Elaine Meinel Supkis
Two tremendously interesting geological stories appeared this week. They both concern the discovery that large sections of the lithosphere have collapsed in certain parts of the earth. This information doesn't surprise me at all, I think this is common place and is part of the natural effects of tectonic plate movement and over the last 3 billion years, has greatly altered the nature of the proto-continents as well as the sea beds.
Scientists are to sail to the mid-Atlantic to examine a massive "open wound" on the Earth's surface.
The hole in the crust is midway between the Cape Verde Islands and the Caribbean, on the Mid-Atlantic Ridge.
The team will survey the area, up to 5km (3 miles) under the surface, from ocean research vessel RRS James Cook.
Dr MacLeod said the hole was an "open wound on the surface of the Earth", where the oceanic crust, usually 6-7km thick (3.7-4.3 miles), was simply not there.
One of the things that always intrigues me is the number of earthquakes at the 10km level. Many 8 to 9 mag earthquakes like the terrible Boxing Day Tsunami event, are at that depth. Click on the chart here to enlarge it. This is from 3/3/2007, a normal day with a long list of earthquakes. Nearly half of them are at the 10 km depth.
Up until recently, we were taught that the lithosphere was the same all over except where it was being subducted under a continent, for example. Also, theories about tectonic plate movements suggested that the continents were basically unchanging except at the outer edges where they would bump into each other or join together like India crashing into Asia. But as scientists probe this planet's innermost structures, a totally different picture is now emerging, one that is very disturbing.
The continents are actually quite prone to falling apart because the base upon which they rest can suddenly collapse.
The discovery that a segment of the ocean floor, not just the lithosphere but the whole thing, fell away suddenly into the depths of the mantle, is an eye-opener indeed. This event happened where the earth's plates are moving apart but I suspect this is the wrong imagery. Perhaps the better idea is to think of the split that runs the entire planet from the Artic to the Antarctic plate is a serious crack in the earth.
If we visualize this crack, it opened approximately 200 million years ago. The ground began to fall and a rift valley opened up and this was no ordinary rift valley. Many of these open up all the time all over the earth. This one was very long and very deep. The rift in Siberia at this time opened up and out poured the greatest lava flow that we know of. Because of this, Siberia grew thicker and bigger.
But North America, South America and Africa began to split apart and instead of lava flowing in huge amounts, a teeming rift valley was born. And when the oxygen levels collapsed, causing the greatest extinction on earth at the end of the Permian, many of the survivors lived in this epic rift valley. What tremendous changes in the climate and earthquakes, tsunamis and other events happened when this mighty rift valley deepened and deepened until a line of linked lakes fed by water pouring off the sides of the ever-higher cliffs and then one day, the ocean came roaring into this rift, totally severing these three continents?
Since then, material from the mantle has been flowing out of this gigantic crack. The continents aren't gliding along, they are not floating, they are being pushed apart by the epic forces of the inner energy of the planet. Perhaps the weight of the oceans are pushing down and thus, like a toothpaste tube, forcing lava upwards.
But this collapse of the whole seabed is interesting because there are obviously some very powerful forces at work and I think this is happening all over the planet, not just underwater!
(1) Department of Geosciences, Purdue University, 47907 West Lafayette, IN, USA
Accepted: 1 March 1982
Abstract: Geoid height anomalies, as determined by satellite altimetry, suggest that the Cape Verde Rise is in local isostatic equilibrium, supported by a low-density root of altered lithosphere. A depth anomaly map shows the Cape Verde Rise to be approximately 1600 km wide and 2km high. Removal of a quadratic surface from the observed geoid heights leaves a residual positive anomaly with the same shape as the rise and an amplitude of about 8 m. The ratio of residual geoid height anomaly to depth anomaly is consistent with an isostatic root only 40 km deep on average.
So, the lithosphere there is 'altered'. Unfortunately, I couldn't read the entire paper. I have noticed that more and more information is online but at the same time, they are locking it away from anyone without a deep wallet and since I am not an university employee, etc, this is prohibitively expensive. So I will hazzard that the fact that volcanoes formed at this spot is because the ocean's base, its lithosphere, is deformed there and it would not shock me to learn the entire lower base simply fell through and is now falling through the less-dense mantle.
