Caracterização morfológica e tipológica dos zircões do Diopsídio Norito Pium, Gnaisse Bom Jesus, Suítes Pedra Branca e Planalto, Subdomínio de Transição, Província Carajás

Abstract

The characterization typological and morphological of zircons was carried out in samples of four units belonging to the Transition subdomain (Carajás Province): Diopside Norito Pium, Bom Jesus Gneiss, Pedra Branca suite and Planalto suite. The Diopside Norito Pium has the shape of a large body extending parallel EW regional foliation. Described as a granulite complex Mesoarchean, composed of gabbro, quartzonorito of foliated aspect, generally displaying igneous textures recrystallization, and association with charnockitic rocks Neoarchean. Gneiss Bom Jesus is a calc-alkaline leucosienogranito mesoarqueano, intensely deformed and metamorphosed with evidence anatexis. It occurs as a track north of the town of Canaan, Carajas Province. Geochronological dating performed on three samples of Gneiss Bom Jesus gave widely varying ages (3.0 Ga, 2.95 Ga, 2.93 Ga, 2.85 Ga and 2.83 Ga) and difficult to interpret. Pedra Branca suite comprises tonalite and trondhjemites, Neoarchean of age, with high content of Ti, Zr and Y. The Planalto suite consists of several elongated plutons Neoarchean in EW, of monzogranitic composition sienogranitic. The morphological, textural and chemical studies obtained by scanning electron microscopy and catadoluminescência zircon crystals were performed according to Pupin classification. The sample GRD- 05, corresponding to Diopside Norito Pium encompasses zircons Stype, besides the appearance of P and J types crystals show edges with high CL and exhibit subhedral forms, subrounded and core predominantly with convoluted zoning high CL, and rarely billing both the edge and in the core and xenocrysts inclusions. The gneiss Bom Jesus is peraluminous crustal source, since most of the analyzed zircons are the type S, subordinate type Q. The size fractions (250-180μm, 180-125μm, 125-75μm) showed the presence of euhedral cores, subordinate rounded with high CL and well defined oscillatory zoning (xenocrysts?). It has high ratios Th / U and low Ca and U. contents have the edges are formed by (a) subhedral crystals anhedral, sub-round with little apparent oscillatory zoning CL moderate and low ratio Th / U and low Ca and (b) crystals anhedral to subhedral with areas with no oscillatory zoning with low CL and low ratio Th / U and high content of Ca. Pedra Branca suite consists predominantly of zircons S-type, predominantly the S16 and S17 subtypes, with face {211} well developed indicating crystallization of aluminous liquids, besides the type J and P (P1 and P3) with face {110}. Some crystals show xenocrysts inclusions with moderate CL display subhedral edges and shapes, and rarely euhedral core subrounded high CL, with evident billing in most crystals occurring at both the edge and core, sometimes intercepting the whole crystal. The plateau has subalkaline Suite affinity metaluminous and peraluminous subordinate, plus a possible match with hydrated granites associated with charnockitic series, since it is the predominant types S and J and P-type subordinate in zircons in the samples analyzed AMR - 187 and 109 ARC-. The analyzed zircons have external morphology and extremely variable internal texture, due to the complex geological history where the mineral was submitted, in particular episodes of magmatic crystallization or metamorphic recrystallization.