Scioly.org

Sleepy wrote:At an invitational earlier this year, I received this question:

The mantle's transition zone is characterized by an abundance of what compound?

And the answer was "hydroxide".

Can anybody explain why? I can't find any information on the internet about this.

From a Google search and some prior knowledge: the mantle transition zone apparently contains a lot of the mineral peridotite (an ultramafic rock), which is formed by adding hydroxide to olivine. I'm not sure if that's much of an answer (the question is rather strangely worded, since there shouldn't be much free hydroxide anywhere in the mantle).

Why does the brittle-ductile change occur? From a search it says because fractures become closed, what does this mean?
This is the website http://www.tulane.edu/~sanelson/eens1110/deform.htm

freed2003 wrote:Why does the brittle-ductile change occur? From a search it says because fractures become closed, what does this mean?
This is the website http://www.tulane.edu/~sanelson/eens1110/deform.htm

The change is just a result of the chemical properties of the mantle; at a certain temperature it starts behaving more like a fluid than a solid, and reacts accordingly to stress.

freed2003 wrote:Why does the brittle-ductile change occur? From a search it says because fractures become closed, what does this mean?
This is the website http://www.tulane.edu/~sanelson/eens1110/deform.htm

The brittle-ductile transition zone (its proper name) is characterized by a certain depth where the temperature is hot enough to change the rocks from a solid state to a more plastic and fluid state. Above the transition zone where the rocks are colder and more rigid, they break more easily when subjected to stress when compared to rocks below the transition zone where rocks are hotter and plastic enough to where the plastic can be bent/folded more easily.

I think it's saying fractures are closed below the transition zone because the rocks are more fluid and the rock is able to bend so that the fractures are closed within the rock, although I'm not 100% sure... that would be my guess.

EDIT: Sorry Unome, I was typing my answer as you submitted your's so I didn't see your answer, and I don't know how to delete my post. I guess there are 2 answers now!

Why are Dynamic tests so loooooooong?

jakool6 wrote:Why are Dynamic tests so loooooooong?

Because you're in Ohio

jakool6 wrote:Why are Dynamic tests so loooooooong?

Ohio has good dynamic tests though!! At least, I like them . But I agree haha. Did you take the westlake test? That one was insanely long.

Sleepy wrote:

freed2003 wrote:Why does the brittle-ductile change occur? From a search it says because fractures become closed, what does this mean?
This is the website http://www.tulane.edu/~sanelson/eens1110/deform.htm

The brittle-ductile transition zone (its proper name) is characterized by a certain depth where the temperature is hot enough to change the rocks from a solid state to a more plastic and fluid state. Above the transition zone where the rocks are colder and more rigid, they break more easily when subjected to stress when compared to rocks below the transition zone where rocks are hotter and plastic enough to where the plastic can be bent/folded more easily.

I think it's saying fractures are closed below the transition zone because the rocks are more fluid and the rock is able to bend so that the fractures are closed within the rock, although I'm not 100% sure... that would be my guess.

EDIT: Sorry Unome, I was typing my answer as you submitted your's so I didn't see your answer, and I don't know how to delete my post. I guess there are 2 answers now!

To get your own post deleted, either message a moderator or report your own post, so that a moderator sees that it is to be deleted. Either method should work.

How come at first the strength of rocks increases?

driedmango wrote:

jakool6 wrote:Why are Dynamic tests so loooooooong?

Ohio has good dynamic tests though!! At least, I like them . But I agree haha. Did you take the westlake test? That one was insanely long.

I took it just now; 137/240 (plus or minus 5 I'd say, depending on grading proclivities) in just under 70 minutes, but alone with no notesheets. Apparently good enough for second place (gg Mason's super-high score), though doubtless teams have improved since then. A very difficult test indeed (usually I can solo Dynamic tests in under 40 minutes, so this one was surprisingly long).