Minerals
of REE in the komatiitic series rocks of the South-East Fennoscandia.
Kulikova V.1,
Kulikov V.1, Bychkova Ya.2
1Institute
of Geology of the Karelian Research Center RAS, Petrozavodsk, Russia,
vkulikova@onego.ru
2Institute
of geochemistry and analytical chemistry RAS, Moscow, Russia,
bychkova@geokhi.ru
During the study of komatiitic
basalts and their comagmatic plutonic rocks of Paleoproterozoic Windy Belt rift
(in this case, the Goletz mountain on NW extremities of the range with the same
name locates on the territory of Karelia and the Arkhangelsk region) from the
top of the variolies enriched part of a lava flow (fig. 1) authors obtained new
data on mineralogy. By the help of microanalyzer «INCA Enerdgy 350» on the basis
of a scanning electronic microscope «VEGA II LSH» in the Institute of geology
Karelian SC of the Russian Academy of Sciences the main minerals were diagnosed
and research, such as: zone plagioclases and pyroxenes, rare quartz,
chromespinelides and ore minerals (native iron, pentlandite, chalcopyrite, rare
sphalerite, native silver with uranium, and also zircon, etc.). Preparation of
the device for work and its sizing was executed by A.N.Ternovoy. Under the
maintenance of main components composition of minerals change. Plagioclase in
intervals of (%): Al2O3 - 22.75 - 27.92, SiO2 - 40.02 - 43.82, CaO - 22.72 –
23.91, FeO – 7.03 - 11.36, sometimes with MgO, TiO2, Cr2O, etc. Pyroxenes, on
the average (%):SiO2 - 54.19, TiO2 - 0.80, Al2O3 - 5.45, MgO - 16.95, FeO -
10.84. K2O - 0.26, CaO - 11.51. Earlier maintenances of rare-earth elements (ICP-MS
in Laboratory of mechanisms and transports in geology, Toulouse, France) in the
rocks (fig. 2) have been specified. Allocating spectra in some covers and in
various differentiators of intrusions have uniform configuration and reflect
processes of the fractionation in magmatic chambers (the most differentiated
rocks accumulate REE). For the first time authors established the appearance of
La and Ce in the field spars and, presumably, cerite, (fig. 3, tab. 1).
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Fig. 1. Section through
Golets mountain. By V.V. Kulikova on the base of works in 1984-1987,
including V.S.Kulikov, V.D.Sljusarev, A.N.Semenov data (1963) . 1 -
deposits of unstated age; 2 – shaled lavas; 3 - pillow lavas with
distinct column like separateness in the base of covers; 4 – massive
zones of streams; 5 - pillow lavas; difficult differentiated covers (6 –
8): 6 – roof slag zones with strike structures, 7 – layering of strike
and spinifex structures with variolites, 8 – ultramafic rocks; 9 –
almond basalts; 10 – metamorphosed tuff and tuff-conglomerate of Vilenga
retinues. 11 – numbers of covers, including on withdrawing from a cut
line. 12 –Golets geographical point. Breaks are shown by stroke – a
dotted line.
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Fig. 2. Allocating of
normalized on chondrite (Evensen et al., 1978) maintenances REE of Rujga
intrusion (1-3) and some covers of Golets (4-6). 1 – peridotite, 2 –
melano-gabbronorite, 3 – gabbro, 4 – cumulative komatiite. 5 –
high-magnesia komatiitic basalt (HMKB), 6 – low-magnesia komatiitic
basalt (LMKB). |
Probably, if values negative or
close to zero εNd for volcanic rocks of Golets (-0.4 ± 0.9) and intrusive rocks
of the Rujga massif (-2.0 ± 0.8) can testify to the enriched character of mantle
source for there melts or their contamination by crust substance during
introduction and crystallization. Composition of the field spars enriched by
light REE testify similar process during elevating and outpouring of a lava in
the conditions of the top part of the earth crust.
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Fig. 3. Examples of Ce-including
area in field spars of Golets (tab. 1). |
Table 1. Composition of Ce-including
field spars from komatiitic basalts of Golets (a range the Windy Belt, SE
Fennoskandia)
|
№№
of
specters |
Components
(%) in plagioclase
(fig. 3)
|
|
SiO2 |
Al2O3 |
FeO |
MgO |
CaO |
BaO
|
P2O5 |
La2O3 |
Ce2O3 |
|
3 - 1 |
|
10 |
39.75 |
24.21 |
11.28 |
|
23.06 |
|
|
|
1.70 |
|
11 |
39.55 |
24.50 |
11.30 |
|
23.64 |
|
|
|
1.01 |
|
12 |
38.20 |
24.83 |
10.67 |
|
22.24 |
|
|
1.93 |
2.13 |
|
13 |
38.28 |
25.08 |
10.43 |
|
21.88 |
|
|
1.90 |
2.43 |
|
14 |
40.38 |
24.39 |
11.32 |
|
22.94 |
|
|
|
0.96 |
|
20 |
39.53 |
24.98 |
11.14 |
|
23.22 |
|
|
|
1.13 |
|
3-3 |
|
11 |
40.03 |
23.50 |
10.00 |
|
21.08 |
|
|
2.26 |
3.13 |
|
13 |
40.31 |
24.12 |
9.85 |
|
20.79 |
|
|
2.04 |
2.88 |
|
14 |
43.82 |
22.91 |
9.60 |
|
19.66 |
|
|
1.70 |
2.31 |
|
18 |
48.66 |
20.41 |
9.21 |
0.52 |
19.11 |
|
|
0.80 |
1.29 |
|
19 |
41.30 |
23.88 |
10.84 |
|
22.40 |
|
|
|
1.58 |
|
3-4 |
|
1 |
39.77 |
23.18 |
10.43 |
|
20.68 |
|
|
2.38 |
3.56 |
|
|
2-6 |
|
3 |
39.37 |
23.74 |
9.83 |
|
19.95 |
0.82 |
|
2.94 |
3.35 |
|
4 |
40.87 |
23.51 |
10.03 |
|
20.68 |
|
|
|
2.72 |
|
5 |
41.02 |
23.65 |
11.43 |
|
22.54 |
|
|
|
1.36 |
|
2 |
41.42 |
23.17 |
11.94 |
|
22.73 |
|
|
|
0.73 |
|
9 |
41.34 |
23.54 |
11.28 |
|
22.54 |
|
|
|
1.30 |
|
3-7 |
|
5 |
39.36 |
22.22 |
12.21 |
|
19.51 |
|
|
2.87 |
3.82 |
|
6 |
40.67 |
21.88 |
12.44 |
0.51 |
21.11 |
|
|
1.38 |
2.01 |
|
Composition of minerals
– 3-8 |
|
2 |
40.57 |
22.70 |
12.08 |
|
22.40 |
|
|
0.99 |
1.27 |
|
9 |
38.05 |
20.52 |
12.12 |
|
19.36 |
|
0.72 |
3.77 |
5.46 |
|
8 |
39.68 |
21.66 |
11.75 |
|
19.95 |
|
|
2.83 |
4.13 |
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