Re: Pangaea

[cnedin@geology.adelaide.edu.au (Chris Nedin)]

Stan Frieson wrote:

> From: Vicki Rosenzweig <@lepomis.psych.upenn.edu:murphy!acmcr!vr@uunet.uu.net>
> > I don't _think_ the number of plates is fixed
> > over geological time, either.
>
>Oh goodness no.  Some purely oceanic plates can get totally
>subducted.  For instance, there is a place in the South Pacifc
>where a combination of a couple of island arcs and a gravitic
>anomoly suggest the last remnants of such a plate exist right
>now.  The Juan de Fuca plate may well be destined for this end.
>
>And then, existing plates can split - the African plate may
>be in the middle of doing so right now, along what is called
>the Great Rift Valley (where all the good hominid fossils
>are found).

Also the Indian plate and the Australian plate were once separate, allowing
India to do the plate tectonic version of the global tour. However, around
45 Mya the Indian and Australian plates amalgamated, with the spreading
ridge between then becoming dormant and movement northward taken up by the
spreading ridge between Australia and Antarctica. This had a profound
effect on the Himalayas, since the forces acting on them increased
dramatically, causing them to become much higher. Around 25 Mya subduction
south of New Guinea caused a lessening of the forces acting on the
Himalayas which resulted in the topography being unsuported and thus has
caused the mountains to fall out the side towards China.

Chris