YOUNGEST PRECAMBRIAN DYKE ROCKS IN NORTH KARELIA,
EAST FINLAND
AARTO HUHMA
HUHMA, Aarto 1981: Youngest Precambrian dyke rocks in North
Karelia, East Finland. Bull. Geol. Soc. Finland 53—2, 67—82.
The dykes which are the subject of the present paper are the youngest
rocks in the area. These include microtonalite dykes about 1850
Ma old and lamprophyre dykes about 1830 Ma old.
A total of 18 modal and chemical analyses (mainly by XRF) were
made on the microtonalite dykes, showing that they vary largely in
composition.
Only a few lamprophyre dykes are encountered and one of them
was analysed chemically. The dykes are mesocratic biotite-lamprophyres.
Aarto Huhma, Laajalahdentie 9 A,
SF-00330 Helsinki 33, Finland.
Introduction
Age d e t e r m i n a t i o n s f r o m N o r t h K a r e l i a
s h o w t h a t t h e oldest P r e k a r e l i a n rocks,
gneisses, a r e a b o u t 2600—2800 Ma old (Simonen 1980). Distinctly y o u n g e r a r e t h e K a r e l i a n
i n t r u s i v e rocks (»the M a a r i a n v a a r a granite»),
w h i c h d a t e at a b o u t 1860 Ma ( H u h m a 1976).
These rocks a r e cut by distinctly y o u n g e r
d y k e rocks, t h e m i c r o t o n a l i t e a n d l a m p r o p h y r e d y k e s to be d e a l t w i t h in this p a p e r
(Fig. 1). T h e l a m p r o p h y r e d y k e s h a v e earlier
b e e n described b y H a c k m a n (1914).
T h e f i r s t l a m p r o p h y r e d y k e w a s discovered
by J . N. Soikero in t h e s u m m e r of 1912 on
t h e w e s t e r n s h o r e of a small lake, Niinilampi,
a b o u t 1 k m SE of a f a r m called Hovi. A
second d y k e w a s e n c o u n t e r e d some 1.5 k m
f a r t h e r west. T h e distance b e t w e e n t h e d y k e s
is a b o u t 2 k m .
In t h e s u m m e r of 1913 V. H a c k m a n dis1
covered a t h i r d d y k e only a f e w m e t r e s f r o m
t h e f i r s t one. None of t h e t h r e e d y k e s is
t h i c k e r t h a n 20 to 30 cm.
H a c k m a n g a v e a c o m p r e h e n s i v e description of t h e m i n e r a l composition of t h e d y k e s
a n d p r e s e n t e d a m o d a l composition a n d t h e
chemical d a t a on the basis of w h i c h h e classif i e d t h e rock as c a m p t o n i t e (ouachitite). As
w e shall see later, h o w e v e r , t h e n o m e n c l a t u r e
is not q u i t e a p p r o p r i a t e .
E x p l o r a t i o n activity b y O u t o k u m p u Oy
r e v e a l e d m o r e d y k e s in t h e s a m e a r e a ; c u r r e n t l y six d y k e s or p a r a l l e l d y k e s w a r m s a r e
k n o w n . S o m e s u p p l e m e n t a r y studies on t h e
m i n e r a l a n d chemical composition of t h e
d y k e s w e r e u n d e r t a k e n f o r this p a p e r .
T h e m i c r o t o n a l i t e d y k e s w e r e f i r s t discovered in t h e course of geological studies at
K a a v i in 1954 in the a r e a of m a p sheet 4311
(Fig. 1). T h e y h a v e b e e n r e p o r t e d p r e v i o u s l y
by H u h m a (1970, 1971, 1975, 1976).
68
Aarto
Huhma
USSR
!«*Ä94Ö
Niinivaara.
fcO
\
OUTOKUMPU»
6950
•)uo&di"/\
Fig. 1. Simplified geological
map of the western part of
North Karelia. 1. Prekarelian rocks, 2. Karelian rocks,
3. Microtonalite dykes, 4.
Lamprophyre dykes. A940 =
Dated microtonalite, A159 =
Dated lamprophyre, 1—18 =
Analysed
microtonalites
Tables 1 and 2).
6920
Microtonalite dykes
4311 ( S i v a k k a v a a r a ) , 4222 ( O u t o k u m p u )
and
4221 (Heinävesi) and in t h e e a s t e r n p a r t s of
Mode
of
occurence
m a p sheets 3333 (Juankoski) and 3244 (Vehmersalmi)
Microtonalite d y k e s (the p r e f i x according
to Streckeisen, 1967) a b o u n d in a N - S t r e n d ing zone in t h e w e s t e r n m a r g i n s of m a p sheets
(Fig.
1).
They
discovered outside t h a t area.
have
not
been
The dykes are
wholly unconnected with any larger plutonic
bodies.
Youngest P r e c a m b r i a n dyke rocks in N o r t h Karelia, East Finland
69
Fig. 2. The contact of a
microtonalite dyke with
pegmatite granite.
A
fragment of pegmatite
granite is visible in the
dyke.
T h e d y k e s a r e f r o m a f e w c e n t i m e t r e s to
s e v e r a l m e t r e s wide. It has, h o w e v e r , not
a l w a y s b e e n possible to d e t e r m i n e t h e i r t r u e
w i d t h because t h e y o f t e n occur in t h e m a r g i n s
of outcrops a n d t h u s only one of t h e contacts
is exposed.
If b o t h contacts a r e visible,
w i d t h s such as 15 cm, 50 cm, 2 m a n d slightly
over 10 m h a v e b e e n m e a s u r e d . T h e d y k e s
a r e not v e r y long a n d can seldom be t r a c e d
f r o m one o u t c r o p to t h e next. T h e longest
distance a d y k e has b e e n t r a c e d is a b o u t 50 m;
it has b e e n e s t i m a t e d t h a t one o t h e r cannot
b e longer t h a n 15 to 20 m.
C o m p a r e d w i t h t h e i r length, t h e d y k e s are
o f t e n f a i r l y w i d e and s o m e t i m e s almost isom e t r i c in shape.
T h e n a r r o w dykes, w h i c h a r e only a f e w
t e n s of c e n t i m e t r e s wide, a r e g e n e r a l l y rect i l i n e a r a n d of c o n s t a n t w i d t h a n d cut t h e
c o u n t r y rock w i t h s h a r p contacts. In contrast,
t h e w i d e d y k e s a r e of v a r i a b l e w i d t h and
display contacts t h a t a r e o f t e n zig-zag.
