CHAPTER 2.6
THE MANACOUAGAN IMPACT & WESTERN ANTARCTICA

   
CHAPTER 2.6
THE MANACOUAGAN IMPACT & WESTERN ANTARCTICA


There is a 100 km diameter crater in Manicouagan in Quebec, Canada, dated to circa 214 MYA. In addition, Western Antarctica is a small continent that appears to have been formed around that same time. The Manacouagan impact and the location of the newly formed Western Antarctica could have been antipodal to each other 214 MYA.

So, what are we to make of all of this information? Is this all related to a singular event?

The impact at Manicouagan occurred approximately 214 MYA. It created a crater of 100 km in diameter.

The impact object hit right in the middle of the Canadian shield. There was no water to help abate the force of the impact on the lithosphere.

Although the impact would have been on the smallish side (in terms of uplifting a continent at the antipode), this impact hit solid rock with no mitigating circumstances or any other buffer. The uplifting of a small continent would be possible.

The small continent of Western Antarctica would be a probable candidate, especially since the Standard Theory says that it mostly rose from the sea during the period of 206 MYA and 146 MYA. An actual date of 214 MYA would not be too far away from these indefinite boundaries, especially for an underlying layer that could become covered with mudstone (as in the case of New Zealand) or other sedimentary silt. This process of mudstone accretion would mean that the upper layers would show a later age than the original underlying rock.

But, if Western Antarctica was created at and near the antipode of the Manicouagan impact, where would that creation have been located and where are the "tool marks" that were left behind?


WESTERN ANTARCTICA'S CREATION & JOURNEY


The short answer to this question is: New Zealand. But the whole answer is much more complicated than just those two words.

New Zealand is the visible portion of a much larger structure called "Zealandia." During periods of its history, almost all of the entire structure has been below sea level. Occasionally, a portion of Zealandia has risen up enough to create a significant amount of dry land.

From approx. 150 to 115 MYA, there were extremely large volcanic events in the Zealandia area. Then the volcanism stopped. 50 Subsequent to these events, the land eroded and then built up again. During its history, glaciation lowered the sea levels and, due to New Zealand's high southern latitude, caused glaciers to form. These glaciers eroded the land. Large valleys that appear to be glacial can be seen in the underwater portions of Zealandia.

By 35 MYA, most of Zealandia, with the exception of maybe a few small islands, was below sea level again. The current rise of New Zealand was created from 24 MYA to 10 MYA, with some final touches in more recent history. 45

For our purposes, the important part of this history relates to the large volcanic events that occurred from 150 MYA to 115 MYA.

At approximately 214 MYA, the antipode of the Manicouagan impact would have been somewhat to the north and east (within a thousand miles or so) of the present day site of New Zealand. It is likely that the impact raised up a small antipodal continent with an active hotspot. This continent was Western Antarctica. It is also likely that the Western Antarctica continent was made up almost exclusively of mafic oceanic crust that rode well below the surface of the ocean, except for the uplifted leading edge, which would have forced the subduction of the oceanic crust in front of it.

A look at a relief map of the area near Zealandia shows the tool marks left behind by this continent as it moved SSW, approaching Zealandia, moving through the area, and then swinging to the east as the Coriolis effect influenced its movement.

Western Antarctica is about 2500 miles long. Originally, it probably stretched from just below Fiji's original location out 2500 miles to the northeast, but moving to the SSW.

Fiji's original location was not where it is today. Not only was it located at a different longitude and latitude because its tectonic plate has moved in the past 214 million years (to the north and east), but Fiji was not in the same position in relation to the seamount chain that proceeds from Fiji to New Zealand.

Originally, this seamount chain (with Fiji at the head of it) was all in a straight line. However, plate tectonics caused the head area to form its own mini-plate, which rotated the top of this chain.

The Ministry of Lands and Resources of Fiji explains that when island arcs are stretched, "they split, initially forming a rift and eventually a back-arc spreading centre." 46 pg 3

In the case of Fiji, the stress was so great that the Fiji area broke off into its own small tectonic mini-plate, as shown in the first page diagram on their website. 46

Therefore, even though the seamount chain (headed by Fiji and leading to New Zealand) now is in the shape of a shepherd's crook, it was originally in the shape of a straight line.


THREE PARALLEL LINES


Located about 100 miles to the east of the Fiji seamount chain is the Tonga seamount chain, which runs roughly parallel to the Fiji seamount chain. Another 50 miles to the east, the Tonga trench runs parallel to the Tonga seamount chain.

