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Hf and Nd isotopes in Early Ordovician to Early Carboniferous granites as monitors of crustal growth in the Proto-Andean margin of Gondwana

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Dahlquist, Juan A. and Pankhurst, R.J. and Gaschnig, Richard M. and Pankhurst, R.J. and Rapela, Carlos W. and Casquet, César and Alasino, Pablo H. and Galindo Francisco, Mª del Carmen and Baldo, Edgardo G. (2013) Hf and Nd isotopes in Early Ordovician to Early Carboniferous granites as monitors of crustal growth in the Proto-Andean margin of Gondwana. Gondwana research, 23 . pp. 1617-1630. ISSN 1342-937X

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Abstract

Wereport the first study integrating in situ U–Pb and Hf isotope data frommagmatic zircon andwhole-rock Sm–Nd isotope data for granitic rocks of the Sierras Pampeanas, Argentina, in order to evaluate the Palaeozoic growth of the proto-Andean margin of Gondwana. Early–Middle Ordovician granitic magmatism is by far the most voluminous of the Sierras Pampeanas and represents the most significant magmatic event. These calc-alkaline granitoids were intruded at an active continental margin. εHft values range from −3.3 to −14.7 and εNdt from −3.3 to −6.3 (t=473 Ma), with average TDM Hf and TDM Nd ranging from 1.5 to 2.2 Ga and 1.4 to 1.7 Ga, respectively. Middle–Late Devonian magmatism occurred in the foreland, away from the orogenic front in the west, and included F-U-REE rich A-type granites. The Achala granite, the largest batholith in the Sierras Pampeanas, has εHft and εNdt values ranging from −3.6 to −5.8 and −4.0 to −6.5, respectively (t=369 Ma). Small scattered Early Carboniferous A-type granite plutons were intruded in a dominantly extensional setting and have εHft and εNdt values ranging from−6.7 to+2.2 and−0.5 to−3.6, respectively (t=341 Ma). The generation of Ordovician and Devonian magmas dominantly involved crustal reworking and stabilization rather than the formation of new continental crust by juvenile material accretion, whereas carboniferous magmatism resulted in part from reworking of supracrustal material, but with variable addition of juvenile magmas.


Item Type:Article
Uncontrolled Keywords:U–Pb dating, Hf and Nd isotopes, Zircon, Crustal growth, Proto-Andean margin of Gondwana
Subjects:Sciences > Geology > Petrology
ID Code:56956
Deposited On:10 Sep 2019 11:12
Last Modified:05 Nov 2019 12:29

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