The first sections present an evaluation of Archean SCLM composition, emphasizing its originally highly depleted composition and its modification by later metasomatism. The continental crust consists of various layers, with a bulk composition that is intermediate (SiO2 wt% = 60.6[1]). The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick and is composed primarily of basalt, diabase, and gabbro. Various studies lead to a small range of 0.74–0.86 μW m−3 for the average rate of crustal heat production (O'Nions et al., 1979; Allègre et al., 1983, 1988; Galer et al., 1989). Owing to their low densities, liquids rise upward to form basaltic crust, which makes up most of the seafloor on Earth and the crusts of other rocky planets. Many theories of crustal growth are controversial, including rates of crustal growth and recycling, whether the lower crust is recycled differently from the upper crust, and over how much of Earth history plate tectonics has operated and so could be the dominant mode of continental crust formation and destruction. The continental crust is made mostly of rocks with a composition similar to granite (a light-colored rock you would expect to find in the Sierra Nevada), whereas the oceanic crust is made mostly of rocks with a composition of basalt (a dark- colored rock, like the rocks that make up the Hawaiian volcanoes). Continental crust is the surface that forms land masses, and oceanic crust is the surface found under the ocean floor. (b) Peeling or delamination of densified (e.g., pyroxenitic) mafic lower crustal layer initiated at an intracrustal weak zone. The crust is thickened by the compressive forces related to subduction or continental collision. It is made up of granite rock which is light in color. The crust comprises two layers, but the boundary between them is poorly defined. Red arrows represent asthenospheric mantle flow. The height of mountain ranges is usually related to the thickness of crust. Whereas some regions display clear secondary phases, in other regions, the seismic velocity may increase gradually with depth, producing no distinct intracrustal reflections (Levander and Holliger, 1992). Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character. The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. Walter D. Mooney, in Encyclopedia of Physical Science and Technology (Third Edition), 2003. [13] When continents collide, the crust can thicken to almost 100 km, but that is temporary because it soon spreads out again. Jean-Baptiste Jacob, Jean-François Moyen, in Encyclopedia of Geology (Second Edition), 2021. Different models suggested early creation and subsequent recycling of continental crust material or continuous or episodic crustal growth (the “Anderson-Moorbath debate”). Moho corresponds to a seismic discontinuity, reflecting (a) plagioclase to garnet + pyroxene phase change or (b) a transition from intermediate/mafic compositions to ultramafic (peridotite). A distinction, however, must be made between foundering from other convective processes, such as subduction of oceanic lithosphere. Mooney, in Treatise on Geophysics (Second Edition), 2015. The theory of continental drift was proposed at the beginning of the last century by German scientist Alfred Wegener. The edges of continental fragments formed this way (both sides of the Atlantic Ocean, for example) are termed passive margins. Its existence also provides broad expanses of shallow water known as epeiric seas and continental shelves where complex metazoan life could become established during early Paleozoic time, in what is now called the Cambrian explosion.[6]. The crust and mantle layers are mostly rocks and minerals while the center is a hot metal core. Subduction is related to plate tectonics and is a manifestation of large-scale mantle convection, wherein the dominant length scale of advective heat and mass transfer is the entire mantle. The continental crust is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. Lee, in Treatise on Geochemistry (Second Edition), 2014. Unlike oceanic crust that has young geological rock, continents can have rocks up to 4 billion years old. It appears that throughout the past ~ 2.7 Ga major segments of continental crust over the globe were evolved through similar evolution and petrogenetic histories: early formation of thick sequences of basalts in oceanic environment that resemble those of plume-related oceanic plateaus (e.g. Earth & Environmental Science introduction to oceanic and continental crust. The growth of continents may also have implications for long-term sea-level fluctuations, the evolution of life, and long-term climate change through influences on Earth's albedo (Rosing et al., 2006, 2010). Changes in seismic wave velocities have shown that at a certain depth (the Conr… [10] Geologists suggest that the age of the oceanic crust is around 100 million years, which is still younger than the age of the continental crust. In fact, about 40% of the surface of the earth is made up of this layer. The continental crust is made up of a variety of rocks from sedimentary rocks such as sandstone and limestone to metamorphic rocks such as marble and slate, and igneous rocks like granite. The locations of the presently available seismic refraction/wide-angle reflection profiles on continental crust are shown in Figure 11 and amount to several thousand profiles. The Earth’s crust is broken up into a series of massive sections called plates. The latter process probably involves some form of delamination or gravitational instability at the base of the crust (Kay and Mahlburg Kay, 1991; Jull and Kelemen, 2001). Continental crust definition: that part of the earth's crust that underlies the continents and continental shelves | Meaning, pronunciation, translations and examples These early studies provided the first clear evidence that the seismic structure of the crust varied in a systematic way with geologic setting. This differentiation is imparted by the solid–liquid segregation on a planet with sufficient gravity. Oceanic crust is found under oceans, and it is about four miles thick in most places. The existence of crustal layers, which have a heterogeneous fine structure, can be viewed as the product of igneous differentiation of the crust, whereby silicic melts rise into the upper crust and middle crust, leaving behind a mafic lower crust. continental crust That portion of the Earth's surface overlying the Mohorovičić discontinuity, and with an average density of 2700–3000 mg/m 3.The thickness is variable, mostly 30–40 km, except for areas of recent mountain building where the thickness can be 70 km. Subsequent sections evaluate models for the generation of the Archean SCLM and discuss their implications for early tectonics and the links between SCLM formation and crustal evolution. Gray is continental crust, colored is oceanic crust. W.D. 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