In plate tectonics, sutures are the remains of
subduction zones, and the terranes that are joined are interpreted as fragments of different
palaeocontinents or
tectonic plates.
Outcrops of sutures can vary in width from a few hundred
meters to a couple of
kilometers. They can be networks of
mylonitic shear zones or
brittle fault zones, but are usually both. Sutures are usually associated with
igneous intrusions and
tectonic lenses with varying kinds of
lithologies from
plutonic rocks to
ophiolitic fragments. An example from
Great Britain is the
Iapetus Suture which, though now concealed beneath younger rocks, has been determined by
geophysical means to run along a line roughly parallel with the
Anglo-Scottish border and represents the joint between the former continent of
Laurentia to the north and the former
micro-continent of
Avalonia to the south. Avalonia is in fact a
plain which dips steeply northwestwards through the crust, underthrusting Laurentia. ==Paleontological use==