Araguainha crater
Template:Short description Template:Infobox terrestrial impact site The Araguainha crater or Araguainha dome is an impact crater on the border of Mato Grosso and Goiás states, Brazil, between the villages of Araguainha and Ponte Branca.<ref name=EIDBAraguainha>Template:Cite Earth Impact DB</ref> With a diameter of Template:Convert, it is the largest known impact crater in South America.
The crater has most recently been dated to Template:Nowrap years ago, when the region was probably a shallow sea. The margins of error of this date overlap the time of the Permian–Triassic extinction event, the most severe and catastrophic mass extinction events in Earth's history.<ref>Template:Cite journal</ref><ref name="ChenRichoz2019">Template:Cite journal</ref> The event caused the extinction of 57% of biological families, 62% of genera and 81% of marine species.<ref name=":2">Template:Cite journal</ref><ref name="Benton">Template:Cite book</ref><ref name="BergstromDugatkin2012">Template:Cite book</ref><ref name="SvetsovShuvalov">Template:Cite book</ref><ref name="Tohver2013">Template:Cite journal</ref> The impact punched through Paleozoic sedimentary units belonging to the Paraná Basin formations, and exposed the underlying Ordovician granite basement rocks. It is estimated that the crater was initially Template:Convert wide and Template:Convert deep, which then widened to Template:Convert as its walls subsided inwards.
Description
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Araguainha is a complex crater with annular and radial faults, exposed to the surface and eroded, cut through by the Araguaia River. The crater has an uplifted central core, shaped like an elliptical basin, consisting of exposed basement granite. Surrounding this core is a ring of shocked granite and overlying breccias; then another ring of ridges and mountains, Template:Convert in diameter and up to Template:Convert high, consisting of folded and steeply tilted Devonian sandstones. This central region is surrounded by an annular depression floored by rocks from Devonian and Carboniferous sandstone formations. The outer rim of the crater consists of remnants of semi-circular grabens in highly deformed Permo-Carboniferous sediments. Evidences of impact origin include shatter cones, impact breccias, and shocked quartz.<ref name=":0">Template:Cite journal</ref>
Access and conservation
The Araguainha Dome can be reached by car from Goiânia or from Cuiabá. An unpaved state road, between Ponte Branca and Araguainha, cuts across the central uplift, as does the Araguaia River. As of 1999, the local residents were not yet aware of the dome's nature and scientific importance.<ref name=":0" />
Dating and interpretation
The earliest report on the Araguainha structure was published by Northfleet et al. (1969),<ref name=Northfleet_1969>Template:Cite journal</ref> who interpreted it as an uplift of the Phanerozoic sediments caused by a Cretaceous syenite intrusion. A geological reconnaissance survey by Silveira Filho and Ribeiro (1971)<ref name=Silveira_Filho_Ribeiro_1971>Template:Cite report</ref> noted the occurrence of lavas, breccias, and tuffs around the central core and deduced that Araguainha was a crypto-volcanic structure. Dietz and French (1973)<ref name=DietzFrench_1973>Template:Cite journal</ref> reported the occurrence of impact breccias and shocked quartz, and recognized the structure as an impact crater. A detailed study of the crater by Crósta et al. (1981)<ref name=Crósta1981>Template:Cite journal</ref> and Crósta (1982)<ref name=Crósta1982>Template:Cite thesis</ref> reported further petrological and mineralogical evidence of the impact. Further geomorphologic evidence was published by Theilen-Willige (1981).<ref>Template:Cite journal</ref> A magnetic survey was conducted by Fischer and Masero (1994).<ref name=FischerMasero_1994>Template:Cite journal</ref>
Dome formation was first dated (at Template:Nowrap years ago, with Rb-Sr method) by Deutsch et al. (1992).<ref name=Deutsch_1992>Template:Cite journal</ref> Engelhardt et al. (1992)<ref name=Engelhardt_1992>Template:Cite journal</ref> published a detailed study of the uplifted core and a revised date of about 246 million years ago, later revised to about 244 million years ago. Most recently it was dated by Tohver et al. (2012)<ref name=Tohver_2012/> at Template:Nowrap years ago.
Effects
Recent dating by Tohver et al. (2012),<ref name=Tohver_2012/> to Template:Nowrap years ago, places the impact at dates overlapping estimates for the Permo-Triassic boundary<ref name=Tohver_2012>Template:Cite journal</ref> and the Permian–Triassic extinction event.
Much of the local rock was oil shale. The estimated energy released by the Araguainha impact is insufficient to be a direct cause of the global mass extinction, but the colossal local earth rifting would have released huge amounts of oil and gas from the shattered rock. The resulting sudden global warming might have precipitated the Permian–Triassic extinction.<ref>Template:Cite press release</ref>