their long axes; (iii) a crystalline aggregate of minerals
(e.g. calcite) displaying straight edges and triple
junctions between the grains; (iv) an aggregate of fossil fragments held together by an
interfragment precipitate of calcite or a fine interfragment mud; or
(v) an aggregate of organic material (e.g. lignite or coal). All igneous rocks are characterized by
an aggregate of minerals displaying an interlocking texture. Metamorphic rocks
are characterized by one of the following: (i) a crystalline aggregate of
minerals which display a preferred orientation of their long axes; (ii) a
crystalline aggregate of equidimensional and randomly oriented
non-equidimensional minerals; or (iii) an extremely fine-grained aggregate of
sutured, anhedral, or sometimes elongate minerals.
A Dictionary of Earth Sciences AILSA
ALLABY and MICHAEL ALLABY
Rock
Views 2,215,715Updated Dec
04 2019
rock1 in figurative usage, rock may be taken as
the type of something providing a sure foundation and support, as in the words
of Jesus Christ to Peter in Matthew 16:18, ‘Thou art Peter, and upon this rock
I will build my church.’ In the parable in Matthew 7 of the two houses, it is
the house built on sand which falls, and the house built on rock which stands.
A rock in biblical contexts may also be a source of sustenance (with allusion to Numbers 20:11, in which water issued from the rock struck by the staff of Moses), and a shelter, as in Isaiah 32:2, ‘the shadow of a great rock in a weary land’.
A rock (especially with the notion of one on which a ship may be wrecked) can also be taken as a sign of danger, as in rocks ahead.
between a rock and a hard place in a situation where one is faced with two equally difficult alternatives.
on the rocks (of a relationship or enterprise) experiencing difficulties and likely to fail.
Rock of Ages symbolizing the foundation of Christian belief; the phrase is now probably best-known from the hymn ‘Rock of Ages, cleft for me’ (1773), by the English clergyman Augustus Toplady (1740–78).
A rock in biblical contexts may also be a source of sustenance (with allusion to Numbers 20:11, in which water issued from the rock struck by the staff of Moses), and a shelter, as in Isaiah 32:2, ‘the shadow of a great rock in a weary land’.
A rock (especially with the notion of one on which a ship may be wrecked) can also be taken as a sign of danger, as in rocks ahead.
between a rock and a hard place in a situation where one is faced with two equally difficult alternatives.
on the rocks (of a relationship or enterprise) experiencing difficulties and likely to fail.
Rock of Ages symbolizing the foundation of Christian belief; the phrase is now probably best-known from the hymn ‘Rock of Ages, cleft for me’ (1773), by the English clergyman Augustus Toplady (1740–78).
rock (rock and roll) Form of
popular music characterized by amplified guitars and singing, often with
repetitive lyrics and driving rhythms. Rock music appealed largely to a white
audience who found its forerunner, rhythm and blues, inaccessible. It developed out of the blues and folk music of rural USA to become a major form of cultural
expression in the 1960s. Rock and roll was popularized by Bill Haley and the
film Rock Around the Clock (1956). Its modern offshoots include heavy metal,
grunge, and punk.
Acid Rock
acid rock Igneous rock containing more than about 60% Silica (SiO2) by weight, most
of the silica being in the form of silicate minerals, but with the excess of
about 10% as free quartz. Typical acid rocks are granites, granodiorites, and rhyolites. Compare BASIC ROCK; and INTERMEDIATE ROCK. See also ALKALINE ROCK.
acid rock Igneous rock that contains more than about 60 per cent silica
(SiO2) by weight, most of the silica being in the form of silicate
minerals, but with the excess of about 10 per cent as free quartz. Typical acid
rocks are granites, granodiorites, and rhyolites. See also alkaline rock; compare basic rock and intermediate rock.
intermediate rock Igneous rock whose chemical composition lies between those of basic and acidic rocks, e.g. andesite. The limits are not fixed rigidly and a number of schemes exist that are based on modal mineralogy and the whole rock chemistry (see MODAL ANALYSIS). Compare ACID ROCK; and BASIC ROCK. See also ALKALINE ROCK.
Lithosphere
The tectonic plates of the lithosphere on Earth
Earth cutaway from center to surface, the lithosphere comprising the crust and lithospheric mantle (detail not to scale)
A lithosphere (Ancient Greek: λίθος [lithos] for "rocky", and σφαίρα [sphaira] for "sphere") is the rigid,[1] outermost shell of a terrestrial-type planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.
The layer under the lithosphere is known as the asthenosphere.
Contents
Earth's lithosphere
Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere, and biosphere through the soil forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle. The Lithosphere-Asthenosphere boundary 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.
History of the concept
The concept of the lithosphere as Earth's strong outer layer was described by A.E.H. Love in his 1911 monograph "Some problems of Geodynamics" and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term "lithosphere".[2][3][4][5] 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 Reginald Aldworth Daly in 1940 with his seminal work "Strength and Structure of the Earth."[6] 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.
Types
Different types of lithosphere
There are two types of lithosphere:
- Oceanic lithosphere, which is associated with oceanic crust and exists in the ocean basins (mean density of about 2.9 grams per cubic centimeter)
- Continental lithosphere, which is associated with continental crust (mean density of about 2.7 grams per cubic centimeter)
The thickness of the lithosphere is considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior.[7] The temperature at which olivine begins to deform viscously (~1000 °C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. Oceanic lithosphere is typically about 50–140 km thick [8](but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 280 km;[8] the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.
Oceanic lithosphere
Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convection[9] 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.
Here, 
is the thickness of the oceanic mantle lithosphere, 
is the thermal diffusivity (approximately 10−6 m2/s) for silicate rocks, and 
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 is velocity of the lithospheric plate.
is the thickness of the oceanic mantle lithosphere, is the thermal diffusivity (approximately 10−6 m2/s) for silicate rocks, and 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 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. This is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has 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 the continental lithosphere are billions of years old. 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.[10][11]
Subducted lithosphere
Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary,[12] while others "float" in the upper mantle,[13][14] while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above,[11] similar to the extent of the "tectosphere" proposed by Jordan in 1988.[15]
Mantle xenoliths
Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths[16] 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 the mantle flow that accompanies plate tectonics.[1
