In structural geology
, a suture is a joining together along a major fault
zone, of separate terrane
units that have different plate tectonic
histories. The suture is often represented on the surface by an orogen
or mountain range.
The term was borrowed from surgery
where it describes the sewing together of two pieces of tissue, but the sutures of the skull
, where separate plates of bone have fused, may be a better metaphor.
In plate tectonics, sutures are seen as the remains of subduction zone
s, and the terranes that are joined together are interpreted as fragments of different paleocontinents
or tectonic plate
s of sutures can vary in width from a few hundred meter
s to a couple of kilometer
s. They can be networks of mylonitic shear zone
s or brittle
fault zones, but are usually both. Sutures are usually associated with igneous intrusion
s and tectonic lenses
with varying kinds of lithologies
from plutonic rock
s to ophiolitic
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
to the south.
[Oliver, G. J. H.; Stone, P. and Bluck, B. J. (2002) "The Ballantrae Complex and Southern Uplands terrane" pp. 167–200 ''In'' Trewin, N. H. (editor) (2002) ''The Geology of Scotland'' The Geological Society, London]
Avalonia is in fact a plain
which dips steeply northwestwards through the crust, underthrusting Laurentia.
When used in paleontology
, ''suture'' can also refer to fossil exoskeletons
, as in the suture line, a division on a trilobite
between the free cheek and the fixed cheek; this suture line allowed the trilobite to perform ecdysis
(the shedding of its skin).