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Crustal-thickness variations in the Central Andes

Susan L. Beck, George Zandt, Stephen C. Myers, Terry C. Wallace, Paul G. Silver and Lawrence Drake
Crustal-thickness variations in the Central Andes
Geology (Boulder) (May 1996) 24 (5): 407-410


We estimated the crustal thickness along an east-west transect across the Andes at lat 20 degrees S and along a north-south transect along the eastern edge of the Altiplano from data recorded on two arrays of portable broadband seismic stations (BANJO and SEDA). Waveforms of deep regional events in the downgoing Nazca slab and teleseismic earthquakes were processed to isolate the P-to-S converted phases from the Moho in order to compute the crustal thickness. We found crustal-thickness variations of nearly 40 km across the Andes. Maximum crustal thicknesses of 70 - 74 km under the Western Cordillera and the Eastern Cordillera thin to 32 - 38 km 200 km east of the Andes in the Chaco Plain. The central Altiplano at 20 degrees S has crustal thicknesses of 60 to 65 km. The crust also appears to thicken from north (16 degrees S, 55 - 60 km) to south (20 degrees S, 70 - 74 km) along the Eastern Cordillera. The Subandean zone crust has intermediate thicknesses of 43 to 47 km. Crustal-thickness predictions for the Andes based on Airy-type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation. In contrast, at the boundary between the Eastern Cordillera and the Subandean zone and in the Chaco Plain, the crust is thinner than predicted, suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere. With additional constraints, we conclude that the observation of Airy-type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting Nazca plate and the cratonic lithosphere of the Brazilian craton.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 24
Serial Issue: 5
Title: Crustal-thickness variations in the Central Andes
Affiliation: University of Arizona, SASO and Department of Geosciences, Tucson, AZ, United States
Pages: 407-410
Published: 199605
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 26
Accession Number: 1996-042312
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: South. Ariz. Seism. Obs., Contrib. No. 81
Illustration Description: illus. incl. geol. sketch map
S21°30'00" - S15°00'00", W70°00'00" - W60°00'00"
Secondary Affiliation: Lawrence Livermore National Laboratory, USA, United StatesCarnegie Institution of Washington, Washington, USA, United StatesObservatorio San Calixto, La Paz, BOL, Bolivia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199614
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