The central-eastern part of the Sierra de Velasco (Sierras Pampeanas, NW Argentina) is formed by the large Huaco (40 9 30 km) and Sanagasta (25 9 15 km) granite massifs and the small La Chinchilla stock (2 9 2 km). The larger granites intrude into Ordovician metagranitoids and crosscut Devonian (?) mylonitic shear zones, whereas the small stock sharply intrudes into the Huaco granite. The two voluminous granites are biotitic-muscovitic and biotitic porphyritic syeno-to monzogranites. They contain small and rounded tonalitic and quartz-dioritic mafic microgranular enclaves. The small stock is an equigranular, zinnwaldite-and fluorite-bearing monzogranite. The studied granites are silica-rich (SiO 2 [70%), potassium-rich (K 2 O [4%), ferroan, alkali-calcic to slightly calk-alkalic,
This paper concerns sedimentary, volcanic, metamorphic and igneous rocks of the Sierra de Famatina and adjacent rock series in NW Argentina, for which the name ‘Famatina system’ has been used widely in the literature. It is suggested that this is renamed the ‘Famatina complex’, since ‘system’ is an internationally defined stratigraphical term. The Famatina complex is considered to have formed as an island arc on continental crust, represented in its diversity by metasediments and meta-volcanic rocks of the Sierra de Famatina, with a corresponding back-arc basin exposed in the medium- to high-grade metamorphic rocks of the adjacent Las Termas belt to the east. The Famatina complex was deposited in contact with the eastern Pampean complex (‘Pampia terrane’) at the western active continental margin of Gondwana in latest Proterozoic and Ordovician times. Deposition was, in part, accompanied by voluminous Ordovician magmatism of calc-alkaline composition. NNW-SSE-striking shear zones, dated previously at 402 ± 2 Ma, are interpreted as marking the final stage of collision of the island-arc/back-arc/continent complex. The dynamics of crustal block movements along the most prominent (TIPA) shear zone indicate overthrusting of the eastern Pampean series onto the western Famatina series and, hence, uplift and cooling of the eastern block must have occurred earlier than cooling of the western one. The composition of inherited components in Famatina metasediments and meta-granitoids argues for autochthonous arc-continent convergence rather than accretion of an exotic terrane.
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