All three of these features lead down to New Zealand, where they are obscured. Exiting south of New Zealand is a trench and an intermittent line of higher ground that run almost on top of each other. These combined features continue generally SSW until they reach approximately 60 south latitude, where they veer to the south and then to the southeast. Then they disappear.

What does all of this have to do with Western Antarctica? These are the tool marks left behind by that continent on its journey to the South Pole.

The Fiji seamount chain is the result of Western Antarctica's blob turning slightly to the west as it moved to the south, pushing up a small amount of land as it passed by.

During this part of the journey, the hotspot (located on the north side of the continent, near the blob) was moving in tandem with the continent, but not as fast. As a result, the hotspot was raising up land with a basalt underlayment on the new continent (similar to the western mountains in the Indian peninsula from 65 MYA to 60 MYA).

The tail of the continent was being forced to follow to the southwest, although the underlying magma pulled to the west. This action created the Tonga trench as the tail passed by and pulled to the west.

When the middle of the offset tail outran the hotspot, the offset bottom tail of the new continent was too far to the west to continue covering the hotspot. Therefore, the hotspot started cutting through the Australian plate at that point about 150 MYA (at the northernmost point of the present New Zealand).

The hotspot continued cutting through to the southernmost point of the present New Zealand, when the offset tail of the continent swung over the hotspot again as the blob turned to the south (from southwest) and then to the southeast (due to the Coriolis effect) about 115 MYA.

This swinging motion, and some tail wobble as a result, caused the strangely curved uplifted mountains (as it passed over the hotspot again) in the tail of Western Antarctica.

As Western Antarctica drifted southeast, it collided with Eastern Antarctica. The leading edge of the Western Antarctica continent became enmeshed with Eastern Antarctica. These two enmeshed continents continued to sink towards the South Pole.

The hotspot continued on its path to the southern polar region, becoming uncovered at present day Buckle Island and continuing to the southeast, creating volcanic cones (including Mount Melbourne) on the way to its present location at Mount Erebus on the Ross Ice Shelf of Western Antarctica.

The glaciation around Antarctica during the past 200 million years erased most tool marks in the basin area around Antarctica.


THE SURPRISING TONGA TRENCH


One of the strongest indicators for the scenario that I have presented is the surprising nature of the Tonga Trench. The Tonga Trench is a subduction zone, which caused the formation of the Tonga Islands and the collection of seamounts that lead down to New Zealand.

However, the Tonga Trench is not a typical subduction trench. It is unusual in two respects:
1. It did not start subducting until 43 MYA (up until then, the movement was parallel). Other subducting systems (Japan, the Americas) have been subducting for over 200 million years.

2. The type of subduction is also unusual. The Tonga Trench has a shallow subduction mechanism as opposed to the deep subduction mechanism that is typical. An article entitled "Tonga Slab Deformation: The influence of a lower mantle upwelling on a slab in a young subduction zone" by Michael Gurnis, Jeroen Ritsema, Hendrik-Jan van Heijst and Shije Zhong in Geophysical Research Letters, August 15, 2000 explains:

"The contrast between Tonga-Kermadec and both Japan and South America is striking. Tonga-Kermadec has a transition zone structure dominated by high shear velocities immediately atop a large-scale low velocity anomaly in the lower mantle. Within both the Japan and South American subduction zones, high shear velocity structures in the transition zone continue deep into the mantle." 47 pg 2373
The article also notes:
"In long-lived subduction systems the lower mantle tends to pull slabs down while in Tonga the lower mantle pushes upward." 47 pg 2375
So, what does all of this mean? It means that the Tonga Trench is now subducting in spite of itself. The only reason that it subducts at all is because there is a deep trench and, over time, this inevitably leads to at least some subduction.

However, the Tonga Trench is not a structure that was created by subduction pressures. In fact, it actively resists subduction. Therefore, the Tonga Trench must have been created in some other manner … such as resulting from the creation and passing of a continent like Western Antarctica.


EXPLAINING NEW ZEALAND


The geological history of New Zealand (and Zealandia) is unusual. It is also well-explained by the theory presented in this chapter.

Although the Standard Theory can glibly explain New Zealand and Zealandia as a result of its location on a plate boundary and the sinking of a small continent (Zealandia) after it separated from Antarctica, the Standard Theory doesn't explain important corollary questions that are raised by this standard explanation. These questions are:
1. SINKING - Why did the Zealandia continent sink? How come we don't have sunken continents in lots of other places?

2. WHY FORM JUST NEW ZEALAND? - If the plate boundary is such a big deal, why is the formation of land limited to just the New Zealand area? Why wasn't land created along the plate boundary to the north of New Zealand or to the south of New Zealand?

