The geology of the Western Cordillera and Antiplano west of Lake Titicaca, southern Peru
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The Andes are made up by the two Cordillera mountain chains and are separated by the Altiplano plateau. This account is a description of an area from the axis of the Western Cordillera to the foothills of the Eastern Cordillera at the latitude of Lake Titicaca. It looks at stratigraphy, structure, mineral deposits and volcanic geochemistry, putting them into the context of the evolution of the Andes.Keywords:
Foothills
Massif
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Two stages are outlined in the evolution of the Andes. These stages correspond also to two distinct geological provinces: the western and eastern cordilleras of the Andes. The western cordillera of igneous and volcanic constitution preceded the rise of the eastern cordillera of sedimentary composition. It is suggested that the western cordillera evolved from a volcanic island-arc similar to those that form the Caribbean arc or the Aleutian arc. . . . The Andes are considered as representing a final evolutionary stage in the development of an island-arc that culminates in the formation of an igneous range separated by a geosynclinal depression from the continental land-mass and bordered by a deep oceanic trough facing the Ocean.
Island arc
Trough (economics)
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The Andes constitute Argentina's western boundary with Chile from Latitude 22°50^prime South to Latitude 50°48^prime South. The mountain belt of western Argentina consists of a series of sub-parallel meridional chains, which decrease in number, width, and elevation from north to south. Although the Andes may be considered as a single geographic unit, they are formed by several different morpho-structural elements oriented from north-northwest to south-southeast, and therefore oblique to the trend of the continental divide. The various morpho-structural elements which, from north to south, constitute the Chilean-Argentinian Andes, are as follows: (1) the high plateau of the Puna de Atacama, followed toward the east by the Eastern Cordilleras (Prepuna) and the Subandean ranges, (2) the Pampean ranges, (3) the Precordillera of La Rioja, San Juan, and Mendoza, (4) the Cordillera Frontal, (5) the Cordillera Principal, and (6) the Patagonian Cordillera. The extension and main stratigraphical and structural features of the different morpho-structural elements, as well as the geologic evolution of western Argentina, are summarily described. End_of_Article - Last_Page 408------------
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Continental Margin
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The north central Peruvian Andes (c . 9-11 0S) are divided into the Cordillera Oriental and the Cordillera Occidental. Uplift of this part of the Andes has occurred s ince ~ 10-20 Ma , and since that time deep canyons have been incised (3-4 km of relief) and rugged ranges have been emerged along the crest of the uplift (peak eJevations 5-7 km and relief of 3-4 km) . High-relief ranges are distinct in the Cordillera Oriental, which has the highest peaks in Peru: these include Huscaran (6768 m) in the Cordillera Blanca, and Yerupaja (6634 m) in the Cordillera Huayhuash. These ranges represent the largest glaciated region in equatorial South America, and therefore glacial erosion rate s are presumably higher than adjacent areas. Deep canyon incision has been profound in Pacific-draining rivers that have their source in this glaciated terrain. These deeply inc ised rivers include the Rio Santa, which drains the Cordillera Blanca, and the Rio Pativilica, which drains the Cordillera Huayhuash. The timing of uplift and local intense exhumation varies along strike, but the majority of regional uplift is generally viewed as being Miocene to Plio-Pleistocene. We have focused our thermochronological studies on three areas in this region. 1) The Cordillera Blanca, along the Andean crest and which is bound on its western edge by the Active Cordillera Blanca Normal Fault; 2) the Cordillera Huayhuash, also along the crest of Andes, south of the Blanca, and 3) The Rio Pativilica, whose headwaters drain the Cordillera Huayhuash.
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Tectonic uplift
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The first article in this book is the address that introduced the technical program of the 46th Annual Meeting of the AAPG. The organization and presentation of this symposium volume was developed in an orderly geographic continuity. Modern concepts of structural form and the sequence of tectonic events are carefully reported all along the mountainous western margins of the American continents. The relationship of this structural knowledge to the accumulation of oil and gas is constantly emphasized in the 26 papers contained herein.
Presentation (obstetrics)
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Neogene
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Paleogene
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Morphotectonic and paleoseismic studies carried out in the surrounds of Tuluá (4°N, 76°W) provide strong supporting evidence for ongoing E-W compression in the Cauca Valley, Colombia, during the late Pleistocene and Holocene. This local tectonic regime is kinematically and mechanically connected with the ENE-striking, right-lateral, strike-slip Ibagué fault system, which crosscuts and offsets the Central Cordillera of Colombia.
Foothills
Central Asia
Neotectonics
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Chile, 2,600 miles long and 100 miles wide, extends from the arid deserts of the North to the cold, windy pampas of the South. It occupies the area from the crest of the Andes to the Pacific Ocean. Geologically, it occupies a long, mobile belt lying west of the stable shield area. Through a series of orogenies it has developed the present Cordilleras. This Andean geosyncline has been a zone of weakness from Precambrian time to the present. The Andean Cordillera, one of the highest mountain chains in the world, is complicated geologically and tectonically. Two principal provinces can be described, the Eastern and Western, separated by the great central valley of Chile, in which lies the capital, Santiago. The Western Cordillera, the older, represents an extensive batholith of continental character, and is largely granitic in character. Normal block faulting and folding occur. The principal uplift occurred in the Upper Mesozoic. The Eastern Cordillera is composed principally of metamorphic and sedimentary rocks, although evidences of its crystalline core are common. Structurally they show block faulting, with some evidence of thrusting toward the east. Principal uplift occurred during the Tertiary and Quaternary. Close inshore in the Pacific are troughs 23,000 feet deep. Recent vulcanism is common. At the southern end of Chile the Andes make a strong eastward swing and thence, by an island arc very similar to the Caribbean Island Arc, join the Andes to the mountains of the Palmer Peninsula of the Antarctic, 600 miles south. End_of_Article - Last_Page 408------------
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Establishing the timing of surface uplift in the Central Andes is essential for evaluating the geodynamic mechanisms responsible for mountain building and their role in the development of dry conditions along the western coasts of Peru and Chile. Here, we present new stable hydrogen isotopic values from stream waters and hydration water in volcanic glass from northern Chile (18.5–19.5°S) that show that the Western Cordillera was already elevated by the early Miocene. The hydrogen isotopic values of reconstructed surface waters obtained from ancient and modern volcanic glass indicate that the Western Cordillera in northern Chile attained modern elevations by at least 22.8 Ma. When combined with paleoaltimetric records from the Altiplano and northwestern Puna, these results demonstrate that surface uplift of the Andean plateau was a time-transgressive process that varied not just from west to east but also from north and south along the strike of the orogen. Our paleoaltimetry reconstruction also suggests that the Western Cordillera has blocked moisture coming from the east since at least the early Miocene, consistent with previously published evidence of arid-semiarid conditions in the Atacama Desert. However, hyperaridity on the western Andean slope developed later and appears to correspond with the timing of uplift in the Eastern Cordillera and Altiplano. Our results suggest that the growth of the Central Andean rain shadow relied not only on the elevation of the Western Cordillera but also on the widening of the plateau.
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