In places t h e d y k e s contain c o u n t r y rock
f r a g m e n t s , e.g. p e g m a t i t e g r a n i t e in one e x p o s u r e (Fig. 2). S o m e of t h e f r a g m e n t s a r e
r o u n d e d , some a n g u l a r , v a r y i n g in size f r o m
single c r y s t a l s a n d q u a r t z f e l d s p a r m o t t l e s
to f r a g m e n t s l a r g e r t h a n t h e p a l m of a h a n d .
In a n o t h e r outcrop, d y k e rock p e n e t r a t e s
mica gneiss, M a a r i a n v a a r a g r a n i t e a n d p e g m a t i t e crosscutting a n d b r e c c i a t i n g t h e m so
t h a t t h e d y k e rock e x h i b i t s mica gneiss (Fig.
3) a n d g r a n i t e (Fig. 4) x e n o l i t h s w i t h s h a r p
contacts. T h e l a t t e r m a y b e s e v e r a l m e t r e s
in d i a m e t e r .
A t M ä n t y j ä r v i , Kaavi, t h e r e is an o u t c r o p
of q u a r t z i t e w i t h h o r i z o n t a l bedding.
The
q u a r t z i t e is crosscut b y a s u b v e r t i c a l m i c r o t o n a l i t e d y k e t h a t e x h i b i t s foliation p a r a l l e l
to t h e d y k e (Figs 5 a a n d b). This d y k e (A 940)
has b e e n d a t e d . A n o t h e r p a r a l l e l d y k e occurs
a few metres away.
D u r i n g m a p p i n g u n d e r t a k e n in 1954 a s t u d y
w a s m a d e of t h e joints in a r e s t r i c t e d area.
This s t u d y d e m o n s t r a t e d t h a t the joints e x hibit f o u r m a x i m a , t w o of w h i c h a r e associated w i t h t h e o c c u r r e n c e of m i c r o t o n a l i t e
dykes. T h e d y k e s p r e f e r t h e joint m a x i m u m
N35W, 75E. A n o t h e r joint m a x i m u m , less
o f t e n f a v o u r e d by t h e dykes, is t h a t of N25W r
70
Aarto
Huhma
Fig. 3. A fragment of
mica gneiss in a microtonalite dyke. The scale
as in Fig. 4.
25W. T h e f o r m e r r e p r e s e n t s jointing, w h o s e
s t r i k e p a r a l l e l s t h e s t r i k e of schistosity b u t
w h i c h dips p e r p e n d i c u l a r to t h e dip of
schistosity.
T h e l a t t e r coincides w i t h t h e
j o i n t i n g p a r a l l e l to t h e schistosity.
Fig. 4. Fragments of
Maarianvaara granite in
a microtonalite dyke.
i
Petrography
The microtonalite dykes are
plagioclase-biotite-quartz
rocks
clase-biotite-hornblende-quartz
fine-grained
and
plagio-
rocks. P o t a s -
Youngest P r e c a m b r i a n dyke rocks in North Karelia, East Finland
Figs 5 a and b.
71
The contact of quartzite and a
microtonalite dyke.
to this r a t h e r e q u i g r a n u l a r rock, some l a r g e r
e u h e d r a l plagioclase p h e n o c r y s t s r a n g i n g u p
to 1 X 3.5 m m in size occur locally (Fig. 6).
T h e m o r e m a f i c t h e d y k e rock, t h e
abundant are these phenocrysts.
more
The larger
plagioclase p h e n o c r y s t s in t h e m o r e
acidic
d y k e s a r e so indistinct t h a t t h e y can seldom
be seen macroscopically.
T h e h o r n b l e n d e - b e a r i n g d y k e s also contain
h o r n b l e n d e as l a r g e r p h e n o c r y s t s u p to 3—
5 m m in length.
In rocks poor in h o r n b l e n d e
this m i n e r a l c a n n o t be discerned b y t h e n a k e d
s i u m f e l d s p a r occurs only accessorily, even
in t h e v a r i a n t s richest in q u a r t z . A t its most
a b u n d a n t , p o t a s s i u m f e l d s p a r is e n c o u n t e r e d
as a s e c o n d a r y f r a c t u r e filling.
T h e a b u n d a n c e of q u a r t z v a r i e s f r o m a
f e w p e r cent to almost 30. Bio<tite t e n d s to
be r a t h e r common, a n d plagioclase, w h o s e
a b u n d a n c e f r e q u e n t l y exeeds 50 °/o, is t h e
p r e d o m i n a n t m i n e r a l . H o r n b l e n d e m a y be
lacking b u t it m a y r e a c h a b u n d a n c e s as high
as 15.8 %> (Table 1).
T h e d y k e s f r e e f r o m or poor in h o r n b l e n d e
r e s e m b l e f i n e - g r a i n e d mica schist (e.g. Fig.
5 a), so m u c h so that, in h a n d specimens, it is
o f t e n impossible to distinguish t h e m f r o m
mica schist. T h e d y k e s a r e foliated a n d w i t h out layering. To complicate t h e picture, t h e
mica schist contains n o n - l a y e r e d portions.
T h e g r a i n size of t h e d y k e s is f a i r l y small,
v a r y i n g b e t w e e n 0.05 and 0.5 m m . In a d d i t i o n
eye. Hence, ophitic or p o r p h y r i t i c
textures
a r e a b s e n t f r o m t h e dykes.
T h e e q u i g r a n u l a r p o r t i o n s e x h i b i t distinct
o r i e n t a t i o n owing to t h e p r e s e n c e of biotite
(and h o r n b l e n d e ) . O t h e r w i s e t h e rocks are
completely h o m o g e n e o u s w i t h o u t a n y zoning
or l a y e r i n g .
T h e o r i e n t a t i o n of t h e l a r g e r plagioclase
and hornblende phenocrysts often differs
f r o m t h e o r i e n t a t i o n of t h e m o r e f i n e - g r a i n e d
portions.
Plagioclase varies b e t w e e n An 2 5 a n d An 4 3
in composition a n d s h o w s only slight sericitization.
T h e l a r g e s t plagioclase p h e n o c r y s t s a r e
c h a r a c t e r i z e d by t w i n n i n g (albite, pericline,
Karlsbad). T h e biotite is reddish b r o w n and
i n t e n s e l y pleochroic. T h e h o r n b l e n d e is bluish
green, s t r o n g l y pleochroic a n d occurs as b l u n t
prisms. T h e l a r g e r h o r n b l e n d e crystals o f t e n
72
Aarto
Huhma
Table 1. Mineral composition of microtonalite dyke rocks.
