Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Lor on 25/08/2010 09:14:50
-
Did the ice age or glaciers have any impact on the forming or metamorphism of rocks other than the obvious wear, grinding etc? the intense pressure for instance-was that in any way comparable to the pressure say of how diamonds underground were formed?
-
No, although glaciers leave distinctive deposits (called till) that may become lithified in the future (and are then called tillites), glaciers do not generate sufficient heat or pressure to cause lithification. This is the process whereby loose sediments (e.g. sand) become solid rock. Broadly speaking if the rocks are buried deep enough and are hot enough they undergo metamorphism and become metamorphic rocks. The type of metamorphic rock depends on what the rock was before it was squashed and cooked – shale for instance becomes slate.
Metamorphism generally occurs at temperatures greater than 200 C and at depths greater than 10km or so (although it can be argued that different grades of coal represent a a metamorphic sequence at lower temperature and pressure
The immense pressure required to form diamonds is found deeper than 150km below the surface and they are only brought to the surface by 2 types of volcanic eruption. Where they are found in sediments (like in parts of west Africa) it is because the rock that contained them has been eroded away and the diamonds washed down with the sediments.
-
Thanks for the reply and info. I'm sure I'll be picking your brain again sometime soon. [:0]
-
That's not to say that there are no compressive effects. 10,000+ feet of ice does compress the rocks below them, even to the point of pressing the crust into the mantle. When the ice melts, isostatic rebound allows the depressed crust to uplift. This is a factor in the amount of calculated sea level rise if the climate warms enough to melt ice caps.
-
i've got another probably stupidly simplistic question for you -but you know what they say-there are no stupid questions-so here it is.
It was said the earth had no more 100 years supply of oil deposits left-although i beleive they found a crapload of more recently but what if any is the effect of removing the earths oil? will it make any impact? i would think so but I am probably wrong.
[?]
-
If you're talking about direct effect of removal on the crust- very very minor, if any, real effects.
-
Whilst Jim Bob is probably best qualified to answer this, generally, oil (and gas) is trapped in the pores between the quartz grains that form most hydrocarbon reservoir rocks and does not add to the "strength" of the rock.
Furthermore, when oil is extracted, water is pumped in to another part of the reservoir to push as much oil out as possible, so water replaces the oil.
Some people have suggested that an alternative to water would be to use CO2 from carbon capture systems on power stations, potentialy killing two birds with one stone so to speak.