This 2 parter series was extremely interesting. I'm glad you talked about the evolution of Earth's tectonic processes.... and I, too, highly dislike the 'Boring Billion' title. So much happened in that time that it wasn't really boring at all. I'm also glad you talked about Venus as well. Personally, I found that idea of Venus melting its surface completely every 100 million years to be a bit far fetched. I always figured that because it took a hard hit causing it to flip 180° vertically that that played a major role in it not developing a similar plate tectonic system like Earth or a magnetic field Mainly because I have often wondered if rotation of the planet has an influence on the process of convection in the mantle. I know the heat from core starts it... but I've pondered about if there's something like the Coriolis effect influencing it. Plus, Venus' mantle seems to be hotter than Earth's and I very much agree with you on the plastic tectonic system occurring there currently as well as here early on. Once more I really enjoyed this series. Thank you for posting it 😃
Good follow up video glad to see the situation with Venus be addressed one name I have seen for describing the more localized regional domain of Venusian tectonics is chunktonics as they argued the smaller more localized behavior of tectonics is more analogous to pack ice on a body of water. That work mainly focused on the open lowlands of Venus rather than its more complex terrains nothing signs of what might be transtension and transpression along the edges of relatively undeformed chunks of crust I'm mixed on that opinion but it seems that while the literature has moved on from the cyclic cataclysmic stagnant lid idea it has sadly persisted as a zombie in science communication circles. I should note that while Venus has no water Ocean the lower atmosphere of Venus is in a supercritical state due to the high pressures and temperatures which gives it properties of both liquids and gases with at least some evidence suggesting that there are distinct carbon dioxide nitrogen mixing ratios between the two layers so in some sense you can argue that Venus has an ocean of carbon dioxide. As for the future of plate tectonics I feel it should be noted that Mars even in its clearly tectonically waning state appears to still have "active hot spots which can at least on occasion erupt onto the surface. Granted the youngest example appears to be roughly the same approximate age as a nearby impact crater suggesting the melt had help reaching the pressures needed to breach the surface but there were at least some weak quakes deep down which have been interpreted as possibly being magmatic fluids moving far below the surface. Granted Mars is a puny world so it probably didn't have a plate tectonic like cycling but evidence for hotspot like location specific prolonged volcanic activity has been shown to hold for the Moon and appears to hold in the case of both Mercury and Mars given limited data we have there. Insight was nice but it was a single seismometer and operated for a limited time before the Martian dust accumulation killed it. A network of radiogenic detectors across the surface of Mars would be nice. Not going to happen so long as the whole neoliberal political ideology on spending money for science persists but we can dream right? For Venus Silicon Carbide semiconductors and to a lesser extent Gallium nitride (I think it involves Gallium I know but I forget what exactly its mixed with) seem to be a promising possibility for enabling electronics t9o function at Venusian temperatures and pressures with in combination with clockwork mechanisms for functions which don't need electronics might finally open up a possibility to get some actual ground measurement data. The tricky part there is powering any lander and or rover with the best option due to the thick reflective clouds reflecting away most incoming sunlight likely being wind power. Venus has slow wind speeds but because of the density of supercritical fluids near the surface they are carrying lots of momentum. As for Earth tectonics The article on "Buoyant hydrous mantle plume from the mantle transition zone focused on the study of buoyant hydrous upwelling seems to be quite relevant and informative in the onset of more dynamics plate tectonics. This is specifically in regards to its thermodynamics and the type of volcanism associated with these fairly rare and geochemically distinct volcanoes which appear be a close match for the large continental flood basalt eruptions associated with the break ups and failed break ups of supercontinents. Kuritani, T., Xia, QK., Kimura, JI. et al. Buoyant hydrous mantle plume from the mantle transition zone. Sci Rep 9, 6549 (2019). doi.org/10.1038/s41598-019-43103-y The close match in magma chemistry particularly rich in phosphorus and other sediment derived volatile elements along with the clear seismic tomographic data showing that the modern example