1
Quartz
Plagioclase
(An)
Biotite
Hornblende
Accessories
Quartz
Plagioclase
(An)
Biotite
Hornblende
Accessories
13.4
42.0
(40)
25.7
15.8
3.1
2
3
4
5
12.1
21.1
8.1
4.3
54.5
37.3
51.1
68.3
(30) (50—45) (35—30) (45—30)
20.8
30.5
38.6
16.8
9.2
7.7
0.7
6.9
3.4
3.4
1.7
3.7
6
7
14.8
12.5
58.7
59.9
(40) (45—25)
11.8
18.0
12.5
5.7
2.2
3.9
8
11.2
52.9
(30)
23.3
10.3
2.3
9
14.5
20.9
53.2
51.0
(40) (45—40)
24.8
26.0
4.7
2.8
2.1
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
11
12
13
14
15
16
17
18
Average
19.9
18.2
23.2
52.2
44.0
50.6
(32) (35—20) (40—35)
25.9
35.6
21.0
—
—
3.2
2.0
2.2
2.0
100.0
100.0
100.0
19.8
10.7
28.5
25.8
23.4
54.2
50.5
49.7
50.0
55.0
(30) (35—30) (35—28) (45—35) (35—25)
21.7
38.8
20.9
23.1
18.3
3.8
0.3
0.5
tr
0.9
0.3
3.3
100.0
100.0
100.0
100.0
100.0
10
100.0
16.8
51.6
(35)
25.0
4.4
2.2
100.0
Accessories:
1. sphene, apatite, orthite, epidote, zircon
2. sphene, epidote, zircon, apatite, orthite, opaques, microcline
3. opaques, apatite, sericite, orthite, zircon
4. apatite, zircon, orthite
5. opaques 2.0 %>, orthite, sphene, rutile, zircon, apatite 1.7 °/o
6. opaques, apatite
7. opaques, sphene, epidote, sericite, apatite, orthite, zircon
8. sphene, opaques, apatite, orthite
9. apatite, orthite, zircon, opaques
10. chlorite, sphene, sericite, microcline, saussurite, opaques, apatite, orthite, zircon
11. chlorite, apatite, opaques, zircon, epidote, sphene, microcline
12. opaques, apatite, sericite, orthite, zircon
13. microcline, sphene, apatite, orthite, sericite, zircon
14. sphene, apatite, zircon
15. opaques, apatite, zircon
16. apatite, sphene, zircon, orthite, microcline
17. sphene, apatite, orthite, zircon, opaques
18. microcline, sericite, chlorite, apatite, orthite, zircon
c o n t a i n a p p r e c i a b l e plagioclase, ilmenite a n d
s p h e n e inclusions. T h e r e f r a c t i v e i n d e x d e t e r m i n a t i o n s indicate t h a t t h e compositions
of h o r n b l e n d e in t w o s a m p l e s can be e x pressed (according to F r e u n d , 1955, p. 163)
as Mg, i 0 Fe J 0 (y = 1.675) a n d M g „ F e 3 5 (y =
1.688). Q u a r t z occurs as small grains. T h e r e
a r e n u m e r o u s accessories (Table 1) and t h e
d y k e s occasionally contain a l m a n d i n e (n =
1.792) mottles 1.5 to 2 cm in d i a m e t e r .
T h e crosscutting m o d e of o c c u r r e n c e of t h e
d y k e s is clearly s h o w n in t h e t e x t u r e ; see
t h e p h o t o m i c r o g r a p h (Fig. 7) of t h e contact
b e t w e e n t h e q u a r t z i t e a n d a dyke.
T h e m o d a l m i n e r a l composition given in
T a b l e 1 s h o w s t h a t t h e a b u n d a n c e s of plagioclase, biotite a n d h o r n b l e n d e v a r y r a n d o m l y
as a f u n c t i o n of q u a r t z a n d do not e x h i b i t a n y
f u n c t i o n a l r e l a t i o n to t h e q u a r t z .
P l o t t e d in Fig. 8 is t h e a b u n d a n c e of h o r n b l e n d e a g a i n s t t h a t of q u a r t z . T h e f i g u r e
demonstrates
that the
hornblende/quartz
r a t i o of t h e d y k e s is scattered, p r o b a b l y owing
to c o n t a m i n a t i o n .
Youngest Precambrian dyke rocks in North Karelia, East Finland
73
Fig. 6. A microtonalite
with plagioclase phenocrysts. lOx. Nic. + . Photo
E. Halme.
Chemical
composition
E x c e p t f o r samples 5 a n d 15, w h i c h w e r e
analysed by wet-chemical methods
(Huhma,
1975), t h e samples collected f r o m t h e microt o n a l i t e d y k e s w e r e assayed by X R F at t h e
Fig. 7. The contact between quartzite and dyke
(quartzite on the left).
lOx. Nic. + . Photo E. Halme.
O u t o k u m p u Oy Geological L a b o r a t o r y of E x ploration. T h e a n a l y t i c a l d a t a of t h e d y k e s
a r e listed in T a b l e 2.
T h e chemical composition is i l l u s t r a t e d by
a M g O — S i 0 2 d i a g r a m (Fig. 9). T h e t h r e e
samples richest in SiO ä (Nos 16—18) consti-
-o
Table 2. Chemical compositions, Niggli values, and CIPW norms of some microtonalite dyke rocks.
