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Geology of the Central Andes (13–26° S)[edit]
- Tectonic setting
- Regions
- Coastal strip
- Cordillera Occidental
- Altiplano Basin
- Cordillera Oriental
- Sub-Andean fold and thrust belts
- Volcanism
- Orogeny
- Early orogenies
- Andean orogeny
- Bolivian Orocline
- Economic geology
- Bolivian tin belt
- Gian copper porphyritic
- Guano
- Evaporites
Early Andean subduction in the Jurassic formed a volcanic arc in northern Chile known as La Negra Arc. The remnants of this arc are now exposed in the Chilean Coast Range. Several plutons were emplaced in the Chilean Coast Range in the Jurassic and Early Cretaceous including the Vicuña Mackenna Batholith.[1] Further east at similar latitudes, in Argentina and Bolivia, the Salta rift system developed in during the Late Jurassic and the Early Cretaceous.[2]
From the Late Miocene onward the region that would became 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.[3] 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.[4] At the same time the Andes around the Altiplano region broadened to exceed any other Andean segment in width.[5] Possibly about 1000 km of lithosphere has been lost due to lithospheric shortening.[6] During subduction the western end of the forearc region[note 1] flexured downward forming a giant monocline.[7][8] By contrast the region east the Altiplano is characterized by deformation and tectonics along a complex fold and thrust belt.[7] Over-all the region surrounding the Altiplano and Puna plateaux have been horizontally shortened since the Eocene.[9]
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.[6][note 2] Along the Argentine Northwest the Andean uplift has caused Andean foreland basins to separate into several minor isolated intermontane sedimentary basins.[10]
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).[11][7] The bend in the Andes and the west coast of South America known as the Bolivian Orocline was enhanced by Cenozoic horizontal shortening but existed already independently of it.[7]
Besides direct causes the particular characteristics of the Bolivian Orocline–Altiplano region are 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. 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.[5] Capitanio et al. attributes the rise of Altiplano and the bending of the Bolivian Orocline to the varying ages of the subducted Nazca Plate with the older parts of the plate subducting at the centre of the orocline.[12] 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.[8]
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.[13]
- ^ Charrier et al. 2006, pp. 47–48.
- ^ 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.
- ^ Charrier et al. 2006, pp. 100–101.
- ^ Charrier et al. 2006, p. 97.
- ^ a b Cite error: The named reference
Ormewas invoked but never defined (see the help page). - ^ a b DeCelles, Peter G.; Horton, Brian K. (2003). "Early to middle Tertiary foreland basin development and the history of Andean crustal shortening in Bolivia". Geological Society of America bulletin. 115 (1): 58–77.
{{cite journal}}:|access-date=requires|url=(help) - ^ a b c d Isacks, Bryan L. (1988). "Uplift of the Central Andean Plateau and Bending of the Bolivian Orocline". Journal of Geophysical Research. 93 (B4): 3211–3231.
{{cite journal}}:|access-date=requires|url=(help) - ^ a b Tassara, Andrés (2005). "Interaction between the Nazca and South American plates and formation of the Altiplano-Puna Plateau: Review of a flexural analysis along the Andean margin (15°-34°S)". Tectonophysics. 399: 39–57.
{{cite journal}}:|access-date=requires|url=(help) - ^ Hongn, F.; del Papa, C.; Powell, J.; Petrinovic, I.; Mon, R.; Deraco, V. (2007). "Middle Eocene deformation and sedimentation in the Puna–Eastern Cordillera transition (23°–26°S): Control by preexisting heterogeneities on the pattern of initial Andean shortening". Geology. 35 (3): 271–274. doi:10.1130/G23189A.1.
{{cite journal}}:|access-date=requires|url=(help) - ^ Pingel, Heiko; Strecker, Manfred R.; Alonso, Ricardo N.; Schmitt, Axel K. (2012). "Neotectonic basin and landscape evolution in the Eastern Cordillera of NW Argentina, Humahuaca Basin (~24°S" (PDF). Basin Research. doi:10.1111/bre.12016. Retrieved 26 December 2015.
- ^ Cite error: The named reference
Ramosmemoir2009was invoked but never defined (see the help page). - ^ Capitanio, F.A.; Faccenna, C.; Zlotnik, S.; Stegman, D.R. (2011). "Subduction dynamics and the origin of Andean orogeny and the Bolivian orocline". Nature. 480: 83–86. doi:10.1038/nature10596. Retrieved 26 December 2015.
- ^ Hartley, Adrian J. (2003). "Andean uplift and climate change". Journal of the Geological Society, London. 160: 7–10.
{{cite journal}}:|access-date=requires|url=(help)
Cite error: There are <ref group=note> tags on this page, but the references will not show without a {{reflist|group=note}} template (see the help page).