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Re: Tectonic News
On Mon, 12 Dec 2005 08:58:12 -0500 "Thomas R. Holtz, Jr."
> > From: Dora Smith [mailto:email@example.com]
> > Sent: Sunday, December 11, 2005 6:16 PM
> > I have a question, though. How old is the Rift Valley?
> Neogene, but I'm not sure of more than that. Some hunting in the
> tectonic and stratigraphic lit for East Africa would give you the
> answer, though.
Some sections in the Awash area contain late Middle Miocene
vertebrate-bearing sediments (~ 11 mya), meaning that sediment was
infilling a large depression at that time. Also meaning that this
particular depression predates the beginning of the rifting process. But
IIRC, there are basalts in the area, suspected of being rift basalts,
that are dated as Oligocene. (~ 30 mya). So the earliest glints of the
rift process may be as old as Paleogene (mafic-rich volcanic activity
usually precedes the valley-forming block faulting). At the other end of
the time scale, Mount Kilimanjaro is a rift-related composite volcano of
Speaking of large depressions....
Has anyone else noticed that people on the streets/cafes/malls/grocery
stores/work are crankier *more* than usual this holiday season?