Early Carboniferous sub- to mid-alkaline magmatism in the Eastern Sierras
Pampeanas, NW Argentina: A record of crustal growth by the incorporation of
mantle-derived material in an extensional setting
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2012
Authors
Alasino, Pablo H.
Dahlquist, Juan A.
Pankhurst, R.J.
Rapela, Carlos W.
Larrovere, M.A.
Fanning, C.M.
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Elsevier Science B. V., Amsterdam
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Abstract
A recently discovered granitic intrusion at Cerro La Gloria in western Sierra de Famatina (NW Argentina) is
representative of sub- to mid-alkaline Carboniferous magmatism in the region. The main rock type consists
of microcline, quartz and plagioclase, with amphibole, magnetite, ilmenite, biotite, epidote, zircon, allanite
and sphene as accessory minerals. We report a U–Pb zircon SHRIMP age for the pluton of 349±3 Ma
(MSWD=1.1), i.e., Tournaisian. Whole-rock chemical composition and Nd isotope analyses are compatible
with an origin by melting of older mafic material in the lower crust (εNdt between −0.58 and +0.46 and
TDM values of about 1.1 Ga). The pluton is intruded by penecontemporaneous to late alkaline mafic dykes
that are classified as back-arc basalts. Coeval, Early Carboniferous A-type granites occur farther east in the Sierras
Pampeanas, probably generated during lithospheric stretching. Overall, the Early Carboniferous granitic
rocks show a west-to-east mineralogical and isotopic zonation indicating that magma genesis involved a
greater contribution of juvenile material of mantle character to the west. Based on the observed patterns
of geochronology, geochemistry and field relationships we suggest that A-type magma genesis in the Eastern
Sierras Pampeanas was linked to an Andean-type margin where the lithospheric mantle played a role in its
generation.