Oceanic Crust
The oceanic crust is the outermost layer of Earth's lithosphere that is found under the oceans. It is composed of basalt and gabbro, which are types of igneous rocks that form from the solidification of magma. The oceanic crust is thinner and denser than the continental crust, with an average thickness of about 7 kilometers.
Composition
The primary minerals found in oceanic crust include plagioclase feldspar, pyroxene, and olivine. These minerals form as the magma cools and solidifies, creating a fine-grained texture in the basaltic rocks. Gabbro, which makes up the lower layer of the oceanic crust, is a coarse-grained rock composed mainly of calcium-rich plagioclase feldspar and pyroxene.
Formation
Oceanic crust is formed at mid-ocean ridges through the process of seafloor spreading. Magma from the mantle rises up and spreads out along the ocean ridges, creating new oceanic crust as it cools and solidifies. Over time, this process results in the continuous renewal of the oceanic crust.
Age of Oceanic Crust
One of the key features of oceanic crust is its relatively young age compared to the continental crust. The oldest oceanic crust is around 200 million years old, while the majority of it is less than 100 million years old. This is due to the constant creation and destruction of oceanic crust through the process of plate tectonics.
Study Guide
- Describe the composition of oceanic crust and explain how it differs from continental crust.
- Explain the process of seafloor spreading and its role in the formation of oceanic crust.
- Discuss the age of oceanic crust and the reasons behind its relatively young age compared to continental crust.
- Compare and contrast the minerals found in basalt and gabbro, the two primary rock types that make up oceanic crust.
- Illustrate the relationship between oceanic crust and plate tectonics, and how it contributes to the dynamic nature of Earth's lithosphere.
By understanding the composition, formation, and age of oceanic crust, students can gain insight into the geological processes that shape the Earth's surface and contribute to the dynamic nature of our planet.
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