Araguaina Crater (dome of Araguaina, port. Cratera de Araguainha ) - impact crater on the border of the states of Mato Grosso and Goias , Brazil , between the settlements of Araguaina and Ponti Branca . Its diameter is 40 km, which makes it the second largest crater in South America. Perhaps this is the continent's oldest crater.
Araguaina | |
---|---|
port. Cratera de araguainha | |
Image of a crater, NASA World Wind | |
Specifications | |
Diameter | 40 km |
Type of | Shock |
Location | |
A country |
|
States | Mato Grosso , Goiás |
The crater was formed 254.7 ± 2.5 million years ago, at the end of the Permian period , when this area was probably a shallow sea. The time of crater formation is very close to the Permian – Triassic border, when one of the largest mass extinctions in the history of the Earth occurred . The impact broke through sedimentary rocks and exposed the Ordovician basement granites. It is believed that at first the crater was 24 km wide and 2.4 km in depth, and then expanded to 40 km, as its shaft collapsed inward.
Content
Description
Araguaina is a complex crater with ring and radial faults. It is expressed in relief, although severely destroyed by erosion, and is crossed by the Araguaya River. The central zone of the elliptical shape is elevated; there granites come to the surface. Around this core is a ring of shock-metamorphosed granite covered with breccia . It is surrounded by a ring of ridges and hills up to 150 m high, consisting of creased and steeply inclined Devonian sandstones . The diameter of this ring is 6.5 km. It is surrounded by an annular depression, the bottom of which is lined with Devonian and Carboniferous sandstones. The outer contour of the crater consists of the remains of semicircular grabens in strongly deformed Permian-Carboniferous deposits. Signs of impact origin include cracking cones, impact breccia, and impact quartz [1] .
History and Research
The first report on the structure of Araguaina was published in 1969 by Norzflit et al., Who interpreted it as an uplift of the Phanerozoic deposits caused by the Cretaceous intrusion of syenite . Geological exploration of 1971 (Silveira Filo and Ribeiro) noted deposits of lava, breccia and tuff around the central core, and concluded that Araguaina is a crypto-volcanic structure. In 1973, Robert S. Daets and B. M. French reported the presence of shock breccia and shock quartz and defined the structure as a shock crater. A detailed study of the crater in 1981-1982 (Alvaro Penteado Krosta) gave new petrological and mineralogical signs of the impact. In 1981, geomorphological evidence was published (Theilen-Willige). In 1992, the shock event was first dated using the rubidium-strontium method (Deutsch et al.); The measured age was 243 ± 19 Ma ago. In 1992, Engelhardt et al. Published a detailed study of the raised core and estimated its age at 246 million years; this estimate was later revised (with a result of about 244 million years). Magnetic measurements were carried out in 1994 by Fisher and Maseru.
The latest estimate of the age of the crater is 254.7 ± 2.5 million years, which approximately corresponds to the age of the Permo-Triassic border [2] . There is an assumption that a certain contribution to the corresponding extinction could be made by the release of oil and gas from the rich shales that are common in these places [3] .
Access and Saving
The dome of Araguaina can be reached by car from the city of Goiania or Cuiaba . The dirt road MT-306 between the towns of Ponti Branca and Araguaina crosses the central elevation. As of 1999, the local population did not know anything about the nature of the dome and its scientific significance.
Notes
- ↑ Álvaro P. Crósta. Araguainha dome - The largest astrobleme in South America // Sítios Geológicos e Paleontológicos do Brasil: journal / Schobbenhaus, C .; Campos, DA; Queiroz, ET; Winge, M .; Berbert-Born, M .. - 1999. - 1 July.
- ↑ E. Tohver, C. Lana, PA Cawood, IR Fletcher, F. Jourdan, S. Sherlock, B. Rasmussen, RIF Trindade, E. Yokoyama, CR Souza Filho, Y. Marangoni. Geochronological constraints on the age of a Permo – Triassic impact event: U – Pb and 40 Ar / 39 Ar results for the 40 km Araguainha structure of central Brazil (Eng.) // Geochimica et Cosmochimica Acta: journal. - 2012 .-- 1 June ( vol. 86 ). - P. 214—227 . - DOI : 10.1016 / j.gca.2012.03.03.005 . - .
- ↑ Biggest extinction in history caused by climate-changing meteor . University of Western Australia University News Wednesday, July 31, 2013.