1
Si02
TiOs
AI2O3
FeO
MnO
MgO
CaO
Na-'O
KoO
P2O5
53.45
1.23
16.38
8.31
0.07
3.98
6.71
2.48
1.97
0.62
95.20
2
54.59
1.01
17.07
7.10
0.03
4.03
5.68
3.32
1.81
0.38
95.02
3
54.61
1.89
16.35
9.27
0.06
3.30
5.48
1.29
2.84
0.85
95.94
4
56.39
1.28
15.77
9.29
0.05
3.28
3.97
3.19
3.13
0.53
96.88
5
6
56.8
56.82
1.0
0.94
15.94
18.7
7.551 6.37
0.02
0.10
3.22
3.02
5.24
6.25
3.45
3.70
1.75
1.53
0.24
0.45
99.313 93.78
7
56.83
0.87
16.75
5.90
0.02
3.38
6.09
3.49
1.77
0.37
95.47
8
56.88
1.23
16.08
8.20
0.07
2.41
6.35
4.33
1.82
0.62
97.99
9
56.97
1.93
15.74
8.45
0.05
2.71
6.10
2.42
2.14
0.78
97.30
a
18
10
11
12
13
14
15
16
17
56.98
0.82
16.23
5.95
0.03
3.21
4.78
2.08
2.55
0.36
92.99
57.42
0.94
16.02
6.54
0.03
2.84
3.65
3.14
2.45
0.33
93.36
57.54
1.60
15.20
9.59
0.09
2.80
3.56
3.07
3.20
0.69
97.34
57.65
1.13
15.47
7.19
0.04
2.40
4.55
3.06
2.24
0.51
94.24
57.87
0.91
14.95
8.37
0.07
2.08
3.98
3.81
2.22
0.44
94.70
59.27
1.19
18.25
6.07 2
0.08
3.20
4.37
2.83
2.80
0.31
98.42 4
64.34
0.63
15.79
6.00
0.02
1.17
3.75
3.87
1.66
0.41
97.64
67.36 68.55
0.52
0.49
15.68 16.19
5.82
5.03
0.02
0.01
0.87
1.24
4.47
3.51
2.73
4.18
1.58
1.71
0.31
0.31
99.73 100.85
Niggli values
177
186
204
286
184
203
207
191
193
258
276
157
168
187
180
170
195
206
si
30.2
35.2
37.4
37.8
39.8
29.7
32.6
32.2
31.9
29.5
34.0
34.1
29.8
32.5
31.1
al
28.4
31.0
30.8
36.4
34.4
27.2
27.6
23.0
32.7
34.8
35.1
40.8
34.3
35.8
fm
33.3
33.8
32.3
39.7
36.8
40.7
40.5
15.7
19.2
21.1
21.1
21.3
18.2
14.1
12.7
17.4
15.0
15.3
16.1
19.6
21.1
13.6
20.0
c
18.7
18.8
21.5
12.1
16.6
18.0
15.1
15.0
14.1
14.8
14.6
16.7
13.0
16.7
15.7
19.3
alk
10.8
13.5
9.8
16.2
0.28
0.21
0.22
0.37
0.45
0.34
0.41
0.32
0.28
0.39
0.22
k
0.34
0.26
0.59
0.39
0.24
0.23
0.25
0.34
0.36
0.49
0.44
0.34
0.31
0.45
0.26
0.27
0.24
mg
0.50
0.37
0.44
0.39
0.38
0.43
0.46
0.50
4.7
1.5
2.4
2.1
2.9
2.2
2.6
4.0
2.4
0.9
1.9
1.6
ti
2.7
4.5
3.1
2.3
3.0
2.3
0.5
1.1
0.5
1.0
0.7
0.4
0.7
0.5
0.2
0.5
0.8
0.5
0.8
0.8
0.4
1.1
0.7
0.7
P
CIPW norms
Q
C
Or
Ab
An
Di
Hy
II
Ap
6.6
11.6
21.0
27.7
1.3
23.9
2.3
1.5
95.9
5.9
0.1
10.7
28.1
26.0
15.6
3.2
16.8
10.9
21.6
7.1
1.2
18.5
27.0
16.2
21.5
1.9
0.8
95.0
22.2
3.6
2.0
95.9
23.2
2.4
1.3
96.9
5.5
10.3
31.3
29.2
0.2
20.3
1.9
0.6
99.3
11.8
0.2
9.0
29.2
23.0
17.7
1.8
1.1
93.8
9.0
5.1
10.5
29.5
24.8
2.5
16.6
1.7
0.9
95.5
10.8
36.6
19.1
7.1
15.5
2.3
1.5
98.0
14.1
0.2
12.6
20.5
25.2
16.7
2.2
15.1
17.6
21.4
13.9
2.3
14.5
26.6
16.0
10.7
1.9
18.9
26.0
13.1
14.2
1.0
13.2
25.9
19.2
10.5
0.1
13.1
32.2
16.9
14.3
3.3
16.5
24.4
19.7
22.3
1.8
9.8
32.7
15.9
30.4
2.1
9.3
23.1
20.1
25.0
1.8
10.1
35.4
15.4
19.2
3.7
1.8
97.3
17.6
1.5
0.9
93.0
17.5
1.8
0.8
93.4
22.1
3.0
1.6
97.3
17.4
2.1
1.2
94.2
19.2
1.7
1.0
94.7
17.3
2.2
0.7
98.4
12.9
1.2
1.0
97.6
13.0
1.0
0.7
99.7
10.6
1.0
0.7
100.9
Youngest Precambrian dyke rocks in North Karelia, East Finland
75
H o *
"tf w w w
cvi oo cd rh oi
CM
16
14
12
10
q q q
cd ^ cd
6
4
2
qcd öq
o q
cd oi
cm
">
J2 11 10 18J6 | l 7
.15
q q r-j
in o -t
Fig. 8. Hornblende as a function of the quartz
in the microtonalites.
q q q
cd
N N cö^
o t h e r samples.
q
in ^
cm q
c i tjh
H
M
t u t e a g r o u p t h a t d i f f e r s completely f r o m t h e
A n o t h e r g r o u p of t w o samples
(Nos 1 a n d 2) occurs in t h e opposite m a r g i n
q
cd
of t h e d i a g r a m (high MgO a n d low S i 0 2 , in
^
c o n t r a s t to t h e first group).
All t h e o t h e r
samples (excluding No 15) a r e located w i t h i n
a
q q
cd oi
very
narrow
SiO a
zone
in
which
MgO
varies b e t w e e n 2 and 3.4 %>. This g r o u p includes b o t h h o r n b l e n d e - f r e e and h o r n b l e n d e -
q
b e a r i n g rocks.
cd cm
T h e f i r s t g r o u p is f r e e f r o m
h o r n b l e n d e , w h e r e a s t h e second g r o u p conq
tains it in a b u n d a n c e .
q
ö
explanation
e f f e c t of c o n t a m i n a t i o n .
q q
t*- cd
q
cm
t- ö
h
o
h
ö ö ö
f o r these
The most
three
probable
groups
is
the
For example,
nos
16—18 a r e s i t u a t e d in M a a r i a n v a a r a g r a n i t e .
co o ^
cd oo cd
q q
cd cm
(D N M
^ ^ TfH
-H
o
K
%
01
o
•1 '2
4 •
o No h o r n b l e n d e
q
cd iri
cm
O
Ö
co
r> CO
CO CO
cg
o
cd tjh
cm
ÖÖÖ
D - CM
qö
o
oi r^
q t> q
cd oi cd
q
o
o
Hn m
l• fe
C fe
m ^fÖ
e few
u
cy o<
w
hÄ a
o<<
Hornblende-bearing
3 •
lo ^ f—I q
CO CO O ö
-H -sf o
CO CO ^
•
MgO
"
4X
o
i
w
tu^
[> o
q cm a s
lo iri - —
iH
II II o 1!
