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The manuscript is part of the postdoctoral research project of Maria Alejandra Boffadossi, supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina. This work has been funded by projects from the Agencia Nacional de Promocion Cientifica y Tecnologica (ANPCyT; PICT 1754/16), the Junta de Andalucia (A-RNM-005-UGR18 and FIPS, PY20-01387) and the Spanish Science Ministry (REViSE-Betics-PID2020-119651RB-100). Special thanks are given to the Asociacion Universitaria Iberoamericana de Posgrado (AUIP), Centro de Investigacion en Quimica Sostenible (CIQSO-Spain), Mineralogisch-Petrographisches Institut (Germany), and Instituto Geologico y Minero de Espana (IGME) for their financial support for a research stay at the University of Huelva (Spain), geochemistry and geochronology data presented in this work. The authors also say thanks to Jean Sanders for her English style revision. Finally, we would also like to thank the very careful and helpful suggestions by Igor Broska and an anonymous reviewer, and the handling of editor-in-chief Greg Shellnutt.

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A bimodal source for the generation of tonalitic to granitic magmas in a non-subduction-related magmatic belt: An example from the Sierra Chica of C & PRIME;ordoba, Argentina

Publicado en:Lithos. 452 107207- - 2023-09-01 452(), DOI: 10.1016/j.lithos.2023.107207

Autores: Boffadossi, M Alejandra; Diaz-Alvarado, Juan; Pinotti, Lucio P; Jung, Stefan; D'Eramo, Fernando J; Pedrera, Antonio; Millan-Martinez, Maria; Demartis, Manuel; Azor, Antonio; Muratori, Eugenia

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Resumen

A notable consensus prevails about the hybrid nature of intermediate calc-alkaline magmatism. Accordingly, petrogenetic models envisage the addition of young mantle material and cortical recycling in those geological settings where intermediate magmas are dominant. Most exhaustively studied examples are: 1) magmatic arcs associated with subduction zone settings where oceanic crust and sediments are introduced into the mantle wedge, and 2) deep crustal sections are pervaded by hot, H2O-rich mantle-derived liquids. Nevertheless, back-arc or foreland terranes of several hundred kilometers in width, frequently characterized by high heat flux, crustal melting, recycling and melt fractionation, are crucial areas to evaluate the generation of intermediate magma-tism. The Sierra Chica of C & PRIME;ordoba (Argentina) provides an excellent example to study these processes. The high-grade crustal segment shows metamorphosed pelitic and basaltic protoliths that were part of an old sedimentary succession. We evaluate the evolution of this bimodal source during two consecutive early Paleozoic orogenic periods when it was established as the source area of intermediate to silicic magmatism far from the contem-porary magmatic arcs. Field relations and new geochemical and geochronological data revealed the occurrence of two magmatic events during Cambrian and early Ordovician periods. Cambrian migmatization and partial melting (-528 to 505 Ma) is represented by irregular-shaped monzogranites and tonalites, while early Ordovician magmatism (-480 Ma) is characterized by dyke-shaped pegmatites and tonalite-trondhjemites. The preservation of two contrasting igneous lineages suggests a genetic linkage between metapelitic and amphibolitic migmatites and between granitic and tonalitic-trondhjemitic partial melts. Coeval with this magmatism, Famatinian tonalitic-trondhjemitic to monzogranitic magmas intruded upper crustal levels in Sierra Chica and other parts of Si-erras of C & PRIME;ordoba. Geochemical signatures point to a bimodal (mafic/felsic) source for this intermediate to silica -rich magmatism. The evolution of partial melts studied in the Sierra Chica is depicted on the basis of geochemical projections with fractionation and hybridization models, in order to establish the primary liquids of this Famatinian magmatic belt. Trends defined by Famatinian tonalites, trondhjemites and granodiorites suggest that primary Ca-rich melts (tonalites and trondhjemites of this study) evolved through fractionation of plagioclase (30-50 vol%) compatible with the preservation of inferred co-magmatic Pl-cumulates within these plutonic bodies. Peraluminous granites and monzogranites can be explained by a simple restite unmixing process involving alkali-rich liquids generated in the metapelitic part of the source. The addition (hybridization) of up to 30 vol% of granitic melts to the tonalite-trondhjemite end-member may account for the composition of other Famatinian granodioritic to monzogranitic intrusive rocks from the plutonic belt.

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