What is the composition of the oceanic crust?

The oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium.

What is the average composition of oceanic crust?

basaltic
Ocean Floor Volcanism and Construction of the Crust On average, oceanic crust is 6–7 km thick and basaltic in composition as compared to the continental crust which averages 35–40 km thick and has a roughly andesitic composition.

What is the composition of oceanic crust and continental crust?

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).

Why is oceanic crust made of basalt?

As the material rises, the pressure that helps keep it solid decreases. This allows hot mantle rocks to partially melt and produce basaltic liquid. This so-called “melt” is less dense than surrounding solids, and so it buoyantly rises to the surface to form the crust.

How is the oceanic crust formed?

Oceanic crust is constantly formed at mid-ocean ridges, where tectonic plates are tearing apart from each other. As magma that wells up from these rifts in Earth’s surface cools, it becomes young oceanic crust. The age and density of oceanic crust increases with distance from mid-ocean ridges.

Why is the oceanic crust made up of igneous rock?

This process occurs when oceanic crust is pushed back into the mantle at subduction zones. As old oceanic crust is subducted and melted into magma, new oceanic crust in the form of igneous rock is formed at mid-ocean ridges and volcanic hotspots.

What is the bulk composition of oceanic crust?

Mafic and ultramafic plutonic rocks constitute the bulk of the oceanic crust (>60\% by volume). Most of the gabbroic rocks have mineralogies dominated by plagioclase, olivine, pyroxenes, and minor spinel (Fig. 5).

What is the general composition of new oceanic crust formed along divergent plate boundaries?

The crustal material created at a spreading boundary is always oceanic in character; in other words, it is igneous rock (e.g., basalt or gabbro, rich in ferromagnesian minerals), forming from magma derived from partial melting of the mantle caused by decompression as hot mantle rock from depth is moved toward the …

What is the composition of oceanic crust Class 7?

The oceanic crust is made up of silica (si) and magnesium (ma) and therefore also called Sima.

What is the composition of magma that forms at divergent margins?

plates move apart at a divergent plate boundary, the release of pressure produces partial melting of the underlying mantle. This molten material, known as magma, is basaltic in composition and is buoyant.

How is molten rock formed at divergent boundaries?

This reduction in overlying pressure, or decompression, enables the mantle rock to melt and form magma. Decompression melting often occurs at divergent boundaries, where tectonic plates separate. The rifting movement causes the buoyant magma below to rise and fill the space of lower pressure.

What is continental crust and oceanic crust Class 7?

The continental crust is 10 to 30 kms thick, and it is mainly composed of silica and alumina (called sila). The oceanic crust (land under oceans) is 5 to 10 kms thick, and is mainly composed of silica and magnesium (called sima).