Yet another theory about why the Tibetan plateau looks the way it does. I discovered the story isn't as simple as today's news makes out. First, geologists disagree a great deal about these things and secondly, I think everyone is right but also do not notice tremendous similarities between all these mountain-building/depression making events. I found quite a few on every other continent.
By Paul Rodgers
Published: 18 February 2007
The discovery of the missing mantle - the cold, heavy rock beneath the crust - was revealed last week by Professor Wang-Ping Chen at the University of Illinois, whose team used more than 200 super-sensitive seismometers strung across the Himalayas, from India deep into Tibet.
"While attached, this immense piece of mantle under Tibet acted as an anchor, holding the land above in place," said Professor Chen, whose results are to be published in the Journal of Geophysical Research. "Then, about 15 million years ago, the chain broke and the land rose."
By pushing the Himalayas to their current altitude, more than 8,000m above sea level, and raising the Tibetan plateau to 5,000m, the detachment of the block was responsible for both the monsoon rains that make south Asia so fertile and the Gobi desert in central Asia. Warm winds blowing from the Pacific Ocean cool as they rise over the mountains, releasing the moisture they contain as torrential rains, leaving almost no water to fall on the arid interior of the continent.
One thing about wanting pet theories to work is to look at one or another aspect. Then the puzzle seems to 'fit'. But always, when arranging a theory, one has to look at all possible similar situations and see if they match in any way. The fact of this matter is, definitely something is at work with the Tibetan plateau, the fact that the center of the Tibetan highlands is an awful lot like so many other centers of massive mountainbuilding/continental collisions means there is something rather common about all these situations. Namely, they are all operating on the same principles.
I used a box of Jiffy mix yellow cake and baked it at 400 degrees. Then I let it cool rapidly and it collapsed very neatly. A fun experiment if you don't mind a cake raw in the center and over-baked on the edges.
In this case, I would suggest that when plates, both oceanic and continental, collide and one begins to climb over the other, it is like baking a cake, literally, since this friction and compression 'cooks' everything, the whole beings to rise until a critical point is reached and then the center collapses, leaving a classic ring of mountains around a depressed center.
Perhaps the mantle, after a lot of landmass piles up on top of it and it is compressed more and more, a section in the center breaks off and begins to sink. As this slips lower, the mountains around the developing sinkhole rise, sort of like if you press down on a pillow, the edges rise.
Today's article about Tibet is supposing all of Tibet rose very high and then the center collapsed, of course, the pillow pictures here were pressed down, not collapsed, but it does illustrate more clearly than the cake pictures, what a depression looks like, certainly, the action of infalling does displace material to the outside edges.
When writing about nature or science, we often look for descriptions and analogies that are easily visualized. Just like plate tectonics used the image of jigsaw puzzles to explain the interactions of continents and ocean beds.
Here is a drawing I did on a satellite photograph of the India/Tibetan complex. The red lines are where either rift zones are developing or rivers like the Indus are running. The zone where northern India is pressing hardest into Asia seems to be along the blue line with the n curves. The greatest mountain-building is right along this long, curved line where India is obviously going under Asia. Behind this line of sharp peaks lies the wrinkles in the landscape that shoved ever-upwards for 40 million years or so.
Satellite Photo NASA
We should remember that when any oceanic plate even begins to push towards a continent that is stubornly in the way, lines of volcanoes form, linking them increasingly until the wayward plate makes landfall which is what starts the serious uplifting.
Then around 15 million years ago, the center began to fall which is why the mountains don't get bigger and bigger, the deeper one goes into the Tibetan plateau.
The riddle here is not the mountains on the front range where obviously, two continents are colliding, it is on the back side where there are mountains but not so much as a volcano or peak in the center. Why would the center remain so 'quiet'?
Kapp's research challenges the idea that the 16,000-foot-high Tibetan plateau, the highest-elevation region on Earth, is losing elevation. Previous research reported the Tibetan plateau reached its highest elevation eight million years ago and is now slowly deflating as it spreads out over India.
"My hypothesis predicts that the plateau is getting higher. The other theory suggests the plateau is collapsing," he said.
