Andrea Bartorelli
Core of the Serra da Cangalha crater in Tocantins StateAndrea BartorelliAmid the flat landscape and soy plantations of the city of Campos Lindos, in Tocantins State near the border with Maranhão State, three concentric mountain ranges rise in an almost circular pattern. Known as the Serra da Cangalha, this cluster of mountains reaching approximately 400 meters in height was created about 250 million years ago by the impact of a meteorite. The mountains form what geologists call an impact crater. They are in fact inside a crater measuring 13.7 kilometers in diameter, which can be seen only by flying over the region or from space. Almost 40 years ago it was suspected that these structures, first observed in 1960 by a team engaged in geological explorations for Petrobras, were part of an impact crater. But more evidence was needed. Now a team led by geologist Alvaro Crósta, of the University of Campinas (Unicamp), has obtained it. On expeditions to the region, geophysicist Alberto Marcos Vasconcelos collected rock samples that preserve both macroscopic and microscopic records of the impact of a celestial body there (Journal of South American Earth Sciences, August 2013). According to Crósta, some of the samples indicate that these rocks, now exposed in the shallower regions of the Earth, were formed at extremely high pressure, up to 10 gigapascals. Such high pressure occurs only in those collisions or in deep regions of the planet, hundreds of miles below the surface. Crósta says that the rocks that are now at the same level as the land were once under a layer of almost 500 meters of sediment, which over the course of 250 million years was swept away by erosion.
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