The classification of magmatic breccias and implication in the evolution of the Nova

Abstract

To understand magmatic phenomena, it is important to know how the bodies had been lodged in lithosphere, and the best registers of the formation of a magmatic chamber are the magmatic breccias. They are formed in the contact between the pluton and the host rocks. The classification proposal, in general, allows the reconstruction of the emplacement of the magma, through the description of certain textures and structures found in the units that may be sequenced and associated to magmatic processes, and of the geodynamic context of the volcanic environment, when structural data are taken into account. The rocks in the northeast of the Nova Iguaçu Alkaline Complex are an example. There, some characteristics had been observed: textural maturity, clast/ matrix relationship and characteristics of matrix and clasts. The methodology involved mapping in 1:10.000 scale, petrography, analysis of sections by electron microscope and chemical semi-quantitative analyses. These characteristics, allowed to recognize that the emplacement of the alkaline complex occurred in three phases: first, the break-up of host gneisses, besides the volumetric expansion of the pluton and thermal exchanges between the pluton and surroundings; second, the hydrotermal action of magmatic fluids; third, the intrusion of magma between blocks. This process repeated continuously in each magmatic pulse