10 votes
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When a tectonic plate subducts, does any of the subducted material melt, or is it just the mantle above the subducted slab that melts?

This is a very good question Inkenbrandt. It is quite common for even some graduate students to think that the majority of partial-melting comes from the slab: when it is the the mantle above the fore-...
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9 votes
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Is a billion years of Earth's history missing?

There was an article in that year's Scientific American, which I've read in the Polish edition. I don't have that paper now, but I think this was that one: http://www.scientificamerican.com/article/...
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8 votes
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Why does a subduction zone produce a serpentinization diapir rather than volcanism?

First of all, your statement implies that volcanism didn't occur in Troodos. That is not true. Troodos was even referred to as "Troodos Volcano" once in Miyashiro's 1973 article about Troodos. A ...
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8 votes

Why does a subduction zone produce a serpentinization diapir rather than volcanism?

After some brief research, serpentinite diapirism occurs due to deep penetration of seawater at temperature around 100-200$^o$C [1]. To the south of the rift that was forming the ophiolite sequence ...
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  • 360
8 votes
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Has an entire plate ever subducted?

Excellent question! Indeed, entire plates have subducted before. One example is the Intermontane Plate (Wikipedia). This plate sat west of North America around 195 million years ago. The plate ...
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  • 2,688
8 votes
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Volcanoes in the Alps and Himalayas and the subduction of Tethys Sea

The end of the Tethys Sea and the initiation of the continent-continent collision that formed the Himalayas is thought to have happened about 65 Ma ago (recent studies suggest maybe only 35 Ma). And ...
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7 votes

Can garbage be sent into the (near-)center of the world?

No. In fact, I don't know why David Hammen didn't say that instead of commenting. The deepest hole that mankind ever dug was barely a scratch on the Earth's surface when you look at its size. They ...
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7 votes

Megathrust earthquakes on subduction zones

Megathrust is not a particularly well defined term but in my experience it generally refers to very large earthquakes that occur on the subduction interface. The subduction interface is the main ...
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7 votes

Has an entire plate ever subducted?

As a complement to the two other answers, the work of van de Meer et al., 2012 is worth mentioning. In this article, the authors tried to explore the Triassic-Jurassic plate tectonic evolution of the ...
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6 votes
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Exhumation of blueschist

Fast exhumation is not necessary to retain blueschist mineral assemblage. This is the classical difference between prograde and retrograde metamorphism, and it's not limited to blueschists. Why do we ...
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5 votes

Has an entire plate ever subducted?

I'll add to Richard's contemporary answer and add that we have plenty of evidence for subducted plates in the geological past. The evidence lies in the form of ophiolites. Ophiolites are fossil ...
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5 votes

Why are oceans so deep?

The deep zones in the ocean are not where new rock is formed. The trenches are the areas where rock is subducted back into the mantle. Here's a picture to visualise it: USGS/USGov, modified by Eurico ...
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5 votes

How does a subduction zone form mountains?

When the subducted oceanic plate slides beneath the continental crust, it causes crustal thickening and sometimes crustal folding. In addition to this, rising plumes of magma are created when the ...
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5 votes
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Are the Olympic Mountains (in Washington state) geologically unique?

Short answer: yes, there are other mountains which contains oceanic crust in their lithologies. The process you described as "the upthrust of ocean crust" is called obduction. The resulting rock ...
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5 votes

Megathrust earthquakes on subduction zones

Yes, mega thrust earthquake can occur in any point of any subduction zone. However, some areas areas are much more active than others, meaning that the frequency of earthquakes and energy released per ...
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5 votes
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Why are there no subduction trenches on continental land?

Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense. Hence ocean crust "goes down" more easily, and the density can even help pull the ocean ...
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5 votes

When did the proto-Himalayas become non-volcanic?

We don't know for sure because A. the evidence has almost all been erased by the continued crustal shortening of the area where the volcanic arc(s) would have been. B. the region is huge and volcanism ...
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4 votes

Exhumation of blueschist

I don't know whether its currently the favoured explanation, but in California people made reference to something informally referred to as the watermelon seed theory . The general idea being that the ...
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  • 3,780
4 votes
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What are the geological mechanisms for sea floor spreading in the Bismarck Sea?

Ah yes, this is a very good question. The formation of back-arc spreading centers is an open research problem, and happens to be the main topic of my office mate's dissertation! While these aren't ...
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  • 6,356
4 votes
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How does 10mm/yr of plate subduction provide enough material to create eruptions?

Yes, the situation is much more complex than you make out - the generation of melt is typically caused by partial melting of the mantle wedge located beneath the volcanic arc. This process is mainly ...
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4 votes

Why are there no subduction trenches on continental land?

As mentioned in another answer: Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense. Let's look at a simulation of what might happen. Here's a figure ...
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3 votes
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Identifying serpentinite reworked during high-T metamorphism

Of course, any ultramafic rock will ultimately melt at about 2000 deg C, but long before that there will be some interesting phase transitions, possibly involving serpentine > talc > olivine + ...
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2 votes
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What geological mechanisms result in the great depth of the Mariana Trench?

As taken from Wikipedia: There are several factors that control the depth of trenches. The most important control is the supply of sediment, which fills the trench so that there is no bathymetric ...
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2 votes

Geometrical differences of subduction zones

Differences in subduction geometry depend mostly on what type crust takes part in the collision (oceanic to oceanic, continent to continent, oceanic to continent), the speed of the two (or three) ...
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2 votes

Is the concept of seismogenic zone still relevant after the 2011 Japan earthquake?

Tohoku is the seismogenic zone, the asperity model explained this small repeating earthquake well. It was said massive earthquake will occur in Nankai Trough. As their expectation was wrong, [Kato and ...
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2 votes

How does 10mm/yr of plate subduction provide enough material to create eruptions?

10mm a year is a huge volume when you multiply with lithosphere thickness and length of the boundary, but you are right - it's more complex than this. Melting is caused by the interplay of ...
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2 votes

Can garbage be sent into the (near-)center of the world?

One of the flaws with using subduction zones as dumps for toxic chemicals so they can be broken down by heat and pressure at depth is the rate of sinking of the subducting plate. Subduction is a very ...
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2 votes

Will California become a subduction zone in the distant future

Before the transform process of the San Andreas Fault zone we know today, there was indeed a subduction zone event taking place in this same region near now coastal California during the late Jurassic ...
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