Geoscience Reference
In-Depth Information
Figure 7.25.
(a) The basalt-intrusion model after 20 Ma of erosion of intrusion and
country rock. (b) Temperature-depth paths for rocks finally exposed at the surface in
model (a). (c) Granite intrusion after 20 Ma of erosion of intrusion and country rock.
(d) Temperature-depth paths for rocks finally exposed at the surface in model (c).
Notation is as in Fig. 7.23. (From Fowler and Nisbet (1982).)
the hot base of the upper sheet. If local partial melting occurs (e.g., in the upper
sheet on the extreme left of the model), prograde effects are seen.
Simultaneously with the metamorphism of the upper block, the underthrust
block experiences prograde metamorphism. As erosion takes place, the deep-level
rocks are lifted towards the surface. This has a cooling effect, which progressively
halts and reverses the rise in temperature of the rocks in the underthrust block.
