Much of this website will cite cratering evidence from North America, because that is where the author physically is located. This look at southern Africa was started because the ring of the Mabule crater is the most obvious circle globally in gravity maps. But, I also wanted to see if cratering as I am coming to understand it from North America holds true over the entire globe. With this look at many of the larger craters found around South Africa, I believe it confirms that my understanding of cratering applies globally.
Figure 1: The Witwatersrand Basin of the Kaapvaal craton under South Africa’s Vredefort Dome Structure holds the largest goldfields in the world. How did the gold get there? Did the Vredefort Structure/crater have anything to do with it? Was it the collision between two tectonic plates? Was it eroded out of long forgotten mountains into a near shore reef? How does the cratering history of South Africa relate to its gold??
Figure 2: Gold in the Witwatersrand Basin is found in “reef” deposits, where the native gold occurs as particles that are believed to be detrital in origin. The particles of gold are found among rounded quartz and pyrite pebbles along with an abundance of kerogen and bitumen in the “carbon” reefs. Many yellow-green diamond are found in some “reefs,” and were a valuable commodity in the early nonmechanized mining era. Now, all of these superfluous items are smashed fine to get at the gold.
Figure 3: (A) Google earth image of Vredefort Dome Structure with enhanced color, showing the arced ridges of the Collar giving it the unmistakable visual image of a crater. The collar is a circular thrust, and is in keeping with a crater, but the thrust layers continue outwards for an additional 80-100 km. The collar thrust was a circular expression of the shear energy, but it was not the only one. (B) Isopachs contour lines based on the amount of annealing in the Planar Deformation Features (PDF) are indicated. The contour lines suggest the location of four straight lineaments (CGRS) that cross the energy pattern of the crater that were also produced by points of shear.
Figure 4: PDF samples not from South Africa, but showing two sets of PDFs in each sample. The second set annealed spots in the earlier set. PDF are a type of very fine parallel fractures in the quartz crystals. They are produced by shock-waves passing through the crystal. Multiple craters from different direction produce different sets of PDFs. When later sets occur, the shock-wave’s passing is accompanied by significant heat and the second set of heat waves anneals (melts together) spots in the first set of PDFs. So, the pattern of differing amount of annealing in Figure 2B is an indication of the total amount of heat from the passing of multiple shock-waves at that location.
Figure 5: Looking at a larger area around the Vredefort structure. Moving outwards, the three views show the persistence of linear patterns that cross the crater. These linears have a small circle relationship and are referred to as Concentric Global Ring Structures (CGRS) because in many instances concentric patterns can be traced globally. Some linears will persist in being seen at greater distance, while others appear and disappear. Circular lineaments also appear, marked with dotted lines and pairs of white arrows. The collar is marked “a” in image A and continues inside the double ring in the other two views. Pairs of white arrows show annulus rings for the impact continue outward to the limit of the viewing field.
Figure 6: The annulus rings continue outward with the collar between the first two, smallest, rings. The 5-ring is labeled in both images for comparative purposes. A few of the other circles that can be seen in these topographic images are marked. Panning up and down in Google Earth will show some circles to be more visible at one elevation and other circles at another. Should this variability of viewing decrease our confidence in identifying the cratering rings? I would say, no. It is to be expected as distance makes some linears less prominent while others blend together to form other patterns. Resolution is an important characteristic, but the release wave-valley (dark ring/“crop marks”) inside the yellow rings in Image B provide confirmation that the higher density ridge exist under the yellow circular lineaments although they are much less noticeable.
Figure 7: Witwatersrand Basin’s goldfields contain the Vredefort Dome Structure (crater) at its center, and the recognized circular lineaments of that crater (Figure 5A) extends over most of the basin. But, rather than the circular pattern of the crater, the goldfield and lifted lithology reflect more of the linear patterns that we saw in Figure 4. WHY???
Figure 8: To effectively see craters and their effect on the lithology, we have to learn to operate in gravity maps. This is the gravity map of Africa, with the Google Earth Landsat image of the exact same area so you can compare and orientate yourself. For this discussion we want to limit our area to southern Africa where the Vredefort Structure and the Kaapvaal Craton are located.
Figure 9: When we get up closer in gravity maps they make more sense, but it is sometimes difficult to retain our orientation. For ease of recognition, I have outlines southern Africa and Madagascar in black rather than include the Landsat image for comparison. In a gravity map, high gravity is shown in red and low gravity is shown in dark blue. Sometimes the high gravity correlates with high topography, and sometimes it does not. Consider the high gravity just off the edge of southern Africa. It is red, but there are no mountains sticking out of the water along that section of the coast. The most visible nearly complete circular form in high gravity is this circle near Africa’s tip. I have named it the Mabule crater.
Figure 10: (A) The Mabule crater with two pairs of circles showing the high ridge for the two rings between these pairs of circles. Some of the linear patterns that are seen in the topography close ups of the Vredefort crater can be seen crossing the entire continent. (B) Some of the other circles visible in topography shown in black. The Ghanzi circle/crater corresponds directly to the Congo Craton and the Giyani circle/crater corresponds to the Zimbabwe Craton. Several circles can be seen around the area of the Kaapvaal Craton, but none of them correspond to its structure.
