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TOPIC: Sudbury Impact Structure


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A mountain-sized meteorite appears to have created Sudbury's gigantic crater and sent a tsunami racing though ancient oceans, say scientists who have uncovered a thick layer of debris the extraterrestrial interloper hurled all the way into Michigan.
A Canadian-U.S. team says the two-to-four-metre-thick layer of "ejecta," which they found south of Lake Superior, bears the clear signature of a meteorite.

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A meteorite that slammed into Earth 1.85 billion years ago at the present site of Sudbury, Ontario, is now making news 500 miles away in northeastern Minnesota.
When the Ham Lake fire burned more than 118 square miles in northeastern Minnesota and Ontario in May, geologists had a field trip scheduled along the Gunflint Trail for the annual meeting of the Institute of Lake Superior Geology.

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To make the Sudbury impact crater, the meteorite would have to have been about 10 kilometres  in diameter travelling at 143,232 kilometres per hour. Shock waves from the meteorite as it plunged into Earth likely caused up to 27,000 cubic kilometres of crust to melt.
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Anyone who loves looking up at the trees can't help but be saddened by the fire that laid bare forests along the Gunflint Trail. But for U of M geologists Mark Jirsa and Paul Weiblen, the excitement starts with looking down.
Earlier this month, with the fire still burning in the background, Jirsa made one of the most significant discoveries of his career.

"I probably would not have seen them if it hadn't been in a burned area" - Mark Jirsa.

Those rocks are now believed to be ash and debris from an enormous meteorite, that crashed 700 miles away in Sudbury, Ontario, 1.8 billion years ago. Never according to the U of M geologists has this type debris been found so far away from the Sudbury impact site.

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Namex is pleased to announce that it has completed 1,985 metres of diamond drilling to test three first priority targets as identified from its recently completed technical report.
Two holes were drilled to test a high intensity magnetic and electromagnetic anomaly at Fraser Lake, on the Golden Pine property. Drilling encountered highly brecciated banded iron formation, with pyrite and calcite veinlets and some rocks best described as Sudbury breccia. Namex was targeting iron formation hosted gold mineralisation common to Archean volcanic belts, such as the Geraldton-Longlac, Central Patricia and Pickle Crow mines in northwestern Ontario. The proximity of this anomaly to the Sudbury meteorite impact event was particularly compelling.

On the Golden Pine East, Namex drilled four holes totalling 477 metres. All holes were drilled from a singular location to try and determine the strike, dip and extension to depth of the A-1 surface gold showing. Two of these holes also tested high priority IP targets along the contact between Huronian sediments on the north and felsic meta-volcanics to the south. Historical surface channel sample returned a 2.2m width running 1.302 ounces gold/ton (44.64 g/t). The main gold mineralisation here reportedly occurs as microscopic grains not visible in hand specimen. Although gold mineralisation appears to be associated with sulphides and quartz veining no distinction is possible in hand specimen or drill core between barren and mineralised rock. Fine disseminated sulphides have been noted occurring sporadically in the core in all four holes, however, logging and sampling is presently on going.
The third area of drilling was on the Post Creek property, to test two priority IP anomalies along the projection of the Whistle Offset. Two holes totalling 775 metres tested Quantitative Section anomalies identified by Matrix GeoTechnologies. The holes encountered extensive zones of brecciated rock. The detailed core logging of these holes will need to be completed (and possibly petrographic analyses) to determine if these sections may be Sudbury or footwall breccias.

Source

geocover2000_81.18339W_46.60087N
Expand (135kb, 628 x 529)
Golden Pine East
Latitude: 46° 46′ N Longitude: 80° 50′ W

The Sudbury Basin, also known as Sudbury Structure, is a large impact crater in Ontario, Canada.
Latitude: 46° 36′ N Longitude: 81° 11′ W


Geology:
The entire Golden Pine property is underlain by a 2.0 km wide northwest trending Archean Black Creek greenstone belt comprised of mafic and felsic volcanic rocks. This belt is flanked unconformably by steeply dipping Proterozoic Huronian quartzite and conglomerate rocks (Mississaugi Formation) in the northeast and granitic rocks to the southwest. The volcanic assemblage of rocks that underlies the property is host to a number of significant gold and base metal occurrences within or adjacent to the property. Over half of the former Terra Incognita claim block and eastern portion of the former Black Creek claim block is obscured by thick overburden cover.

