 The true history of the Geology of this continent is written in the lines of movement in surface melt formations like that. The stone doesn't lie. And it's story doesn't agree with standard theory at all.
 Because here the ice provided enough of a heat sink to quench, and preserve some of the extra terrestrial material that brought all the heat. You see it in the black arrowhead splash of molten material blown off to the side, and framed so nicely by the lighter native rock. The whole region is as level as a parking lot. Drainage is poor. And, for the most part, where you see green in these images you are looking at peat of varying depths.
Below is a false color radar image depicting elevation. It's graded from darkest-lowest to lightest-highest elevation. The whole region is almost as flat as a parking lot, and the deference in elevation for the area of the black splash from lowest to highest is only a couple of feet. But the ghostly image of the splash and it's associated rivers of melted stone show up clearly as raised features in the terrain.  The color of the peat bogs in the area are a good proxy for the contours of the depressions. The darker the color, the deeper the depression. The rock composition for the general area of the black splash is labeled on the USGS's geologic maps as: "Para gneiss and schist-rich migmatite- grades into undivided meta sedimentary rocks."
Migmatite is a rock of both metamorphic, and igneous, origin that exhibits characteristics of both rock types. Migmatites form under extreme temperature conditions during metamorphism through the heating (but not quite melting) of rocks in the presence of a lot of water. And where partial melting occurs in pre-existing rocks. They aren't crystallized from a totally molten material, and are not generally the result of solid-state reactions. Migmatites are composed of a new material crystallized from incipient melting, and an old material that resisted melting. Exactly the kind of rock we would expect in the burn scars of comet induced, hydrothermal explosions in the ice sheet.
And the meta sedimentary rocks are described as:
"Meta sedimentary rocks-undivided-greywacke, slate, local units of conglomerate, arentite, graphic slate, fine-grained felsic volcanogenic, and volcaniclastic rocks, lean oxide iron-formation and its metamorphic equivalent. Includes the Knife Lake Group and the Lake Vermilion Formation in northeastern Minnesota."
 So the full range of temperatures, and conditions we should expect of an impact in the ice sheet, from hydrothermal to pyro-clastic, is represented by the rock of the blast burns in the area. But the problem with the words "volcanogenic", and "volcaniclastic", is that there is no volcano there. The bedrock is Archaean. There hasn't been any volcanic activity there in 2.5 billion years And, without a volcano, you can't make a case for volcanism as the heat source for the pyroclasts, and metamorphic facies.
 The lines were formed as the stone was flash melted in the heat of the impact. The Ice added a different variable though. And it took the impact much the same way reactive armor works on a battle tank.
Instead of a crater we see the signature of the violence In the fast flowing rivers of melted stone. Flowing among the shattered remains of the Ice sheet
 The area is sometimes referred to as "The Patterned Peat Lands of Northern Minnesota". The whole region is as flat and level as a parking lot. Drainage is poor. And peat bogs are everywhere. But contrary to some of the old literature. The peat didn't form the patterns. It only conforms to them. And fills in the low spots with green color; the deeper the peat, the darker the green. So it's almost a proxy for the contours of the depressions.
 Most of the old literature focuses a lot of attention in the peat depressions and their possible formation. There is speculation that Multiple glaciations caused the patterns. Or Lake Agassiz, or that one, or more of related glacial mega floods may have had something to do with it.
But the profoundly simple fact is that ice sheets, and glacial lakes don't make pyroclasts, or blast melt. They can only erode away some of the surface detail. And if you look closely you will see that there is no missing surface detail in those melt flows. The solidified melt shows almost no exfoliation, or decomposition. There is no glacial scaring on them at all. And Except for some peat growing here and there in the cracks, and depressions, the melted flows are as pristine as the day they first cooled. And yet the bedrock is Archaean. There hasn't been any volcanic activity there in 2.5 billion years.
