mid-ocean-ridge basalt

geology

Also known as: MORB

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June 30, 2026

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Mid-ocean-ridge basalt (MORB) is a type of igneous rock that forms at divergent plate boundaries along the crests of oceanic ridges. These basalts have a very specific chemical composition, being subalkaline tholeiites that are depleted in volatile elements like lanthanum, cerium, sodium, and potassium.1

MORB is generated in the asthenosphere, about 70 kilometers deep, from the partial melting of mantle rocks like peridotite. This melting is often triggered by a decrease in pressure as the peridotite rises due to mantle convection. The MORB magmas then flood rift valleys at the ocean floor, forming volcanoes and dikes, and ultimately creating the oceanic crust. MORB is the most abundant rock on Earth's surface.21

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igneous rock
Divergent plate boundaries
…they are referred to as mid-ocean-ridge basalt (MORB). They are subalkaline tholeiites that contain olivine in the norm and less than 0.25 percent potash. The chemistry suggests that MORB was generated from a mantle that was depleted of volatile elements (e.g., lanthanum [La], cerium [Ce], sodium, and potassium) in a…
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…they are referred to as mid-ocean-ridge basalt (MORB). They are subalkaline tholeiites that contain olivine in the norm and less than 0.25 percent potash. The chemistry suggests that MORB was generated from a mantle that was depleted of volatile elements (e.g., lanthanum [La], cerium [Ce], sodium, and potassium) in a…
Read More