Page 420 - Global Tectonics

402 CHAPTER 12

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

Figure 12.15 Temperature fields in a numerical model of whole mantle convection that incorporates two continents
5800 km wide (modified from Lowman & Jarvis, 1999, by permission of the American Geophysical Union. Copyright

© 1999 American Geophysical Union). Dark and light shading represent cool and warm temperatures, respectively;
markings at the top indicate the locations of the continental margins. The continents collide at the model symmetry
plane between panels (a) and (b), forming a supercontinent of width 11,600 km. As subduction (dark downwellings)
between the two continents ceases, new subduction zones form along the continent margins. Eventually a central
upwelling of warm material forms beneath the supercontinent. The supercontinent rifts between panels (k) and (l)
some 600 Myr after its formation.