 It may not be so obvious to someone on the ground but from high altitude it's clear that he patterns are fact the un-eroded patterns of material movement in clastic flows, and partially melted surface rock. That's where I want to draw your attention. So, if you can, imagine the surface with all vegetation striped away. The giant fragments of the shattered ice sheet were the obstacles the blast melt was flowing around, and through.
 I don't believe for a minute that those pristine surface melt formations date back 2.5 billion years. I think the ice sheet was blown away by the event that formed them and has never returned since. And if I am correct they are the geologically recent blast-burn scars of some of the so called Younger Dryas Impact events.
My interpretation of the terrain comes from a close study of the lines of material movement, and flow in the clasts, and volcanogenic material. Like most other clastic materials, they were moving rapidly. And they solidified suddenly almost in mid flow. Those lines of movement are a snapshot in time. And they are an accurate record of the motions of the flows during their last moments in a fluid state. So it goes to fluid mechanics, and becomes a detailed study in the fluid motions of pyroclastic materials. You couldn't ask for a more complete, and honest data set. And every last detail of it's its story is permanently, and faithfully etched in the lines of movement in the rivers of melted, and flowing, stone. The movements of an unconstrained fluid are defined by the forces moving it. And for our purposes we'll need to refine that profoundly simple observation a little more and say that there are two fundamental forces to consider; gravity, and pressure. The region is as level as a parking lot. There has been no volcanic activity there in 2.5 billion years so there is no volcanic vent. Which tels us that all of the material movement was pressure driven. And that the heat, and pressure, came from above. The lines of flow in an unconstrained, and driven fluid are always away from the driving force. Even if the fluid is melted stone being driven up hill. A case in point would be a pyroclastic surge driven up, and over, a ridge top. The lines of flow describe the lines of force. The lines of force describe the force itself. And, like iron filings on a piece of paper can describe the fields of a magnet below, the lines of movement, and flow, in clastic materials that solidified suddenly, in mid flow, from a fluid, and driven, state, can be used to accurately describe something of the the energies, and directionality, of the forces that melted, and moved them. You can easily follow the lines of flow back to the source of heat, and pressure, every time. And you can learn a quite bit about that heat source as you do. The "Patterns" are in fact, the patterns of movement, and material flow in "volcaniclastic", and "volcanogenic", rock. And there is no volcanic vent they can be associated with.
The surface rock of the blast burns grades from migmatites, which were formed from ordinary sedimentary deposits that were heated almost to the melting point under terrific heat, and pressure. And in the presence of a lot of water. To "volcaniclastic" rock which was probably the same stuff. But heated all the way to a fast flowing state, and fluffed up a bit with hot gasses. And finally, to the completely melted "volcanogenic" rock whose chemistry seems to say it originated from somewhere else. But there is no volcanic vent that can be associated with them. There isn't even a geomagnetic anomaly that can be interpreted as an ancient, and hidden vent.
So in each of the blast burns we see the full range of conditions and temperatures from hydrothermal to "volcanogenic". Those materials, in context with each other they way they are, and without a volcanic vent to blame for the heat. And the patterns of movement, and heat flow, in the melted, and semi melted, rock describe a giant, multiple, hydrothermal explosive event in the ice sheet that was different, and more powerful, and violent, than anything ever studied before. And, without a volcano to blame, we have to acknowledge that the heat that made it all happen didn't come out of the ground.
If the black material (slate, graphitic slate, "volcanogenic"?) is the remains of a carbon rich, nickel iron poor, comet fragment, what do you think a detailed spectra graphic analysis would look like? I don't expect to find any shock metamorphism because the hydrothermal explosions would have worked like reactive armor on a battle tank. But, if it's what I think it is, it would have vaporized high in the atmosphere as all of its kinetic energy was translated into heat. And it would have continued on as a superheated, supersonic, downdraft of thermal plasma like a moving explosion. Only to be re-condensed, quenched, and preserved by the hydrothermal reactions with the ice. And if it turns out to be ordinary Earth rock I'm going to be very confused.
Here's a PDF with a little more.
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