2 Weathering
13
GO
(,0
0.720
0.715
0.710
0.705
0.700
0
,.,/
+
B-~
B'5
B'3
!
Z
,.
I
I
r
!
2
3
~
5
'TRb / ~6Sr
Fig. 2.1. Isochron diagram showing the influence of weathering on the Rb-Sr isotope
system or samples from a 450 Ma old granite pluton. B-l: fresh rock; B-5 and B-6: strongly
weathered samples. (after Dasch 1969)
6.1
5.2
~3
3.4
2.5
16
0.7
0
2580 -. 16Ma
..j..J'"
6, j
e J ~
i
I
!
J
i
k
!
i
i
I
I
1
i
i
i
i
20
40
60
80
100
120
140
160
'TRb/"Sr
Fig. 2.2. Rb-Sr isochron diagram for fresh (open circles) and altered samples It]lied circles)
from a 2600 Ma old granite body (after Worden and Compston 1973)