O O II +
0) <D
fe fe o 9,
O K
q q
c
rH ö Ö
o o
II II
-3
C0 CO•3
•Ö TJ
oo
•? 1 7ni ns
a> CD
fe fe B
TH <Nm **
9»
8* »13
• 14
o 17
o18
50
60
Si0
70
%
2
Fig. 9. MgO — SiOa diagram of microtonalites.
76
Aarto
Huhma
Fig. 10. Photomicrograph
of lamprophyre. Biotite
(dark) and apatite (light)
phenocrysts clearly visible. 20x. Nie.—. Photo E.
Hänninen.
Lamprophyre dykes
Petrography
Mode
T h e rock is d a r k g r e y or almost black a n d
f i n e - g r a i n e d w i t h n u m e r o u s small
mica
flakes. S o m e of t h e micas occur as l a r g e
b u n d l e s one s q u a r e c e n t i m e t r e or m o r e in
size. P h e n o c r y s t s of o t h e r m i n e r a l s a r e also
present, b u t t h e y a r e not as c h a r a c t e r i s t i c
and conspicuous as is t h e mica (Fig. 10).
of
occurrence
In a d d i t i o n to t h o s e described by H a c k m a n
(1914), t h e E x p l o r a t i o n Dept. of O u t o k u m p u
Oy has discovered m o r e l a m p r o p h y r e dykes,
b r i n g i n g t h e c u r r e n t n u m b e r of k n o w n d y k e s
o r d y k e s w a r m s u p to six (Fig. 1).
The width
of t h e d y k e s v a r i e s f r o m a f e w c e n t i m e t r e s
to 70 centimetres, b u t u s u a l l y f r o m 25 to 50
centimetres.
In some
localities
the
dykes
h a v e been e n c o u n t e r e d in only one outcrop,
w h e r e a s in o t h e r s t h e y can be t r a c e d f o r over
100 m e t r e s f r o m one outcrop to t h e n e x t . T h e
d y k e s u s u a l l y occur alone, b u t in some places
two or t h r e e p a r a l l e l d y k e s lie close together.
T h e contacts of t h e d y k e s a r e v e r y s h a r p
a n d rectilinear. T h e p r e d o m i n a t i n g t r e n d is
N73W; only r a r e l y do t h e y d e p a r t f r o m this
direction a n d t h e n v e r y slightly. T h e dip is
s u b v e r t i c a l to vertical. T h e d y k e s cut b o t h
t h e b a s e m e n t gneiss and t h e p e g m a t i n e veins
in it. Locally t h e y include small f r a g m e n t s
of c o u n t r y rock.
T h e g r o u n d m a s s consists of v e r y f i n e g r a i n e d biotite, plagioclase (c. An a ) ), potassiu m f e l d s p a r , q u a r t z , apatite, c a r b o n a t e , epidote, ilmenite, sphene, rutile, spinel, b a r i t e
and zircon.
T h e m i n e r a l composition w a s
d e t e r m i n e d by X - r a y techniques, t h e rock
being too f i n e - g r a i n e d for t h e m i n e r a l s to
be i d e n t i f i e d w i t h c e r t a i n t y b y optic methods.
Biotite, augite, apatite, orthoclase, calcite a n d
q u a r t z occur as pehnocyrsts, w h e r e a s calcite
and q u a r t z o f t e n exist as t h e filling of
amygdules.
Chemical
composition
T w o w e t - c h e m i c a l analyses of t h e l a m p r o p h y r e d y k e s a r e given: t h e f i r s t one is by
Youngest Precambrian dyke rocks in North Karelia, East Finland
Table 3. Chemical composition of the lamprophyre dykes.
SiOo
TiO->
ZrO
ai2o3
Cr 2 0 3
Fe->Oa
Feb
MnO
MgO
CaO
BaO
SrO
Na->0
k>6
P->Oä
S
Cl
CO»
H>0 +
H>0—
1
2
43.40
1.98
n.d.
12.71
n.d.
1.94
5.80
0.34
8.64
9.67
n.d.
n.d.
3.06
4.66
3.44
0.27
0.10
2.56
0.78
0.17
45.51
1.61
0.13
13.43
99.52
98.44
0.01
3.27
5.25
0.12
5.78
7.72
1.19
0.60
3.84
3.94
2.91
0.22
n.d.
1.34
1.24
0.33
Cu
Zn
Ni
Co
Pb
108 ppm
218 »
75 »
38 »
150 »
1. The analysis by Hackman (1914)
2. The analysis of the sample A159
n.d. = not determined
H a c k m a n (1914) (No 1 in T a b l e 3) a n d t h e
o t h e r t h a t of s a m p l e A159 (No 2 in T a b l e 3),
analysed at t h e O u t o k u m p u Oy Geological
L a b o r a t o r y of E x p l o r a t i o n .
77
m a p sheet 4311 05D (6996.60/435.09) a n d one
f r o m a l a m p r o p h y r e d y k e (A159), at Niiniv a a r a , Kaavi, on m a p sheet 4311 07B (6988.78/
442.94) (see Fig. 1 a n d T a b l e 5).
T h e m i c r o t o n a l i t e d y k e occurs in K a r e l i a n
q u a r t z i t e (Fig. 5) and t h e l a m p r o p h y r e d y k e
in P r e k a r e l i a n gneiss. T h e d a t i n g s w e r e based
on zircon a n d s p h e n e (Table 5).
T h e age of t h e l a m p r o p h y r e d y k e w a s
d e t e r m i n e d f r o m t h r e e zircon f r a c t i o n s (Fig.
12). T h e zircon in f r a c t i o n A is clear a n d
seems to h a v e existed in l a r g e crystals t h a t
w e r e b r o k e n d u r i n g crushing. This zircon
f r a c t i o n gives an age of 1830 Ma, w h i c h is
also t h e age of t h e dyke.
T h e zircons in f r a c t i o n C a r e r o u n d e d . T h e y
s h o w an age of 2460 Ma according to t h e continuous d i f f u s i o n model of W a s s e r b u r g (1963)
a n d a r e obviously f r o m an e x t e r n a l source.
F r a c t i o n B is an a d m i x t u r e . T h e results of
t h e s p h e n e d a t i n g s a r e s u m m a r i z e d in T a b l e
5 and in Fig. 12.
T h e zircon g r a i n s s e p a r a t e d f r o m t h e m i c r o tonalite d y k e (A940, T a b l e 5) w e r e all r o u n ded and r e s i d u a l and g a v e an age of 2640 Ma
according to t h e continuous d i f f u s i o n model
Ab +An + Ne
T h e chemical composition indicates t h a t
t h e s e rocks contain conspicuous a m o u n t s of
K and P. T h e i r Ba, Sr, a n d Zr c o n t e n t s a r e
also m a r k e d .