Figure 11: Using the gravity map, the Chobe, Bulaway, and Zimbabwe craters show up. They all have a distinct effect obliterating the strong circular pattern of the northern edges of the Mabule crater’s rings. This is an indication that these northern craters arrived after the Mabule crater.
Figure 12: There are at least two other larger craters that will need to be accounted for in a final sequence of impact to account for the total lithology. The Indlovu crater, centered near the east coast, produced an up-thrust with its outer ring within the center of the Bulaway and Zimbabwe craters. I will propose the Giyani crater arrived after the Indlovu crater interacted with the Bulaway and Zimbabwe craters and after the Mabule crater had set the continental edges to the south.
Figure 13: The inner Indlovu cratering rings seen in the gravity image. The reader is encourage to note the pattern in shades of blue in the ocean floor east of the continent, as indication of higher gravity left from up-thrust of shock-wave/compression shear from the cratering center.
Figure 14: Limpopo Metamorphic Belt complex terrain formed where the Indlovu crater overlapped the earlier Bulaway craters. The Bulaway crater would have heated the rock into a plastic state, so that the up-thrust of the Indlovu’s ring would buckle it up on edge to form the Northern Marginal Zone. The Indlovu crater-rings also overlapped the Mabule crater where the Witwatersrand strata would later occur and both of them contributed to the energy event’s heat and pressure that would draw the carbon, gold and diamonds from deep in the mantle.
Figure 15: The Witwatersrand Basin is centered under the Vredefort crater, as shown by the last ring in Figure 5A. It is cut off on the west by the Open-ring of the Mabule crater, on the east by the Open-ring of the Indlovu crater and on the north by the Bulaway crater. The up-thrusting shear from these three craters were still in the substrate and active when the Vredefort impactor arrived so all could interact together.
Figure 16: The Bushveld complex is actually a triangular area where the Indlovu, the Bulaway, and the Mabule craters overlap. I will propose the Mabule arrived last contributing its energy and sediments to the already occurring Indlovu and Bulaway craters. The later arriving Giyani crater may have pulled the differentially heated, more plastic, rock up in its crater rebound.
Figure 17: The Bushveld Complex primarily consist of two formationsthe lower complex, a layered “reef” of igneous intrusions, and an upper layer of red granite. While the standard explanation for both layers requires feeder sources from within the crystalline basement or even from the mantle below the Moho; in a cratering context, I proposing they were the first vapor condensate sediments from the three overlapping crater’s vapor clouds (igneous condensates).
Figure 18: The Kaapvaal craton underlies the Witwatersrand Basin and the Vredefort crater, and the craton generally conforms to the crater-ring of the Koster crater. As this craton’s borders do not respect the Indlovu, Bulaway, Giyani, or Mabule craters’ thrust-rings, this crater was laid over them.
Figure 19: Additional conformation that the Kaapvaal Craton was produced in a cratering sequence comes from the Koster craters limiting by additional smaller craters. Craters 1-4 are sketched craters that conform to those limiting edges with energy patterns in the gravity image. Study the four rings to see if you can recognize the gravity indication of a high and low pattern consistent with the input of a shock/release-wave.
Figure 20: Attempting to find conformation of the Koster crater, the tomography of southern Africa was viewed. The Bushveld Province (BP) in image A corresponds to the Koster impactor’s landing spot. Tracing it through the tomographic slices, the bowl shaped arc (1) of its compressed layer (red) are recognized.
Figure 21: The blue center of the green at the center of the Koster crater shows its center was pushed deep offsetting or producing a disconformity that has become known as the Moho.
Figure 22: But, there is an even larger, deeper center to the northeast under the Limpopo Metamorphic Belt that I have labelled the Barbirwa crater. The additional heat center is a major cause behind the Limpopo Metamorphic Belt’s occurrence at this point. Reexamining the tomographic slices at this point suggest they do not go deep enough to capture the bottom of the arc at this point.
Figure 23: Looking at the reaches of the Barbirwa crater in Landsat, it is evident that we are dealing with a crater of much larger dimensions even including an up-thrust in 3-ring that is a major contributor to Madagascar’s topography.
Figure 24: Looking at Barbirwa crater in gravity, we can see up-thrust all around the third ring. Not only in Madagascar and the gravity plateau south of it, but also in the parallel ridge of high gravity to the west of the continental edge. This suggest the Mabule did not operate alone forming the edges of the continent, but its energy and thrust were combined with the earlier Barbirwa’s in that area to determine the ultimate gravity pattern.
Figure 25: Looking once again at the tomographic sections, I have attributed bowl 1 to the Koster crater, however the distinct red compression may not be the bottom of the bowl because a faint blue layer occurs below it, and another red faint layer below that. The 3 red/compression bowl may be the bottom of the Bulaway crater. The 4 would represent the location of the Barbirwa crater occurring below this section. The significant arc 2 would be the correct location for the Indlovu crater’s bowl.
