Sudbury impact crater in Canada. The oval shape in the image below is the last surviving evidence of

Sudbury impact crater in Canada.The oval shape in the image below is the last surviving evidence of a angled blow that hit the hard metamorphic rocks of the Canadian craton around in the Proterozoic era. It has been subjected to nearly two billion years of erosion, three mountain building events and a much later smaller impact, and hosts mineral deposits unique in their mode of formation: impact melting and segregation.The impactor was estimated at 10-15 Km across, about the size of Mt Everest. It left behind a much larger crater than is visible now, estimated to have been 250Km across, and fired ejecta that have been found as far away as Minnesota and Michigan in the USA, over 800Km away. They consist of marine sediments that have been shattered by the resulting earthquakes that are overlain by a layer accretionary lapilli, spheres of ash cemented by condensed vapour that landed on a primeval sea and sank to the bottom. The crater is the second largest on Earth, after the Vredefort impact structure in South Africa.Back in the 60’s and 70’s, its origin in an asteroidal cataclysm was disputed, but further analysis has revealed the full panoply of impact evidence, including shatter cones, shocked quartz, an underlying layer of smashed rock (called a breccia) and geodesic sphere shaped carbon molecules called buckyballs that contain heliium with an extraterrestrial isotopic signature. The buckyballs originated in space and survived the impact and subsequent adventures the rocks lived through during their geological history.This structure also hosts one of the world’s largest nickel copper deposits. When the bolide smacked into the (then) volcanic rocks of proto Canada a large lava lake formed. This lake slowly solidified, in a similar pattern to large igneous intrusions such as South Africa’s Bushveld complex (as a sandwich of gabbro, the intrusive equivalent of basalt in between layers of norite, olivine rich rock and granophyre, which represent the last remaining silica rich fraction that floated to the top). During this cooling and crystallisation process, metals segregated out, including nickel, copper, gold and platinum group elements. These elements are now mined around the crater’s rim from the layers in which they segregated, making Sudbury one of the world’s largest sources of nickel and copper.The impact also created a complex system of hydrothermal vents, which may have provided nutrients and a good environment for early life, made up of communities of extremophile bacteria.LozImage credit: NASAhttp://www.thelivingmoon.com/43ancients/02files/Earth_Images_09.html#Sudburyhttp://stardust.jpl.nasa.gov/news/bucky.htmlhttp://www.mngs.umn.edu/meteoriteimpact.pdf -- source link
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