Andean orogeny
The Andean orogeny (
Overview
Subduction orogeny has been occurring in what is now western South America since the break-up of the
Low angle subduction or
The tectonic growth of the Andes and the regional climate have evolved simultaneously and have influenced each other.[5] The topographic barrier formed by the Andes stopped the income of humid air into the present Atacama desert. This aridity, in turn, changed the normal superficial redistribution of mass via erosion and river transport, modifying the later tectonic deformation.[5]
In the Oligocene the Farallon Plate broke up, forming the modern Cocos and Nazca plates ushering a series of changes in the Andean orogeny. The new Nazca Plate was then directed into an orthogonal subduction with South America causing ever-since uplift in the Andes, but causing most impact in the Miocene. While the various segments of the Andes have their own uplift histories, as a whole the Andes have risen significantly in last 30 million years (Oligocene–present).[6]
Orogeny by segment
Colombia, Ecuador and Venezuela (12° N–3° S)
Tectonic blocks of
The
Northern Peru (3–13° S)
Long before the Andean orogeny the northern half of Peru was subject of the accretion of terranes in the Neoproterozoic and Paleozoic.[10] Andean orogenic deformation in northern Peru can be traced to the Albian (Early Cretaceous).[11] This first phase of deformation —the Mochica Phase[A]— is evidenced in the folding of Casma Group sediments near the coast.[10]
Sedimentary basins in western Peru changed from marine to continental conditions in the
After a period without much tectonic activity in the Early Eocene the Incaic Phase of orogeny occurred in the Mid and Late Eocene.[11][12] No other tectonic event in the western Peruvian Andes compare with the Incaic Phase in magnitude.[11][12] Horizontal shortening during the Incaic Phase resulted in the formation of the Marañón fold and thrust belt.[11] An unconformity cutting across the Marañón fold and thrust belt show the Incaic Phase ended no later than 33 million years ago in the earliest Oligocene.[10]
In the period after the Eocene the Northern Peruvian Andes were subject to the Quechua Phase of orogeny. The Quechua Phase is divided into the sub-phases Quechua 1, Quechua 2 and Quechua 3.[B] The Quechua 1 Phase lasted from 17 to 15 million years ago and included a reactivation of Inca Phase structures in the Cordillera Occidental.[C] 9–8 million years ago, in the Quechua 2 Phase, the older parts of the Andes in northern Peru were thrusted to the northeast.[10] Most of the Sub-Andean zone of northern Peru deformed 7–5 million years ago (Late Miocene) during the Quechua 3 Phase.[10][12] The Sub-Andean stacked in a thrust belt.[10]
The Miocene rise of the Andes in Peru and Ecuador led to increased orographic precipitation along its eastern parts and to the birth of the modern Amazon River. One hypothesis links these two changes by assuming that increased precipitation led to increased erosion and this erosion led to filling the Andean foreland basins beyond their capacity and that it would have been the basin over-sedimentation rather than the rise of the Andes that made drainage basins flow to the east.[12] Previously the interior of northern South America drained to the Pacific.
Bolivian Orocline (13–26° S)
Early Andean subduction in the Jurassic formed a volcanic arc in northern Chile known as
Pisco Basin, around latitude 14° S, was subject to a marine transgression in the Oligocene and Early Miocene epochs (25–16 Ma[18]).[19] 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.[19]
From the
The region east of the Altiplano is characterized by deformation and tectonics along a complex fold and thrust belt.[23] Over-all the region surrounding the Altiplano and Puna plateaux has been horizontally shortened since the Eocene.[26] 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.[22][F] Along the Argentine Northwest the Andean uplift has caused Andean foreland basins to separate into several minor isolated intermontane sedimentary basins.[27] 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.[28]
The uplift of the Altiplano is thought to be indebted to a combination of
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
The Cenozoic orogeny at the Bolivian orocline has produced a significant
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.[31]
Central Chile and Western Argentina (26–39° S)
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.[3] The eastward migration of the arc is thought to be caused by subduction erosion.[32]
At the latitudes of 32–36° S —that is
Before the Miocene uplift of the Principal Cordillera was over, the Frontal Cordillera to the east started a period of uplift that lasted from 12 to 5 million years ago. Further east the Precordillera was uplifted in the last 10 million years and the Sierras Pampeanas has experienced a similar uplift in the last 5 million years. The more eastern part of the Andes at these latitudes had their geometry controlled by ancient faults dating to the San Rafael orogeny of the Paleozoic.[33] 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.[36][37] Similarly the San Rafael Block east of the Andes and south of Sierras Pampeanas was raised in the Miocene during the Andean orogeny.[38] In broad terms the most active phase of orogeny in area of southern Mendoza Province and northern Neuquén Province (34–38° S) happened in the Late Miocene while arc volcanism occurred east of the Andes.[38]
