Potassium-argon ages of some Bolivian rocks

Evernden, Jack F.; Kriz, S. J.

doi:10.2113/gsecongeo.72.6.1042

Cited by 87 publications

(66 citation statements)

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“…Felsic to intermediate shallow level intrusions, volcanic stocks, and ignimbrites, emplaced or erupted between 26 and 2 Ma, are found on the western margin of the Eastern Cordillera, more-or-less within the region of active mantle melting indicated by helium emissions-magmatic activity here prior to ϳ26 Ma is rare. (b) Plot of age against distance perpendicular to the active arc of Neogene volcanic and plutonic rocks in the Andes between 16°S and 22°S (compiled from Evernden et al 1977;Grant et al 1979;Lahsen 1982;Schneider 1985;Redwood and MacIntyre 1989;Hoke et al 1993;Kennan et al 1995;Barreiro et al 1998;Worner et al 2000;Barke and Lamb 2006;Barke et al 2007;Hoke and Lamb 2007). EC, Eastern Cordillera.…”

Section: Uplift Due To Erosion Sedimentation and Magmatic Additionmentioning

confidence: 99%

Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

Lamb

2016

Can. J. Earth Sci.

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Abstract:The Cenozoic geological evolution of the Central Andes, along two transects between ϳ17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion, and magmatic addition. Prior to ϳ25 Ma, during a phase of amagmatic flat-slab subduction, thick-skinned crustal shortening and thickening (nominal age of initiation ϳ40 Ma) was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography at this time in the Altiplano and the western margin of the Eastern Cordillera appears to be ϳ1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ϳ27-25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1-1.5 km of rapid uplift (over Ͻ Ͻ5 Myrs) of the Altiplano and western margin of the Eastern Cordillera and establishing the present day lithospheric structure beneath the high Andes. Since ϳ25 Ma, surface uplift has been the direct result of crustal shortening and thickening, locally modified by the effects of erosion, sedimentation, and magmatic addition from the mantle. The rate of crustal shortening and thickening varies with location and time, with two episodes of rapid shortening in the Altiplano, lasting <5 Myrs, that are superimposed on a long-term history of ductile shortening in the lower crust, driven by underthrusting of the Brazilian Shield on the eastern margin.

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Section: Uplift Due To Erosion Sedimentation and Magmatic Additionmentioning

confidence: 99%

Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

Lamb

2016

Can. J. Earth Sci.

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“…The most regionally extensive unit is the oldest: a suite of redbeds that reaches a 5-km thickness and spans the late Paleocene through Oligocene (Figure 7, Stage 1) (Alonso et al 1991, Evernden et al 1977, Kennan et al 1995, Pascual et al 1978, Sempere et al 1997, Vandervoort 1993. These units may have accumulated in a foreland basin (Sempere et al 1990a) that is associated first with Incaic deformation west of the basin (∼38 Ma), and later with an early phase of deformation to the east (Kennan et al 1995, Sempere et al 1997.…”

Section: Sedimentary Basin Variation Within the High Plateaumentioning

confidence: 99%

“…After about 13 Ma, accumulation of strata on the Altiplano was characterized by thinner units (totaling less than 2000 m, Evernden et al 1977) that are spatially variable. Progressive tilting of these units indicates a complicated history of local deformations as well (Figure 7, Stage 4).…”

Section: Sedimentary Basin Variation Within the High Plateaumentioning

confidence: 99%

The Evolution of the Altiplano-Puna Plateau of the Central Andes

Allmendinger

Jordan²,

Kay³

et al. 1997

Annu. Rev. Earth Planet. Sci.

815

658

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▪ Abstract The enigma of continental plateaus formed in the absence of continental collision is embodied by the Altiplano-Puna, which stretches for 1800 km along the Central Andes and attains a width of 350–400 km. The plateau correlates spatially and temporally with Andean arc magmatism, but it was uplifted primarily because of crustal thickening produced by horizontal shortening of a thermally softened lithosphere. Nonetheless, known shortening at the surface accounts for only 70–80% of the observed crustal thickening, suggesting that magmatic addition and other processes such as lithospheric thinning, upper mantle hydration, or tectonic underplating may contribute significantly to thickening. Uplift in the region of the Altiplano began around 25 Ma, coincident with increased convergence rate and inferred shallowing of subduction; uplift in the Puna commenced 5–10 million years later.