This is in line with the collapsed sector in the middle. Perhaps speed which this giant crack in the earth is moving open has caused tremendous instability, perhaps even stretching of the lithosphere? If we view this crack not as a narrow area but as the distance between the East Coast of the USA and the West Coast of Africa or the East Coast of South America versus the West Coast of Africa, then the truly awesome and terrifying proportions of this disordering of the planet can be grasped: it holds a fifth of the planet's ocean waters, about 106,400,000 square kilometers (41,100,000 sq mi); it is between 2,000 to 3,000 miles across! How swiftly has it widened?
According to scientists, it is slightly less than 6 cm a year. But over 200,000,000 that covers quite a few miles! North America split away first which is why it is 3,000 miles away from Africa, South America is less because the great crack took time, opening up like a giant zipper, bit by bit, over time, the ocean invading dry land relentlessly.
There is no 'ring of fire' involved in all this, except for a few volcanic locations such as Iceland or the Canary Islands, there is not much earthquake or volcanic activity in this dynamic rift zone. The goo flowing out of this gigantic crack is so dynamic, it is shoving North and South America right over the Pacific plate and all other plates in the West. The mountain building this is causing is epic. The mountains on the East Coasts are extremely old: pre-split.
From my own blog (seriously, it was the number one article in the Google search!) last summer, a meteorite or comet struck Antarctica at the same time this great split began. We don't know if there is a direct connection but perhaps there is? This meteorite strike the may have ended the Permian era was far bigger than the one that might have delivered the death blow to the age of dinosaurs 65 million years ago.
We know from gravity pictures of the moon, for example, a major meteorite strike will cause geological changes on the opposite side of the blow, in this case, the Artic may have responded to the shattering blow and perhaps this made all the natural valley systems turn into major rift zones and the tearing happened where the mantle had the least landmass-pressure?
I would have to make an animation showing how this might have worked (anyone out there have the skills? I'll draw the cartoons.)
Since today's article is about how the mantle rather than magma, was directly created when part of the lithosphere collapsed into the mantle, proof of this is the appearance of 'serpentine rock' so I decided to look up other places with this sort of rock.
Naturally occurring asbestos, often found in serpentine rock formations, is present in several foothill areas of Placer County. When naturally occurring asbestos containing material is disturbed asbestos fibers may be released and become airborne, thereby creating a potential health hazard.
So this is where asbestos comes from! North America is one place with lots of asbestos mines! If this is so, then the lithosphere has fallen in the past! Maybe this happens over and over again. I suspect that where there is asbestos, there was an ocean rift that exposed the mantle. Since the older parts of the landscape on dry land have sectors with asbestos, these means it is not a once in a very rare while thing but has happened over and over and over again.
LiveScience Staff Writer
Scientists scanning the deep interior of Earth have found evidence of a vast water reservoir beneath eastern Asia that is at least the volume of the Arctic Ocean.
The discovery marks the first time such a large body of water has found in the planet’s deep mantle.
The finding, made by Michael Wysession, a seismologist at Washington State University in St. Louis, and his former graduate student Jesse Lawrence, now at the University of California, San Diego, will be detailed in a forthcoming monograph to be published by the American Geophysical Union.
Now something really bothers me about satellite photos of the Earth: where ever there is massive mountain-building such as the Himalayan, right next door, there is a collapse. Many places on Earth are circles of mountains surrounding a totally collapsed valley. Some of these are gigantic like the Central Valley of California and the Central Valley of Chile!
Now we learn the lithosphere under China has collapsed and even more interesting for me, the one under the USA and Mexico where Texas, New Mexico and eastern Arizona come together has collapsed, too!
All over that very region, there is rifting! Many cracks that open and spew out lava, lots of 'teeth' mountains caused by these tears! At the same time, the entire continental mass is being relentlessly shoved over the Pacific so this made no sense at all except now it does. Perhaps this is why Baja California is detached from Mexico? Namely, it runs parallel to the western edge of this possible collapsed lithospheric plate. Certainly, the history of that region includes the tipping of the entire landscape in odd directions, not merely responding to the east-west axis actions but north-south such as the tilting of Arizona which has caused the Mogollan ridge to rise so suddenly above the much lower Phoenix/Tucson landscape. And which created the Grand Canyon as the water still flowed south despite the landscape tilting more and more to the north.