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About 1.8 billion years ago, a meteorite or comet the size of Mount Everest slammed into what is now Canada.

According to James Mungall, a University of Toronto geologist, the impact turned part of the Earth's crust inside out and dusted the surface with a rare metal.
Mungall and other experts studying impact craters, such as this one in Sudbury, Ontario, hope to understand how a period of continual bombardment about four billion years ago shaped the planet.
Until now researchers had found scant evidence that a meteorite could pierce through Earth's upper crust and alter its compositional makeup.

"Over a few hundred million years when this was going on, there must have been a lot of mixing going on in the upper crust" - James Mungall.

David Kring is a planetary scientist at the University of Arizona in Tucson and an authority on impact craters. He said the findings from Sudbury are similar to those he and his colleagues have reached from studying a crater in Chicxulub, Mexico.

"I don't think it is yet widely appreciated, but impact cratering has the capacity to redistribute the chemical elements in the Earth's crust" - David Kring.

An emerging theory in the field of impact crater research is that the largest of these impact events early in Earth's history may have created the conditions needed for the evolution of life.
The impacts would have heated water in the Earth's crust and created vast hydrothermal vent systems. Many scientists believe these unusual underwater ecosystems helped give rise to early life.
Researchers assumed volcanic activity mostly created hydrothermal vent systems.

"But four billion years ago a dominant source was impact-generated hydrothermal systems" - David Kring.


Sudbury Impact Structure

The field of impact crater research is just coming into prominence in the scientific community. 15 years ago scientists couldn't even agree that the Sudbury crater resulted from a meteorite impact.
The signs of the impact are vague, because most of the crater has eroded. Geological processes, such as plate tectonics and volcanism, have almost completely eroded Earth's oldest impact craters.
But the Sudbury and Chicxulub craters, along with a third in Vredefort, South Africa, are still visible enough to provide clues to the planet's formative years.
Today the Sudbury impact basin is about 60 kilometres long and 30 kilometres wide. Mungall and his colleagues believe the crater was originally about 250 kilometres in diameter.
Scientists looking for signs of the impact must cover a large area of ground, and much of the evidence they look for is small.
The most convincing pieces of evidence are shatter cones—coned-shaped fractures in the rock ranging in size from inches to tens of feet across.

"The only way you can get shatter cones is when extremely strong shock waves are passing through material. They don't form any other way. The only other places you see them on Earth are around nuclear test sites" - James Mungall.

Other bits of evidence include microscopic, flaky diamonds formed by the passage of shock waves through carbon-rich rocks. The shock waves also transform tiny mineral crystals into glass.
To make the Sudbury impact crater, the meteorite would have to have been about 10 kilometres in diameter travelling at 143,232 kilometres per hour.
Shock waves from the meteorite as it plunged into Earth likely caused up to 27,000 cubic kilometres of crust to melt.
A plume of superheated rock from the deepest part of the 30- to 40-kilometer-thick crust then flew upward and landed on top of the impact site, essentially turning the crust there inside out.
It is also suggested that the meteorite vaporised on impact. Its components then condensed and rained back down.
This would account for the increased concentrations of iridium—a rare metal found mainly in the Earth's mantle and in meteorites—found in the upper layers of the crater's crust.

The Sudbury site also has relatively low concentrations of magnesium and nickel, two elements that are common in Earth's mantle. The researchers therefore concluded that the iridium originated from the meteorite.
According to Kring, of the University of Arizona, events like those at Sudbury 1.8 billion years ago and Chicxulub 65 million years ago were tiny compared to those during the period of heavy bombardment in Earth's formative years.
His calculations suggest there were perhaps as many 40 impact events that produced craters at least 1,000 kilometres in diameter during that time.

"That would have redistributed the chemical elements in Earth's crust to a great extent" - David Kring.

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