Re: Tectonic News

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

Along the Kenyan rift doming started ca 20 mya ago and extensive volcanism 
at ca 15 mya. The Ethiopian section is older with extensive plateau basalts 
of Eocene age and the rift was well established by the mid-Miocene. However 
the elevation of the Ethiopian highlands was mostly during the pliocene and 
pleistocene. It should be noted that the Ethiopia and Kenya sections of the 
Rift form separate domes with a lower saddle in the Turkana area.

It should also be noted that rifts can remain active for long periods at 
very low spreading rates. The best example is the rift between Australia 
and Antarctica which developed during the Cenomanian but extended very 
slowly (0.5 cm/year) until the Eocene and was only a few hundred kilometers 
wide after 50 million years. During the Eocene the spreading rate increased 
to ca 7 cm/yr and there was a Southern Ocean between Australia and 
Antarctic already during the Oligocene.

Tommy Tyrberg


>I have a question, though. How old is the Rift Valley? Shouldn't the 
continent have rifted by now >unless something happened to the rifting 
process?


>Yours,
>Dora Smith
>Austin, TX
>villandra@austin.rr.com