of Mt. Paektu clearly resides beneath the stagnant Pacific Slab suggests that these compositionally distinct kinds of magmas are derived from the recrystallizing slabs expelling incompatible elements from their structure and enriching the overlying mantle in compositionally lighter elements until a critical threshold is reached where the compositionally lighter material begins to ascend towards the surface decompressing as it does so. It is striking that the timescale given for the onset of true plate tectonics in your model lines up within a hundred million years of the simple thermodynamics model on when the corresponding chemical phase transitions needed to initiate hydrous compositional upwelling became thermodynamically possible as the reaction becomes more efficient at lower temperatures. Here the MTZ or mantle transition zone is the layer where the temperature and pressure are optimal for this process to occur which has been getting deeper over time as a consequence of the continued cooling of the mantle. Given this evidence it seems like it is likely quite important for the story of modern plate tectonics both in its onset as well as its continued evolution with some lines of evidence which while quite crude and limited in the amount of available data suggest that the average rate of motion of tectonic plate movements has been speeding up over the last billion years. If true this might indicate that there will/would be an optimum rate of tectonic movement enabled by the ongoing mineral hydration process of Earth's mantle and the slowing of the more general deep mantle convection. At least the Seismic tomography seems to support the existence of slab pull fed deep convection with some shallower compositional upwelling processes which seems important to starting the break up of supercontinents at the very least.
Hopefully a helpful pointer for komatiite, it was really difficult for me too, as I assumed it was something like "coma-teeite", similar to how I heard you say it. This was until my dad, a South African, told me about the Komati river, pronounced "co-matty"! Suddenly it clicked into place, komatiite is in fact just "co-matty-ite", which I at least found a lot easier to say. That double 'i' is evil and misleading, makes me think of Hawaii :) Ophiolite sequences fascinate me, if you know of Macquarie island, it is my dream field destination. "Mid-tertirary" (WHY can't australia get with the time and use neogene and paleogene already?) oceanic crust just shoved up and outta the water for all to see, it's very exciting! Until now I had no idea alternate models for tectonic activity existed, or even that plate tectonics did not apply before a certain point! Perhaps we could call the old system "convection tectonics", and the transitionary period "proto-plate tectonics". I like the term "plastic tectonics" makes more sense and can be applied generally, something like that to differentiate it. "Sloppy plate tectonics" while unscientific is very funny and actually somewhat accurate with a hotter lithosphere and sagduction haha Venus fascinates me too, as cool as the global resurfacing hypothesis is, I find it quite unlikely to consider it a primary planetary mechanism! What of the involvement of oceans? Is the hydration of the oceanic crust significant? I notice that the terrestrial crust here on Earth is a lot more akin to what we see on Venus, it is the oceanic crust and current plate margins that differ the most.
i've seen a few places where Charles Lyell would bang on about using outdated and incorrect naming as well, as it plants wrong ideas that are hard to get rid of later. It's important.
Prof. Baumann can you point to a video in your prolific videography explaining why older mafic crust subducts compared to newer mafic crust. Why is it denser?
Sorry I am so late on this. Mafic crust is denser because it contains mostly heavy elements like iron, although it does contain some lighter ones such as magnesium. Felsic crust contains lighter elements like aluminum, calcium, and potassium. Mafic crust subducts because it is denser, but that is only part of the reason. It also subducts because it is thinner, by a lot. This may seem counter intuitive, but the thicker felsic crust is just too thick and buoyant for subduction, at least on the continents.
Well done! My only question relates not to the timing of the onset of plate tectonics, but more to the "current state". How does the "slab pull" model justify itself in relation to the "shallow slab" apparent tomography of the Farallon Plate beneath the North American craton, or other "slab break" theories currently in vogue? Understanding that the current relationship between the Pacific Plate with NA is turning into more of a transform fault zone, could this be an example of your idea of smaller plates getting larger? Or is something else at work? Also understanding that there is a lot of debate over both the shallow slab and slab break theories...
