ESTRUCTURAS MAGMÁTICAS EN GRANITOS

PINOTTI, L., D'ERAMO, F., DEMARTIS, M., TUBÍA J. M. , CONIGLIO J.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2010 vol. 67 p. 562 - 572

0004-4822

ABSTRACT: Magmatic structures in granites. Structural aspects of granites related to mechanisms for structures development and theirtiming 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 onlyhardly preserved in granitic bodies. In this contribution, several magmatic structures in granitoid plutons from SierrasPampeanas are showed, where small plutons and batholithic-sized bodies are both analysed. We discuss: a) map-scale lithologicalvariations, such as principal magmatic units, where magma dynamics are evidenced by mixing processes within magmaticchamber; b) metre to decametre-scale magmatic layering that may be isomodal or modally-graded; c) overprinting submagmaticstructures indicating interplay between plutons or pluton internal units according to regional deformation; d) compositemagmatic 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) localhydrodynamic sorting related to density currents in a mush; c) mechanical disruption and chemical hybridization of mafic magmasduring ascent and emplacement; among others. The identification of preserved structures in granitoids, their timing andmechanisms of formation, as well as the structural dynamic of the surrounding crust, play a prominent role in proposing emplacementmodels for granitic plutons.