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Neoproterozoic backarc basin; sensitive high-resolution ion microprobe U-Pb and Sm-Nd isotopic evidence from the eastern Pampean Ranges, Argentina

Monica P. Escayola, Marcio M. Pimentel and Richard Armstrong
Neoproterozoic backarc basin; sensitive high-resolution ion microprobe U-Pb and Sm-Nd isotopic evidence from the eastern Pampean Ranges, Argentina
Geology (Boulder) (June 2007) 35 (6): 495-498

Abstract

The Eastern Pampean Ranges comprise high-grade supracrustal sequences with linear belts of mafic-ultramafic bodies representing ophiolite remnants. New U-Pb and Nd isotopic data suggest that the tectonic evolution of the Pampean Ranges started ca. 640 Ma with the deposition of supracrustal sequences in a backarc basin between a Neoproterozoic magmatic arc to the east and the Pampia terrane to the west. Ophiolite remnants of this backarc basin yielded a whole-rock isochron indicating the age of 647+ or -77 Ma (2sigma ) and epsilon (sub Nd) (initial time [T]) of +5.2. Sensitive high-resolution ion microprobe U-Pb data for detrital metasediments show provenance patterns with two main age populations: the older 1.1-0.9 Ga, and the younger between ca. 0.7 and 0.6 Ga. The Neoproterozoic population is relatively more abundant in sediments of the easternmost units of the Eastern Pampean Ranges and becomes less abundant toward the west. Depleted mantle ages show a similar pattern, with ages generally increasing from east (1.42 Ga) to west (1.76 Ga), suggesting the presence of Neo-proterozoic sources to the east of the ranges. The provenance data do not support previous evolution models for the Eastern Pampean Ranges, according to which the supracrustal sequence represents the passive margin of the Rio de la Plata craton. Early Cambrian collision and high-grade metamorphism mark the final stages of evolution of the belt and were shortly followed by calc-alkaline metaluminous and peraluminous granitic magmatism ca. 530-514 Ma. The results suggest that the geological evolution of the Eastern Pampean Ranges took place between ca. 640 and 514 Ma, coeval with other Brasiliano orogens in Brazil (e.g., the Paraguay and Araguaia fold belts).


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 35
Serial Issue: 6
Title: Neoproterozoic backarc basin; sensitive high-resolution ion microprobe U-Pb and Sm-Nd isotopic evidence from the eastern Pampean Ranges, Argentina
Affiliation: Universidad Nacional de Salta, Salta, Argentina
Pages: 495-498
Published: 200706
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 13
Accession Number: 2007-059763
Categories: Geochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2007121
Illustration Description: illus. incl. sects., geol. sketch map
S32°15'00" - S30°49'60", W65°30'00" - W64°00'00"
Secondary Affiliation: Universidade de Brasilia, BRA, BrazilAustralian National University, AUS, Australia
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: 200731
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