Geology Reference
In-Depth Information
A
B
A
B
(a)
(b)
(c)
2
2
1
3
(d)
Figure 6.7
(a) Intersecting dykes, A being younger than B. Note that the appar-
ent displacement of B results only from dilation by emplacement of A, and from
lateral movement within the younger dyke, (b) Branching dykes, of the same age,
(c) Section of dyke, A, which has entered a fault. The fault intersects a series of
strata containing a sill, B. (d) Filed example of cross cutting dykes through a
gabbro intrusion, numbered to indicate relative ages, Isle of Skye, Scotland.
is emplaced into the still-molten interior between the chilled margins of an earlier
intrusion, this is termed a multiple intrusion. The formation of multiple dykes
may be favoured by emplacement at sufficient depth for cooling to be suffi-
ciently slow for dykes to be partially molten at the time of emplacement of
the next intrusion. A particular association of multiple dykes, termed a sheeted
complex, forms part of ophiolite complexes, and these are described in detail in
Chapter 8. In rarer cases, a multiple intrusion might be composed of two con-
trasted magma types. These are termed composite dykes or sills. An example
