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Magmatic history and crustal genesis of western South America; constraints from U-Pb ages and Hf isotopes of detrital zircons in modern rivers

Martin Pepper, George E. Gehrels, Alex Pullen, Mauricio Ibanez-Mejia, Kevin M. Ward and Paul Kapp
Magmatic history and crustal genesis of western South America; constraints from U-Pb ages and Hf isotopes of detrital zircons in modern rivers
Geosphere (Boulder, CO) (July 2016) 12 (5): 1532-1555

Abstract

Western South America provides an outstanding laboratory for studies of magmatism and crustal evolution because it contains Archean-Paleoproterozoic cratons that amalgamated during Neoproterozoic supercontinent assembly, as well as a long history of Andean magmatism that records crustal growth and reworking in an accretionary orogen. We have attempted to reconstruct the growth and evolution of western South America through U-Pb geochronologic and Hf isotopic analyses of detrital zircons from 59 samples of sand mainly from modern rivers. Results from 5524 new U-Pb ages and 1199 new Hf isotope determinations are reported. Our data are integrated with previously published geochronologic and Hf isotopic information, yielding a combined record that includes >42,000 ages and >1900 Hf isotope analyses. These large data sets yield five main conclusions: (1) South America has an age distribution that is similar to most other continents, presumably reflecting processes of crustal generation and/or preservation related to the supercontinent cycle, with age maxima at 2.2-1.8 Ga, 1.6-0.9 Ga, 700-400 Ma, and 360-200 Ma; (2) <200 Ma magmatism in western South America has age maxima at ca. 183, 166, 149, 125, 110, 88, 65, 35, 21, and 4 Ma (with significant north-south and east-west variations), yielding an average cyclicity of approximately 33 m.y.; (3) for the past 200 m.y., no correlation exists between magmatism and the velocity of convergence between central South America and Pacific oceanic plates, the age of the downgoing plate, or the absolute motion of South America; (4) Hf isotopes record reworking of older crustal materials during most time periods, with incorporation of juvenile crust at ca. 1.6-1.0 Ga, 500-300 Ma, and ca. 175-35 Ma; and (5) the Hf isotopic signature of <200 Ma magmatism is apparently controlled by the generation of evolved crust during crustal thickening and eastward arc migration, versus juvenile magmas during extensional tectonism and westward and/or outboard migration of arc magmatism.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 12
Serial Issue: 5
Title: Magmatic history and crustal genesis of western South America; constraints from U-Pb ages and Hf isotopes of detrital zircons in modern rivers
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 1532-1555
Published: 20160722
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 143
Accession Number: 2016-085263
Categories: Sedimentary petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201641
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