Mid-oceanic back

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A mid-ocean ridge (MOR) is a volcanically active mountain range in the deep sea that extends along the seam of two divergent lithosphere plates. On the central axis of this mountain range, new oceanic crust is constantly being created, this process is called ocean floor spreading. The backs run through all the ocean basins. The largest part of this system is the Mid-Atlantic Ridge, where the Atlantic Ocean widens by two centimeters annually. Due to numerous transform disturbances, the entire back system is divided into individual segments.

In addition to the subduction zones and the hot spots, the mid-oceanic ridges are among the centers of igneous activity on Earth. A manifestation of this magmatism are the so-called black smokers.

Crust formation

The lithosphere plates, which can be regarded as rigid, "swim" on the tough sublithospheric mantle, which slowly rises under the spreading zone in the course of mantle convection. On ascent, the pressure and thus the melting point decrease, so that the components of the mantle rock with the lowest melting points liquefy (so-called partial melting). This starts at a depth of 10 to 70 kilometers, depending on the water content of the mantle and the spread rate. The liquid part rises in cracks and rock spores and forms a magma chamber at a relatively low depth under the back.

Ocean crust is made up of three layers with a similar, basic composition. The upper layer consists of basalt, which has emerged from lava, which has penetrated from the magma chamber to the seabed and quickly solidified there. Typical for this layer is therefore pillow lava. The middle layer consists of solidified magma, which did not reach the bottom of the sea, but crystallized out relatively quickly in the form of corridors. The corresponding gang rock is very similar to the basalt of the seabed. Both are referred to as (abbreviated MORB) due to a special geochemical signature containing only basaltic rocks on the mid-ocean ridge. The lower layer consists of the deep rock Gabbro, whose mineral stock is identical to that of the MORB. It represents the slowly cooled and crystallized melt of the magma chamber. Below the crust, the ultramafic lithospheric mantle joins. In oceanic lithosphere, it is mostly composed of resin burgite, the mantle rock that remains after the MOR magma has melted out.

The young crust of the mid-ocean ridge has many crevices and cracks. In addition, it is still very hot at a certain distance from the seabed, especially in the vicinity of the magma chamber. Seawater that penetrates deep into the crevices is heated up to 400 °C to 500 °C, causing hydrothermal circulation (see also ocean)