Abstract

TOSELLI, Alejandro J.  and  ROSSI, Juana N.. Devonian-Carboniferous Granitoids In The Northwestern Pampean Ranges And Their Relations With The Source And To The Late- To Post-Orogenic Magmatic Setting In Famatinian Cycle.. Ser. correl. geol. [online]. 2019, vol.35, n.2, pp.1-10. ISSN 1666-9479.

The Devonian-Carboni-ferous magnesian and ferroan alkali-calcic per-aluminous granitoids, that intrude in the North Western Pampean Sierras allow the geotectonic interpretation of this period since, although they are small intrusive, they are numerous and with petrographic, mineralogical, geochemical and isotopic variable characters, that allow to establish the evolutionary sequences and the shallow emplacement levels. These intrusives that were generically assigned to the Achalian Cycle, here we consider them as corresponding to the distensive stage of the Famatine Cycle collapse, since in general they do not present tectonic deformation. Granites are peraluminous, alkaline-calcic and grouped in magnesian, which present high model ages (TdM >1.5 Ga), and ferroan granites with younger model ages (TdM <1.3 Ga). Also, some have a muscovite signature, with Rb/Sr >5, while another group has a biotitic signature with Rb/Sr <5 relationships. The normalization of rare earths to continental crust, in all cases present negative Eu anomaly and in the comparisons with the sedimentary rocks with which they are probably related (Puncoviscana, Ancasti and La Cébila formations) show distribution patterns with similarities and di-fferences to granite averages. The projections of some trace elements such as Rb, Ba, Sr, Hf, Ta, Nb, Y and Yb in different petro-tectonic diagrams indicate that the intrusives are of syn- to post-collision origin, intruded in intraplate environment. Also, it is evident that in general they are very differentiated granites, which have interesting contents of W and Sn, as well as Th and U, with the common presence of fluorite. The isotopic ratios of f⁷Sr/⁸⁶Sr), eNd (¹⁴³Nd/¹⁴⁴Nd) and Sm/Nd fractionation (fSm/Nd) and TdM (Ga) (time depleted mantle) show the cortical origin of the same, from recycled sediments of upper continental crust that is assimilated in some cases to the Puncoviscana formation.

Keywords : Devonian-Carboniferous plutons. Magnesian and ferroan alkali-calcic per-aluminous grani-toids. Upper continental crust recycled origin..

        · abstract in Spanish     · text in Spanish     · Spanish ( pdf )