Geology of Bolivia
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Geological units:
Quaternary deposits Quaternary volcanics Tertiary deposits Creataceous-Tertiary volcanics Cretaceous age rocks Devonian age rocks Silurian age rocks Ordovician-Silurian age rocks
Precambrian undifferentiatedThe geology of Bolivia compromises a variety of different lithologies as well as tectonic and sedimentary environments. On a synoptic scale geological units coincide with topographical units, to begin the country is divided into a mountainous western area affected by the subduction processes in the Pacific and a eastern lowlands of stable platforms and shields. The Bolivian Andes is divided into three main ranges these are from west to east; the Cordillera Occidental that makes up the border to Chile and host several active volcanoes and geothermal areas, Cordillera Central once extensively mined for silver and tin and the relatively low Cordillera Oriental that is a fold and thrust belt. Between the Occidental and Central Cordillera the ~3,750 meter high Altiplano high plateau extends. This basin host several freshwater lakes, including Lake Titicaca as well as salt-covered dry lakes that brings testimony of past climate changes and lake cycles. The eastern lowlands in Santa Cruz, Chuquisaca, and Tarija Departments are old Paleozoic sedimentary basins that host valuable hydrocarbon reserves. Further east close to the border with Brazil lies the Guaporé Shield made up of stable Precambrian crystalline rock.
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Andes
The Andes of Bolivia begun to rise about 200 million years ago (mya) during the Jurassic. The western margin of what is now South America had been the place of several other orogenies before the Andes rose. It has been hypotecized that the central Andes gained its great height 26 to 14 mya as result of a compressive failure of the lithosphere beneath Bolivia and neighboring areas. The great heights of the Altiplano, Codillera Occidental and Cordillera Oriental are isostatically compensated by a up to 70 km deep crust. It's not known to which extent climate changes induced by the rise of the Andes caused the extreme aridity of Atacama Desert and adjacent parts of Bolivia or if a preexisting desert climate and associated low erosion rates allowed the mountains to build up to their current heights. A hypothesis holds that scarce sediment supply to the Atacama Trench caused by arid climate induced high shear stresses in the subduction process that enchanced the Andean mountain building.
The relatively low Cordillera Oriental, located east of Cordillera Central, are part of a fold and thrust belt and exposes Silurian and Ordovician age strata some of which are fossil-bearing.
The western volcanoes of Bolivia are part of the Central Volcanic Zone of the Andes, a major upper Cenozoic volcanic province.
Eastern lowlands
The geology of the eastern lowlands is dominated by the ancient Paleozoic sedimentary Chaco-Tarija Basin that has considerable hydrocarbon reserves. During the Carboniferous, the Chaco-Tarija Basin was covered by thick sequences that included sandstone filled channels. In the 1970s these sandstone were interpreted as tillite from the late Paleozoic glaciations, but new interpretations consider them to be of marine origin but still glacially influenced. The depositional environment for these channel systems has been likened to that on the floor of the present day Labrador Sea, which was influenced by repeated Pleistocene glaciations . The late Cenozoic deformation associated with the Andean orogeny forced hydrocarbons sourced in Devonian shales to migrate to shallower stratigraphical levels.
Guaporé Shield
In the north and east of Santa Cruz Department the crystalline and Precambrian Guaporé Shield (also called Central Brazil Shield) makes up most of the bedrock but is mostly covered by Tertiary laterites and Quaternary alluvial basins. High metamophism rocks occur in the Bolivian part of the Guaporé Shiled partly due to the 2000 millions years old "Transamazonian Tectono-Thermal Event" that affected parts of South America. Low metamorphism rocks occurs as well. The Guaporé Shield is believed to extend beneath a the Phanerozoic Tarija-Chaco and Beni Basin sediments into the Andes. Weakenses in the Guaporé Shield have been suggested to be responsible for the formation of the Arica Elbow. The East-West Río Mercedes Line in the Guaporé Shield host several Proterozoic diabase intrusions. As of 1985 the rocks of Guaporé Shiled were considered to be poorly known.
See also
References
- ^ The Use of Solar Energy for Improving the Living Conditions in Altiplano/Argentina
- ^ Geology of the Altiplano, Oregon State University
- ^ Neogene climate change and uplift in the Atacama Desert, Chile
- ^ Tectonics and Climate of the Southern Central Andes, Annual Review of Earth and Planetary Sciences, 2007.
Cite: "precipitation and erosion may influence the kinematics and locus of tectonic activity in orogens." - ^ David R. Montgomery, Greg Balco and Sean D. Willett. 2001 Climate, tectonics, and the morphology of the Andes
Cite: "...like tectonics, nonuniform erosion due to large-scale climate patterns is a first-order control on the topographic evolution of the Andes." - ^ Lamb and Davis. 2003. Cenozoic climate change as a possible cause for the rise of the Andes, Nature
- ^ Baker, M.C.W. and Francis, P.W. 1978. UPPER CENOZOIC VOLCANISM IN THE CENTRAL ANDES - AGES AND VOLUMES
- ^ a b Petroleum Basins of South America, Hydrocarbon-Bearing Late Paleozoic Glaciated Basins of South America, page 175. 1995
- ^ Petroleum Basins of South America, Hydrocarbon-Bearing Late Paleozoic Glaciated Basins of South America, page 180. 1995
- ^ Petroleum Basins of South America, Hydrocarbon-Bearing Late Paleozoic Glaciated Basins of South America, page 178. 1995
- ^ Litherland,M. and Bloomfield, K. 1981. The proterozoic history of eastern Bolivia, Precambrian Reseach, vol 15, issue 2.
- ^ METALLIFEROUS ORE DEPOSITS OF BOLIVIA
- ^ Jones, J.P. 1985. The southern border of the Guaporé Shield in western Brazil and Bolivia: An interpretation of its geologic evolution
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