∼3.25 Ga Barberton Greenstone Belt Asteroid Impact
The ∼3.26–3.24 Ga asteroid impact on the Barberton greenstone belt represents the first documented example of a "possible" cause–effect relation between extraterrestrial bombardment and major tectonic and igneous events. This study is by Glikson and Vickers(2006). The asteroid ejecta are located immediately above a sharp break between a >12 km-thick mafic–ultramafic volcanic crust and turbidite–felsic volcanic rift-facies association. A boundary there is correlated with break and peak magmatic and faulting events, represented by the truncation of a 3.255–3.235 Ga volcanic sequence at the Sulphur Springs Group (SSG) by a turbidite-banded iron formation–felsic volcanic association. These events are accompanied by ∼3.252–3.235 Ga granitoids. The top of the komatiite–tholeiite–rhyolite sequence of the SSG is associated with a marker chert defined at 3.238–3.235 Ga, abruptly overlain by an olistostrome consisting of mega-clasts of felsic volcanics, chert and siltstone up to 250×150 m-large, intercalated with siliciclastic sedimentary rocks and felsic volcanics.
The structure and scale of the olistostrome is interpreted as intense faulting and rifting, supported by topographic relief represented by deep incision of overlying arenites (the Corboy Formation) into underlying units. The age of these fault and rifts overlaps the 3.255–3.235 Ga peak igneous activity represented by the SSG and the Cleland plutonic suite and the 3.258 Ga Barberton impact unit. Should correlations between the Barberton impact units and magmatic and tectonic events in the Pilbara Craton be confirmed, this would imply impact-triggered reactivation of mantle convection, crustal anatexis, faulting and strong vertical movements in Archaean granite–greenstone terrains associated with a large asteroid impact, culminating in transformation from sima-dominated crust to continental rift environments.
Read more about this topic: Kaapvaal Craton
Famous quotes containing the words belt and/or impact:
“The admission of the States of Wyoming and Idaho to the Union are events full of interest and congratulation, not only to the people of those States now happily endowed with a full participation in our privileges and responsibilities, but to all our people. Another belt of States stretches from the Atlantic to the Pacific.”
—Benjamin Harrison (1833–1901)
“Too many existing classrooms for young children have this overriding goal: To get the children ready for first grade. This goal is unworthy. It is hurtful. This goal has had the most distorting impact on five-year-olds. It causes kindergartens to be merely the handmaidens of first grade.... Kindergarten teachers cannot look at their own children and plan for their present needs as five-year-olds.”
—James L. Hymes, Jr. (20th century)