Plate Motion / Convection Currents

[kingwinner]

1. Are ALL terranes on the continents coming from the ocean where they are scraped off in continental-oceanic subduction zones?

 

2. Is the "theory of microplate terranes" suggesting that ALL continents are a patchwork of terranes (from the ocean)?

 

3. I don't quite get the 3 underlined parts of this paragraph:

"The earth is a convecting system becuase broad upwellings of asthenosphere caused by the sinking of lithospheric plates (why is it sinking? so are we constantly getting closer to the core?) transport heat. Where the plates pull away from each other at the mid-ocean ridges, magma from the asthenosphere rises to the surface, where it cools to from new lithosphere. As the lithosphere moves away from the mid-ocean ridge, it cools and becomes more dense and begins to subduct into the asthenosphere. (how come the lithosphere suddenly subduct without any plate collision?) The downward pull of the subducting lithosphere is probably the main driving force for tectonic plate motion (is this whole paragraph describing the cause of plate motion as convection currents? I don't see how this describes the earth as a convecting system...it seems to me that this paragraph does not relate to convection currents in any way...)"

 

Can someone explain? I would appreciate!

[Southtown]

Utoh! We have a thinker... ;)

 

http://www.creationscience.com/Trenches5.html#wp1111128

[Turtle]

1. Are ALL terranes on the continents coming from the ocean where they are scraped off in continental-oceanic subduction zones?

 

2. Is the "theory of microplate terranes" suggesting that ALL continents are a patchwork of terranes (from the ocean)?

 

3. I don't quite get the 3 underlined parts of this paragraph:

"The earth is a convecting system becuase broad upwellings of asthenosphere caused by the sinking of lithospheric plates (why is it sinking? so are we constantly getting closer to the core?) transport heat. Where the plates pull away from each other at the mid-ocean ridges, magma from the asthenosphere rises to the surface, where it cools to from new lithosphere. As the lithosphere moves away from the mid-ocean ridge, it cools and becomes more dense and begins to subduct into the asthenosphere. (how come the lithosphere suddenly subduct without any plate collision?) The downward pull of the subducting lithosphere is probably the main driving force for tectonic plate motion (is this whole paragraph describing the cause of plate motion as convection currents? I don't see how this describes the earth as a convecting system...it seems to me that this paragraph does not relate to convection currents in any way...)"

 

Can someone explain? I would appreciate!

 

1. No; oceans came after a crust cooled on Earth.

2. I don't know that theory offhand.

3. Subduction is a plate boundry, but not all boundries subduct. The mechanics of the convection model remain speculative. If you need this particular version in memory for a test, then learn it verbatim. In any case, read widely. ;)

[Tagred]

1. Though not ALL terrains are of the same age most continental rock was formed early on in earth's evolution.

 

2. Not too sure what its asking but, continental rocks are different in composition and density to oceanic rock again, micro terranes could be the last remnants of previous continental drift episodes

 

3. I would disagree that upwellings are driven by the sinking of lithosphere. Upwellings, hotspots, spreading centres etc are a result of either a wekaness or increased activity below the oceanic crust and when heated are less dense than cool rock, which is why at spreading centres you see ridges, as it spreads out it is eroded, cooled and increases in density.

 

Subduction of oceanic lithosphere is a driver of continental drift however, along with spreading centres. Oceanic rock will always subduct under continental rock because of density (without going into any other fault systems)

 

I think that passage doesnt describe enough about either convection systems of continental drift, it seems more like a half explanation for both, if u know what i mean.

[Turtle]

1. Though not ALL terrains are of the same age most continental rock was formed early on in earth's evolution.

 

2. Not too sure what its asking but, continental rocks are different in composition and density to oceanic rock again, micro terranes could be the last remnants of previous continental drift episodes

 

3. I would disagree that upwellings are driven by the sinking of lithosphere. Upwellings, hotspots, spreading centres etc are a result of either a wekaness or increased activity below the oceanic crust and when heated are less dense than cool rock, which is why at spreading centres you see ridges, as it spreads out it is eroded, cooled and increases in density.

