Hello,

I've just added a picture to try to explain what this old OU program was showing :-)

I’ve just watched a TV documentary attempting to explain plate tectonics. Whilst this and many others show well the creation of the plates at the Mid Atlantic Ridge, they do not explain why they are also sliding left and right along fracture zones across the ridge.

 I remember seeing a long time ago, an old ‘OU’ black and white TV programme saying that these fractures form concentric rings right around the earth sliding past one another.

Can anyone explain why this is the case and why also, these seemly important movements are not considered in future predictions of how the plates may well look in the distant future?

Thanks,

Daniel.

Obviously magmas erupt differently.  Usually felsic based mineral magmas are explosive and mafic based mineral magmas fluidy.

 Explosive eruptions are mostly explained by the fact that the magma contains greater amounts of silica, however if the temperature was higher would that not decrease the viscosity?  Yet with higher temperatures there is a greater liklihood of an influx of more mafic minerals which typically have a higher melting point, overall making the magma less felsic.

So is magma viscosity really more influenced by temperature which effectively controls the silica content? rather than just the physical properties of silica making things viscous?

I would assume that as the Earth cooled, the surface would form more or less uniformly. Obviously, this is not the case. What happened to give us continents and tectonic plates where they are?