20
Peter Stille and Graham Shields
0.728
0.724
,~ 0.720
03 0.716
0.712
0.708
~,e,e .,.,,~- F 2
,o /
~
F3
'
o.'
i
*
0.4
8
12
1,6
a~Rb / 8~Sr
A
50
t.0
30
|
'o F
/,
9
/ o Ft,
'~ F /,~,
L/p Fa
O ~ f .
z .
0
05
l0
t5
'o K / 36At (10 -J)
Fig. 2.7. Rb-Sr (A) and K-At (B) isochron diagrams for fresh and altered feldspars. (Clauer
1981)
2.4 Products of Chemical Weathering
Most of the important clay minerals are derived from biotites and feldspars. They
determine the Rb-Sr and K-Ar isotope characteristics of the weathering profile.
Let us turn to these products of weathering themselves, their isotopic systems and
behavior during weathering.