3. PLATE BOUNDARY - Why is this plate boundary so peculiar (see above discussion of the Tonga Trench)? Why would this plate boundary be so inactive above New Zealand and then so active (but not necessarily subductive 49 ) when it hits New Zealand … and then inactive after it passes New Zealand?
The Standard Theory does not have any good answers for these questions. However, the theory of an uplifted and moving Western Antarctica and its follow-on hotspot answers these questions nicely.

In effect, New Zealand and Zealandia are the creations of a slot that was cut into the lithosphere of the Australian plate by Western Antarctica's hotspot when it was uncovered and traveled under that portion of the Australian tectonic plate. The slot began when the hotspot emerged from under the middle of Western Antarctica's tail, because the lower tail was offset. The slot ended when the lower tail again covered the hotspot when Western Antarctica turned to the south and southeast due to the Coriolis effect, and the offset tail was forced to the west.


NEW ZEALAND GEOLOGICAL HISTORY


Zealandia has been a shallow continental shelf area for most of its existence. As such, it built up great amounts of sedimentary mudstone called "Greywecke" over millions of years of continental runoff and marine deposition.

Zealandia has experienced three separate instances of orogeny (uplifting). The first orogeny occurred about 350 MYA, called the Tuhua orogeny. It uplifted some of the undersea land in Zealandia (a small amount of which is still dry land today) through volcanic means and perhaps some folding of the sedimentary areas. 51

This land was later eroded away, leading to more deposition of mudstone. From 150 MYA to 115 MYA there was a large amount of volcanic activity, which was the source of the second orogeny, called the Rangitata orogeny. 50 This time period covers the time when the Western Antarctica hotspot cut through the lithosphere at the New Zealand location. This gash in the lithosphere created a permanent weakness that could respond to nearby mantle pressure.

Once again, the land was eroded by sea, weather and glaciation. By 35 MYA, very little dry land was left. Starting around 30 MYA 52 and picking up steam from 22 MYA to the present day, the Kaikoura orogeny has uplifted New Zealand to its present situation. 53

During the past several million years, erosion and sedimentary deposition have been the major factors in building up the below-sea-level expanse of Zealandia. As far as I can tell, Zealandia never sank … its above-sea-level land eroded away and was later rebuilt through volcanic action in the slot that was cut into the lithosphere.

I believe that glaciation was a major factor in eroding and spreading out the dry land to expand the footprint of Zealandia. On both sides of the slot, Zealandia shows what look to be large glacial valleys that led to what would have been sea level during the ice ages (when the sea level was, necessarily, substantially lower).


THE MANICOUAGAN SMOKING GUN


Let's review what we now have for the elements of a smoking gun for the Manicouagan impact.
1. CRATER - There is a 100 km diameter crater at Manicouagan in Quebec in Canada that is dated to circa 214 MYA.

2. HOTSPOT - There is evidence of the hotspot cutting a slot at New Zealand 150 - 115 MYA and raising up mountains on the Western Antarctica continent. There is later evidence of a line of volcanoes going from Buckle Island to Mount Erebus in the Ross Ice Shelf of Antarctica, continuing the path of the hotspot, which is an anchored characteristic, not so susceptible to the pull of the Coriolis effect. At present, the hotspot is located at Mount Erebus.

3. BLOB WITH A TAIL - We have Western Antarctica, which was supposedly raised from the sea in the vague time frame of 206 - 146 MYA. If the volcanism began 214 MYA, then sediment deposition from 206 MYA to 146 MYA would make sense.

4. CONTINENTAL MOVEMENT - We have the tool marks of the Fiji seamount chain, the Tonga seamount chain and the Tonga Trench. We also have the New Zealand hotspot slot and the continuation of the pushed up land (but below the surface) and the trench as the Coriolis effect changed the direction of the continental movement.

5. TANDEM MOVEMENT - We have the orogeny on Western Antarctica, the hotspot slot at New Zealand, the strange curved mountains at the end of the tail of Western Antarctica, the continuing trail through Buckle Island and the line of volcanoes (including Mount Melbourne) that lead to Mount Erebus, where the hotspot is located today.
This sequence leaves us with a very complete picture of the formation and movement of the Western Antarctica continent and hotspot, based upon the antipodal effects of the impact at Manicouagan.

The only thing missing is a major extinction!

The impact occurred 214 MYA. The closest major extinction was the Triassic, which occurred 202 MYA.

However, there was a minor extinction (only about 18% of species were eliminated) that occurred right around 214 MYA. It seems that we can't blame Western Antarctica for the Triassic extinction. Apparently, the result from this smaller (compared to Chicxulub) impact was not enough to set off a major extinction. A minor extinction will have to do.