Elaine Meinel Supkis
Today, the BBC had an interesting article about Antartica. This set me to wondering about the geology of that continent and which direction it is moving and if the change in the ice sheet's density is triggering a lot of the tectonic plate activity this last decade.
By Helen Briggs
BBC News science reporterThe Antarctic ice sheets started building up 30 million years ago
The gateway between the Atlantic and Pacific at the bottom of the globe opened up 41 million years ago, according to a study of old fish teeth.The research in Science pushes back the date of the forging of Drake Passage to twice as long ago as once thought.
US geologists believe it kick-started the ocean current that swirls around Antarctica, helping to bring about a dramatic cooling effect.
The continent was transformed from lush forest to the icy landscape of today.
"We're saying we now have a date for the opening of the Drake Passage that looks like it's early enough that it may have contributed to the cooling," said Ellen Eckels Martin of the University of Florida, US.
"It illustrates that ocean circulation may play a very important role in climate change."
I checked out what happened 40 million years ago. This is exactly when India finally smashed into Eurasia. Science Week:
1) Is Everest now at its highest point, or was it once even loftier? What was the greatest height attained by the vast highlands of the Tibetan plateau, and when did this occur? New work[1] shows these questions can be tackled -- if not yet answered definitively -- by analysing the isotopic composition of ancient raindrops. With this approach, the authors show that Tibet continuously grew northward over millions of years in response to the thickening of Earth's crust associated with the collision of the Indian and Asian continental plates. The driving forces for this collision are generated deep in Earth's mantle. But the key to unravelling the uplifting history of the central Tibetan plateau is found in lake sediments on the plateau, some of which formed as long ago as 40 million years.2) In these lakes and their surrounds, changes in the oxygen-isotope composition of surface water (which is controlled by regional climate and elevation) are recorded in sediments. Systematic variations in oxygen-isotope composition across the plateau reveal that spatially variable uplift of the plateau to 4000 meters or more above sea level was intimately linked to the timing and rates of convergence of India and Asia. Rowley and Currie[1] estimate that uplift to 4000 meters was initiated as long ago as 40 million to 50 million years, in the early stages of that convergence.
As it slugged it out up there, the Himalayan plateau began to rise relentlessly and the Himalayan mountains began to soar. And the weather patterns of the Northern Hemisphere changed drastically then this uplift cut off aircurrents that used to flow from the Atlantic to the Pacific. And in the same time frame, Antarctica slid all the way down to the South Polar region and the volcanic island arc that juts out of Antarctica slipped away from the arc of South America's southern most terminal and the ocean raced into the breach.
Also, 40 million years ago, the Pacific Plate suddenly changed direction.Plate Tectonics:
Geologists believe that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a veritable conveyor belt of volcanic islands.Hawaii itself consists of five connected volcanic mountains that were built by this lava plume rising from the mantle. Kilauea, the world’s largest active volcano, is still rumbling because the island has yet to move completely off the hot spot. The farther the other islands in the chain are from Hawaii, the greater their age. About 150 miles to the northwest is Oahu, which burst out of the sea about 3.5 million years ago. Midway, one of the oldest islands in the chain, was formed between 15 and 25 million years ago.
About 2,000 miles from Hawaii, the chain abruptly veers and extends north as a line of submerged volcanoes known as the Emperor Seamounts. This suggests that the Pacific Plate changed course about 40 million years ago. Where the chain’s long march ends the volcanoes are more than 70 million years old. And, not surprisingly, off the southwestern coast of the island of Hawaii, beneath the ocean surface, Loihi, the next Hawaiian Island, is forming as the Pacific Plate continues its journey over this hot spot.
This is an odd coincidence! One wonders if the impact of India disorganized more than one tectonic plate! Perhaps they sort of cartwheeled around each other and this is when Antarctica suddenly was torn from the same sort of juncture with South America that Central America makes between the two giant continents to its north and south! It has the same sort of "s" shape! Perhaps this connection might break just as dramatically! We know the earth can have lurching events as well as simple inching along events. The change of direction of the Pacific Plate was sudden and there was no "warning signs", namely, one day it was merrily slipping along one baby step after another and then the next day heading off in a totally new direction. So the 40 million year mark is an important event, it changed a lot of things simultaneously.
The Rockies form a majestic mountain barrier that stretches from Canada through central New Mexico. Although formidable, a look at the topography reveals a discontinuous series of mountain ranges with distinct geological origins. The Rocky Mountains took shape during a period of intense plate tectonic activity that formed much of the rugged landscape of the western United States. Three major mountain-building episodes reshaped the west from about 170 to 40 million years ago (Jurassic to Cenozoic Periods). The last mountain building event, the Laramide orogeny, (about 70-40 million years ago) the last of the three episodes, is responsible for raising the Rocky Mountains.
The Rocky Mountains ended their most active phases at 40 million years. Which opens the possibility that the cessation of Pacific Plate movement in one direction had an effect on the North American continent. Now, instead of mountain building from compression, we see depressions forming such as the most dangerous one of Yellowstone which is only 2-3 million years old. The Grand Tetons are part of this collapse for they are the outer edge, tilting upwards as Yellowstone and Jackson Hole falls.
Here is a map showing where the most spreading activity vs subduction actions. The Pacific Plate next to South America is spreading much faster than any other sector. What this means for us all is confusing, to say the least. If one looks at all the "future plate movement" maps on the web from various universities the one thing that stands out is how the all see different outcomes. And every day, scientists learn more details about the past which revises possible projections into the future.
Right now, we also see several long-term rift events in Africa and North America and the Middle East. Opposite that are the several new volcanic arcs that run from Alaska to Siberia and the Japan/Philippine ranges down to the spectacular and very dangerous Java/Sumatra arc. Coincidentally, these are where the vast majority of the world's worst earthquakes are. And where a tremendous number of people live for it is also very fertile and auspicious for trade and the growth of exotic spices and foods.
Australia is moving relentlessly north nearly as freely as India moved. For some reason, some continents move faster than others. The Arctic sector is moving the least but we don't know much about Antarctica, is it now free to wander? Will it trigger titanic events far afield? Is this connected with the formation of Yellowstone and other rifting/falling events in the other continents? For I would bet, there is some harmonic unity to these matters.
The volcanoes of Antarctic just might waken again. The arc that juts out like an arm reaching to South America was formed by both uplift and volcanic action. For the last 40 million years, Australia and the Antarctic have been moving rapidly away from each other. What with Australia moving up into the Pacific, will Antarctica sail up into the Atlantic? Or is it, too, going north up into the Pacific? This could be rather messy, like bumper cars heading for the same spot in the middle.
British Army Antarctic Expedition:The Danco Coast has examples of a whole range of rock types. Sedimentary rocks include reworked volcaniclastic ash-fall tuffs (sometimes with fossil bands) and volcaniclastic basin (trench) filling turbidites. These may well have been metamorphosed to varying degrees. Igneous rocks include many primary volcanic rocks and a range of intrusive igneous rocks, which form the bulk of the Danco Coast.
I wonder what would happen if the very tenuous snake-like connection between North and South America breaks? We have a canal already runing athwart the Isthmus! What if the oceans were to pour into each other? Certainly, that would change the weather world-wide just as much as other factors like the rise or fall of CO2 levels, for example. And volcanic activity certainly changes weather systems, too! All I know is, the next several years will be very interesting, if you are a geologist.
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