Tectonics and the origin of magma the earth works: examining plate tectonics st is: 8 what causes the tectonic plates to move? a. ocean currents b. volcanoes c. the coriolis effect d. convection in the mantle earthquakes 9.the mid-ocean ridge occurs along a: a. convergent boundary where new crust is formed b. transform boundary where crust is subducted c. divergent boundary where sea-floor spreading takes place d. divergent boundary where subduction takes place opposite 10. when two continental plates pull apart a forms. a. subduction zone b. mountain range c. earthquake d. rift valley than 11. oceanic crust is continental crust. alled a a. less dense b. more dense than 12. continental crust is oceanic crust. rt is called a: a. thicker b. thinner 13. a place where an unusually hot part of the mantle rises through the crust causing volcanic activity is called a a. divergent boundary b hot spot c convergent boundany d. transform boundary m boundary 14. the fact that ice floats on top of water is like the fact that a. the mantle causes earthquakes and volcanoes b. the mantle is colder than the crust c. the less dense crust sits on top of the mantle d. the crust is melting f the

Answers:

1- Option (D)

2- Option (C)

3- Option (D)

4- Option (B)

5- Option (A)

6- Option (B)

7- Option (C)

Explanation:

The lithospheric plates float over the viscous layer of the asthenosphere due to the initiation of convection current in the mantle. These currents are formed because of the heat that is radiated from the core of the earth. In a divergent plate boundary, the two plates move away from one another. Due to this, seafloor spreading takes place and leads to the eruption of magma forming a ridge which is commonly known as the Mid-Oceanic ridge. Here, new materials are added to the crust. When the continental plates are stretched and pulled apart due to the extensional force, it results in the formation of a rift, and gradually with time, it forms a rift valley. This rift valley later give rise to the formation of seas and oceans due to the tectonic activities. The oceanic crust is made up of denser basaltic rocks containing a high amount of magnesium, calcium, iron, and aluminum, whereas the continental crust is comprised of less dense granitic rocks containing silicate minerals, feldspar. So the oceanic crust is denser than the continental crust. The thickness of the continental and oceanic crust is about 35-45 km and 5 to 10 km respectively. Hence, the continental crust is very thick. The hotspots are the regions that are comprised of mantle plumes, where the magma is so intense that it rises up to the surface forming volcanoes or volcanic landforms. The ice floating over water is similar to that of the moving of the crusts over the mantle. The thickness and density, both play a significant role in keeping the crust at the top of mantle maintaining the state of equilibrium. This is known as isostasy.

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