The Tectonic and Geological Environment of Coastal South America
9
Ridge is a broad (250-km-wide) continuous aseismic ridge that rises to as
much as 4000 m above the adjacent seafloor. Gutscher et al. (1999b) proposed that a lost oceanic plateau (Inca Plateau, a mirror image of the Marquesas Plateau) has subducted beneath northern Peru. The combined
buoyancy of the Inca Plateau and the Nazca Ridge supports a 1,500-kmlong segment of flat-dipping subducting Nazca Plate and shuts off arc volcanism. The coastal region of south-central Peru displays raised marine
terraces indicating strong uplift since the Late Pliocene. Southward progressing uplift rates during the Late Pleistocene reached 0.7mm year- 1
(Machan~ and Ortlieb 1992). Two major areas of ridge collisions occur
along the Pacific margin of Chile, the aseismic Juan Fernandez Ridge and
the Southern Chile Rise. The ridge is discontinuous, averaging 50km in
width, and is composed of irregular small seamounts ( 1 ,000 to 1,500 m
above the seafloor). The slab dip is shallow, about 15°.
The Southern Chile Rise, a spreading-ridge system, has been colliding
with the Andean margin since 14 Ma (Cande and Leslie 1986). The intersection point of the Chile Rise and the Andean margin is migrating northward with time. The Southern Chile Rise collision has caused uplift and
plutonism on the continental margin adjacent to the impact point in late
Neogene and Quaternary times.
3.2 Tectonic History
Throughout most of its Phanerozoic history, South America's western
margin was bordered by a paleo-Pacific Ocean, which connected to the
Paleozoic and Mesozoic basins of the ancestral Andean chain and also to
pericratonic basins along the western side of South America. Twice during
the Paleozoic Era this southwestern side of Gondwana was a convergent
margin with proto-Andean chains that largely separated the paleo-Pacific
from interior epicontinental seas (Gohrbandt 1992). Four major orogenies
are associated with these convergent intervals and correspond to widespread unconformities on the platform (Zalan 1991). To the east of the
ancestral Andean chain, four large basins developed on the South American platform: the Parana, Solimoes, Parnaiba and the Amazonas. In the
late Paleozoic there was major accretion and subduction along the southwest side of Gondwana, and in the Permian and Triassic periods the La
Ventana-Cape Fold Belt developed in north-central Argentina, one that
correlates with southern Africa (Milani 1992).
Lateral growth of the continental margin ended in the Paleozoic, and in
the early Mesozoic a magmatic arc and associated back-arc basins were
developed on the late Paleozoic basement (Mpodozis and Ramos 1989).
9
Ridge is a broad (250-km-wide) continuous aseismic ridge that rises to as
much as 4000 m above the adjacent seafloor. Gutscher et al. (1999b) proposed that a lost oceanic plateau (Inca Plateau, a mirror image of the Marquesas Plateau) has subducted beneath northern Peru. The combined
buoyancy of the Inca Plateau and the Nazca Ridge supports a 1,500-kmlong segment of flat-dipping subducting Nazca Plate and shuts off arc volcanism. The coastal region of south-central Peru displays raised marine
terraces indicating strong uplift since the Late Pliocene. Southward progressing uplift rates during the Late Pleistocene reached 0.7mm year- 1
(Machan~ and Ortlieb 1992). Two major areas of ridge collisions occur
along the Pacific margin of Chile, the aseismic Juan Fernandez Ridge and
the Southern Chile Rise. The ridge is discontinuous, averaging 50km in
width, and is composed of irregular small seamounts ( 1 ,000 to 1,500 m
above the seafloor). The slab dip is shallow, about 15°.
The Southern Chile Rise, a spreading-ridge system, has been colliding
with the Andean margin since 14 Ma (Cande and Leslie 1986). The intersection point of the Chile Rise and the Andean margin is migrating northward with time. The Southern Chile Rise collision has caused uplift and
plutonism on the continental margin adjacent to the impact point in late
Neogene and Quaternary times.
3.2 Tectonic History
Throughout most of its Phanerozoic history, South America's western
margin was bordered by a paleo-Pacific Ocean, which connected to the
Paleozoic and Mesozoic basins of the ancestral Andean chain and also to
pericratonic basins along the western side of South America. Twice during
the Paleozoic Era this southwestern side of Gondwana was a convergent
margin with proto-Andean chains that largely separated the paleo-Pacific
from interior epicontinental seas (Gohrbandt 1992). Four major orogenies
are associated with these convergent intervals and correspond to widespread unconformities on the platform (Zalan 1991). To the east of the
ancestral Andean chain, four large basins developed on the South American platform: the Parana, Solimoes, Parnaiba and the Amazonas. In the
late Paleozoic there was major accretion and subduction along the southwest side of Gondwana, and in the Permian and Triassic periods the La
Ventana-Cape Fold Belt developed in north-central Argentina, one that
correlates with southern Africa (Milani 1992).
Lateral growth of the continental margin ended in the Paleozoic, and in
the early Mesozoic a magmatic arc and associated back-arc basins were
developed on the late Paleozoic basement (Mpodozis and Ramos 1989).