"We're in a place where continents are slamming against each other. Instead of Tibet crumpling like an accordion, we see these rift valleys. The rifts are from the east-west stretching of the plateau."
Back when India was moving towards Asia, was the Asian south shore low-sloping? We know from looking at the fastest moving plate with a continent today, Ausralia, there are a huge number of major earthquakes along the leading northern edge of the continental plate and laced along this is a number of volcanic islands that not only show up on the surface but also rise in the ocean's bed. Australia is forcing the low-lands landmass of the Indochina continental shelf to curl in on itself.
As I looked at various scientific articles on the internet, it became very clear that everyone thinks they got the solution to the riddle of the Tibetan plateau but they can't even agree if it is sinking or rising or what, much less, what is at work here.
I would suggest this: if all other ring mountains with sinking centers all LOOK the same then the same geological forces are at work with all of them. We know the California is being ripped apart by slip/sliding ocean plates but the entire USA is supposed to be moving west which is why we have the huge Rock Mountain range that runs from the border of Mexico all the way through southern Canada. But California isn't rising at all! The center is sinking and already, the ocean is trying to flood it from both ends! One would think this would be the last place where sinking would be happening yet Death Valley, in the center of this sinking landmass, is the lowest place in the Western Hemisphere!
Since both geological features have many features in common, the huge mountain range on one side and a lower but still thick range of mountains on the other edges, then we must reconsider what is happening when plates collide!
There are important consequences of deeply penetrating slabs. Our models show that plumes preferentially develop on the edge of slabs. In areas on the CMB free of slabs, plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin. However, in areas beneath slabs, the basal thermal boundary layer would be thicker and plume formation infrequent. Beneath slabs, a substantial amount of hot mantle can be trapped over long periods of time, leading to “mega-plume” formation.
One thinks of Yellowstone here. Yes, isn't it very odd in a troubling way that right behind the Rocky Mountains which, like the Himalayans, is in the MIDDLE of things rather than on the outermost edge like South America's Andes, and even they have depressions and plains running along the coast right in front of them! They are NOT forming on the outermost edge of the continental shelf.
The Yellowstone complex is where land rises and falls like Mother Earth's chest rising and falling as she breaths, and in this odd depression right on the heels of the Rocky Mountains, surrounded by a ring of mountains, do we see a pattern here? Is this hotspot that the continent has travelled over so if one looks to the West, one sees the past incarnations of this depression/hotspot. So the entire continent is moving to the west but there are these odd hotspots that are also depressions.
Of course, Yellowstone is like a pebble compared to the size of the mighty California Central Valley and Death Valley complexes much less, the absolutely huge Tibetan plateau!
From the University of Arizona article:
So Kapp and Guynn used a computer to strip away the DEM's superficial layers to expose the underlying structure of the plateau. Once they created a bare-bones map of the region, the curving patterns of the rifts were clear.
"I took away all the secondary faults and then the pattern jumped out," Kapp said.
Because India is crashing into Tibet, geologists call India "the indentor." Kapp says that because India is hitting Tibet head-on, the Tibetan plateau is developing splits, or rifts, that curve away from the axis of impact.
Once Kapp figured out what caused the rifts, he and Guynn created mathematical models to test the idea. According to the models, a head-on punch split the plateau just the way Kapp predicted.
And the splits and rifts grow because it is sinking. As my blue lines showing mountains and ridges drawn on the satellite photo show, yes, the curves are definitely there. But also, there is the troubling situation on the west side of India: it looks to me like India is tearing away from Pakistan, geologically as well as politically. And there, in the middle of yet another but much smaller ring of mountains, a geological structure that looks and awful lot like the collapsed cake above, is yet another central sink hole!
I am certain, if I were to look at all the satellite photos of the world, I would see more and more such structures, the California and the Tibetan ones being merely the most obvious.
