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Petrurgiya of the traps of Vendian Volyn-Brest province
Kuzmenkova O.F.*,
Barantseva S.E.**, Poznyak A.I.**,
Lugin V.G. **
*
Belorussian Geological Exploration Research institute, Minsk, Belarus,
kuzmenkovaof@mail.ru
**Belorussian State
Technological University, Minsk, Belarus,
keramika@bstu.unibel.by
The
glass is regarded as a supercooled melt of high viscosity in petrurgy of
basaltic casting [3, 5]. Different crystallization schemes of basaltic
melt, controlled by defined oxygen fugacity and the degree of
nonequilibrium of melting process (cooling time) are used to get
petrositalls: pyroxene-plagioclase in the case of equilibrium
crystallization; pyroxene in the case of highly nonequilibrium
conditions (pyroxene includes
iron minals and Cermak molecules); magnetite- pyroxene in the case of
hypothermia in an oxidizing atmosphere (pyroxene has lowiron calcium and
magnesium content). Features of
glass formation, structure and behavior of glass
during cooling (crystallization properties) have a practical importance
for the control of technological processes of obtaining
glass-crystalline materials with required properties.
We
studied samples of two petrochemical types of basalts of Low Vendian (Neoproterozoic)
trap formation of Volyn-Brest magmatic province (VBP) [6]. Only 3 bulk
samples weighing 2.5 kg, consisting of 13 point samples, taken from
different parts of the basalt flows. Tholeiitic basalts of the normal
range of the upper volcanic strata of VBP from the career Politci-2
(Ivanovo village, Vladimirets district, Ukraine), wt%: SiO2 -
47,34; TiO2 - 1,50; Al2O3 - 14,33; Fe2O3
- 3 20; FeO - 8,62; MnO - 0,25; MgO - 7,71; CaO - 10,99; P2O5
- 0,21; Na2O - 2,29; K2O - 0,35; LOI - 2,03; Σ -
100.51 (wet chemistry method,
M.P. Semenenka Institute
for Geochemistry, Mineralogy and Ore Formation, National Academy of
Sciences of Ukraine),
and borehole 776, depth 187.0 - 218.0 m (Novoselki village, Malorita
district, Belarus), wt%: SiO2 - 49,75; TiO2 -
2,60; Al2O3 -
13,48; Fe2O3t - 14,55; MnO
- 0,19; MgO - 5,66; CaO - 9,04; P2O5 - 0,28; Na2O
- 2,41; K2O - 0,80; LOI - 1,03; Σ - 99,79 (217.5 m, XRF
method,
Institute of Geology
of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian
Academy of Sciences).
Widespread within the province subalkaline olivine basalts of the lower
volcanic strata from borehole 1831d, depth 265.8 - 361.5 m (Khotislav
village, Malorita district, Belarus), wt%: SiO2 - 48,51; TiO2
- 1,65 ; Al2O3 - 15,24; Fe2O3
- 5,78; FeO - 7,36; MnO - 0,21; MgO - 6,96; CaO - 7,44; P2O5
- 0,25; Na2O - 2,50; K2O - 0.85; LOI - 1,06; Σ -
99,59 (nearby borehole 1825, 294.9 m, a wet chemistry method,
M.P. Semenenka
Institute for Geochemistry, Mineralogy and Ore Formation, National
Academy of Sciences of Ukraine).
XRF analyzes performed for all point samples in State IPM NASB.
The
samples of basalts crushed to grain size 0.074 mm were subjected to a
multi-stage heat treatment to the temperatures of 1150ºC, 1170ºC and
1200ºC, 1250ºC, 1300ºC to form a melt. From these samples of glasses
were welded in a gas furnace batch windows at a maximum temperature of
1420 + 10°C with exposure for 1 hour. To study the crystallization
tendency of glasses the gradient thermal treatment of glasses in the
temperature range 560 -
1000oC was done, and then
crystallization at fixed values
of
temperature 850oC, 900oC and 1000oC
with delay 30 minutes was done. Heating were carried out at atmospheric
pressure in an electric furnace in nonbuffered by oxygen oxidizing
atmosphere in corundum crucibles with 250oC temperature rise
per hour, followed by inertial cooling. Studies have been accompanied by
petrographic study of heat-treated basalts cakes, x-ray, thermal, and
microprobe analysis.
The
temperature range of samples initial melting has been defined as 1150o
- 1190oC, the dependence of temperature on variations of
their chemical composition has been traced: if the higher content in the
basalts of refractory silica and calcium, the later they start to melt;
the more titanium and iron contant - the sooner. The active degassing
and homogenization of the melt for the olivine basalts of subalkaline
series (Na2O + K2O = 2,5 - 5,1%) is achieved at a
temperature of about 1250ºC, and at 1300ºC - formation crystallites of
augite, magnetite and hematite during
cooling with forming a glass-spherolitic
structure. Tholeiitic basalts of the normal range (Na2O + K2O
= 1,1 - 3,0%) melted into a homogeneous mass with a small amount of
swilles at the temperature of about 1300ºC, degassing process is nearing
completion, the crystallites of augite and hematite formed during
cooling with development of spherolitic-lattice structure .
