Age of the El Hornito pluton and thermobarometry of its thermal aureole: Insights into achalian (Devonian) magmatism in the Sierras Pampeanas of Argentina

MUÑOZ, BRIAN LUCAS; ENRIQUEZ, ELIEL; MOROSINI, AUGUSTO FRANCISCO; DEMARTIS, MANUEL; ORTIZ SUÁREZ, ARIEL EMILIO; PINOTTI, LUCIO PEDRO; D'ERAMO, FERNANDO JAVIER; CHRISTIANSEN, RODOLFO OMAR; BASEI, MIGUEL ANGELO; GROSSO CEPPARO, PABLO M.; PAGANO, DIEGO SEBASTIAN; RAMOS, GABRIEL ALEJANDRO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2022 vol. 114

0895-9811

Acomprehensive study of the El Hornito Pluton, located in the Sierra Grande deSan Luis (Argentina) is presented in this work. The intrusive body is acomposite pluton constituted by four main units: 1) Granitic Porphyritic Unit,2) Granitic Red Unit, 3) Granitic External Unit and 4) Mafic-Hybrid Unit. The main intrusive (granitic) units are crosscut bysyn-magmatic felsic dikes. A Devonian age of 385 ± 2 Ma was obtained by U?Pb SHRIMP analyses on zircons belonging to theGranitic Porphyritic Unit. This age is considered representative of the ElHornito Pluton crystallization since the Granitic Porphyritic Unit is the mostvoluminous one. The Granitic Red Unit crops out in the central zone of the ElHornito Pluton and hosts the largest proportion of the rocks that comprise theMafic-Hybrid Unit, where mingling/mixing processes are evident. The host rockslocated in the western sector of the El Hornito Pluton present an intensecontact metamorphism. Electron microprobe analyses of plagioclase, garnet,biotite, and muscovite in a garnet-sillimanite hornfels were performed tocalculate thermobarometry from multireaction procedures in these hornfels,yielding P-T values of 3.7 ± 1.1 kbar and 626 ± 32 ◦C.These conditions are considered representative of the emplacement level of theEl Hornito Pluton. Theresults of this study show that the El Hornito Pluton was emplaced at a depthof 14.1 ± 4.2 km, evidencing deeper crustal levels of emplacement than theAchalian granites of the Sierra de C´ordoba. Theage obtained in this work, along with others reported for the Sierras de SanLuis and C´ordoba, indicate that the intrusions occurred first inthe west and later in the east. Moreover, according to the emplacement levelsat which intrusions took place, different exhumation rates are proposed to haveoccurred across the orogen (in an NE-SW direction) after the Devonianmagmatism, being greater in the Sierra de San Luis (southwest) than in theSierras de Córdoba (northeast).