Revista de la Asociación Geológica Argentina
versión ISSN 0004-4822
PINOTTI, Lucio P. et al. Magmatic structures in granites. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.4, pp. 562-572. ISSN 0004-4822.
Structural aspects of granites related to mechanisms for structures development and their timing of formation are still a subject of lively debate. Many authors suggest that structures generated during magmatic stages (i.e. from early magmatic flow with mineral grains suspended in melt to late magmatic grain-supported flow) are only hardly preserved in granitic bodies. In this contribution, several magmatic structures in granitoid plutons from Sierras Pampeanas are showed, where small plutons and batholithic-sized bodies are both analysed. We discuss: a) map-scale lithological variations, such as principal magmatic units, where magma dynamics are evidenced by mixing processes within magmatic chamber; b) metre to decametre-scale magmatic layering that may be isomodal or modally-graded; c) overprinting submagmatic structures indicating interplay between plutons or pluton internal units according to regional deformation; d) composite magmatic layering and schlieren commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones. These structural features can be ascribed to three main processes: a) assembly of differentiated magmatic pulses; b) local hydrodynamic sorting related to density currents in a mush; c) mechanical disruption and chemical hybridization of mafic magmas during ascent and emplacement; among others. The identification of preserved structures in granitoids, their timing and mechanisms of formation, as well as the structural dynamic of the surrounding crust, play a prominent role in proposing emplacement models for granitic plutons.
Palabras llave : Structure; Granite; Rheology of magma; Sierras Pampeanas.