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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 170 million years old, while parts of the continental lithosphere are billions of years old. [12] [13]
The age of the oceanic crust can be used to estimate the (thermal) thickness of the lithosphere, where young oceanic crust has not had enough time to cool the mantle beneath it, while older oceanic crust has thicker mantle lithosphere beneath it. [19] The oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries ...
Seismic evidence shows that oceanic plates do thicken with age. This suggests that the LAB underneath oceanic lithosphere also deepens with plate age. Data from ocean seismometers indicate a sharp age-dependent LAB beneath the Pacific and Philippine plates and has been interpreted as evidence for a thermal control of oceanic-lithosphere thickness.
Lithosphere – Outermost shell of a terrestrial-type planet or natural satellite; Ocean – Body of salt water covering most of Earth; Plate tectonics – Movement of Earth's lithosphere List of tectonic plate interactions – Types of plate boundaries; Supercontinent – Landmass comprising more than one continental core, or craton
The depth of the seafloor on the flanks of a mid-ocean ridge is determined mainly by the age of the oceanic lithosphere; older seafloor is deeper.During seafloor spreading, lithosphere and mantle cooling, contraction, and isostatic adjustment with age cause seafloor deepening.
Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. (The rate at which new oceanic lithosphere is added to each tectonic plate on either side of a mid-ocean ridge is the spreading half-rate and is equal to half of the spreading rate). Spreading rates determine if the ridge is fast, intermediate, or slow.
Each boundary type is associated with different geological marine features. Divergent plates are the cause for mid-ocean ridge systems while convergent plates are responsible for subduction zones and the creation of deep ocean trenches. Transform boundaries cause earthquakes, displacement of rock, and crustal deformation. [8] [27] [26] [28]
The lithosphere consists of the outermost light crust plus the uppermost rigid portion of the mantle. Oceanic lithosphere ranges in thickness from just a few km for young lithosphere created at mid-ocean ridges to around 100 km (62 mi) for the oldest oceanic lithosphere. [7] Continental lithosphere is up to 200 km (120 mi) thick. [8]