A combined zircon Hf isotope and whole-rock Nd and Sr isotopes study of Carboniferous A-type granites, Sierras Pampeanas of Argentina

Author(s)

Dahlquist, Juan A. ^[1] ; Galindo, Carmen ^[2] ; Morales Camera, Matias M. ^[1] ; Moreno, Juan A. ^[1] ; Alasino, Pablo H. ^{[3, 4]} ; Basei, Miguel A. S. ^[5] ; Macchioli Grande, Marcos ^{[3, 4]}

Affiliation

^[1] Univ Nacl Cordoba, Fac Ciencias Exactas Fis & Nat, Ctr Invest Ciencias Tierra CICTERRA, CONICET, Av Velez Sarsfield 1611, Edificio CICTERRA, Cordoba - Argentina

^[2] Univ Complutense, Fac Ciencias Geol, Dept Mineral & Petrol, CSIC, Inst Geociencias IGEO, Madrid 28040 - Spain

^[3] INGeReN CENIIT UNLaR, Av Gob Vernet & Apostol Felipe, RA-5300 La Rioja - Argentina

^[4] Ctr Reg Invest Cient & Transferencia Tecnol La Ri, Prov La Rioja UNLaR SEGEMAR UNCa CONICET, Entre Rios & Mendoza S-N, RA-5301 Anillaco - Argentina

^[5] Univ Sao Paulo, Inst Geociencias, Rua Lago, BR-05508080 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 100, JUN 2020.
• Web of Science Citations: 0

Abstract

We report new whole-rock Nd and Sr isotope data for two strongly peraluminous and one slightly peraluminous Carboniferous A-type granitic plutons in the eastern Sierras Pampeanas of Argentina. Our study also integrates previous petrological and geochemical information with in situ U-Pb and Hf isotope data from magmatic and inherited zircon. Strongly peraluminous samples have pronounced negative epsilon Nd-t values (-7.6 and -7.0) and very high (Sr-87/Sr-86)(t) values (0.728778 and 0.747092). These are similar to isotope compositions reported for the Puncoviscan Series, a metasedimentary sequence metamorphosed during the Lower Cambrian and intruded by these granites. Nd and Sr isotope data for the slightly peraluminous sample (epsilon Nd-t = - 3.5 and Sr-87/Sr-86(t) = 0.708074), together with previously reported petrological and geochemical data, indicate that the basement of the Sierras de Cordoba participated in the generation of the parental magma. The new data are not easily reconciled with the positive zircon epsilon Hf-t values previously reported for these samples, which suggest dominantly juvenile material in the source. We propose that Hf was transferred from inherited zircon toward the magmatic rim, without complete isotopic homogenization with the magma, as has been hypothesized in previous works. Our results reveal that the indiscriminate use of Hf databases can lead to false inference of crustal growth by mantle addition through time and misleading comparisons between granitic rocks worldwide. (AU)

• FAPESP's process: 18/06837-3 - U-Pb zircon geochronology and HF data from magmatic zircon in devonian-carboniferous granites as monitors of crustal growth and geodynamic setting, pre-andean continental margin of SW Gondwana
• Grantee: Miguel Angelo Stipp Basei
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• FAPESP's process: 15/03737-0 - The Rio de La Plata Craton and the Western Gondwana Assembly
• Grantee: Miguel Angelo Stipp Basei
• Support Opportunities: Research Projects - Thematic Grants