Environmental Engineering Reference
In-Depth Information
Chapter
12
Rock formation and deformation
Earth's surface evolution does not end with a global mosaic of mobile crustal plates and
morphotectonic landforms, for these great structures undergo detailed geological changes
during their global voyage. They are rather like a ship which picks up commodities and
crew at one port and leaves them at another, processing raw and waste materials
en route
and undergoing repairs and structural refits as job requirements change. A ship's plates,
rivets and fittings as its working life ends are not all those of its maiden voyage. In a
similar way, individual
lithologies
or rock types accreted to continental plates are
subjected to alteration or erosion and whole terranes may be added, removed or relocated.
These changes may appear to occur randomly. In practice, rock type, process and
resultant rock condition and landforms are intimately linked through a rock cycle whose
components also share specific plate and global locations (Figure 12.1).
Figure 12.1
The rock cycle, following Primary (igneous) and
Secondary (sedimentary) loops. Rock material assemblages
are highlighted in boxes between the operational processes of
the cycle. Metamorphism and deformation can occur in any
part of the loop.
