Page 303 - Global Tectonics

288 CHAPTER 10

(a)
85°W 80°W 75°W 70°W 65°W 60°W 55°W
(b)
5°S South American 5°S
Plate 70 W 10 S
10°S
Central Andes 10°S Eastern Cordillera
Chaco Plain
Peru
15°S 15°S Arequipa Massif 15 S
Nazca Ridge Chile Brazilian

20°S Nazca F.Z. ANCORP Shield 20°S Western Cordillera Altiplano
PROFILE

Nazca Trench Subandean
25°S 25°S
Plate
30°S 30°S Coastal Cordillera Puma 25 S
Juan Fernández Ridge Pacific Ocean Precordillera Santa
Bárbara
Southern Andes Pampeanas
35°S 35°S
Pacific Ocean Central Sierras
Valley
Mocha F.Z.
40°S 40°S

LOFZ
Chile Rise
85°W 80°W 75°W 70°W 65°W 60°W 55°W
Figure 10.1 (a) Shaded relief map of the central and southern Andes showing topographic features of the Nazca and
South American plates. Map was constructed using the same topographic data and methods as in Fig. 7.1. Black dots
are active volcanoes. LOFZ is the Liquiñe-Ofqui fault zone. Box shows location of Fig. 10.1b. ANCORP profile shown in

Fig. 10.6. (b) Physiographic provinces of the central Andes (modified from Mpodozis et al., 2005, with permission from

Elsevier).

central Andes of Peru, Bolivia, northern Chile, and theless, some common elements are evident that
Argentina (Fig. 10.1). Here, the Andes exhibit the provide important boundary conditions on noncolli-
highest average elevations, the greatest width, the thick- sional orogenic processes. One of these constraints is
est crust, and the greatest amount of shortening in the that the active margin of South America was character-
orogen (Isacks, 1988; Allmendinger et al., 1997; ANCORP ized by either a noncompressive or an extensional
Working Group, 2003). This central segment illustrates regime during the Late Jurassic and Early Cretaceous
how many of the characteristic features of large (Mpodozis & Ramos, 1989). At this time, most of the
orogens may form in the absence of continent–conti- margin lay below sea level as a series of extensional
nent collision. backarc and marginal basins (Fig. 9.34) formed above a
The Andean mountain chain, or cordillera, extends subduction zone (Dalziel, 1981; Mpodozis & Allmend-
some 7500 km from Venezuela and Colombia in the inger, 1993; Mora et al., 2006). This history shows that
north to Tierra del Fuego in the south. Along its length, by itself subduction cannot account for the formation
the orogen displays a remarkable degree of diversity in of Andean-type orogens. Rather, mountain building in
structure, geologic history, and tectonic evolution. This this setting results only when ocean–continent conver-
diversity complicates determinations of the factors that gence leads to compression in the overriding plate (Sec-
control orogenesis within its different segments. Never- tions 9.6, 10.2.5).