Geology Reference
In-Depth Information
Fig. 2.15
Definition of the
order N
of a tectonic plate
Fig. 2.16
Modern plate tectonic configuration and triple
junctions. Plate boundaries are a slightly modified version
of those proposed by Bird (
2003
). There are 23 major
plates, 42 triple junctions (
red circles
), and 63 plate
boundaries (
green lines
)
configuration, assuming a simplified version of
the plate boundaries proposed by Bird (
2003
).
This configuration does not include plates and
microplates whose relative velocity is negligi-
ble with respect to adjacent plates, for example
Adria in the central Mediterranean, or that are
expression of forearc deformation, such as the
Burma platelet in Southeast Asia (e.g., Vigny
et al.
2003
). In addition, it does not include
small triple junction microplates such as the Juan
Fernandez (e.g., Anderson-Fontana et al.
1986
)
and Galapagos (e.g., Lonsdale
1988
) microplates
in the Pacific. It is not difficult to prove that two
simple equations allow to express the number of
plates
p
as a function of the number of plate
boundaries,
b
, and triple junctions,
j
.
They are:
b
D
3.p
2/
j
D
2.p
2/
(2.34)
In fact, if we start from a hypothetical Earth
with only three plates (
p
D
3), then it is quite
evident that we have
b
D
3and
j
D
2. In order to
generate a new plate, we must split an existing
one. This operation requires cutting two edges
of the plate through the insertion of two new
triple junctions and a new edge connecting them.
Therefore, for each new plate we add two triple
junctions, thereby
j
is always even. Regarding
the number of plate boundaries, although we add
only one new edge, the operation of cutting two