Great question. As you know that plate was a lot bigger. And as that plate goes onto the mantle, it may not to so evenly. The edges could be deep diving why the middle may not because of uneven mantle convection. Or it could be as that subduction begins the fault zone is shallower. Even though shallow subduction happens, it eventually gives way to deeper angle subduction. If it didn’t, we would still get eruptions in Wyoming. Plus the Yellowstone hotspot may have messed with the system.
Even when it comes to biology, I never liked the term "the boring billion". Not to mention, if you look at the atmosphere at the beginning of the BB, and at the end of the BB, it didn't turn out to be so boring after all... So I can only imagine that for a geology guy, it would be so much worse.
Did the formation of large oceans have anything to do with kick starting subduction. Ocean began forming 3800 ma...it would have taken a while for the mass of an ocean to affect the lithosphere but would the weight of an ocean have enough effect to kick start subduction? All these other analogues Venus io etc have one glaring absence.. a large ocean.
Question. If the source of plate movement is plates being pulled at subduction zones as plates sink then how do you explain movement of plates that don't sink? For instance the north American plate is moving westward but the plate isn't sinking at a subduction zone.
Continental crust is too buoyant. The ocean crust gets old and dense then faults eventually sinking into the mantle assisted by convection. As for why rifts form in thick continental crust, we don't know
I get how Ocean plates are naturally denser because their source material is olivine and 2 other primary minerals (can't remember names). Oceanic plate results from partial melting of mantle at spreading zones. Continent plates grow from partial melting of oceanic plate. Thus the mantle is densest, oceanic lighter and continental the lightest. Throw in the cooling of oceanic plates as they age and you get the differing bouyancies. But unless I'm greatly mistaken that doesn't explain lateral movement only vertical. Another question. Slab pull at a subduction zone would put create tensioned forces on the plate of possible shear but not cooling forces. Rock is extremely good at resisting compressions forces but not shear and tension forces. Admittedly the crustal and mantle layers of the plate would handle these forces differently. The crust being more brittle would fracture while the mantle being more ductile would stretch. The problem, if my logic is accurate, is that one of the defining characteristics of plate tectonics is large provincial horizontal thrust faults (can't remember the exact name for them). These faults though would develop under compressional forces not tensional. Likewise if the mantle were stretching from the tensions forces you end up with a similar problem. The spherical nature of earth and the fact the mantle is beneath the crust means it must cover less area for basic geometric reasons. But if the mantle is stretching as a result of the tension forces the the mantle would have to shear away from the crust or the crust would have to fracture and spread. We see areas where the crust has spread like the basin and range but that is localized (on a continental scale) and it would have to be plate wide to accommodate plate wide tensional forces. Therefore it seems like the driving force behind plate tectonics must be compressional in nature not tensions which implies plates sliding off spreading ridges or mantle convection currents. Hope I made questions and reasoning clear.
I had another thought. The new crust at spreading ridges results from pressure changes causing partial melting of mantle minerals. If this partially melted mantle material isn't physically moving away from ridge then it would quickly become depleted in the light elements that melt first. If it didn't move then the new ocean crust would become denser over time, which obviously isn't the case or there'd be obvious bouyancies discrepancies over the millions of years time spans. The way I see it, there are two options. The new source mantle material comes from the sides and sinks as the left over mantle minerals becomes denser. This would I think create a counter spreading convection force which seems unlikely. The second option is the new source mantle material would rise from below and spread away from the ridges along with the crust, essentially forming the mantle basement rock of the plate. But at this point its denser than the underlying mantle material so it should sink. Not sure if this supports pushing or pulling of the plates but it must have some affect one way or the other.
