Figure 21.1 The continental shields and mountain systems of the world are composed, in part, of metamorphic rocks (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).

• long periods of deformation (exceeding 100 Ma)

• deformation progresses generally landward
  1. Deep water sediments deform first

  2. Igneous intrusions and metamorphic rocks form central core complex

  3. A general thickening of rock sequence occurs and uplift begins

  4. As crystalline core is uplifted, the flanking shallower water deposits are deformed

Figure 21.2 Idealized cross-section through a geosyncline showing the shallow-water miogeosyncline and the deep-water eugeosyncline (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).

1. Island Arcs

   
   
   Figure 21.3 The development of a mature volcanic island arc at an oceanic-oceanic convergent boundary (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).
   
   
   

2. Continent-Ocean Collisions

   
   
   Figure 21.4 Subduction-type orogenesis along an active continental margin. A) Passive plate margin. B) Plate convergence generates a subduction zone. C) Partial melting of subducted plate generates the volcanic arc. D) Continued growth of the complex mountain system through deformation of the shallow- and deepwater sediments (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).
   
   
   

3. Continent-Continent Collisions

   
   
   
   Figure 21.5 Orogenesis and continental collisions. A) Converging plates generate a subduction zone and initiate island arc volacnism. B) Sediments scraped from the subducting plate and igneous activity add to the size of the volcanic arc. C) Closing of the back-arc basin deforms the entrapped marginal sediments and volcanic arc. D) A continental collision closes the ocean basin, resulting in further deformation and metrmorphism of the sediments and volcanic rocks (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).