2013

Abstracts Travel
Program Organizing committee

 Geochemical peculiarities of phlogopite from Devonian alkaline picrite found in the Braginsky and Loevsky saddle (Belarus)

Ignatkevich E.S.*, Varlamov D.A.**

*Belarusian scientific research and designed institute of oil, Gomel, Belarus;

**Institute of Experimental Mineralogy RAS, Chernogolovka, Rassia.

elena_krajneva@mail.ru

 

This paper is one of the first reports on the chemical composition of dark-colored rock-forming minerals of late Devonian magmatic rocks of the Braginsky and Loevsky saddle (Belarus). Samples of alkaline picrite from the core of the drill hole Vasilyevskaya 1 (depth 1785 m)  were selected for the research.

The mica forms phenocrysts and microcrystals in the picrite. In accordance with the IMA recommended nomenclature [3] the composition of micas from alkaline picrite is approximated to the composition of the phlogopite (table). Attention is drawn to a high content of titanium oxide in the phlogopite (6,77-9,48 wt.% TiO2) as a criteria of high degree of differentiation. A high content of titanium oxide in the melt increases a distribution ratio of barium in the mica [1]. Barium enrichment is significant for the phlogopite in point. Its content reaches about 4 wt. % of BaO, which makes it possible to call the phlogopite one of barium [3]. Magnesium and iron oxides content ranges 6-7 wt. % and, in general, it corresponds to the composition of the phlogopites of ultrabasic rocks (Mg/Fe > 3) [1]. Alumina content is increased in these phlogopites (Al2O3 = 10,9-13,1 wt.%), which suggests high-temperature conditions of their crystallization.

 

Table. Chemical compound (comp. %) and formular coefficientes of phlogopite

Oxide

SiO2

TiO2

Al2O3

Cr23

Fe2O3

MnO

MgO

CaO

Na2O

K2O

Ni

Ba

Sum

Comp. %

39.9

6.6

12.5

0.0

7.5

0.1

19.8

0.2

0.4

8.8

0.0

4.0

99.8

38.8

6.9

13.0

0.0

7.8

0.1

19.9

0.2

0.6

9.2

0.2

3.9

100.4

Element

Si

Ti

Al

Cr

Fe

Mn

Mg

Ca

Na

K

Ni

Ba

Formula coefficient

3.03

0.38

1.12

0.00

0.43

0.01

2.24

0.01

0.06

0.85

0.00

0.12

12.00

2.94

0.39

1.16

0.00

0.44

0.01

2.24

0.01

0.08

0.89

0.01

0.12

12.00

 

Wide variations of a chemical composition of phlogopite allow its use as an indicator to diagnose rocks. On the correlation graph TiO2 Al2O3 of R.H. Mitchell [2] the phlogopites in point get in the minette field (figure).

 

 

 

 

 

 

 

 

 

 

 

Figure. Diagram Al2O3 TiO2 for phlogopite

 

Identified geochemical peculiarities of phlogopite indicate alkaline conditions of crystallization and a high degree of differentiation of magma.

Literature

 

1.      Antipin V.S., Kovalenko V.I., Ryabchikov I.D. Distribution ratios of rare elements in magmatic rocks. Moscow: Nauka, 1984. 253p.

2.      Mitchell R.H. Kimberlites, Orangeites and Related rocks // Plenum. Publications Inc. New York. 1995.

3.      Rieder ., Cavazzini  G., D'yakonov Y. S. & others. Nomenclature of the micas // The Canadian Mineralogist. 1998. V. 36. pp.41-48.