C o m p a r i s o n of t h e chemical compositions,
n o r m a t i v e m i n e r a l s a n d Niggli v a l u e s of t h e
c a m p t o n i t e s (1—5) a n d l a m p r o p h y r e s in K a a vi (6—7) (Table 4) indicates the dissimilarities
b e t w e e n t h e s e groups. See also Fig. 11.
Dating
T w o s a m p l e s w e r e d a t e d : one f r o m a m i c r o t o n a l i t e d y k e (A940) at M ä n t y j ä r v i , K a a v i , on
Table 4. Diagram after Fig. 2 by Rock (1977, p. 136).
Dashed line indicates the basalt screen of Manson
(1967).
78
Aarto
Huhma
Table 4. Chemical compositions, CIPW norms and Niggli values of lamprophyres.
1
2
3
4
5
6
7
40.70
3.86
16.02
5.43
7.84
0.16
5.43
9.36
3.23
1.76
0.62
44.4
3.3
14.3
3.9
7.4
n.m.
7.1
10.6
3.2
1.7
n.m.
44.67
3.26
14.35
4.50
7.19
n.m.
7.02
9.45
2.99
1.91
n.m.
43.01
2.72
14.64
4.83
7.26
n.m.
6.78
10.25
3.27
1.90
n.m.
42.96
2.75
14.82
4.64
7.44
n.m.
6.68
10.18
3.41
2.02
0.71
43.40
1.98
12.71
1.94
5.80
0.34
8.64
9.67
3.06
4.66
3.44
45.51
1.61
13.43
3.27
5.25
0.12
5.78
7.72
3.84
3.94
2.91
94.41
95.9
95.34
94.66
95.61
95.64
93.83
CIPW norms
Or
Ab
An
Lc
Ne
Dx
Hy
Ol
Mt
II
Ap
10.40
14.09
24.02
7.17
14.67
7.42
—
7.87
7.33
1.47
10.05
13.36
19.63
—
7.43
26.30
11.23
10.14
19.66
—
9.50
24.92
_
7.06
7.00
5.20
n.m.
11.94
12.02
19.17
—
9.12
21.37
13.81
12.35
7.18
10.76
7.34
14.64
7.20
5.66
6.27
n.m.
11.29
17.55
20.10
—
4.20
21.31
_
8.19
6.53
6.20
n.m.
Niggli values
si
al
fm
c
alk
k
mg
ti
p
96
22.2
44.3
23.5
10.0
0.26
0.43
6.82
0.62
102
19.3
45.1
26.0
9.6
0.29
0.54
5.68
n.m.
105
19.9
46.7
23.8
9.7
0.30
0.53
5.78
n.m.
98
19.7
45.2
25.1
10.0
0.28
0.51
4.67
n.m.
Si0 2
TiOg
AI2O3
Fea03
FeO
MnO
MgO
CaO
NaaO
K->0
P2O5
8.40
6.73
5.22
1.68
15.02
2.81
3.76
8.15
23.28
23.06
7.77
—
5.11
9.21
_
10.40
4.74
3.06
6.89
98
19.9
44.8
24.8
10.5
0.28
0.51
4.71
0.69
100
17.3
45.0
23.9
13.9
0.50
0.66
3.44
3.37
120
20.8
41.0
21.8
16.4
0.40
0.55
3.19
3.24
_
_
_
1. Average of 15 camptonites (Johannsen, op.cit., Vol. IV, p. 65)
2. Average of 14 camptonites (Nockolds, 1954)
3. Average of 78 camptonites (Metais and Chayes, 1963)
4. Average of 107 camptonites (Rock, 1977)
5. Estimated mean composition of 95 camptonites (Rock, 1977)
6. Lamprophyre by Hackman (1914)
7. Sample A159
n.m. = not mentioned
of W a s s e r b u r g (1963); t h u s a n e x t e r n a l source
is suggested.
The microtonalite dyke contains abundant
s p h e n e w i t h an age of 1850 Ma. It is, h o w ever, u n k n o w n w h e t h e r this can b e t a k e n as
t h e age of t h e d y k e or w h e t h e r t h e s p h e n e is
m e t a m o r p h i c in origin.
Discussion
Microtonalites
The microtonalites are fine-grained dyke
rocks of tonalitic (or q u a r t z dioritic) composition.
Youngest P r e c a m b r i a n d y k e rocks in North Karelia, East Finland
CO
C - CD O l
CM O l CM O l CO
CO O l
C-
C D CO
CO ^
O l CO
^
O I O O l C D CM
t - O l CM i ß I ß
Iß
^
I ß CO
T P CO
CM - H
O
T»<
CO CO
•—i rt 4 CO ^t 1
^
C— CM L O O
LO
t - 0 0 T-H TjH CO
CO O l CM CM
Lß t >
M ^
O OJ
^
Iß
l>
i ß rjn i ß O C D
CM CO »—( i ß i ß
CO i ß O l
H
CO
O
C D CO ^
Ol C-
ifi
H M
T f CM
CO
t> .
Iii
T h e usage of t h e t e r m s t o n a l i t e and q u a r t z
diorite is s o m e w h a t a m b i g u o u s in t h e l i t e r a t u r e and o f t e n r e f e r s to t h e s a m e rock.
J o p l i n (1964) calls rocks w i t h less t h a n 10 %>
q u a r t z , q u a r t z diorite a n d those w i t h m o r e
t h a n 10 °/o q u a r t z , tonalite.
In t h e classification by J o h a n n s e n (1941,
Vol. II, p. 378), all t h e rocks described in t h e
p r e s e n t p a p e r f a l l into t h e class of tonalites
228P. His q u a r t z b o u n d a r y is at 5 °/o.
R e f e r r i n g to tonalites, S h a n d (1949) states:
»This division includes all o v e r s a t u r a t e d
rocks in w h i c h t h e a n o r t h i t e molecule exceeds
t h e orthoclase molecule, r e g a r d l e s s of t h e
n a t u r e of t h e d a r k minerals».
According to t h e s y s t e m by S h a n d , t h e
rocks u n d e r consideration belong to tonalites,
m o r e precisely to indices X O / and XO<5.
S a m p l e s 4 and 14 (index XOß), h o w e v e r ,
S h a n d w o u l d h a v e considered as g r a n o d i orites.
According to t h e m o r e r e c e n t classification
by I U G S (1973) t h e rock samples in T a b l e 1
a r e tonalites b u t some of t h e m a r e close to
q u a r t z diorite; No 5 is t h e only q u a r t z diorite.
