Page 305 - Global Tectonics

290 CHAPTER 10

10˚N

0˚

South American
Plate
10˚S

Brazilian shield
Nazca
Plate
Nazca Ridge 20˚S

30˚S

40˚S
Chile Rise

90˚W 75˚W 60˚W

Figure 10.2 Earthquake focal mechanism solutions in South America from the Harvard CMT catalogue for shallow

(<70 km) earthquakes (1976–1999) (image provided by M.-A. Gutscher and modified from Gutscher et al., 2000, by
permission of the American Geophysical Union. Copyright © 2000 American Geophysical Union). Shaded relief map is
from data base of Smith & Sandwell (1997). Dark gray triangles are volcanoes.

respond to the partially subducted Nazca Ridge and tions that the subduction of thick, buoyant oceanic
the fully subducted ridge beneath the Inca Plateau. A lithosphere leads to flat subduction and can terminate

lithospheric tear may occur at the northwestern edge magmatism by eliminating the asthenospheric wedge
of the flat slab. These relationships support interpreta- (Section 9.6).