INSUGEO   12554
INSTITUTO SUPERIOR DE CORRELACION GEOLOGICA
Unidad Ejecutora - UE
artículos
Título:
The juxtaposition of Cambrian and early Ordovician magmatism in the Tafí del Valle area. Characteristics and recognition of Pampean and Famatinian magmatic suites in the easternmost Sierras Pampeanas
Autor/es:
LÓPEZ, JOSE PABLO; TASSINARI, COLOMBO CELSO GAETA; DÍAZ-ALVARADO, JUAN; ACOSTA NAGLE, ANA EUGENIA; SCHLEICHER, ANJA; BELLOS, LAURA IUDITH; RODRÍGUEZ, NATALIA; ALTENBERGER, UWE
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Año: 2020 vol. 104
ISSN:
0895-9811
Resumen:
Along more than 1000 km, the boundary between the Pampean and Famatinian belts separates the Cambrianmagmatism to the east (540-515 Ma) from the easternmost granitic rocks ascribed to the Famatinian orogeny tothe west (early Ordovician). The geochronological and geochemical study presented in this work has revealed thefirst Cambrian magmatism in the Sierras de Aconquija and Cumbres Calchaquíes at the northeastern edge of theFamatinian belt. Pabellon ´ (522 ± 2.8 Ma) and Nu? norco ? Grande (478.3 ± 2.3 Ma) intrusive units form part of thesmall plutons exposed together in the Tafí del Valle area, which have been related according to their geochemicalcharacteristics. The good correlation observed between ages and characteristic geochemical signatures havemotivated the comparison with other intrusive complexes along the Pampean and eastern Famatinian belts,resulting in regional diagnostic geochemical features and a petrogenetic and evolutive proposal for the Cambrianand early Ordovician magmatism in the eastern Sierras Pampeanas. Easternmost early Ordovician granitic rocksconstitute a calcic, weak to moderately peraluminous series. They are Sr-rich tonalitic to monzogranitic magmas(SiO2 >62 %wt.) with steep REE patterns, positive and negative Eu anomalies, high Sr/Y and moderate Ce/Ybratios. Accordingly, the water-fluxed melting of a mafic source under high to moderate pressures may beinvolved in the origin of silica- and Ca-rich parental magma. The shallower evolution of these melts consists of Pldominated fractionation trends that finally constituted Pl-rich crystal mushes (tonalites) and more felsic residualliquids. Regarding Cambrian granodiorites and monzogranites, any petrogenetic scheme must consider themagnesian, high-K calc-alkalic characteristics for a short-range silica variation, low to moderate peraluminosityand high zircon saturation temperatures (>850 ◦C). Source conditions are determined by the presence of Pl andHbl in the solid assemblage based on the REE patterns. These geochemical characteristics point to the extensiveHT-LP melting of a dominantly crustal source, probably assisted by the injection of hot H2O-rich mafic melts.