T h e c o m p a r i s o n b e t w e e n t h e m e a n of t h e
18 microtonalites in t h i s p a p e r a n d t h a t of
t h e 19 t o n a l i t e s of J o h a n n s e n ( J o h a n n s e n ,
op. cit. Vol. II, p. 386) s h o w s t h a t t h e s i m i l a r ity is n o t v e r y conspicuous (Table 6).
On the o t h e r hand, t h e Niggli v a l u e s of the
m e a n of t h e m i c r o t o n a l i t e s (No 1) a r e q u i t e
close to t h a t of Niggli's tonalitic m a g m a t y p e
(No 2) (Niggli, op. cit.):
3
+ : O ! COcd COcd
CO^^CO^ CO
^
+ cd cd
CU 0)
c ÜÜc c S
oü uo o a; d) O öCU
Jti
.h°£ aX a .3"•S
Q
N m
N
N N W3 Cfl
<
CQ O Q P
oi
LO
<
79
Niggli values
si
al
fm
c
alk
k
mg
ti
P
201
32.7
34.4
17.7
15.2
0.32
0.39
2.6
0.7
200
33
33
22
12
0.40
0.50
n.d.
n.d.
80
Aarto
Huhma
2800,
NIINIVAARA
A159
2460^
1900.
1830^/+b
D
SIZE
(g/cm ) FRACTION
1000
A159A
B
C
D
0
1.0
3,0
5,0
2 0 7 p b / 235U
ZIRCON
ZIRCON
ZIRCON
SPHENE
11,0
T h e age of t h e m i c r o t o n a l i t e d y k e s h a s not
been established for s u r e b e c a u s e t h e d y k e
only c o n t a i n s r e s i d u a l zircons (2460 Ma). T h e
s p h e n e age, 1850 Ma, can be i n t e r p r e t e d as
t h e age of m e t a m o r p h i s m . Geological evidence, h o w e v e r , suggests t h a t it is also t h e
age of t h e dyke.
T h e m i c r o t o n a l i t e d y k e s crosscut t h e M a a r i a n v a a r a g r a n i t e t h e age of w h i c h is 1860 Ma.
T h e o t h e r limit of t h e age is set b y t h e l a m p r o p h y r e d y k e t h a t is 1830 Ma old.
According to Rock (1977, p. 125), l a m p r o p h y r e s a r e a l w a y s t h e latest m a n i f e s t a t i o n of
igneous activity in a given region, accomp a n y i n g aplites, p e g m a t i t e s or c a r b o n a t i t e s .
T h u s t h e age of t h e m i c r o t o n a l i t e d y k e s p r o b a b l y falls b e t w e e n 1860 Ma a n d 1830 Ma.
T h e r e is no reason to d o u b t t h a t t h e real age
of t h e m i c r o t o n a l i t e d y k e s is a b o u t 1850 Ma.
Lamprophyres
Hackman
camptonites
According
d y k e rock
(1914) called l a m p r o p h y r e d y k e s
and ouachitites.
to t h e chemical composition, t h e
belongs to Niggli's shonkinitic
+46
+46
+46
3.4-36
13,0
+ 100
100-200
ROUNDED
+ 200
15,0
U
(«g/g)
56
69
165
102
17,0
Fig. 12. Concordia diagram for U-Pb ratios of
zircons
and
sphene.
Lamprophyre A159, Niinivaara, Kaavi.
m a g m a t y p e (Niggli, 1923, pp. 193, 395), as do
most c a m p t o n i t e s (Niggli, op. cit., p. 353).
Hence the n a m e s used b y H a c k m a n , a l t h o u g h
comprehensible, a r e r e j e c t e d in this p a p e r .
T h e n a m e c a m p t o n i t e ( J o h a n n s e n , 1941,
Vol. IV, p. 64) w a s given to d a r k g r e y to
black d y k e rocks of basaltic h a b i t t h a t occur
as satellites of foyaitic and t h e r a l i t i c p l u t o nites. T h e y h a v e not b e e n f o u n d in t h e a r e a
n o w discussed.
According to J o h a n n s e n (op. cit.), c a m p t o nites contain p h e n o c r y s t s of biotite, b a r k e vikite a n d t i t a n a u g i t e , a n d o f t e n olivine in
a f i n e - g r a i n e d to d e n s e g r o u n d m a s s .
The
g r o u n d m a s s consists of plagioclase l a t h s a n d
microlites of a m p h i b o l e a n d augite.
According to Niggli, c a m p t o n i t e s m a y also
contain n e p h e l i n e , leucite a n d o t h e r f e l d spathoides (Niggli, op. cit., pp. 214—215).
In t h e opinion of S t r e c k e i s e n (1978) t h e
m i n e r a l composition of c a m p t o n i t e s includes
a m p h i b o l e (barkevikite, kaersutite), t i t a n a u gite, olivine, a n d / o r biotite in a g r o u n d m a s s
of l a b r a d o r i t e , amphibole, p y r o x e n e w i t h
s u b o r d i n a t e a l k a l i n e f e l d s p a r a n d foids; ±
apatite, iron ore, calcite, zeolite etc.
Youngest Precambrian dyke rocks in North Karelia, East Finland
Rock (1977) gives t h e following d a t a on of
the camptonites:
Olivine
free
Table 6. Averages of the chemical compositions,
Niggli values and CIPW norms of the microtonalites and tonalites.
1
Olivine
bearing
Amphibole only
»
+ clinopyroxene
»
» + biotite
»
+ biotite
Clinopyroxene + biotite
Biotite only
14
40
13
10
1
14
56
18
6
2
—
—
Totals
78
92
Ouachitites, t h e o t h e r n a m e proposed by
H a c k m a n , a r e r e g a r d e d as o l i v i n e - f r e e biot i t e - m o n c h i q u i t e s , w h i c h occur as d a r k d y k e
rocks in n e p h e l i n e - s y e n i t e . T h e m o n c h i q u i t e
in O u a c h i t a R i v e r in A r k a n s a s has t h e f o l l o w ing m o d e : analcime 15, d a r k mica 44, p y r o x ene 26, m a g n e t i t e and p y r i t e 6, calcite 9
( J o h a n n s e n , op. cit., Vol. IV, pp. 391, 382, 384),
(cf. Niggli, op. cit., p. 215).
T h e n a m e ouachitite (and monchiquite) is
t h u s obviously i n a p p r o p r i a t e to t h e l a m p r o p h y r e discussed here.
