Lithosphere

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Earth cutaway
The tectonic plates of the lithosphere.

The lithosphere[1] is the solid shell of the planet Earth. This means the crust, plus the part of the upper mantle which behaves elastically over long time scales.

Under the lithosphere is the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. This part can flow.

The lithosphere provides a conductive lid on top of the convecting mantle: it reduces heat transport through the Earth. A lithosphere (Ancient Greek: λίθος [lithos] for "rocky", and σφαίρα [sphaira] for "sphere") is the rigid,[1] outermost shell of a terrestrial-type planet or natural satellite which is defined by its rigid mechanical properties. On Earth, it is composed of the crust and that portion of the upper mantle which behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.

Types of lithosphere :-[change | change source]

There are two types of lithosphere:-

  1. Oceanic lithosphere, which is associated with oceanic crust and exists in the ocean basins. Oceanic lithosphere is typically about 50–100 km thick
  2. Continental lithosphere, which is associated with continental crust. Continental lithosphere has a range in thickness from about 40 km to perhaps 200 km, of which about 40 km is crust.

The lithosphere is divided into tectonic plates, which move gradually relative to one another.

Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle, and causes the oceanic lithosphere to become increasingly dense with age. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years, but after this becomes increasingly dense than asthenosphere.

When a continental plate comes together with an oceanic plate, at a subduction zones, the oceanic lithosphere always sinks beneath the continental.

New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 200 million years old, while parts of the continental lithosphere are billions of years old.

Another distinguishing characteristic of the lithosphere is its flow properties. Under the influence of the low-intensity, long-term stresses that drive tectonic motion, the lithosphere is like a rigid shell. It changes mainly by breaking ("brittle failure"). The asthenosphere (the layer of the mantle below the lithosphere) is heat-softened and adjusts by plastic changes ("deformation").

Oceanic lithosphere is made up of mostly basalt and gabbro. Continental lithosphere is made up of granite and gneiss.

Related pages[change | change source]

References[change | change source]

  1. IPA: lith'usfēr, from the Greek for "rocky" sphere

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