Recycled Pampean crustal sources for Devonian-Carboniferous strongly Peraluminous A-type granites from the Characato granitic complex (Achala batholith), Sierras Pampeanas (Argentina): Geochemical, geochronological, isotopic constraints and petrogenesis

DAHLQUIST, JUAN ANDRES ; BASEI, MIGUEL A. S. ; RAMACCIOTTI, CARLOS DINO; ZANDOMENI, PRISCILA SOLEDAD; MORALES CÁMERA, MATIAS; GALINDO, CARMEN; MACCHIOLI GRANDE, MARCO

Journal of South American Earth Sciences

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdan ; Año: 2018

The Achala batholith, the largest in the Sierras Pampeanas, is composite and it is not entirely clear how many separate plutons make it up, nor their intrusive history. U-Pb dating of magmatic zircon by LA-ICP-MS confirms that strongly peraluminous A-type monzogranites located in the northern part of the Achala batholith, the Characato granitic complex, were emplaced at ca. 360 Ma. Thus they represent a relatively young intrusive phase in the construction of the Achala batholith, which began at ca. 380 Ma. The Characato monzogranites have crustal Nd- and Sr- isotope signatures (εNdt -6.0 to -6.1 and 87Sr/86St 0.7074 to 0.7131) and complex inherited age spectra with Neoproterozoic, large Early Cambrian and minor Mesoproterozoic and Ordovician inherited zircons resembling those of the basement of the Sierras de Córdoba (including igneous and metamorphic rocks) where they are intruded. In particular, two populations of Neoproterozoic detrital zircon ages are the typical signature of the Puncoviscan metasedimentary series whereas Early Cambrian ages are representative of the Pampean magmatism and high-grade metamorphism. It is suggested that the parental magma of the Characato granitic complex was generated by partial melting of this basement. The monzogranites are strongly peraluminous (A/CNK > 1.1) with fractionated compositions (high Rb/Sr and Rb/Ba) indicating dry melting (or with low water activity) of an evolved continental biotite-rich source. The abundant Early Cambrian inherited zircon population has highly positive but variable εHft value. We suggest that the Characato monzogranite magmas were mostly derived from Early Cambrian high-grade migmatitic and strongly peraluminous granitic rocks that were themselves derived from the Puncoviscan series sedimentary rocks such as the Los Tuneles phyllites that include Neoproterozoic zircon with positive εHft values. In our interpretation the Hf content in Cambrian magmatic zircon resulted from Hf transfer from the inherited Neoproterozoic zircon population. This interpretation is consistent with Nd whole-rock isotopes data.