This is an approximately circular trachyte plug 1 km in diameter, cutting Precambrian granite. Santa Marta I, lying 2 km southwest of Fazenda do Toninho, is gabbroic.
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This is a small eroded volcanic neck cutting Carboniferous sandstones and consisting principally of breccias and tuffs, but with some flows.
Catalao II lies 15 km north of Catalao I and detailed descriptions are not readily accessible. It forms a circular dome with an approximate area of 14 km2, with a strong aeromagnetic expression. The country rocks are Precambrian quartzites and schists which are fenitized.
Catalai I is an approximately circular complex covering 27 km2 and lying 15 km south of Catalao II. It is emplaced in mica schists and quartzites of the Precambrian Araxa Super Group, which it fenitizes.
This complex comprises a series of intrusions and associated volcanics forming a northwest-southeast-trending line over some 10 km. There are four distinct intrusions of peridotite with dunitic cores.
Amorinopolis is a volcanic vent of the Ipora Group standing 250 m above the surrounding Devonian sandstones. It consists of a central plug surrounded by a series of ring dykes, which outcrop as annular ridges, and a system of radiating dykes.
Essentially a volcanic province of flows, pyroclastic deposits and numerous vents and plugs covering in all some 300 km2.
An intrusion some 30 km from north to south and up to 8 km wide, Peixe is emplaced in gneisses of the Araxa Group, but in the south at least, is surrounded by pegmatitic granites.
An intrusion composed of rock described as litchfieldite occurs at Morro da Estrela, 45 km northwest of the town of Porto Nacional.
A major concentration of circular structures occurs in northeastern Brazil in the states of Maranhao and Piaui with one in Goias. Most show evidence of doming and they are thought probably to be underlain by alkaline intrusions. Those listed are taken from Rodrigues and Lima (1984).