67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 38

THE GULL WING DELAMINATION ON THE BODY 
   

Dark green- five sets of delaminated gull wings on the body (denoting four distinct rifts). Each pair of gull wings has one dot for each of its curve midpoints. The classic set at the end of the cove seating (see Part 36 and before) is the third or middle set in this view. This is easier to see in the more elaborate annotations below. This is a pure, pared-down version so as not to distract from the main subject of this post which is the delamination itself and the direction of stretch vectors. 

Light blue- these are tell-tale rift lines that join to the five sets of gull wings. They, of course, had to delaminate as well, meaning that this delamination process was planar. In other words, it involved lines delaminating across an area as opposed to points or quasi points delaminating along a single line. The five sets of gulls wings could be described as the latter, but they are simply part of the former. So they define a line along the edge of the area swept by the planar delamination of the ridges. And of course, the gull wings are really just part of the ridges anyway. They just happen to be more recognisable, have a colourful history and garner more press in this blog for that reason. 

Photo 2- a top-down view of the five delaminated gull wing sets for orientation purposes. 

 
Dark green- the five sets of delaminated gull wings on the body.

Yellow- the set of gull wings on the head lobe cove that matches to the middle set on the body. Notice how the right hand yellow dot isn’t on the shape that looks as if it matches to the shape on the body whereas the left dot is. That’s because this shape is the upper, second set of gull wings on the head (and third vertically delaminated set including the set on the body). It obscures almost all of the true head rim match below it, which is the first head rim set of gull wings. Just that tiny amount of the right hand wing is showing itself. The other four sets of gull wings on the body don’t have discernible gull wing shaped matches that are mirror-matched to the head rim. That’s because the first two sets by the horseshoe crater are just remnants of the third set and the fourth and fifth sets along the Babi shear line towards Aker are just vestigial bumps because they delaminated so far back. However all sets are surrounded by a multitude of mirrored matches from head rim to body (Parts 1-8 and 18).

Photo 3- the ESA regions map for 67P. 

 

BACKGROUND

In previous parts we’ve only ever looked at a single delamination of the gull wings, creating two matching sets. Those are the second and third sets from top-right in the header. That was where the classic set tore away from the side of the horseshoe crater and slipped along the shear line. By doing so, the sliding wings opened up the shallower crater above and to the side of the horseshoe crater. And the slide or rift along the shear line opened up the curved fissure that fed the single hole which then delaminated into three. The hole delamination occurred during the head stretch or herniation from the body and those three holes stayed with the head lobe after the main head shear. 

Now we’re adding three more sets of gull wings. That betrays three more delaminations, making a total of five gull wing sets and four delaminations. Four sets are definitive matches and the fifth is highly compelling.

For numbering purposes, we’ll call the top-right set of gull wings the first set. It’s the set adjoining the Site A rim. So the fifth set is at bottom left. The second set would be the set that the classic set delaminated from on the horseshoe crater rim. This set then slid back from the rim in a different radial direction from the classic set, more in keeping with the monolithic slide (Part 33). The classic set, which matches to its vertically delaminated twin on the head rim, 1000 metres above, is the third set. And the set at the other end of what was dubbed the ‘green rectangle’ (Parts 5,7,8) is the fourth set. The area between the third and fourth sets corresponds exactly to the area matched to the head lobe rim underside in Part 1. The area between the fourth and fifth sets corresponds to the area matched to the head rim in Part 2. 

Just to be clear, the matches in Parts 1 and 2 were mirrored matches from body lobe to head lobe while these lateral delaminations in this post are translational matches like spreading a pack of cards across a croupier’s table and seeing the parallel long edges of the cards matching. That’s the same type of match as the red triangle recoil. It means the cards must have delaminated across Babi as shown in the header before their intervening mirror matches on the shear line could be matched to the head rim. That in turn means that Hathor must have been undergoing exactly the same stretching and delamination as the green dots in the header. It had to do so in order for the mirrored matches to be so faithful after the lateral delamination had occurred. Hathor is the cliff on the head lobe underside (omitted on the ESA regional map). It was clamped to the body prior to shear and so it’s not at all surprising that Hathor has to have stretched in the same manner as the header photo dots and in lock step with those actual green dots it was clamped to. Indeed, this was touched on in Part 37, regarding the terracotta stepped feature that is very evident in Hapi and mirrored on Hathor a long way down under the head rim. 

So the gull wing delamination in the header indirectly betrays a substantial sideways stretch as you look at the Hathor cliff, the underside of the head lobe. That will further our understanding of the dykes running up the Hathor cliff in due course. The dykes were introduced in part 8.

As well as the card-spreading trick it would be as well to bear in mind that three of the ridges fanned out so their ‘card edges’ aren’t parallel. So a fan analogy applies as well as the card-spreading analogy but they are topologically identical: planar, translational delaminations. 

Four of the five ridges exhibit mini matches as if the original pack of cards had been sculpted along its edge with bumps and dips before being delaminated. 

