GeologyRocks

Yeah, I saw that. I hope they make their findings available on the net as they go along

Does anyone have any ideas about how this could have formed? The website of the project doesn't seem to give much background to the study or location so its hard to even speculate.

When they refer to crust, do they mean "Mantle that is more hard then mush? Like frozen magma.

Might the enormous pressure of 3 miles of ocean weighing down on the area discourage the freezing? Discourage the formation of "crust"?

Maybe pressure can be as important a variable as temperature in any material's change of state. If so, then it should also apply to rock.

Or have I got that backwards?

Mike

Mike,

 Contrary to popular belief the majority of the mantle is not 'mush' but is solid rock albeit slightly 'mushier' than that of the crust at the surface but definately not like the movies!

As I understand it volcanism at mid-ocean ridges is generally caused by the mantle material rising up to fill the void left by the crust being pulled apart (debate about push vs pull for another time!). As it rises  up the pressure on it decreases but it's temperature remains roughly constant. This leads to adiabatic melting as the pressure is no longer sufficient to keep the material in a solid state.

 So, the question remains as to what process prevented the mantle from undergoing this adiabatic melting. Ideas anyone?

 Alex

The rock is peridotite, which is the residue left when mantle partially melts at ridges (or at least thats my understanding of it). This suggests that melting had already occured, the rock had already cooled and the crust (consisting of material melted & removed from the peridotite) that was once overlaying the layer has since been removed.

I'm wrong actually. The rock is serpentinite- a metamorphosed form of peridotite. Interestingly the density of serpentinite is much less than that of peridotite, so adiabatic uplift could be part of the reason we see this rock exposed.

Hi,

Have any of you seen this web site? http//www.noc.soton.co/uk and looked under mid ocean ridges, and mantle.  or the part in What is the Calsberg Ridge?  This may add to our knowlege. 

Pear

Hi,

Does anybody know whether serpentinite bears any relation to serpentine found on the Lizard in Cornwall, or is it just a nomenclatural coincidence?

Cheers!

Hi,

I do not know the relationship about the lizard, but I have seen a picture of the green rock (serpentine) from the Cuesta College Dept. field trip on Hiway 41 in CA. The green rock intrudes and fills in the (crack) dike from an ancient volcanic activity.  I drove past this on a monthly basis five years ago.  You can see this picture from the Cuesta College Geology Dept. web site.

Pear.

Ben,

Same stuff. The Lizard is interpreted as an ophiolite - a slice of oceanic material.
Serpentine = mineral
Serpentinite = rock