Location, Location, Location - A Natural History of the New World - page 78

The Southern Andes and Lowlands
The crustal extension (stretching) that preceded separation of South Amer-
ica from Africa was accompanied by extensive volcanism that deposited
fl ood basalts 2000 m thick in the Paranà Basin of southeastern Brazil and
westward. The weathering of ancient crystalline rocks has created struc-
tures such as the granitic Sugar Loaf near Rio de Janeiro. The actual separa-
tion of South America from Africa beginning in the south at about 120 Ma
created lowlands along the passive eastern coast called pull-apart basins,
and they have been accumulating plant and animal remains from the Cre-
taceous onward. One of these lowlands is the Magellanes Basin of southern
Argentina, with Cretaceous fl oras preserved in the Springhill Formation.
Another is the San Jorge Basin, which is the principal source of Argentina's
extensive oil reserves. Moreover, as South America was forced against the
Pacifi c plate, the movement exerted compression forces along the active
western margin. A subduction zone called the Peru-Chile Trench devel-
oped that, along with movement at the triple junction of the South Amer-
ica, Nazca, and Antarctic plates, caused uplift of the Southern Andes. The
glaciated landscape produced by these forces is spectacular and inspiring
(fi g. 2.39). As Charles Darwin wrote in his Journal of Researches , now known
Figure 2.39 Torres del Paine National Park, north of Punta Arenas, Chile. Photograph by
J. Arthur Herrick.