Figure 26: The Indlovu crater is large, but much of it extends over the ocean. By contrast, the Mabule crater is primarily contained by the edges of the continents. I will propose the Mabule crater formed the foundation of South Africa, and was the transition between craters laying down the crystalline crust and the smaller craters that produced the sedimentary cover for the land. The primary difference between the land and the ocean’s floor is not some distinction between basalt and granite, but timing in the cratering sequence when materials in the mantle had been turned over sufficiently to produce as condensates the sandstone, limestone and shales rather than the granitics and basalts of the earlier sediments.
Figure 27: The Indlovu crater stands out in gravity. Elsewhere I recognize a mascon is pulled up inside the Open-ring of a crater. The high gravity between the two white arrows is a mason, whose compression ring is shear from the Mabule crater and the blue/red Open-rings of the Indlovu crater represents its uplifted cratering bottom that limits the mascon’s expression by the Open-ring. I propose the Mabule crater arrived the day after the Indlovu. But, as large as the Indlovu crater is, it was not the first in this area.
Figure 28: The Orange crater, at ~6,900 km diameter to the outside ring shown here, and ~8,000 km diameter to the outermost ring in Figure 29, may be the largest crater in our Solar System or a CGRS beyond that crater’s rim. More study is needed.
Figure 29: The Orange crater starts near the mouth of the Orange River, but extends well into both the Atlantic and Indian Oceans. Its most distinctive topographic features are on the island of Madagascar where three sections of shoreline follow concentric to the rings
Figure 30: While the topography above the water might not show evidence for the impact, the energy pattern in the seafloor’s gravity map does testify to the cratering origin. The ridge between the two red rings and the release-valley between the two blue rings is exactly the structure expected from the compression wave followed by the trough of the release wave from a shock/release-wave pair. I refer to this pattern as the Energy Envelope of an impact. This large energy envelope came from an equally large impact. As the ridge winding through from west to east is part of the “southern Mid-Atlantic Ridge transitioning into the Indian Ridge south of Africa.” It still is a gravity ridge having nothing to do with the concept of Plate tectonics. Cratering does not ignore the evidence for ridges and valleys on the ocean’s floor, but it recognizes different reasons for their structure and origin.
Figure 31: This is the west end of Figure 29. It shows that the energy envelope evidence make much more sense when we are able to find the added circles (energy envelopes) of overlapping craters. Crater 1 here defines a section of the Orange crater rim that conforms to the red-rings, and outside crater 1 there is a distinct blue ring cutting this up-thrust red-ring. The blue-ring trough of the Orange crater is also much more distinct within this white-ring. Whether this is an earlier or later crater is indeterminate at this time. If it is an earlier larger crater, it is a distinct possibility that the up-thrust ring of the Orange crater is a mascon within the Open-ring (white-ring) of crater 1. The regular blue lines that cross the Orange crater ridge-ring are reminiscent of the release-wave valleys traced crossing the Sierra Nevada in Chapters 6 and 7.
Figure 32: This is the east end of the Orange crater’s rings shown in Figure 29. Here an even larger crater 1, recognized by its blue-ring inside the white-ring, suggest the Indian Ridge is a mascon, but it is not from the Orange crater. Within this crater 1 a second crater can also be seen crossing the rings of the Orange crater and the Indian Ridge. Ring-2 is largely recognized by the blue-ring inside the white-ring produced by a release-wave valley in the energy signature.
Figure 33: The strongest evidence to recognize the Orange crater continues to be the blue-ring (release-valley) inside the higher gravity ridge/red-ring (compression-rings). While significant parts of the high gravity ridge can be seen, a nearly continues blue release-valley can be traced once the reader has learned to pick them out.
Figure 34: This photo essay has recognition a series of much larger craters than the Vredefort Dome Structure/crater suggest a cratering history that goes back beyond the depths of topographic sections. The origin of the gold is relatively simple. It involves a multi-stage process of larger and large craters pulling up gold and other minerals in a sequence of cratering events which heated the substrate and repeatedly subjected it to surface crystallization under extreme pressure, then lifted the mineral in up-thrusting mascons in the Open-rings of those craters. It was not a continuous cycle of deposition, burial, pushed deep into the earth, and then re-eroded in a continuous maniacal cycle of millions of years, but large craters with huge heat and pressure acting on or near the surface during a limited time of bombardment that produced today’s surface lithology.
Figure 35: These craters not only left a record on the surface of the earth seen in gravity maps, but left a record in their compression layers down into the lithosphere and asthenosphere. We are not looking at a lithosphere and asthenosphere that is mobile, carrying the tectonic plates in continuous wonderings over the planet, but a wholly static lithosphere and asthenosphere topped by the mantle and crust with innumerable discontinuities produced by the deep reaches of the compression layers of many of these craters. Generally and primarily unchanged since the cratering stopped.
South Africa Kaapvaal
- Much of this website will cite cratering evidence from North America, because that is where the author physically is located. This look at southern Africa was started because the ring of the Mabule crater is the most obvious circle globally in gravity maps. But, I also wanted to see if cratering as I am coming to understand it from North America holds true over the entire globe. With this look at many of the larger craters found around South Africa, I believe it confirms that my understanding of cratering applies globally.