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Earth and Space Sciences · Glossary

What is Subducting slab?

Definition 14.2 University Earth and Space Sciences — Year 1 · Chapter 14 — Active Margins

The subducting slab is the part of the sinking plate that has already gone down into the mantle: a sheet of oceanic lithosphere, with its crust on top, inclined beneath the overriding plate from the trench to depths of several hundred kilometres.

A subduction zone in section (schematic: lithosphere and slab drawn to the scale bar, relief above the sea floor greatly exaggerated). The slab dips gently beneath the forearc and more steeply below; the volcanic arc stands above the place where the top of the slab is about 100\, km deep. The cold slab drags its isotherms down into the mantle (dashed: one isotherm), and the mantle of the wedge is dragged down along it. Dots: earthquakes, on the plate boundary near the trench and inside the slab below. Water released by the slab rises into the wedge; melt rises to the arc.
A subduction zone in section (schematic: lithosphere and slab drawn to the scale bar, relief above the sea floor greatly exaggerated). The slab dips gently beneath the forearc and more steeply below; the volcanic arc stands above the place where the top of the slab is about 100 km100\,\mathrm{km} deep. The cold slab drags its isotherms down into the mantle (dashed: one isotherm), and the mantle of the wedge is dragged down along it. Dots: earthquakes, on the plate boundary near the trench and inside the slab below. Water released by the slab rises into the wedge; melt rises to the arc.
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