THE GULL WING DELAMINATION IN DETAIL 

In the header photo, three of the light blue lines arc from a single axis point on Babi. Those three lines lead to the middle three sets of gull wings and show definitively that those three sets delaminated laterally from each other. The middle set of these three is the classic set at the end of the cove seating. These three lines have several ups and downs along their length that can be matched as mini matches. These can be seen more easily in the unannotated version. There’s a small amount of foreshortening and stretching of these mini matches but they are clearly there. That’s why these three sets of gull wings and their ridges are definitively linked. 

The first gull wing set, kissing the Site A crater rim, has a blue line leading to it as well but that line has been intentionally detached from the main, sharper, shadowed ridge coming up from lower down in Babi. That’s because it’s a slippage rather than the neat arcing round from a single axis that characterises the other three. So it’s a slipped card rather than an arced fan leaf. Two of the three fan leaves arced off on one side of the main ridge, creating the fan of three and this first one slipped the other way from the main ridge and stayed nominally parallel rather than arcing on an axis. And yet, remarkably, the very same mini matches can be matched to this slipped ridge as for the other three, although they’re slightly more stretched about. Therefore the first set of gull wings is also definitively matched to the other three. 

The first ridge line also has its own mini ‘fanning out’ delamination, which is a short arcing on an axis from halfway along (not annotated). That means there’s a mini fan of two or even three short ridges for the first two gull wing sets as well as the slippage. But the slippage component for the full length of the first and second ridges looks to be overwhelmingly dominant with just this small, sympathetic fanning. 

So if the first four gull wing sets have been definitively matched via their ridges, that leaves just the fifth set. That set isn’t so compelling when trying to link it via ridges. A tentative line has been drawn as a preliminary indication of what is probably a slipped ridge from the fan of three but it can sometimes take several different views under different lighting to start seeing matches. The fifth gull wing set nevertheless looks highly compelling in the side view photos below.

And the light blue ridges aren’t the only way of matching the fifth set to the other four. This set also exhibits what appear to be a similar pair of pimples to the fourth set (next to their pairs of green dots). The pimples on the fourth set are definitely pimples and not rocks. Those on the fifth set haven’t been confirmed as pimples and may be rocks but it would be highly coincidental if they were rocks. And the real clincher is that both sets exhibit three faint, rectilinear features to the lower left of their green dots. That’s also in line with the delamination direction, which is promising. 

SIDE VIEW OF THE GULL WING DELAMINATION 

Photo 4- side view of the gull wing delamination. 

 
Dark green- (zoom needed) the gull wing sets as in the header. The first set is on the right and the fifth set is on the left. 

Light blue- the ridges as annotated in the header. The exact axis of the fan of three was difficult to pinpoint but it’s very close.

Beige- these two dots are below the third pair of green dots which denote the classic gull wings. The beige dots are kissing the front, central bases of the two slurry piles that oozed out from under the gull wings. Those two piles are what pushed them up into gull wings in the first place. You can just about see the concentric ripples in the nearer pile. These are clearer in photos in Part, 5,7 and 8. They’re also visible in the orientation photo above (photo 2), especially the pile that’s nearer in this view. It’s a near-perfect semicircle with concentric inner semicircles, like a dollop of thick custard or slumping concrete. 

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The first three gull wing sets in photo 4 are discernible as pairs of wings and so have pairs of dots. The fourth and fifth are more in profile so they have one dot each. This is in keeping with the fact that the first three sets got dragged back towards Ash (towards us in this view) by the monolithic slide (Part 33). The first set got yanked the most because it was probably attached to rock C which was, at that time, part of the monolith that slid. The second set was on the horseshoe crater rim so it was yanked a little less and pulled along the main delamination force vector a bit more. And the third set, the classic cove set, was being yanked partly towards Ash but mostly along the main delamination vector, which is along the shear line. The last two sets were further from the monolithic slide so they kept faithful to the predominant line of the delamination vector along the shear line. Also, being the two furthest removed from the first set, the fourth and fifth sets are barely discernible as gull wings. They’re more like wide bumps with two pimples on top.

Photo 5- the header photo with additional annotations. 

   

The header was left uncluttered so as to focus on the gull wings and their ridges. These additional annotations add context.

Dark green- five gull wing sets.

Light blue- delaminated ridges linking the gull wing sets.

Dark blue dot- a single dot showing the current north pole.

Brown- two dots. The one next to the blue dot is the paleo pole preliminary adjustment as described in Part 37. The one to the right, up the rim of Site A is the estimated position of the actual paleo pole during the initial stages of head herniation. Its positioning is also discussed in Part 37. 

Pink- one dot. This is sitting in the middle of the horseshoe crater.

Fuchsia- these two dots denote the tips of the delaminated India shapes (Part 37). They slid by the same distance as the distance between the second and third gull wing sets. That’s because they are part of that delamination, i.e. the slide from the horseshoe crater rim to the classic gull wings position. Part 37 showed the India shapes from above. This lock-step slide with the gull wings along the small curved section of the shear line is quite clear in that photo.