Geologists already know that vents in the ocean that tap into the Mantle are hotspots for precious metals, such as silver, gold, zinc, and copper. Tucson, where I lived much of my childhood, was one of the top copper production centers in the world for a long while. Tucson was a depression surrounded by, of course, a ring of mountains (ahem) some of which were granite mountains and others, volcanic. Indeed, I always found it rather odd that the Tucson valley was pretty much ringed in, sort of like Mexico City. And thinking about the copper mines of Chile: it is the desert that lies in a depression between the ocean and the Andes, isn't it?
I decided, there has to be a 'central valley' in Chile so I googled those words and look at what appeared: EUREKA!
The Central Valley is the heart of Chile and the classical geography of Chile reappears here: the mountain range of the Coast, the depression called “Valle Central” (Central Valley), limited to the East by the Andes Mountains.
Climate - This portion of Chile boasts an ideal climate, which explains why 80% of the population lives here. The seasons are well-defined, with hot summers (maximum 28 to 32 C (82-90 F) in Santiago, one of Chile's warmest cities, fall and spring with cool, pleasant breezes, and short winters with low temperatures very occasionally dipping below 0C (32F). Winter daytime temperatures may reach 18C (64F), but usually hover around 14C (57F). Rainfall, generally restricted to the winter months, increases towards the south. Humidity is low, reducing the disagreeable effects of heat and cold. Rain in winter and abundant snow in the higher mountains, that allows irrigating 600 km. of the central valley farmland. Summers are dry and sunny. This is the agricultural and industrial core of Chile, where 75 per cent of the population lives and the four major cities are located. Good roads join the mountains to the ocean and, in one same day. it is possible to ski and also bathe in the sea.. all kinds of adventures to choose from.
So, even though South America is most definitely travelling to the west to the point, huge mountains are building along the western front of the continent, right between these huge mountains and the ocean plates that are being shoved by Australia, we see....a DEPRESSION! And on one side, a small ridge of mountains hemming it in! This isn't round or huge like Tibet but is long and thinner than California's bigger structure.
But they all operate on the same rule: when continents collide and high mountains build, a central valley will form! No matter where or what! There is no special thing operating here that is unique to one or the other, they are all the same in this regard.
Just as one can see clearly, the continents have huge rifts like the Amazon valley or India itself: here are more maps showing how, even as continents collide, they still are ripping apart at the same time:
The African rift valley is quite obvious and famous. But of course, the huge rifting that already filled with the Red Sea's waters is where Africa has rotated off and probably had crashed into more than once, Arabia is now seperated from Africa unlike 90 million years ago. Africa is crowding the Mediterranean ocean but then, that is a mega-depression like all the others, one of the very deepest and we now know the Mediterranean ocean has dried up several times in the past which made is a huge Death Valley, right?
Many geologists assume Africa will plow into Europe but I think it might rotate away, pivotting on Spain, moving to the west eventually. Except the Atlantic rift is shoving things, widening the ocean. We really can't tell yet, not enough to make secure predictions.
The fact that eastern Africa is ripping apart is important since this is connected with India floating off into Asia. Why would India move faster than other continents? And why is Australia hightailling it so quickly across the Pacific?
While drawing maps of India crashing into Asia, I noticed some things. There is definitely an either/or--yin/yang to rift valleys world-wide: either they fill with water or they fill with lava. And the action of rift valleys forming on one side of moutain building compression with a line of lower mountains on the ocean side, meant that India, as it sailed from Africa to Asia, left a definite trail of these abandoned lower mountain ranges which were on the ocean side of the trailing edge of the continent.
I exaggerated the Sychelles Islands and other Indian Ocean chains that geologists say, were left behind by India as it floated northwards. Or, as I exaggerated here, India actually has rotated, moving in a curve into Asia, not straight-on. One reason I feel this is so is because Nature dislikes straight lines except with rifts! and these rifts are not that straight so there must have been some gentle curving due to the continent slithering somewhat sideways. I wish I could do a moving cartoon of this.
India probably had six or seven rift valleys form, each one flooding with ocean waters as the continent moved north-eastwards. The rifting where Pakistan and India join is probably due to this still-continuing northeastern orientation of the movements in the mantle.