The
difference in melting temperature at 50°C may be connected with lowering
the melting temperature role of fluids. Olivine basalts are richer in
water (1.023%) than the tholeiites (1.031%) as a free unbound water,
which they lose at low temperatures (up to 100˚C), so and
constitutional, which it gives at high temperatures (1250 - 1300ºC).
However, in the temperature range 1000 - 1100˚C tholeiites give water
more rapidly and become more porous than the olivine basalts, which
allows to use of the past as a component in the manufacture of ceramic
tiles for interior wall facing [2].
Completed multi-stage heat treatment of the sample
alevro-pelitic vitro-litho-clastic tuff of
tholeiitic basalt from the borehole 776 and alevro-psammitic
litho-vitro-clastic tuff of olivine basalt from the borehole 1831d
confirmed the trend identified for the basalts.
Synthesized at a maximum temperature of boiling 1420 + 10°C
basaltic glasses of investigated samples are black and have satisfactory
working characteristics. The viscosity of the glass obtained from the
olivine basalts, slightly lower than from tholeiitic, which allows to
pull out a thin and long filaments with no visible defects. Obviously,
it is connected with more alkaline composition of the melt from olivine
basalts, than from tholeiites, as for natural basaltic magmas is known
that more alkaline melts are more viscosity [1, 4, etc.]
The
optimum sitallization temperature of tholeiitic and olivine basalts
exhibition of 900oC has been adopted. Studing of polished
surfaces of heat-treated at 900oC glasses by microprobe
analysis showed, that based on tholeiite petrositalle have single (less
than 0.5%) augite crosswise microlites with clavate ends and of the size
of 10 microns in length and about 1 micron in width. Augite crystallites
(more than 40%) of the size of 5 - 10 microns in length and
not more than 1 micron in width are stretched in
one direction in the petrositalle sample from olivine basalt. It form a
felt structure of the sample with elements of spherolitic structure,
similar to that described for the cake of this basalt at 1300ºC by
optical microscopy. Location of spherolites as a whole resembles a
system hexagonal honeycomb. The growth of crystals, apparently carried
out from the periphery of the spherolites to it center, as evidenced by
the thickness increase to the edges of the spherolites. The study of the
chemical composition of the crystals was not avail, as their thickness
is less than the resolution of the instrument. However, there was a
trend to increase the content of iron and chromium in the crystallites
with respect to the glassy phase. The mineral phase of hematite has a
small crystal size (less than 1 micron) and is fixed only by X-ray
analysis.
Thus,
the crystallization of basaltic melt, studied on the samples after
heating the basaltic powder to a temperature of 1250 - 1300ºC, as well
as samples of basaltic glass, cooked at a
temperature of 1420 ± 10°C and then heat-treated
at 900ºC with exposure for 30 minutes, was passed, apparently on
magnetite-pyroxene scheme. Set parameters in the melting furnace
(atmospheric pressure, the oxygen nonbuffered oxidizing environment,
rapid cooling) provided a non-equilibrium solidification process. Rapid
cooling of the melt explains the absence of mineral phases plagioclase
and olivine in the crystallization products. Augite, in contrast, may
have in such circumstances a wide range of crystallization temperatures
(1200 - 1150ºC to 800ºC), which explains its presence in the products of
fusion at low and high temperatures. Magnetite crystallizes in the form
of fine dust or dendrites in the interval from the liquidus temperature
to 620 - 650oC. Iron is readily converted to ferric, and
magnetite is replaced by hematite in the oxidizing atmosphere of an open
system by oxygen during cooling of samples [1, 3, 4]. At the same time
required for basalt stone casting spherolitic structure with radiating,
stellate or radial-fibrous structure of the spherolites is forming. The
optimal size of spherolites is 60 - 90 microns,
and we obtained petrositalle prototypes with spherolites size 40 - 60
microns [3, 5].
Tholeiitic basalts from career Politci-2 (Ukraine), which were
previously exported to the Republic of Belarus for the production of
mineral wool, and the tholeiitic basalts from borehole 776 (Belarus)
have identical technological properties. Glasses, welded from
subalkaline olivine basalts are more technological in the development of
fibers, and based on it petrositalls have a higher degree of
crystallinity, suggesting, respectively, their best physical and
mechanical properties, than petrositalls by tholeiites.
This study was financially supported by BRFFR grant
Х11-132.
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