 

Subduction of oceanic lithosphere is a driver of continental drift however, along with spreading centres. Oceanic rock will always subduct under continental rock because of density (without going into any other fault systems)

 

I think that passage doesnt describe enough about either convection systems of continental drift, it seems more like a half explanation for both, if u know what i mean.

 

1) Much of continental rock is sedimentary & metamorphic & is continuously formed/reformed.

2) The Columbia Plateau Basalts errupted from seams on dry land.

3) Hot spots & spreading centers occur on continents as well as undersea; Yellowstone Supervolcano is over a hotspot, & the Great Rift Valley in Africa is an active spreading center.

Plate boundries do not always subduct; the San Andreas Fault is a strike-slip plate boundry, the Himalyas continue to push up from a locked plate boundry.

;)

[Turtle]

___Science is always amendable. New research in geology reveals evidence of how Earth's early geology developed.

http://uanews.org/cgi-bin/WebObjects/UANews.woa/9/wa/SRStoryDetails?ArticleID=11692

 

This quote from the linked article:

"Comets have played a relatively minor role in inner solar system impacts, Strom, Malhotra and Kring also conclude from their work. Contrary to popular belief, probably no more than 10 percent of Earth's water has come from comets, Strom said.

 

After the Late Heavy Bombardment, terrestrial surfaces were so completely altered that no surface older than 3.9 billion years can be dated using the cratering record. Older rocks and minerals are found on the moon and Earth, but they are fragments of older surfaces that were broken up by impacts, the researchers said.

 

Strom said that if Earth had oceans between 4.4 billion and 4 billion years ago, as other geological evidence suggests, those oceans must have been vaporized by the asteroid impacts during the cataclysm."

;)

[Tagred]

1) Much of continental rock is sedimentary & metamorphic & is continuously formed/reformed.

2) The Columbia Plateau Basalts errupted from seams on dry land.

3) Hot spots & spreading centers occur on continents as well as undersea; Yellowstone Supervolcano is over a hotspot, & the Great Rift Valley in Africa is an active spreading center.

Plate boundries do not always subduct; the San Andreas Fault is a strike-slip plate boundry, the Himalyas continue to push up from a locked plate boundry.

;)

1) In terms of the terraines they were formed early on in earth history (relatively). And terraines as most geologist would know them (at least the years of my study) were normally restricted to central land masses. Although I gather the goal posts can be moved, which is no bad thing.

 

2) Absolutely right, but in general terms density of continental rock is lighter than oceanic. trying to keep within the question, maybe im being too generalistic

 

3) I purposely added the caveat not including any other fault system. In subduction zones oceanic rock will always subduct under continental. I tried to reply in the context of the question rather than add perhaps more confusion.

 

I could have gone into minute details of the whole convection & tectonic cycle but though it best to keep it at a "general" level to answer the question. Perhaps I was wrong.

 

I need to read more posts on this forum, and gather more info as to what amounts of detail and qualification is needed to avoid confusing others and embarrassing myself.

 

Please excuse me if I'm not up to standard just yet, i need a little time ;) . I hate being technical when theres no need and vice versa. :doh:

[HydrogenBond]

What confuses me is that originally there was only one singular super continent, Pangaea, earlier in the earth's evolution when there was more mantle heat. That remained until quite recently in geological time, after the earth had time to cooled, i.e., 200Million years ago. Why did a cooler earth cause such large scale continental drift when the hotter earth with its singular land mass, probably had more internal convection? It seems backwards to me.

[Turtle]

I could have gone into minute details of the whole convection & tectonic cycle but though it best to keep it at a "general" level to answer the question. Perhaps I was wrong.

 

I need to read more posts on this forum, and gather more info as to what amounts of detail and qualification is needed to avoid confusing others and embarrassing myself.

 

Please excuse me if I'm not up to standard just yet, i need a little time ;) . I hate being technical when theres no need and vice versa. ;)

___The post is fine Tagred; just the right mix to stimulate conversation. ;)

 

Why did a cooler earth cause such large scale continental drift when the hotter earth with its singular land mass, probably had more internal convection? It seems backwards to me.

 

___I think it may have to do not so much with the amount of heat driving the convection as the direction(s), amplitude, volume, & interference of the convection currents. As temperatures change, these interactions also change dynamically. Cooler stiffer rock no longer floats around at relative ease & begins locking & breaking with the uneven stresses.