Yellow- the cove seating which matches to the present-day cove on the head lobe. 

Red- the three dots next to the pink dot show rock C’s seating from which it broke away. Rock C used to form the top part of the back rim of the horseshoe. The two dots to the right show rock C itself.

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Photo 6- this photo is as photo 5 but with head lobe annotations added, along with the fissure for the 3 delaminated holes on the head. Also, an interesting mini match. 

   

Yellow- the upper-left line is the bottom rib of the middle scallop in the cove. If the head stretch and herniation are reversed, this second scallop collapses onto the first one, which means this yellow rib collapses onto the bottom rib of the first scallop (which is the head rim itself). The head rim has a similar but subtly different profile to the middle scallop rib. But when they are clamped together, their combined profile marries to the yellow curve on the body lobe at lower-right.

Light blue on head lobe- these two dots show the middle and upper delaminated holes that slid from one lower hole on the first scallop. Each one is next to its respective scallop of the three scallops. The bottom scallop and its hole are half out of sight, half in shadow so the bottom hole can’t be seen. That hole is really just the gas-scoured base of the original hole and not discernible as a hole. The three nested holes were originally kissing the yellow curve on the body along the line where the slate blue line runs. 

Slate blue- this is along a section of the yellow curve on the body. This is the seating of the delaminated hole. Or rather, the hole was just above this line which was the fissure opened up by the slide of the classic gull wings from the horseshoe crater rim. The near end of the slate blue line is kissing the gull wings that slid because the fissure is defined by the slide. Just below this near end, you can see a shadowed area at the bottom of the shear line cliff (not the darker shadow that the line is touching- that’s the gull wings). The shadowed area at the bottom of the cliff is curved and has a small rib halfway up. This curved recess may be the other half of the longitudinally sliced dyke on the Hathor cliff that runs to the scoured hole base described above (and in Part 36). It’s in exactly the right place, completely constrained by all the other matches around it. It doesn’t look as if it extends up far enough because it should extend to the yellow line. However, the photo is deceptive. Behind the dark shadow of the gull wing (its left wing in this view) there’s a fairly deep recess. It looks as if we can see everything with the shadow being divided from the brighter part by a defined ridge but the left gull wing hides the channel.  

Bright blue- these are short lines at the end of two of the three fanned-out ridge lines. They’re mini matches and, along with the tips of the bright blue ridge lines, they form a triad of parallel lines. So these two ridges, from their shared axis point to their tips look like tridents. Its highly recommended to look at the unannotated version to see this because the dots completely obscure the feature. The way in which the lower trident’s prongs are twisted round anticlockwise by 90° and the staff stretched is entirely consistent with the stretch vector of the delaminated gull wings. So much so that you can visualise how the fine movement of the slide must have played out, like a movie. 

CONCLUSION

The five sets of gull wings clearly delaminated in the comet’s long axis direction, along the shear line and away from the pole. This particular direction of stretch is wholly expected. It’s both radial and straight down the long axis. Or, to be exact, parallel to the long axis running through the core a few hundred metres below. And this spectacular mode of crustal stretch via multiple delaminations has already been seen occurring at the south pole, on the red triangle and with the main sink hole on Site A. But you can have only a single line running both down the long axis and through the north pole point. The whole delaminated area obviously can’t do that. But the five sets of gull wings form a quasi line with almost no area. They spread along that long axis line and radially from the pole, give or take some pushing about that was probably after the delamination anyway (due to the monolithic slide). But their accompanying ridges are spread down into Babi and fan round across the delaminated area. There’s a lattice of stretch vectors at play, with any particular point in the layers yielding only partially to its local, surface, radial vector from the pole. That’s because it was also being dragged along as part of a delaminating layer. And the tensile force direction for the delaminating layers was dictated by the long axis stretching. That is, the long axis-dominated core stretching under the crustal layer. The gull wings are a special case because they’re sitting along that line which would give them the same force vector whether radial or core/long axis-driven. But the further down Babi we go, the more the ridges were torn (literally) between the core-driven long axis stretch delaminating the crust in nominally parallel layers and wanting to do the simple radial slide. The radial slide was at a different angle, in fact, varying angles to the long axis delamination direction. This will be looked at more in the next part and involves the idea of the entire rotation axis being brought into play, as it should be, for the core.

We shall see that for the Babi crust, the radial force vector won out in the end but the initial delamination of the layers left its signature over the whole region in spite of this. This has implications for the morphology of Babi and, indirectly, for the missing slabs A and B, which are missing from site A and Babi respectively (Part 9). That will be addressed in the next part. 

PHOTO CREDITS:

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

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2 thoughts on “67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 38

  1. Pingback: Part 62- The Morphological Evolution of Ma’at 01, 02 and 03 | 67P/Churyumov-Gerasimenko- A Single Body That's Been Stretched

  2. Pingback: Part 64- The Evidence for Long-Axis Stretch Along the Head Lobe Shear Line at Hapi/Babi | 67P/Churyumov-Gerasimenko- A Single Body That's Been Stretched

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