At more southern latitudes (36–39° S) various Jurassic and Cretaceous marine transgressions from the Pacific are recorded in the sediments of Neuquén Basin.[H] In the Late Cretaceous conditions changed. A marine regression occurred and the fold and thrust belts of Malargüe (36°00 S), Chos Malal (37° S) and Agrio (38° S) started to develop in the Andes and did so in until Eocene times. This meant an advance of the orogenic deformation since the Late Cretaceous that caused the western part of Neuquén Basin to stack in the Malargüe and Agrio fold and thrust belts.[39][38] In the Oligocene the western part of the fold and thrust belt was subject to a short period of extensional tectonics whose structures were inverted in the Miocene.[39][I] After a period of quiescence the Agrio fold and thrust belt resumed limited activity in the Eocene and then again in the Late Miocene.[38]
In the south of Mendoza Province the Guañacos fold and thrust belt (36.5° S) appeared and grew in the Pliocene and Pleistocene consuming the western fringes of the Neuquén Basin.[39][38]
Northern Patagonian Andes (39–48° S)
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Southern Patagonian Andes (48–55° S)
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The early development of the Andean orogeny in southernmost South America affected also the
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.[42][J]
About 15 million years ago in the Miocene the Chile Ridge begun to subduct beneath the southern tip of Patagonia (55° S). The point of subduction, the triple junction has gradually moved to the north and lies at present at 47° S. The subduction of the ridge has created a northward moving "window" or gap in the asthenosphere beneath South America.[45]
Notes
- ^ The Mochica Phase and the other phases in Peru were named by Gustav Steinmann (1856–1929) who established the first chronology of structural events in central Peru.[10]
- ^ The validity in of this subdivision to describe the latest Andean orogeny in Peru has been questioned considering that deformation could have been continuous and migrating along the Andes.[12]
- Cordillera Oriental of Ecuador.[10]
- ^ A series of iron ore deposits in the northern Chilean Coast Range known as the Chilean Iron Belt are related to the magmatism of La Negra Arc.[13]
- ^ Northern Chile and the westernmost fringes of Bolivia.
- ^ At least during the last 55 millions years.
- ^ These sediments are grouped in the Abanico and Farellones Formation.[34]
- Vaca Muerta Formation.[39]
- Cura-Mallín Basin as evidenced by structural studies of Loncopué Trough.[40] However, evidence for Oligocene extension and rifting in the south-central Andes has been questioned.[41]
- glacial valleys.[42]
References
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- ^ Frutos, J. (1990). "The Andes Cordillera: A Synthesis of the Geologic Evolution". In Fontboté, L.; Amstutz, G.C.; Cardozo, M.; Cedillo, E.; Frustos, J. (eds.). Stratabound Ore Deposits in the Andes. Springer-Verlag. pp. 12–15.
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- ^ Salfity, J.A.; Marquillas, R.A. (1994). "Tectonic and Sedimentary Evolution of the Cretaceous-Eocene Salta Group Basin, Argentina". In Salfity, J.A. (ed.). Cretaceous Tectonics of the Andes. pp. 266–315.
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- ^ Mpodozis, Constantino; Arriagada, César; Roperch, Pierrick (October 6, 1999). Cretaceous to Paleogene geology of the Salar de Atacama basin, northern Chile: A reappraisal of the Purilactis Group stratigraphy. Fourth ISAG, Goettingen. Goettingen, Germany.
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- ^ a b Macharé, José; Devries, Thomas; Barron, John; Fourtanier, Élisabeth (1988). "Oligo-Miocene transgression along the Pacifie margin of South America: new paleontological and geological evidence from the Pisco basin (Peru)" (PDF). Geódynamique. 3 (1–2): 25–37.
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- ^ Rojas Vera, Emilio A.; Folguera, Andrés; Zamora Valcarce, Gonzalo; Gímenez, Mario; Martínez, Patricia; Ruíz, Francisco; Bottesi, Germán; Ramos, Víctor A. (2011). "La fosa de Loncopué en el piedemonte de la cordillera neuquina.". Relatorio del XVIII Congreso Geológico Argentino. XVIII Congreso Geológico Argentino (in Spanish). Neuquén. pp. 375–383.
- ^ Cobbold, Peter R.; Rossello, Eduardo A.; Marques, Fernando O. (2008). "Where is the evidence for Oligocene rifting in the Andes? Is it in the Loncopué Basin of Argentina?". Extended abstracts. 7th International Symposium on Andean Geodynamics. Nice. pp. 148–151.
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Further reading
- ISBN 9781862392199.