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      • When plates smash into each other at higher speeds, more of the crust at the collision sites becomes brittle, and that makes the region more prone to large quakes.
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  1. The crust is the outermost layer of Earth above the mantle. As discussed earlier, crust can be divided into two types: continental crust and oceanic crust. The continental crust ranges from 25 to 70 km thick and makes up a total of approximately 70 percent of Earth’s total crust volume, though it only covers about 40 percent of the planet’s ...

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  3. As we discussed in Chapter 10, oceanic crust is formed at sea-floor spreading ridges from magma generated by decompression melting of hot upward-moving mantle rock (Figure 10.18). About 10% of the mantle rock melts under these conditions, producing mafic magma.

    • Steven Earle
    • 2015
    • 2.1 Alfred Wegener’s Continental Drift Hypothesis. Alfred Wegener (1880-1930) was a German scientist who specialized in meteorology and climatology. His knack for questioning accepted ideas started in 1910 when he disagreed with the explanation that the Bering Land Bridge was formed by isostasy, and that similar land bridges once connected the continents.
    • 2.2 Layers of the Earth. In order to understand the details of plate tectonics, it is essential to first understand the layers of the earth. Firsthand information about what is below the surface is very limited; most of what we know is pieced together from hypothetical models, and analyzing seismic wave data and meteorite materials.
    • 2.3 Convergent Boundaries. Convergent boundaries, also called destructive boundaries, are places where two or more plates move toward each other. . Convergent boundary movement is divided into two types, subduction, and collision, depending on the density of the involved plates.
    • 2.4 Divergent Boundaries. At divergent boundaries, sometimes called constructive boundaries, lithospheric plates move away from each other. There are two types of divergent boundaries, categorized by where they occur: continental rift zones and mid-ocean ridges.
  4. Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust , composed of troctolite , gabbro and ultramafic cumulates .

  5. Apr 24, 2024 · The main features of the Pacific Ocean floor are the continental slopes, which drop from about 200 meters to several thousand meters over a distance of a few hundred kilometers, the abyssal plains—exceedingly flat and from 4,000 meters to 6,000 meters deep, volcanic seamounts and islands, and trenches at subduction zones that are up to 11,000 ...

  6. Jul 31, 2024 · Seafloor-spreading rates are much more rapid in the Pacific Ocean than in the Atlantic and Indian oceans. At spreading rates of about 15 cm (6 inches) per year, the entire crust beneath the Pacific Ocean (about 15,000 km [9,300 miles] wide) could be produced in 100 million years.