suture

suture
1. A linear belt of highly deformed rocks, including tectonic mélanges, lenses of ophiolites, deep-sea sediments, and usually blueschists, which is interpreted as the boundary between two collided continents or island arcs. The location of a suture between collided masses has often led to controversy, and the recognition that collision zones are in some cases a mosaic of jumbled, sliced, and rotated terranes has led to the realization that sutures may be diffuse, rather than a narrow belt as was formerly thought.

2. The line marking the junction between the septa (see SEPTUM) and the external wall of a cephalopod (Cephalopoda) shell that is visible when the shell has been preserved as an internal mould. In some cephalopods the suture lines are simple curves but in ammonoids (Ammonoidea) the suture becomes crenulate; bends in the suture line that point anteriorly are called ‘saddles’, those pointing posteriorly ‘lobes’. In gastropods (Gastropoda), the suture is the line of junction between two whorls of the shell; the angle the line makes with the horizontal is the ‘sutural angle’.

3. See CEPHALIC SUTURE.