To reiterate, the proposition that ~ 106 km3 of Deccan basalts was erupted from a magma chamber in which it was stored is radical. However, there are several strong points that support this suggestion:
1. The long history of magmatism along the same zone which culminated in the eruption of the Deccan Traps,
2. A lull in the magmatism for 350 My and its subsequent reactivation,
3. DSS results which show that the Moho upwarped beneath the west coast during the late Cretaceous. This could be associated with formation of the magma chamber,
4. Continental scale rifting (Seychelles-India) and Deccan volcanism are contemporaneous. The timing of the major phase of Deccan volcanism is considered to be ~ 66-62 Ma (Courtillot et al., 1986; Venkatesan et al., 1993) and the timing of Seychelles-India breakup is also thought to be late Cretaceous (Biswas, 1982). Note that the breakup of Gondwanaland was a continuous process which started (in the case of greater India) with the separation of Madagascar (at ~ 93 Ma) and by 63 Ma, Seychelles also separated from mainland India (Biswas, 1982; Gombos et al., 1995). The breakup of Seychelles-India is thought to be the main rifting phase associated with Deccan flood basalt eruption and the available data suggest that they were contemporaneous. This age data provides strong evidence in favor of stored magma which underwent progressive melting, in proportion to advancement in rifting (and consequent lowering of liquidus of the magma in the chamber), and resulted in volcanism whose rate and volume corresponded to the rate and scale of rifting.
The time of reactivation of the deep crustal continental rifts coincided with breakup events elsewhere in greater India,
The volcanism in the second phase started out felsic and gradually became mafic over a 30-My period, which points toward progressive lowering of the liquidus, and not a sudden increase in temperature, and
Geophysical evidence points towards thinning of the continental crust north of 15°N, that is exactly beneath the Deccan volcanic province. This provides additional support for the existence of delaminated continental crust there.
I still don't understand how India can have not one but two major rift valleys that suddenly filled with lava, right dead-center even as it smacked into Asia. One would expect uplifting, not rifting. Perhaps the force moving this continent sideways is tearing it asunder. And the continent isn't all that thick since some of the last 90 million years' lava events happened here, the other being the Siberian traps. The Siberian traps coincided with the biggest extinction on earth: the Permian.
The biggest lava events in the USA occured out of the Yellowstone areas as well as just northwards into Idaho. I don't think California's Central Valley or Chile's, for that matter, will fill in with lava. Africa's might. This may be how various continents which were 'lower' in the past and flooded by oceans, might 'fill in'. Namely, rifts filling with lava is how they grow in volume and size instead of wearing down and going underwater.
The main surface outcrop of the volcanic rocks (predominantly basaltic lavas and tuffs) are found on the Siberian Craton (east and south of the thick-dashed line on the map, right), and on the Taimyr Peninsula. However, extensive subcrops of basalt also occur beneath the West Siberian Basin (or Siberian Platform) (Surkov, 2002), beneath the Yenesei-Khatanga Trough, and beneath the Kara Sea; the total area (and volume) of these 'hidden' basalts may exceed those of the main outcrops to the east. Sporadic outcrops of late Palaeozoic or Triassic basalt occur in the Urals and in the Kuznetsk Basin, suggesting that the extent of the province may be even greater than that suggested by Reichow et al. (2002) and Masaitis (1983) (Surkov, 2002).
Right in the center of Russia is this gigantic geological event zone. Russia also has the world's deepest lake, Lake Bikal. And this is another odd geological feature which lies right on the northern edge of the massive mountain-building event zone of Tibet.
Looking at a geological map of China, one sees yet another 'collapsed cake' situation in Chengdu. It is, like the other sinkholes, surrounded by mountains. The sharp pointed eastern edge of India's continent is building mountains on the west flank of Chengdu but all around it are mountains which is a very odd formation for that spot in China!
I found this after looking for only a few minutes. I have no geology degree, I just like to draw stuff. I hope this article pushes real geologists into considering the idea that Tibet is just like many other parts of our planet and maybe someone will cobble together a grand theory to explain why these things happen over and over again, under pressure.
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Elaine Meinel Supkis