Lithosphere and useable mineral resources
The lithosphere, often referred to as the "stone sphere," comprises the Earth's outer, brittle layers, including the upper mantle and the crust. This rigid layer extends to depths of 70 to 100 kilometers and is crucial for understanding geological processes such as plate tectonics, which describes the movement of several major lithospheric plates floating on the underlying, partially molten asthenosphere. The lithosphere is divided into two main types of crust: oceanic and continental. Oceanic crust is generally thinner and denser, composed mainly of basaltic rock, while continental crust is thicker and primarily consists of less dense granitic rock along with sedimentary and metamorphic materials.
The boundary between the lithosphere's crust and upper mantle is marked by the Mohorovičić Discontinuity, or Moho, which indicates a compositional change in the rocks. Within the lithosphere, various mineral resources exist, particularly in the continental crust, which is rich in economically valuable minerals. The study of the lithosphere's characteristics, including sedimentary layers in certain regions, aids in the discovery of resources like petroleum and natural gas. As geological research continues, it is expected that our understanding of the lithosphere will lead to more effective exploration for valuable mineral resources, highlighting the importance of this foundational layer of the Earth in resource management and environmental sustainability.
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Lithosphere and useable mineral resources
The usable mineral resources of the Earth are all within the lithosphere, and knowledge of its properties is particularly important in the search for gas and oil.
Definition
The lithosphere (“stone sphere,” from Greek lithos) consists of the outer, brittle portions of the Earth, including the upper mantle and crust.
Overview
The interior of the Earth has a number of layers, or concentric spheres. At the center of the Earth is the inner core. Then, moving outward, come the outer core, the lower mantle, the upper mantle, and the Earth’s crust. Scientists subdivide the upper mantle into the asthenosphere, a partially molten zone, and, above that, the lithosphere. The lithosphere, then, is the rigid (or brittle) outer shell of the Earth, which extends to a depth of between 70 and 100 kilometers and rests on the asthenoshere. It includes the Earth’s crust and part of the upper mantle.
The upper mantle is approximately 700 kilometers thick. The asthenosphere begins at a depth of approximately 70 to 100 kilometers and shows a rapid increase in density and a temperature in excess of 1,000° Celsius. The asthenosphere is partially molten ultramafic material. Because of its partially molten properties, the asthenosphere probably exhibits plastic flow. Above the asthenoshere, the upper brittle portion of the upper mantle that is part of the lithosphere is a dense ultramafic material that directly underlies the Earth’s crust. The lithosphere comprises seven to ten major lithospheric “plates” that move slowly as they rest on the asthenosphere. plate tectonics refers to the movement of these plates and the land and ocean forms that are created as a result.
Within the lithosphere, the boundary between the upper mantle and the crust is called the Mohorovičić discontinuity, or Moho, which marks a compositional change in the rock. The earth’s crust contains two basic types of crustal material, oceanic and continental, with an average density of 2.9 and 2.6, respectively. Oceanic crust ranges from 5 to 10 kilometers thick and is thinnest over seafloor-spreading areas. Oceanic crust is primarily composed of dense basaltic rock with a thin veneer of silt and carbonate precipitates; however, a variety of minerals have been observed at seafloor vents. Continental crust is primarily composed of felsic granitic rock, which is less dense than oceanic crust; however, continental crust also includes sedimentary and metamorphic rock and even uplifted oceanic basalt. A variety of minerals of varying economic importance occur in the continental crust. The continental crust averages 30 to 40 kilometers in thickness, but it may be more than 70 kilometers thick in some mountain areas.
Oceanic crust is less dense than the parent mantle material. This is probably attributable to partial melting and crystal fractionation. Felsic minerals have a lower melting temperature than mafic minerals, and mafic minerals are the first to crystallize out of a melt. As oceanic crust subducts below continental crust, the subducting plate eventually melts, and its upwelling liquid fraction produces less mafic intermediates.
The lithosphere is highly variable, according to regional studies. In parts of the middle United States and in the Gulf of Mexico region, for example, the crust has thick sedimentary layers. Oil companies were able to measure the seismic wave patterns generated by many controlled explosions and discover petroleum and natural gas within these layers. The later discovery of oil in northern Alaska was prompted by the similarity of the crust there to the crust of these regions. As the study of the characteristics of the lithosphere—including plate tectonics—continues, scientists will increasingly be able to use their knowledge to discover sites of mineral resources.