From the article above:
Previous predictions calculated that if a cold slab of the ocean floor were to sink thousands of miles into the Earth’s mantle, the hot temperatures would cause water stored inside the rock to evaporate out.
“That is exactly what we show here,” Wysession said. “Water inside the rock goes down with the sinking slab and it’s quite cold, but it heats up the deeper it goes, and the rock eventually becomes unstable and loses its water.”
The water then rises up into the overlying region, which becomes saturated with water [image]. “It would still look like solid rock to you,” Wysession told LiveScience. “You would have to put it in the lab to find the water in it.”
Wysession has dubbed the new underground feature the “Beijing anomaly,” because seismic wave attenuation was found to be highest beneath the Chinese capital city. Wysession first used the moniker during a presentation of his work at the University of Beijing.
In places where ocean bed collapses because it is overlaid with non-ocean terraformations, there probably is water. But this collapse is without water, too! Such as the Tibetan plateau, for example. Indeed, I picked several interesting places and behold how frequently there are collapsed areas surrounded by very high mountains! One would imagine that if Italy, for example, is slamming into Europe, raising the Alps, the land leading up to the Alps would be increasingly hilly and mountainous.
But it is NOT! It is totally flat, flatter than all other parts of Italy far from this dynamic area.
This is true of India: where it hits Asia, it is amazingly flat! Ditto the Great Plains of America leading up to the Rocky Mountains. Gently, it tilts upwards and then suddenly, the jumbled mountains begin, as clearly as if a line is being drawn.
I think the 10 km deep lithosphere is very even but is MISSING SECTIONS. And these have collapsed because of the pressure of rifting in the Atlantic. All I can say is, we barely know all that much about our own planet. And the more we learn, the more interesting it is. Solving these riddles is important for humanity, this is our home, after all. It is the most important planet in the entire universe, as far as we humans are concerned.
Ultramafic rocks are scattered throughout the California Coast Range, the Trinity Mountains, and the Sierra Nevada foothills. That serpentine is the state rock proves it has caught the eye of California geologists. However, many are perhaps unaware that serpentinites have spawned a unique flora specially adapted to survive on their nutrient-poor soils.
The Rocky Mountains and the Sierras like the Himalayans, were all once seabeds and the relentless, restless forwards motion of the continent has caused them to tilt and fold upwards but they retain tell-tale signs of their origins including fossil sea lifeforms like sea shells, for example.
But even if these lands were flatter and lower, they would simply be like Death Valley which has little organic vitality. Perhaps the mountain-building is assisted by the fact that part of the lithosphere there has collapsed so it is much easier to fold and bend the softer, more pliable upper crust that used to be sea beds?
SOJA, Constance M., Geology, Colgate Univ, 13 Oak Drive, Hamilton, NY 13346, email@example.com, MINJIN, Chuluun, Geology, Mongolian University of Science and Technology, P.O. Box 46/520, Ulaanbaatar-46, Mongolia, and WHITE, Brian, Department of Geology, Smith College, Northampton, MA 01063
Mongolia occupies a key position for unraveling the complex geologic history of central Asia, which amalgamated through the accretion of “exotic” crustal fragments in the late Paleozoic-early Mesozoic. Study of the paleontology, stratigraphy, and sedimentology of Ordovician-Silurian deposits exposed in two Mongolian terranes is adding new data that will help refine paleogeographic models of Mongolia's terranes. The Mandalovoo terrane comprises a nearly continuous Paleozoic island-arc sequence characterized by mildly deformed volcanic and sedimentary rocks overlain by an Upper Paleozoic post-accretionary complex.
Upper Ordovician-Upper Silurian rocks exposed in the terrane belong to the Mandalovoo Formation, a volcanic-sedimentary sequence estimated to be 2500 m thick. Siliciclastic deposits and fossiliferous limestones are interstratified with pillow basalts, andesites, volcanic agglomerates, and tuffs. Well-preserved fossils indicate a spectrum of shallow- and deep-marine environments associated with the growth and expansion of island-fringing carbonate platforms. Higher in the section, limestones rhythmically interbedded with shales document the transition upward into turbidites that formed along a deep-marine slope, perhaps of the adjacent Gobi Altai terrane.