I love how inquisitive you are. I haven't run the numbers but I know the equations exist. The ocean crust (and lithosphere) also thickens as it ages, eventually becoming more dense than the underlying mantle. That's how I understand it anyway. The faulting is low angle reverse faulting aka thrust faulting. We get them on the continents too, like the Lewis overthrust which has not only been compressed but over thrusted by about 100 km if I remember correctly. The difference with the ocean crust is it goes into the mantle instead of over the continents. We actually do have felsic rock on the ocean floor. It's just not common and leads to dumb claims like the concept of Zeeland as a continent. But the part of the mantle that sources most spreading centers is pretty homogeneous. Earth is old enough to have worked most of that out over the eons. In the Hadean and Archean felsic rocks at rift style places was likely more common. I personally think to understand this better we need to understand Venus.
Serpentinisation within faults causing phylosilicate at boundary layers then lubricating movement between plates? Transition from dry ground wet atmosphere big rainout but due to high atmospheric pressure water boiling at 200 degrees.... This must have supercharged serpentinisation posibly deep to lithosphere and creating early plate boundaries? Deserpentinisation release borosilicate partial melt leaving metamorphic olivine and producing buoyant felsic blobs.
@@stevenbaumann8692 something else I read as a countering argument for very early onset of plate tectonics is the lack of accreted exotic terranes within the broader felsic assemblages at the time. So I have this question for you.... what would a Hadean early archean exotic terrane look like? In my mind, mafic oceanic crust is what dominated the period, so surely exotic terranes would have been the felsic blobs that began coalescing into the proto-cratons.... ie the Cratons themselves are the exotic terranes and are evidence for early accretion processes? Or am I talking lunacy?
This 2 parter series was extremely interesting. I'm glad you talked about the evolution of Earth's tectonic processes.... and I, too, highly dislike the 'Boring Billion' title. So much happened in that time that it wasn't really boring at all.
I'm also glad you talked about Venus as well. Personally, I found that idea of Venus melting its surface completely every 100 million years to be a bit far fetched. I always figured that because it took a hard hit causing it to flip 180° vertically that that played a major role in it not developing a similar plate tectonic system like Earth or a magnetic field Mainly because I have often wondered if rotation of the planet has an influence on the process of convection in the mantle. I know the heat from core starts it... but I've pondered about if there's something like the Coriolis effect influencing it.
Plus, Venus' mantle seems to be hotter than Earth's and I very much agree with you on the plastic tectonic system occurring there currently as well as here early on.
Once more I really enjoyed this series. Thank you for posting it 😃
I’m glad you liked it!
another winner
Good follow up video glad to see the situation with Venus be addressed one name I have seen for describing the more localized regional domain of Venusian tectonics is chunktonics as they argued the smaller more localized behavior of tectonics is more analogous to pack ice on a body of water. That work mainly focused on the open lowlands of Venus rather than its more complex terrains nothing signs of what might be transtension and transpression along the edges of relatively undeformed chunks of crust I'm mixed on that opinion but it seems that while the literature has moved on from the cyclic cataclysmic stagnant lid idea it has sadly persisted as a zombie in science communication circles. I should note that while Venus has no water Ocean the lower atmosphere of Venus is in a supercritical state due to the high pressures and temperatures which gives it properties of both liquids and gases with at least some evidence suggesting that there are distinct carbon dioxide nitrogen mixing ratios between the two layers so in some sense you can argue that Venus has an ocean of carbon dioxide.
As for the future of plate tectonics I feel it should be noted that Mars even in its clearly tectonically waning state appears to still have "active hot spots which can at least on occasion erupt onto the surface. Granted the youngest example appears to be roughly the same approximate age as a nearby impact crater suggesting the melt had help reaching the pressures needed to breach the surface but there were at least some weak quakes deep down which have been interpreted as possibly being magmatic fluids moving far below the surface. Granted Mars is a puny world so it probably didn't have a plate tectonic like cycling but evidence for hotspot like location specific prolonged volcanic activity has been shown to hold for the Moon and appears to hold in the case of both Mercury and Mars given limited data we have there. Insight was nice but it was a single seismometer and operated for a limited time before the Martian dust accumulation killed it. A network of radiogenic detectors across the surface of Mars would be nice. Not going to happen so long as the whole neoliberal political ideology on spending money for science persists but we can dream right?
For Venus Silicon Carbide semiconductors and to a lesser extent Gallium nitride (I think it involves Gallium I know but I forget what exactly its mixed with) seem to be a promising possibility for enabling electronics t9o function at Venusian temperatures and pressures with in combination with clockwork mechanisms for functions which don't need electronics might finally open up a possibility to get some actual ground measurement data. The tricky part there is powering any lander and or rover with the best option due to the thick reflective clouds reflecting away most incoming sunlight likely being wind power. Venus has slow wind speeds but because of the density of supercritical fluids near the surface they are carrying lots of momentum.
As for Earth tectonics The article on "Buoyant hydrous mantle plume from the mantle transition zone focused on the study of buoyant hydrous upwelling seems to be quite relevant and informative in the onset of more dynamics plate tectonics. This is specifically in regards to its thermodynamics and the type of volcanism associated with these fairly rare and geochemically distinct volcanoes which appear be a close match for the large continental flood basalt eruptions associated with the break ups and failed break ups of supercontinents.
Kuritani, T., Xia, QK., Kimura, JI. et al. Buoyant hydrous mantle plume from the mantle transition zone. Sci Rep 9, 6549 (2019). doi.org/10.1038/s41598-019-43103-y
The close match in magma chemistry particularly rich in phosphorus and other sediment derived volatile elements along with the clear seismic tomographic data showing that the modern example of Mt. Paektu clearly resides beneath the stagnant Pacific Slab suggests that these compositionally distinct kinds of magmas are derived from the recrystallizing slabs expelling incompatible elements from their structure and enriching the overlying mantle in compositionally lighter elements until a critical threshold is reached where the compositionally lighter material begins to ascend towards the surface decompressing as it does so. It is striking that the timescale given for the onset of true plate tectonics in your model lines up within a hundred million years of the simple thermodynamics model on when the corresponding chemical phase transitions needed to initiate hydrous compositional upwelling became thermodynamically possible as the reaction becomes more efficient at lower temperatures. Here the MTZ or mantle transition zone is the layer where the temperature and pressure are optimal for this process to occur which has been getting deeper over time as a consequence of the continued cooling of the mantle.
Given this evidence it seems like it is likely quite important for the story of modern plate tectonics both in its onset as well as its continued evolution with some lines of evidence which while quite crude and limited in the amount of available data suggest that the average rate of motion of tectonic plate movements has been speeding up over the last billion years. If true this might indicate that there will/would be an optimum rate of tectonic movement enabled by the ongoing mineral hydration process of Earth's mantle and the slowing of the more general deep mantle convection.
At least the Seismic tomography seems to support the existence of slab pull fed deep convection with some shallower compositional upwelling processes which seems important to starting the break up of supercontinents at the very least.
Hopefully a helpful pointer for komatiite, it was really difficult for me too, as I assumed it was something like "coma-teeite", similar to how I heard you say it. This was until my dad, a South African, told me about the Komati river, pronounced "co-matty"! Suddenly it clicked into place, komatiite is in fact just "co-matty-ite", which I at least found a lot easier to say. That double 'i' is evil and misleading, makes me think of Hawaii :)
Ophiolite sequences fascinate me, if you know of Macquarie island, it is my dream field destination. "Mid-tertirary" (WHY can't australia get with the time and use neogene and paleogene already?) oceanic crust just shoved up and outta the water for all to see, it's very exciting!
Until now I had no idea alternate models for tectonic activity existed, or even that plate tectonics did not apply before a certain point! Perhaps we could call the old system "convection tectonics", and the transitionary period "proto-plate tectonics". I like the term "plastic tectonics" makes more sense and can be applied generally, something like that to differentiate it. "Sloppy plate tectonics" while unscientific is very funny and actually somewhat accurate with a hotter lithosphere and sagduction haha
Venus fascinates me too, as cool as the global resurfacing hypothesis is, I find it quite unlikely to consider it a primary planetary mechanism! What of the involvement of oceans? Is the hydration of the oceanic crust significant? I notice that the terrestrial crust here on Earth is a lot more akin to what we see on Venus, it is the oceanic crust and current plate margins that differ the most.
Thanks! I still can’t say oxygenation to this day either.
i've seen a few places where Charles Lyell would bang on about using outdated and incorrect naming as well, as it plants wrong ideas that are hard to get rid of later. It's important.
And here I'd thought they'd began in the beginning and continue. On all planets, I'd just assumed! Well, eruptions and movement.👍🥰💞✌
Prof. Baumann can you point to a video in your prolific videography explaining why older mafic crust subducts compared to newer mafic crust. Why is it denser?
Sorry I am so late on this. Mafic crust is denser because it contains mostly heavy elements like iron, although it does contain some lighter ones such as magnesium. Felsic crust contains lighter elements like aluminum, calcium, and potassium.
Mafic crust subducts because it is denser, but that is only part of the reason. It also subducts because it is thinner, by a lot. This may seem counter intuitive, but the thicker felsic crust is just too thick and buoyant for subduction, at least on the continents.
@stevenbaumann8692 how come older becomes denser though or is it stretched out and thinner, and therefore easier to pull under?
Well done!
My only question relates not to the timing of the onset of plate tectonics, but more to the "current state". How does the "slab pull" model justify itself in relation to the "shallow slab" apparent tomography of the Farallon Plate beneath the North American craton, or other "slab break" theories currently in vogue?
Understanding that the current relationship between the Pacific Plate with NA is turning into more of a transform fault zone, could this be an example of your idea of smaller plates getting larger? Or is something else at work? Also understanding that there is a lot of debate over both the shallow slab and slab break theories...
Great question. As you know that plate was a lot bigger. And as that plate goes onto the mantle, it may not to so evenly. The edges could be deep diving why the middle may not because of uneven mantle convection. Or it could be as that subduction begins the fault zone is shallower. Even though shallow subduction happens, it eventually gives way to deeper angle subduction. If it didn’t, we would still get eruptions in Wyoming. Plus the Yellowstone hotspot may have messed with the system.
07:03 Awesome animation!
Thanks!
Maybe a better term for plastic tectonics is vertical tectonics?
I could get on board with that
Even when it comes to biology, I never liked the term "the boring billion". Not to mention, if you look at the atmosphere at the beginning of the BB, and at the end of the BB, it didn't turn out to be so boring after all...
So I can only imagine that for a geology guy, it would be so much worse.
I’m glad you get it! 😊👍🏻
Did the formation of large oceans have anything to do with kick starting subduction. Ocean began forming 3800 ma...it would have taken a while for the mass of an ocean to affect the lithosphere but would the weight of an ocean have enough effect to kick start subduction?
All these other analogues Venus io etc have one glaring absence.. a large ocean.
Go yotes ,ahwooo
Question. If the source of plate movement is plates being pulled at subduction zones as plates sink then how do you explain movement of plates that don't sink? For instance the north American plate is moving westward but the plate isn't sinking at a subduction zone.
Continental crust is too buoyant. The ocean crust gets old and dense then faults eventually sinking into the mantle assisted by convection. As for why rifts form in thick continental crust, we don't know
I get how Ocean plates are naturally denser because their source material is olivine and 2 other primary minerals (can't remember names). Oceanic plate results from partial melting of mantle at spreading zones. Continent plates grow from partial melting of oceanic plate. Thus the mantle is densest, oceanic lighter and continental the lightest. Throw in the cooling of oceanic plates as they age and you get the differing bouyancies. But unless I'm greatly mistaken that doesn't explain lateral movement only vertical.
Another question. Slab pull at a subduction zone would put create tensioned forces on the plate of possible shear but not cooling forces. Rock is extremely good at resisting compressions forces but not shear and tension forces. Admittedly the crustal and mantle layers of the plate would handle these forces differently. The crust being more brittle would fracture while the mantle being more ductile would stretch. The problem, if my logic is accurate, is that one of the defining characteristics of plate tectonics is large provincial horizontal thrust faults (can't remember the exact name for them). These faults though would develop under compressional forces not tensional. Likewise if the mantle were stretching from the tensions forces you end up with a similar problem. The spherical nature of earth and the fact the mantle is beneath the crust means it must cover less area for basic geometric reasons. But if the mantle is stretching as a result of the tension forces the the mantle would have to shear away from the crust or the crust would have to fracture and spread. We see areas where the crust has spread like the basin and range but that is localized (on a continental scale) and it would have to be plate wide to accommodate plate wide tensional forces. Therefore it seems like the driving force behind plate tectonics must be compressional in nature not tensions which implies plates sliding off spreading ridges or mantle convection currents.
Hope I made questions and reasoning clear.
I had another thought.
The new crust at spreading ridges results from pressure changes causing partial melting of mantle minerals. If this partially melted mantle material isn't physically moving away from ridge then it would quickly become depleted in the light elements that melt first. If it didn't move then the new ocean crust would become denser over time, which obviously isn't the case or there'd be obvious bouyancies discrepancies over the millions of years time spans. The way I see it, there are two options. The new source mantle material comes from the sides and sinks as the left over mantle minerals becomes denser. This would I think create a counter spreading convection force which seems unlikely. The second option is the new source mantle material would rise from below and spread away from the ridges along with the crust, essentially forming the mantle basement rock of the plate. But at this point its denser than the underlying mantle material so it should sink.
Not sure if this supports pushing or pulling of the plates but it must have some affect one way or the other.
I love how inquisitive you are. I haven't run the numbers but I know the equations exist. The ocean crust (and lithosphere) also thickens as it ages, eventually becoming more dense than the underlying mantle. That's how I understand it anyway.
The faulting is low angle reverse faulting aka thrust faulting. We get them on the continents too, like the Lewis overthrust which has not only been compressed but over thrusted by about 100 km if I remember correctly.
The difference with the ocean crust is it goes into the mantle instead of over the continents.
We actually do have felsic rock on the ocean floor. It's just not common and leads to dumb claims like the concept of Zeeland as a continent.
But the part of the mantle that sources most spreading centers is pretty homogeneous. Earth is old enough to have worked most of that out over the eons. In the Hadean and Archean felsic rocks at rift style places was likely more common.
I personally think to understand this better we need to understand Venus.
Serpentinisation within faults causing phylosilicate at boundary layers then lubricating movement between plates?
Transition from dry ground wet atmosphere big rainout but due to high atmospheric pressure water boiling at 200 degrees.... This must have supercharged serpentinisation posibly deep to lithosphere and creating early plate boundaries?
Deserpentinisation release borosilicate partial melt leaving metamorphic olivine and producing buoyant felsic blobs.
Gondwana?
Gondwana is a paleocontinent that existed billions of years after the Archean
Gowganda is a Proterozoic geologic formation.
@@stevenbaumann8692 something else I read as a countering argument for very early onset of plate tectonics is the lack of accreted exotic terranes within the broader felsic assemblages at the time.
So I have this question for you.... what would a Hadean early archean exotic terrane look like?
In my mind, mafic oceanic crust is what dominated the period, so surely exotic terranes would have been the felsic blobs that began coalescing into the proto-cratons.... ie the Cratons themselves are the exotic terranes and are evidence for early accretion processes?
Or am I talking lunacy?