Pipes de Brecha e atividade magmática explosiva no complexo alcalino-carbonatítico de catalâo I, Goiás

RIBEIRO, R.C.; J.C. GASPAR; I.A. PETRINOVIC; J.A. BROD; T.C. JUNQUEIRA BROD

REVISTA BRASILEIRA DE GEOCIENCIAS

Sociedad Brasilera de Geologia

Año: 2001 vol. 31 p. 417 - 426

0375-7536

Products of explosive magmatic activity and turbulent flow structures occur in the Lagoa Seca area of the Catalão I carbonatite complex,Goiás State, Brazil. The complex consists of silicate rocks (dunite, clinopyroxenite) and carbonatites (sövite, beforsite and associated foscorite,nelsonite, and monazitite). Extensive carbonatite metasomatism converted the ultramafic rocks into widespread phlogopitites. In the Lagoa Seca area,lacustrine sediments discordantly overlie a 15-metre thick unit of horizontally-layered alkaline rocks, composed of a basal apatitite overlain by layersof monazite, ilmenite and clay. This magmatic unit contains cylinder-shaped pipes with circular to elliptical cross-section, limited at the top by thediscordance and at the bottom by foscorites and carbonatites. The pipes are typically filled with coarse-grained breccia, containing fragments of alkalinerocks and of country rocks from the immediate vicinity. The lower portion of some pipes is dominated by fine-grained material, with structures typicalof diluted flows (surges), such as cross-bedding and coarsening-upward bedding. This suggests explosive activity and magma fragmentation withinthe magma chamber.