Ordovician-Silurian deposits exposed in the Gobi Altai terrane exceed 3000 m in thickness and comprise one of the least deformed, best preserved, and most continuous stratigraphic sections in Mongolia. The Lower Paleozoic deposits reveal abundant shallow-water indicators, including oncoidal limestones and cross-bedded sandstones that grade upward into biohermal, fossiliferous limestones and domal stromatolites.
These carbonates are interbedded with shales and overlain by Lower Devonian breccias that comprise angular-subrounded limestone clasts; the entire sequence is capped by younger Devonian-Triassic volcanic-sedimentary deposits. Future research on the preponderance of shallow-marine facies in the Gobi Altai terrane will help ascertain its proximity to other terranes, specifically if it is a backarc basin or a dismembered portion of the Mandalovoo arc terrane.
In other words, this was all ocean bed material. Indeed, huge swaths of what is now dry land, was seabed once, more than 200 million years ago. 300 million years ago and earlier, the dry land eroded at tremendous speed, this is during the first several billion years this planet existed. But once life colonized the oceans and then the lands, the dynamics changed a great deal. The Great Plains have this gigantic reservior of water, the Ogalala, thanks to limestone laid down in the Ordovician and Silurian periods. And of course, oil and gas get trapped by salt or limestone from the same organic forces working on the shallow sea floors.
To maintain isostasy, the forces pushing down from above the fluid's surface - in this case the ocean floor - must equal the forces pushing up from below, caused by the displacement of denser mantle material by the less dense continental rock of the mountains' roots, according to the following formula:
13,000 feet (s.g. of continent - s.g. of water) + 15,000 feet (s.g. of continent)
= thickness of roots (s.g. of mantle - s.g. of continent)
13,000 (2.7 - 1) + 15,000 (2.7) = x (3.3 - 2.7)
(Note that the weight of the first 13,000 feet of continental material above the sea floor is buoyed by the weight of the water around it.) Thus, x (the thickness of the mountain's roots below the sea floor) equals 104,333 feet, and our total mountain range averages 104,333 + 13,000 + 15,000, or 132,333 feet thick. Now, make sure that no other continents are going to get in the way, then go away for a billion or a billion and a half years and let erosion run its course.
Sediments eroded off the mountains will be carried over the edge of the mountains' shore and deposited on the 13,000 foot deep ocean floor. The weight of the accumulating sedimentary deposits will push the deeper sediments down into the mantle, always maintaining isostatic equilibrium (or trying to). When the sediments reach a thickness of around 50,000 feet
( = (13,000 (2.7 - 1) / (3.3 - 2.7)) + 13,000 )
the surface of those sediments will be at sea level, and additional sediments will be washed over them and farther out to sea. As the mountain peaks erode away, isostasy will push the mountains' roots upward, presenting new land to erode, until only the lowest 50,000 feet of the original mountains remains, and whose surface is essentially at sea level as well, forming a peneplain. The roots of the mountains will be sitting in the middle of a flat, nearly sea level continent, ringed by flat plains of horizontal sedimentary deposits. While the total volume of continental material remains the same, the surface area will have increased by 2.65 times.
It seems very odd to me that the mightiest mountains build up higher and higher and don't collapse but they also don't spread, either, they wrinkle up and leave a collapsed core like Tibet. Is this due to stretching the lithosphere as it bulges downwards due to tremendous pressure? And then 'snaps' and releases a section, causing the land on the other side to collapse?
Right next door to where the lithosphere may have collapsed along with a hunk of ocean water, is some other odd things like a rift valley that has the world's deepest lake, which holds one fifth of the world's fresh water!
Lake Baikal is in a rift valley, a gorge where the crust of the earth is pulling apart. At 636 kilometres long and 80 km wide, Lake Baikal has the largest surface area of any freshwater lake in Asia (31,494 km²) and is the deepest lake in the world (1637 metres, previously measured at 1620 metres). The bottom of the lake is 1285 metres below sea level, but below this lies some 7 km (4 miles) of sediment, placing the rift floor some 8–9 km (more than 5 miles) down: the deepest continental rift on Earth. In geological terms, the rift is young and active — it widens about 2 centimeters per year. The fault zone is also seismically active: there are hot springs in the area and notable earthquakes every few years. It drains into the Angara tributary of the Yenisei.
