COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

Suomen Geologinen Seul'a. N: 0 35. Geologiska Sällskapet i Finland. 13
Table 2. Chemical composition.
SampIe Weight % Cation % Molecnlar norm
Si0 2
'0 ' o ••••• " 0 ••••• 64.55 65.47 Si 61.36 62.55 Q 19.38 20.35
Ti0 2
.0 ••••••••• • • 0 ••• 0.64 0.88 Ti 0.46 0.64 Or 21.66 29.25
Al 2 0 S
0 • •••••••• o. O ' o. 15.59 14.26 Al 17.41 16.02 Ab 25.66 28.10
Fe 2
•••••••••• 0 ••••• 0s 0.85 2.61 Fe 3 + 0.58 1.84 An 19.86 11.37
FeO ••• 0 •••• ••• ••• • o. 4.00 3.89 Fe 2 + 3.13 3.10
MnO ..... .... ..... ... 0.09 0.11 Mn 0.06 0.06 Wo 0.37 0.72
MgO ••••• O' ••• • •••••• 2.21 0.96 Mg 3.08 1.32 En 6.17 2.64
CaO ••••• • ••••• O ' o. " 4.28 2.78 Ca 4.33 2.81 Fs 4.81 3.12
Na 2 0 •••• O' 0 ••••••• •• 2.80 3.05 Na 5.14 5.63 Ap 0.31 0.45
K20 ••• O' •••••• • •• • o. 3.60 4.85 K 4.33 5.85 11 0.92 1.26
0 • ••
P20S o. 0 • • ••••• o. 0.17 0.22
••• •• o • • • •• •••• o . CO2 0.08 -
H2O+ ••• • ••••• o ••••• 0.60 0.43 P 0.12 0.18 Mt 0.86 2.74
H20 - .... .... .. .. .. . 0.04 0.05
99.50 I 99.5 6 I I 100.00 I 100.00 I 100.00 100.00
64.70
Cations per Standard cell (Barth's method) ....... / 96.52 96.05
Modal feldspar • ••••••••••••••••••••••• ••• o • • •••• • ••••• • •• •• • • •• •••• 0 •••
Normative feldspar •••
••• • •• o . o ••••••• ••••• • • • 0' •••••••••• 0 •• • o •• •••• ••• 67.18
55.30
68.72
When the amounts of modal and normative feldspar are compared,
differences appear. This also suggests that material has been added, (wen if
in the granitic rock the difference seems rather large in being due only to
this cause.
The rocks examined in this paper belong to the synkinematic group of
the Svecofennidic Range. In this connection it is interesting to examine the
numbers of cations per standard cello
In the rocks investigated this value is on the average 96.28, wen in ac cord
with the average 96. 82 calculated for the group of Sveconfennidic synkinematic
rocks (diorites+granodiorites+granites) using the average chemical
composition given by Simonen (1948).
A comparison can also be made with the results obtained by Marmo
(1955) with Precambrian granites in West Africa. In these granites with a
petrochemistry similar to that of Svecofennidic synkinematic granites, the
number of cations per standard cell is greater than 95.0. It must be noted
finally that synkinematic silicic rocks are rich in soda, whereas the rocks
examined in this paper, especially the most silicic ones, have a notably high
content of potash. As pointed out by Härme (1958) and others, such synkinematic
rocks must have acquired their high potash content secondarily
from the outside.
This is another fact that shows how, in the granitization phenomena
examined in this paper, an addition of material must definitely have taken
place.