Colombia, Ecuador and Venezuela (12° N–3° S) Tectonic blocks of
continental crust that had separated from northwestern South America in the Jurassic re-joined the continent in the Late Cretaceous by colliding obliquely with it.
Dextral fault movement between the South American and Caribbean plate started 17–15 million years ago. This movement was canalized along a series of
strike-slip faults, but these faults alone do not account for all deformation. The northern part of the
Dolores-Guayaquil Megashear forms part of the dextral fault systems while in the south the megashear runs along the suture between the accreted tectonic blocks and the rest of South America.
Northern Peru (3–13° S) in Peru was caused by the Andean orogeny. Long before the Andean orogeny the northern half of Peru was subject of the
accretion of
terranes in the
Neoproterozoic and
Paleozoic. Andean orogenic deformation in northern Peru can be traced to the
Albian (Early Cretaceous). No other tectonic event in the western Peruvian Andes compare with the Incaic Phase in magnitude. Further east at similar latitudes, in Argentina and Bolivia, the
Salta rift system developed during the Late Jurassic and the Early Cretaceous.
Salar de Atacama Basin, which is thought to be the
western arm of the rift system, accumulated during the
Late Cretaceous and
Early Paleogene a >6,000 m thick pile of sediments now known as the
Purilactis Group.
Pisco Basin, around latitude 14° S, was subject to a
marine transgression in the
Oligocene and
Early Miocene epochs (25–16
Ma). In contrast
Moquegua Basin to the southeast and the coast to south of Pisco Basin saw no transgression during this time but a steadily rise of the land. From the
Late Miocene onward the region that would become the
Altiplano rose from low elevations to more than 3,000
m.a.s.l. It is estimated that the region rose 2000 to 3000 meters in the last ten million years. Together with this uplift several valleys incised in the western flank of the Altiplano. In the Miocene the
Atacama Fault moved, uplifting the Chilean Coast Range and creating sedimentary basins east of it. At the same time the Andes around the Altiplano region broadened to exceed any other Andean segment in width. and the
Cordillera Real in Bolivia, the
Altiplano forms an extensive intermontane plateau whose uplift is one of the most striking features of the Andean orogeny. The region east of the Altiplano is characterized by deformation and tectonics along a complex
fold and thrust belt. In southern Bolivia lithospheric shortening has made the
Andean foreland basin to move eastward relative to the continent at an average rate of ca. 12–20 mm per year during most of the Cenozoic. Along the
Argentine Northwest the Andean uplift has caused Andean foreland basins to separate into several minor isolated intermontane sedimentary basins. Towards the east the piling up of crust in Bolivia and the Argentine Norwest caused a north-south
forebulge known as
Asunción arch to develop in Paraguay. The uplift of the Altiplano is thought to be indebted to a combination of
horizontal shortening of the crust and to increased temperatures in the mantle (thermal thinning). Meso-scale tectonic processes aside, the particular characteristics of the Bolivian Orocline–Altiplano region have been attributed to a variety of deeper causes. These causes include a local steepening of the subduction angle of Nazca Plate, increased crustal shortening and plate convergence between the Nazca and South American plates, an acceleration in the westward drift of the South American Plate, and a rise in the
shear stress between the Nazca and South American plates. This increase in shear stress could in turn be related to the scarcity of sediments in the
Atacama trench which is caused by the arid conditions along
Atacama Desert. As Andrés Tassara puts it the
rigidity of the Bolivian Orocline
crust is derivative of the
thermal conditions. The crust of the western region (
forearc) of the orocline has been cold and rigid, resisting and damming up the westward flow of warmer and weaker
ductile crustal material from beneath the Altiplano. The Cenozoic orogeny at the Bolivian orocline has produced a significant
anatexis of crustal rocks including
metasediments and
gneisses resulting in the formation of
peraluminous magmas. These characteristics imply that the Cenozoic tectonics and magmatism in parts of Bolivian Andes is similar to that seen in
collisional orogens. The peralumineous magmatism in
Cordillera Oriental is the cause of the world-class
mineralizations of the
Bolivian tin belt. The rise of the Altiplano is thought by scientist Adrian Hartley to have enhanced an already prevailing
aridity or semi-aridity in
Atacama Desert by casting a
rain shadow over the region.
Central Chile and Western Argentina (26–39° S) of the
Yacoraite Formation at
Serranía de Hornocal in northernmost Argentina. The Andean orogeny caused the tilting of these
originally horizontal strata.At the latitudes between 17 and 39° S the Late Cretaceous and Cenozoic development of the Andean orogeny is characterized by an eastward migration of the
magmatic belt and the development of
several foreland basins. At the latitudes of 32–36° S —that is
Central Chile and most of
Mendoza Province— the Andean orogeny proper began in the Late Cretaceous when
backarc basins were
inverted. Immediately east of the early Andes foreland basins developed and their
flexural subsidence caused the ingression of waters from the Atlantic all the way to the front of the orogen in the
Maastrichtian. Lavas and volcanic material that are now part of Farellones Formation accumulated while the basin was being inverted and uplifted. The Principal Cordillera had risen to heights that allowed for the development of valley glaciers about 1 million years ago. The
Sierras de Córdoba (part of the Sierras Pampeanas) where the effects of the ancient
Pampean orogeny can be observed, owes it modern uplift and relief to the Andean orogeny in the late
Cenozoic. Similarly the
San Rafael Block east of the Andes and south of Sierras Pampeanas was raised in the Miocene during the Andean orogeny.
Northern Patagonian Andes (39–48° S) Southern Patagonian Andes (48–55° S) next to
Nordenskjöld Lake in
Torres del Paine National Park. The syncline formed during the Andean orogeny. The early development of the Andean orogeny in southernmost South America affected also the
Antarctic Peninsula. In the
Late Cretaceous the tectonic regime of Rocas Verdes Basin changed leading to its transformation into a compressional
foreland basin –the
Magallanes Basin– in the
Cenozoic. This change was associated with an eastward move of the basin
depocenter and the
obduction of
ophiolites. As the Andean orogeny went on, South America drifted away from Antarctica during the Cenozoic leading first to the formation of an
isthmus and then to the opening of the
Drake Passage 45 million years ago. The separation from Antarctica changed the tectonics of the Fuegian Andes into a
transpressive regime with
transform faults. ==Notes==