#Mid ocean ridge plus
With time, a column of crust plus mantle lithosphere cools and shrinks as it moves away from the ridge axis as part of the plate. At the axis of the Mid-Oceanic Ridge the underlying column of crust and mantle is hot and thermally expanded this thermal expansion explains why the Mid-Oceanic Ridge is a ridge. The partially molten mantle “freezes” to the sides and bottoms of the diverging plates to form the mantle lithosphere that, together with the overlying “rind” of oceanic crust, comprises the lithospheric plate. Separation of plates causes the hot upper mantle to rise along the spreading axes of the Mid-Oceanic Ridge partial melting of this rising mantle generates magmas of basaltic composition that segregate from the mantle and rise in a narrow zone at the axis of the Mid-Oceanic Ridge to form the oceanic crust. See also: Plate tectonics Transform fault Some spreading axes are located near the edges of ocean basins and behind island arcs. The ridge generally remains in the middle of an ocean basin only if that basin has formed between two continents rifted apart, and the average spreading rates on each flank have been the same. The term Mid-Oceanic Ridge is somewhat a misnomer, having been applied before its tectonic significance (a system of spreading axes connected by transform faults) was appreciated. The white rectangle at 20°S, 12°W defines the location of the contour map of depths over a part of the axis of the ridge in Fig. Lines A-A′ and B-B′ show the locations of the profiles shown in Fig. The distortion caused by plotting these lines on a Mercator projection is indicated by the hourglass-shaped graph on the right, which gives the amount of crust generated at a 100 mm/yr opening rate (1 mm = 0.04 in.). Dotted lines show the volcanic arcs, which are lines of volcanoes and volcanic islands formed from magma rising from the subducted plate. Paired lines on either side of the axis show the amount of crust generated in the last 10 million years at the current opening rates. Bruce Heezen, who pioneered studies of the Mid-Oceanic Ridge, once referred to this feature as a “wound that never heals.”įig. As the plates move apart, new oceanic crust is formed along the spreading axes, and the ideal transform fault zones are lines along which plates slip past each other and where oceanic crust is neither created nor destroyed. The plate boundary of the Mid-Oceanic Ridge comprises an alternation of spreading centers (or axes or accreting plate boundaries) interrupted or offset by a range of different discontinuities, the most prominent of which are transform faults. Wherever plates move apart sufficiently far and fast for oceanic crust to form in the void between them, a branch of the Mid-Oceanic Ridge will be created ( Fig. The origin of the Mid-Oceanic Ridge is intimately connected with plate tectonics. Thus the Mid-Oceanic Ridge is the longest mountain range system on the planet.
![mid ocean ridge mid ocean ridge](https://cdn.iflscience.com/images/4c164d0f-af44-5200-869f-c8180841af1e/default-1469193806-south-east-indian-ridge.jpg)
A largely interconnected system of broad submarine rises totaling at least 60,000–80,000 km (37,000–50,000 mi) long, the precise length depending on what is included and how it is measured.