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).

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.

 

 

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.

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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