T h e m i n e r a l composition of k e r s a n t i t e s
given b y S t r e c k e i s e n (op. cit.) is as follows:
plagioclace
(oligoclase—andesine),
biotite,
augite; ± a l k a l i n e feldspar, h o r n b l e n d e , olivine, q u a r t z , apatite, iron ore, calcite, etc.
According to B e u g e a n d K r a m e r (1977, p.
80), t h e k e r s a n t i t e s a r e alkali-, especially
K - d o m i n a n t a n d t h e y a r e also r e l a t i v e l y rich
in P, Ba, and Zr.
Thus, t h e l a m p r o p h y r e described in t h e
p r e s e n t p a p e r r e s e m b l e s k e r s a n t i t e s to some
degree, a l t h o u g h k e r s a n t i t e s a r e m o r e acidic
containing c. 50 p e r cent SiO;> (Metais &
Chayes, 1963).
W i t h o u t r e n a m i n g t h e rock u n d e r discussion, it can be described as ' b i o t i t e - l a m p r o p h y r e of t h e shonkinitic m a g m a t y p e ' (cf.
Niggli, op. cit.), or 'mesocratic b i o t i t e - l a m p r o p h y r e ' (cf. J o h a n n s e n , op. cit.). Or w h y not
81
Si0 2
TiO?
2
58.31
1.09
16.25
n.d.
7.28 (tot.Fe)
0.05
2.73
4.92
3.14
2.55
0.48
66.22
0.39
15.66
1.22
3.11
0.04
2.15
4.56
4.24
1.42
0.05
96.80
99.06
Niggli values
si
al
fm
c
alk
k
mg
ti
P
201
32.7
34.4
17.7
15.2
0.32
0.39
2.6
0.7
256
35.6
26.1
18.9
19.4
0.18
0.47
1.13
0.08
CIPW norms
Q
c
or
ab
an
di
hy
il
ap
13.3
1.2
12.0
26.6
20.6
0.6
18.2
2.1
1.1
AI2O3
FejOg
Feb
MnO
MgO
CaO
NagO
KJO
P2O5
20.63
0
8.31
35.88
19.50
2.33
11.40
0.74
0.12
1. Average of the 18 microtonalites (Table 2)
2. Average of 19 tonalites (Johannsen, op.cit. Vol.
II, p. 386)
call it 'niinilite'
after the lake
Niinilampi
as a l r e a d y proposed b y H a c k m a n .
R a t h e r t h a n to discuss t h e n a m e of the
l a m p r o p h y r e in K a a v i , t h e m a i n p u r p o s e of
t h e p r e s e n t w o r k w a s to r e p o r t t h e age, 1830
Ma, of t h e y o u n g e s t rock f o u n d in N o r t h
Karelia.
Acknowledgements
— The author is indebted to
Outokumpu Oy for permission to publish this
paper. The samples were chemically analysed at
82
Aarto
Huhma
the Outokumpu Oy Geological Laboratory of Exploration. The age determinations were made
at the Geological Survey of Finland by Mr Hannu
Huhma. Dr. P. Rouhunkoski and Dr. T. A. Häkli
read the manuscript and Mrs Gillian Häkli "translated it into English. To all these persons I express my cordial thanks. And last but not least
I thank my wife for her help.
References
Beuge, P. and Kramer, W. (1977) Lamprophyre
Ostthüringens und ihre anomale Quecksilbergehalte im Ergebnis endogener und exogener
Anreichungsprozesse. Sehr. geol. Wiss., Berlin
8, 79—99.
Freund, H. (1955) Handbuch der Mikroskopie in
der Technik. Bd. IV. Teil 1: Mikroskopie der
Gesteine.
Umschau Verlag, Frankfurt am
Main.
Hackman, V. (1914) Über Camptonitgänge im mittleren Finnland. Bull. Comm. Géol. Finlande 42,
1—18.
Huhma, A. (1970) Short description of the geology
of the Outokumpu district. In Huhma, A. and
Huhma, M., Contribution to the geology and
geochemistry of the Outokumpu region. Bull.
Geol. Soc. Finland 42, 57—88.
— (1971) Maps of the Pre-Quarternary rocks,
4222 Outokumpu, 4224 Kontiolahti and 4311
Sivakkavaara. Geological Map of Finland,
1 : 100 000. Geological Survey of Finland.
— (1975) Precambrian rocks of the Outokumpu,
Polvijärvi and Sivakkavaara map-sheet areas.
English summary: 110—151. Suomen geologinen kartta, Kallioperäkartan selitykset 4222
Outokumpu, 4224 Polvijärvi, 4311 Sivakkavaara. Geological Survey of Finland.
— (1976) New aspects to the geology of the Outokumpu region. Bull. Geol. Soc. Finland 48,
5—24.
IUGS (1973) Plutonic rooks: Classification and
nomenclature. Geotimes, October 1973, 26—30.
Johannsen, A. (1941) A descriptive petrography
of the igneous rocks. Univ. of Chicago Press,
Chicago, Illinois.
Joplin, G. (1964) A petrography of Australian
igneous rocks. Angus and Robertson, p. 187.
Manson, V. (1967) Geochemistry of basaltic rocks:
major elements. In: H. H. Hess and A. Poldervaart (Eds.), Basalts. Wiley, New York, N.Y.,
215—270.
Métais, D. and Chayes, F. (1963) Varieties of
lamprophyre.
Ann. Rep. Geophys.
Lab.,
Wash. 02, 156—157.
Niggli, P. (1923) Gesteins- und Mineralprovinzen,
Band I. Verlag von Gebrüder Borntraeger,
Berlin.
Nockolds, S. R. (1954) Average compositions of
some igneous rocks. Bull. Geol. Coc. Am., 65,
1007—1032.
Rock, N. M. S. (1977) The nature and origin of
lamprophyres: Some definitions, distinctions,
and derivations. Earth Sei. Rev. 13 (1977), 123—
169.
Shand, J. S. (1949) Eruptive rocks. Murby & Co.,
London, 382—385.
Simonen, A. (1980) Precambrian in Finland. Geol.
Surv. Finland Bull. 304, 58 pp.
Streckeisen, A. (1967) Classification and nomenclature of igneous rocks. N. Jb. Miner. Abh.,
107, 2, p. 175.
— (1978) Classification and nomenclature of volcanic rocks, lamprophyres, carbonatites and
melilitic rocks. N. Jb. Miner. Abh., 134, 1, 1—14.
Wasserburg, G. J. (1963) Diffusion processes in
lead-uranium systems. J. Geophys. Res. 68,
4823—4846.
Manuscript received, November 16, 1980.