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Nothingman
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Aren't all rocks that old. I mean... I don't know.
 

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4.374 billion years
So that's a heaping pile of coalescing dust ball igniting into an inferno at 4.6 BYA.

And 226 Million years later the molten rock cooled.

I can see that.

Whoops, Earth is 4.54 Billion years old.

So a cool down in 166 Million years.

That's better.
 

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Aren't all rocks that old. I mean... I don't know.
Rocks are constantly being worn down by erosion and new ones created from volcanoes. So it's really cool to find something in tact that has lasted over four billion years without being destroyed in some way.
 

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Rocks are constantly being worn down by erosion and new ones created from volcanoes. So it's really cool to find something in tact that has lasted over four billion years without being destroyed in some way.
Oh, ok. That makes sense. And that is cool.
 

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There are two types of rock.

The first type is cooled molten lava. Igneous.

The second is compressed sand from erosion of Igneous rock. Sedimentary. Sediments => Sedimentary.

Easy Geology.
 

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Sedimentary is pressurized. So is igneous.

Non-conformities, volcanic arcs, mountain arcs, and large igneous provinces. Now those are pretty interesting.

As are ophiolites. I never spell it correctly.

What we should be talking about is the circular logics used to prove subduction. Did you know the Grand Canyon has volcanism shoot up the sides of it's rifts? Similar as an ocean trench system, such as Tonga does.
 

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Sedimentary is pressurized. So is igneous.

Non-conformities, volcanic arcs, mountain arcs, and large igneous provinces. Now those are pretty interesting.

As are ophiolites. I never spell it correctly.

What we should be talking about is the circular logics used to prove subduction. Did you know the Grand Canyon has volcanism shoot up the sides of it's rifts? Similar as an ocean trench system, such as Tonga does.
Go on then. Talk about these 'circular logics'.
 

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Well, how does one know a plate is subducting?

They simply measure what comes out of a volcano, and the deposits on the surface sea plate. If they match, then that material was subducted into the volcano.

It's been years since I've done this, so this is the best reference I can find.

http://www.nature.com/ngeo/journal/v4/n11/full/ngeo1275.html

Subduction consumes and recycles material from the oceanic plates...

We find that large volumes of H2O, CO2 and sulphur are emitted, which we suggest are derived from the subducting slab.
Got to love the graphics on the "side vents" that form during plate subduction.



Figure 3. The two Jason ROV dives at West Mata volcano discovered not just one active volcanic vent, but two, Hades and Prometheus. Both vents were obscured much of the time by billowing sulfurous gas emissions, but bright orange lava was seen in both vents. The orange glowing lava was visible for minutes at a time. Text courtesy of Dave Clague (on expedition blog); bathymetric chart courtesy of NOAA Vents website.
http://www.volcano.si.edu/volcano.cfm?vn=243130&bgvn=1&rnum=region04&snum=tonga&wvol=westmata&tab=1

Don't get me started on scalar logic and the ITRF calibration product released every 4 or so years.
 

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Well, how does one know a plate is subducting?

They simply measure what comes out of a volcano, and the deposits on the surface sea plate. If they match, then that material was subducted into the volcano.

It's been years since I've done this, so this is the best reference I can find.

http://www.nature.com/ngeo/journal/v4/n11/full/ngeo1275.html

Got to love the graphics on the "side vents" that form during plate subduction.



http://www.volcano.si.edu/volcano.cfm?vn=243130&bgvn=1&rnum=region04&snum=tonga&wvol=westmata&tab=1

Don't get me started on scalar logic and the ITRF calibration product released every 4 or so years.
You don't seem to understand the point of the paper. They aren't using this volcano to prove subduction is occurring, they are using previously determined relationships, between volatiles and subduction, to suggest that this particular volcano is "a proto-arc rather than a proto-backarc volcano" (because the two types have different chemistries). It would help if you actually read the paper, rather than just the abstract.

I shouldn't really waste my time on this, I've got an honours project to be getting on with, but:

One method of determining the existence of subduction is by measuring "what comes out of a volcano".

Beryllium-10, for instance, is produced in the atmosphere by cosmic rays striking nitrogen and oxygen nuclei. It has a half-life of 1.5 x 10^6 years (i.e. 1.5 million years), short enough that it can't have been down there for more than 10 million years, but long enough for it to have descended to about 100 km depth, which is generally the vertical distance between a subducting slab and the associated volcanic arc. So, unless you're going to postulate an otherwise unknown source of nuclear fission within the Earth's mantle, how would you explain the existence of beryllium-10 in unweathered lavas?

But that isn't the only evidence for subduction, is it?

There are Wadati-Benioff zones, i.e. earthquake foci that highlight the profile of the subducting slab, the steepness of which is determined by the age of the plate that is subducting (older, denser plates subduct more steeply than younger, less dense plates).



For example, a seismic profile of the Izu-Bonin-Mariana Arc, taken from http://en.wikipedia.org/wiki/Izu-Bonin-Mariana_Arc, originally produce by Dr. Matt Fouch, Arizona State University. You can clearly see the near vertical WB zone, because the subducting plate is about 170 million years old, it has had plenty of time to cool down and contract.

Then there's seismic tomography, which uses sesimic waves to build up a picture of the resistances of the rocks within the Earth to seismic waves. Blue is relatively cold rock that allows the seismic waves to speed up and red is hotter rock that slows the waves down.


This was taken from Widiyantoro et al., (1999). It shows, to the left, the Ryukyu subduction zone, to the right, the Izu-Bonin subuction zone. At 660 km depth there is a discontinuity (a change in state of the mantle rock, giving it greater density), which is why the, now rather maleable, slab piles up at that depth.

There's also the fact that the Pacific is narrowing as the plate subducts.

There are other methods but I can't be bothered to go into them.

References:
Widiyantoro, S., Kennett, B. L. N. and van der Hilst, R. D. (1999) 'Seismic tomography with P and S data reveals lateral variations in the rigidity of deep slabs', Earth and Planetary Science Letters, 173(1-2), pp. 91-100
 
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