___So much yet to learn about the Earth's core & it's magnetic dynamo I think as well in order to understand the surface effects. ;)

[HydrogenBond]

Well that sort of makes sense except, shouldn't the early earth have more of all the internal dynamics. The oceans were already in place and life was on earth so the crust should have been relatively thick 250M years ago. Common sense would imply the energy from core increased 200M years ago. Maybe the earth's convection changed orientation due to the cooling of the poles increasing the thermal gradient north and south.

[Turtle]

Well that sort of makes sense except, shouldn't the early earth have more of all the internal dynamics. The oceans were already in place and life was on earth so the crust should have been relatively thick 250M years ago. Common sense would imply the energy from core increased 200M years ago. Maybe the earth's convection changed orientation due to the cooling of the poles increasing the thermal gradient north and south.

 

___On the first bolded point, I don't know about the rate of cooling intimately enough to make a conclusion. I might point out that we have little or no evidence for where Pangea drifted around in relation to the poles before it broke up for example.

___Interesting suggestion on the second bolded point; have to think about that. :hihi: :rolleyes:

[kingwinner]

1. Are ALL terranes on the continents coming from the ocean where they are scraped off in continental-oceanic subduction zones?

 

2. Is the "theory of microplate terranes" suggesting that ALL continents are a patchwork of terranes (from the ocean)?

 

3. I don't quite get the 3 underlined parts of this paragraph:

"The earth is a convecting system becuase broad upwellings of asthenosphere caused by the sinking of lithospheric plates (why is it sinking? so are we constantly getting closer to the core?) transport heat. Where the plates pull away from each other at the mid-ocean ridges, magma from the asthenosphere rises to the surface, where it cools to from new lithosphere. As the lithosphere moves away from the mid-ocean ridge, it cools and becomes more dense and begins to subduct into the asthenosphere. (how come the lithosphere suddenly subduct without any plate collision?) The downward pull of the subducting lithosphere is probably the main driving force for tectonic plate motion (is this whole paragraph describing the cause of plate motion as convection currents? I don't see how this describes the earth as a convecting system...it seems to me that this paragraph does not relate to convection currents in any way...)"

 

Can someone explain? I would appreciate!

 

1) Terrane is a crustal block bounded by faults whose geologic history differs from the histories of adjoining crustal blocks. In my text book, it says that the ocean floor carries terranes and as this oceanic plate crashes (and subducts) into a continental plate, terranes are scraped off and become mountains or simply an additional part of the continent...my question is...are all parts of the continents formed this way? Or is the above simply an explanation of how continents EXPANDED?

 

2) Does anyone know about this "microplate terrane theory"?

 

3) I think that paragraph is basically saying that the lithosphere is ALSO part of the convection currents (not just the asthenosphere).

Can someone explain how are the "broad upwellings of asthenosphere caused by the sinking of lithospheric plates"? Where is this sinking occuring? (mid-ocean ridges? if so, how can the lithospheric plates be sinking (subducting) at a divergent boundary?) I really don't know how upwellings of magma are caused by this sinking...

 

It is difficult for me to understand these concepts, I hope can somebody explain them to me :rolleyes:

[Turtle]

1) Terrane is a crustal block bounded by faults whose geologic history differs from the histories of adjoining crustal blocks. In my text book, it says that the ocean floor carries terranes and as this oceanic plate crashes (and subducts) into a continental plate, terranes are scraped off and become mountains or simply an additional part of the continent Or is the above simply an explanation of how continents EXPAND...my question is...are all parts of the continents formed this way?ED?

 

It is difficult for me to understand these concepts, I hope can somebody explain them to me :rolleyes:

___I do hope you try for some extra credit with this; collect the posts & turn them in?

___Anyway, I have a lot of irons in the fire so here is one response for now on the bolded above: These descriptions refer to how continents change, whether that change is expansion or not. Keep in mind the process is ongoing & its initial conditions have their beginning in a largely molten Earth. The simple answer is no; some continents contain rocks some 3.5 Billion years old (Vishnu schists at the bottom of the Grand Canyon for example) which formed (cooled) before Pangea broke up. An ocean isn't required for fracturing into plates. :hihi: