Teotonio

One of the Rondonianas granites (see 025-00-015). Teotonio is a circular intrusion 4 km in diameter cut by the Madeira River, which covers more than half of it. It is emplaced in the Xingu complex of granulites, migmatites and gneisses and comprises peralkaline syenites, monzonites and granites with associated trachytes. The syenites contain microcline, or more rarely orthoclase, lesser albite/oligoclase, aegirine-augite and hornblende/hastingsite but with occasional riebeckite. Biotite is rare. The monzonites contain oligoclase/andesine, aegirine and riebeckite and the granites aegirine-augite, hornblende/hastingsite and a little biotite (Leal et al. 1978).