The source of the shatter cone could be postulated to be endogenous. The shatter cone is supposedly developed by sudden impact, but could also be developed by sudden energy impact that a very large explosion could engender. The reason I don't believe Sudbury shatter cones formed from a meteor impact necessarily is that they are not found at the base of the putative crater very deep, and exposed by erosion, as the so called crater in Sudbury is not eroded to base. Instead they are found outside the rim, and radially away from the center, implying a sudden release of energy radially away from center laterally. This would be consistent with a very large endogenous explosion. Remember we are talking about 300,000 to 3,000,000 hydrogen bombs. Not a tiny pop. The laws of such large explosions are entirely different than conventional research can deduce. Could they produce shatter cones? Well, are you prepared to say they absolutely cannot?
Shatter cones have been described from a number of circular and polygonal structures worldwide, the origin of which has been alternatively ascribed to the impacts of large extraterrestrial projectiles or to catastrophic endogenic processes. Despite their association with enigmatic, catastrophic processes, the nature of shatter cones and the physics involved in their formation have not been comprehensively researched. Results of detailed field and laboratory studies of shatter cones from three areas in the collar of the Vredefort Dome in South Africa are presented.
We know all the features of Sudbury are explosive volcanic and pyroclastic. Few writers dwell on the long pyroclastic history, and the extensive explosive tuff beds, because they are a "problem" for the simple exogenous meteor theory. But if we were to postulate a meteor excavation, then we would have a crater and just a crater with no previous and subsequent volcanic history. There need be no volcanoes there at all. Witness the moon and other earth craters that are accepted as meteoric in origin. There are no volcanoes co-incident. This is because volcanic fluids if you will, are formed at specific plate boundaries and not at random sites which are fortuitously impacted by meteors.
What we find is a long volcanic history, many generations of ore development and filling of the basin with successive lava layers, and then an ending of volcanism with a massive tuff development. The fact that the tuff stayed in there and was not excavated, and the enormous size of the filled basin perhaps 5 to 16 times the size of the next largest "impact crater" in Canada, much of what had to be filled placidly (the lava) argues persuasively for a long running process that ended suddenly, and was not excavated at all. It is still possible of course that both processes played a part, but the nickel need not have come from an asteroid as some suggest. That was put forth seriously by some authors. One need not deny the plentiful natural endogenous ore forming mechanisms that we know took place over 30 million years, from the nickel to the copper zinc at Vermillion both before obviously and after the volcanic explosiongthat we know had to take place by two incontravertible pieces of evidence: 1. the presence of pyroclastic debris, and 2. the presence of the tuff.. I realize tuffs are though some as pyroclasts, but they may be diatremic as in a kimberlite. Diatremes are not pyroclastic, they are explosive. Tuffs are formed by explosive volcanism. So we know we have a felsic volcano that was belching out mountains of rhyolite lava, and also huge bombs, which fell to the south These have a tendency to get plugged by turgid rhyolite and with sea water they often explode. We have seen this in contemporarily. And we know from the massive tuff layers that it went diatremic. It exploded and left a tuff bed behind in the caldera. It was a large tuff bed and large caldera and we see its outline today. And it was a continuum in the cratonic plates that also formed the very large explosive volcanic areas of Timmins, Kirkland Lake, Shining Tree and Rouyn-Val D'Or.
2 GPa to <30 GPa? - Shatter cones - Shatter cones are shock-deformation features that form from impact pressures of typically 2-10 GPa up to ~30 GPa. They represent the only distinctive and unique shock-deformation feature that develops on a megascopic scale (e.g., hand sample to outcrop scale). They appear in outcrops as distinctively curved striated fractures that typically form partial or complete conical structures (image). They are commonly found "beneath impact crater floors", usually in the central uplifts of complex impact structures, but they may also be observed in isolated rock fragments within brecciated units.
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A different view of shatter cones..
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If one had both a meteor impact and a volcanic caldera in the same place, you have an enormous co-incidence. But the volcano would have to happen after the impact at a scale an order of magnitude larger than say Manicougan, and also explode with the largest such explosion of any geologically recorded event. Since we have evidence of the latter, and only a upposition of the former based on the shatter cones and the crushed rim. If we accept the meteor theory, we also have to accept that it caused a history of volcanism, subsequent ore formation and the basin itself got crushed in the Grenville uplift altering the original circular shape of the meteor impact.
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