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“…Second, in the $3-km-high eastern part of the Eastern Cordillera, successions of probable middle Eocene -Oligocene age are exposed along an arcuate, 600-km-long, discontinuous belt of largemagnitude synclines: from north to south, the Morochata, Torotoro, Incapampa, Otavi, and Camargo synclines (Figure 1). Previous investigations have addressed the stratigraphy of both the central zone and eastern syncline belt [Ahlfeld and Branisa, 1960;Lohmann and Branisa, 1962;Ahlfeld, 1965;Ponce de León, 1966;Evernden et al, 1977;Martinez, 1980;Sempere et al, 1989Sempere et al, , 1997Martinez et al, 1990;Marshall and Sempere, 1991;Hérail et al, 1996;Blanco, 1994;Pacheco and Fernandez, 1994;Kennan et al, 1995;Tawackoli et al, 1996;Horton, 1998;Horton and DeCelles, 2001;Müller et al, 2002;DeCelles and Horton, 2003]. However, it is unclear whether these outcrop belts developed as disconnected intermontane basins, integrated foredeep depocenters, or some other type of sedimentary basin.…”

Section: Geologic Frameworkmentioning

confidence: 99%

“…Eight [Evernden et al, 1977], 21.9 ± 0.36 Ma to 20.9 ± 0.32 Ma for six tuffs [Grant et al, 1979], and 19.7 ± 0.8 Ma and 19.0 ± 0.7 Ma for a single tuff [Kennan et al, 1995].…”

mentioning

confidence: 97%

Revised deformation history of the central Andes: Inferences from Cenozoic foredeep and intermontane basins of the Eastern Cordillera, Bolivia

2005

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Investigation of Cenozoic deformation, sediment accumulation, and provenance in the Eastern Cordillera of Bolivia at 17–21°S indicates major shortening (60–140 km) and foredeep development followed by limited internal shortening and intermontane basin development. Contrasting histories of shortening, deposition, sediment dispersal, and detrital composition distinguish a formerly extensive Paleogene foredeep exposed along an eastern belt of synclines from a zone of principally Neogene intermontane basins in the central Eastern Cordillera. New 40Ar/39Ar ages of 25–17 Ma for interbedded tuffs reveal latest Oligocene–early Miocene accumulation in intermontane basins at rates <80 m/Myr, several times lower than Andean foredeeps. Although poorly dated, foredeep evolution probably coincided with middle Eocene–Oligocene deformation and denudation in adjoining regions to the west. A mid‐Cenozoic transition from foredeep to intermontane conditions may be attributable to emplacement of a basement‐involved tectonic wedge beneath the Eastern Cordillera. In this interpretation, wedge emplacement drove flexural foredeep subsidence from roughly 40 to 25 Ma, whereas subsequent accumulation occurred in localized internally drained basins in elevated intermontane areas. Regardless of the regional subsurface structural geometry, 40Ar/39Ar ages define a 25–21 Ma onset of intermontane sedimentation that signifies the termination of major upper crustal shortening over large parts of the Eastern Cordillera and possibly the age of initial shortening in the Interandean and Subandean zones to the east. In contrast to several popular models, the revised tectonic history presented here suggests significant pre‐Neogene shortening in the Eastern Cordillera and underscores the large uncertainties in estimates of long‐term shortening rates in the Andes.

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Potassium-argon ages of some Bolivian rocks

Cited by 87 publications

References 0 publications

Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

The Evolution of the Altiplano-Puna Plateau of the Central Andes

Revised deformation history of the central Andes: Inferences from Cenozoic foredeep and intermontane basins of the Eastern Cordillera, Bolivia

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