Page 222 - Global Tectonics

208 CHAPTER 7

7.9 THE WILSON Archean (Section 11.3.5). The relatively young Meso-
zoic-Cenozoic age of the current ocean basins implies
CYCLE that there have been many cycles of ocean creation and
destruction during the Earth’s history. Very little remains
of these ancient oceans, although their existence is
implied by continental reconstructions (Figs 3.4, 3.5) and
The transition from intracontinental rift to ocean basin by fragments of ancient ocean crust that are preserved
has occurred repeatedly on Earth since at least the Late as ophiolite assemblages (Section 2.5) in orogenic belts

(a) Continental craton
Ocean crust Continental crust Ocean crust
Mantle lithosphere

(b) Narrow rift

(c) Seafloor spreading in expanding ocean
Rifted continental Rifted continental
margin margin
Continent A Continent B

(d) Subduction initiation
Volcanic arc
Continent A Continent B

(e) Contracting ocean

Continent A Continent B

(f) Continental collision and orogeny

Continent A Continent B

Figure 7.41 The Wilson cycle showing: (a) continental craton; (b) formation of a narrow rift; (c) initiation of seafloor

spreading and formation of rifted continental margins in an expanding ocean basin; (d) initiation of subduction; (e) a
closing ocean basin; (f) continental collision and orogeny.