I would add to Bob Pankhurst's last message, that if you use two-point
"isochrons" on weathered rocks for any studies and then can understand
nothing from the data, it serves you right. By such a way you void yourself
of very power instrument.
And if one cannot explain low initials in granites, it is again not a
problem of Rb-Sr method, definitely.

All the best
---------------------------------------------
Yuri A.Kostitsyn
Laboratory of Geochronology
and Isotope Geochemistry
IMGRE
15 Veresaeva str. Moscow 121357 Russia
phone/faxmodem:(095)951-3755 fax:(095)443-9043
---------------------------------------------
-----Original Message-----
From: Bob Pankhurst <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, October 06, 1998 6:42 PM


Grahame Oliver wrote: ".....aren't there egs of Rb-Sr WR
"isochrons" OLDER then U-Pb zircon in the same rock?"

I do not know of any such isochrons.  And I do not know what
"isochrons" are.  As I said, you need good data to reach general
conclusions, and too much of our dogma is based on bad data,
irrespective of which method was used.

Bob Pankhurst