Geology Reference
In-Depth Information
governed by the physical properties of the interstitial melt (viscosity and density)
and the strain-rate in the solid matrix. Their
effectiveness
is controlled by the
rate of cooling - a fundamental time-limiting step as once thermally frozen then
by definition all fluid motion ceases. When mapping and marvelling at the com-
plex structures preserved in plutonic rocks one should always bear in mind that
(a)
(b)
(c)
Figure 7.15
Details of internal contacts in granitoid plutons (see Figure 7.3
for description of contact types) (a) subhorizontal contact between tonalite and
diotite, contact sharp and sinuous (b) Horizontal contact between granite and
diorite. Contact marked by narrow aplite band and cut subsequently by diagonal
aplite vein. Contact sharp, straight. (c) vertical contact between granodiorite and
diorite. Note apophyisis of dark diorite cutting granodiorite gives timing rela-
tionship, contact sharp and sinuous. (d) (on next page) Granite-microgranite
contact, sharp but locally diffuse. Note local E-W alignment of feldspar phe-
nocrysts (magmatic fabric).