Its age is estimated at 25–30 million years, making it one of the most ancient lakes in geological history.
So, even as Japan and all the other 'ring of fire' lands spout volcanoes and the Pacific is shoved under Asia as the great, gigantic tear in the Atlantic shoves all continents aside with tremendous force, despite this, right in the middle of Asia where Siberia and China meet, there is a RIFT? If the lithosphere dropped a 3,000 sq. mile section, then this means the scaffolding between the continental surface and the lithosphere is tremendously weak and stretched and so, surrounded by mountains caused by China slamming into Siberia, we see it opening up RIGHT DOWN THE CENTER, not on one side, but in the middle. The mountains on both sides are MOVING AWAY FROM EACH OTHER even as the Pacific is being violently shoved into this region from the east!
Silurian Time (440 to 410 MA)
During the Silurian, Laurentia collided with Baltica closing the northern section of the Iapetus Ocean. This collision was preceded in many places by the abduction of marginal island arcs, resulting in the formation of the Caledonide mountains in Scandinavia, northern Great Britain and Greenland, and the Northern Appalachian mountains of Eastern North America. North China and South China had rifted away from the Indo-Australian margin of Gondwana, drifting North across the Paleo-Tethys Ocean. Throughout the Early and Middle Paleozoic, the expansive Panthalassic Ocean covered much of the northern hemisphere. Surrounding this ocean was a subduction zone, much like the modern "ring-of-fire" that surrounds the Pacific Ocean.
A craton (kratos; Greek for strength) is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years. Some are over 2 billion years old. Cratons are generally found in the interiors of continents and are characteristically composed of ancient crystalline basement crust of lightweight felsic igneous rock such as granite. They have a thick crust and deep roots that extend into the mantle beneath to depths of 200 km.
The thickness of the crust of the oldest cratonic sectors of continents perhaps isn't general, after all. Maybe they are all in danger of some sort of collapse. We know so little. For example, China should have a very thick crust but this is where the biggest collapse happened!
The North China craton is one of the oldest cratonic blocks in the world. It covers an area of ~1.7 million km2 across most of northern China, the southern part of northeastern China, Inner Mongolia, the Bohai Bay and the northern part of the Yellow Sea. The craton is bounded by the early Paleozoic Qilianshan orogen and the late Paleozoic to Mesozoic Central Asian orogenic belt to the west and north, respectively, and the Mesozoic Qinling-Dabie and Su-Lu ultrahigh-pressure metamorphic belts to the south and east, respectively. The basement of the craton can be divided into Eastern and Western blocks, separated by the Paleoproterozoic Trans-North China Orogen (TNCO).About 300-250 million years (Ma) ago the combined North China and Tarim cratons collided with Siberia to comprise the last stage in the formation of Pangaea. At 220-240 Ma, the North China craton collided with the Yangtze block along the Qinling-Dabie-Sulu orogenic belt. The Eastern Block of the North China craton underwent crustal thinning that began in the Mesozoic and is known to have reduced the thickness of the crust from 200 km to as little as 80 km.
The TNCO is characterized by fragments of ancient oceanic crust, mélanges, high-pressure granulites and retrograded eclogites, crustal-scale ductile shear zones and linear fold belts with sheath folds. These lithotectonic elements contrast with the dominant Archaean tonalite-trondhjemite-granodiorite (TTG) gneiss domes surrounded by minor supracrustal rocks in the Eastern and Western blocks. In addition, petrographic and thermobarometric data have revealed a remarkable difference in metamorphic evolution between the TNCO and the Eastern and Western blocks.
The former underwent a major metamorphic event about ~1.85 billion years (Ga) ago with clockwise P-T paths involving isothermal decompression, suggesting a collisional environment, whereas the latter experienced a major metamorphic event at ~2.5 Ga, with anticlockwise P-T paths involving isobaric cooling related to the underplating of mantle-derived magmas. These differences led some researchers to propose that the TNCO was a continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent craton at ~1.85 Ga.
And this 'thinning' was really a collapse according to this week's startling news! And who knows what mega-earthquakes accompanied these collapses! Perhaps this is what the New Madrid Fault's tremendously violent earthquakes are all about? The continuing, extending collapse of the lithosphere in that sector? I knew one geologist who suspected this long ago, at least 60 years ago.
He may be right in the end!