GEOLOGICA CARPATHICA, 49, 3, BRATISLAVA, JUNE 1998
181192
THE CARRIERS OF MAGNETIC PROPERTIES IN THE
NEOVOLCANIC ROCKS OF CENTRAL AND SOUTHERN SLOVAKIA
(WESTERN CARPATHIANS)
OTO ORLICKÝ
Geophysical Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 28 Bratislava, Slovak Republic; geoforky@savba.savba.sk
(Manuscript received March 18, 1997; accepted in revised form March 24, 1998)
Abstract: The carriers of magnetic properties of rocks were studied using: (1) fully automated measurements of magnetic
susceptibility (
κ
) change of sample influenced by temperature in the range of 196 to 700
o
C, (2) reflected light micros-
copy, (3) electron microprobe analysis, (4) Mössbauer spectroscopy, (5) X-ray powder diffraction analysis.
The carriers of magnetic properties of the Neogene volcanics have been grouped into seven dominant groups (B, C, D,
F, G, I, J) on the basis of the results of method (1) for about 670 individual samples. Groups BF contain titanomagnetites
(TMs) of two magnetic phases of different Curie temperatures (T
C1
, T
C2
); Groups B, C: first phase (T
C1
≈
130220
o
C)
contains quasi homogeneous or partly oxidized TMs of composition Fe
2.35
Ti
0.65
O
4
Fe
2.5
Ti
0.5
O
4
, second phase (T
C2
≈
570
575
o
C) contains oxidized TMs of unknown composition. Groups D, F: both magnetic phases correspond to oxidized TMs
of unknown composition. Group D dominant phase of T
C1
≈
480
o
C and second magnetic phase of T
C2
≈
590
o
C. Group
F contains oxidized TMs, a first magnetic phase of T
C1
≈
420
o
C and T
C1
≈
530
o
C, and a second one of T
C2
≈
600
o
C,
T
C2
≈
590600
o
C. Magnetic phases of T
C
≤
585
o
C also contain small portion of hematite-ilmenites. Group G contains
one magnetic phase of T
C
≈
580
o
C (and Verwey transition temperature of T
V
≈
153
o
C), which corresponds to pure
multidomain magnetite. Group I contains two magnetic phases, a first phase of T
C1
≈
560600
o
C corresponds to
nonstoichiometric magnetite (exceptionally an oxidized TM can be present), and a second phase of T
C2
≈
600630
o
C
corresponding to hematite-ilmenites. The J group contains only one phase of T
C
≈
610640
o
C. This magnetic phase cor-
responds to hematite-ilmenites. The magnetic phases of T
C
≈
585640
o
C correspond to hematite-ilmenites, probably of
composition within the range x
≈
0.090.04 (of equation Fe
2-
×
Ti
x
O
3
). Dominant occurrences of the groups BJ have been
delineated in the geological schemes.
Key words: Neogene volcanics, 7 dominant groups of Fe-Ti magnetic minerals.
Introduction
In the past a detailed paleomagnetic investigation of neovolca-
nics of central and southern Slovakia was performed (Orlický
1992; Orlický et al. 1996). Some knowledge about the magnetic
minerals of the neovolcanics was also obtained (Nairn 1966;
Kropáèek et al. 1981; Pateka 1991; Orlický et al. 1982, 1992;
Orlický 1993, 1996). The above presented results concerned
only limited collections of rocks.
The results presented in this article were obtained by the stu-
dy of rock samples collected from about 650 individual localities.
The dominant minerals that are responsible for the mag-
netic properties in volcanic rocks are within the ternary-sys-
tem FeO-TiO
2
-Fe
2
O
3
(McElhinny 1983). In general, diverse
chemico-physical conditions (partial pressure, temperature,
presence or lack of oxygen, composition of magmatic gases,
speed of the ascent and cooling of a magma, presence or
lack of magmatic water and steam, etc.) have dominantly in-
fluenced the development of magnetic minerals in the vol-
canic rocks (Kropáèek 1986). The crystallization conditions
control the composition of the Fe-Ti oxides, while the cool-
ing histories control crystal size, extent of cation-ordering
and development transformation microstructures including
exsolution and oxidation (Lawson et al. 1987).
In the case of igneous rocks the magnetic minerals (the re-
manence carriers) are the titanomagnetites (TMs) (Fe
3-x
Ti
x
O
4
;
0
≤
x
≤
1; Stacey & Banerjee 1974) or compounds derived by
oxidation, substitution and/or unmixing processes (Hargraves
& Petersen 1971). The TMs consist of the two end members
(spinels) magnetite (Fe
3
O
4
) and ulvospinel (Fe
2
TiO
4
). Experi-
ence in the study of magnetic minerals have pointed out that
they have arisen within the basaltic magma. The basalts and
the nepheline-rich rocks contain xenoliths which indicate that
these rocks have their source within the mantle (Ehlers &
Blatt 1980). In the magnetite-ulvospinel series there is com-
plete solid solution at temperatures in excess of 600
o
C. At
lower temperatures, the solid solution is much more restricted
and there is a tendency for the two phases to exolve (McEl-
hinny 1973). In practice the composition of naturally occur-
ring spinels tends to be displaced towards the hematite-il-
menite series in the direction of increased oxidation. The
oxidation during cooling tends to proceed first through the
production of ilmenite lamellae and then progresses towards
the pseudobrookite series (McElhinny 1973).
Titanohematites are represented by the chemical formula
Fe
2-x
Ti
x
O
3
where x varies between 0.0 and 1.0. Slow cooling
from about 700
o
C results in exsolution of hematite-rich (0
≤
x
≤
0.2) and ilmenite-rich (0.8
≤
x
≤
1.0) components, known
as ilmeno-hematites or hematite-ilmenites (Stacey & Baner-
jee 1974). In the hematite-ilmenite series there is complete
solid solution above 1050
o
C. At lower temperatures the solid
solutions are restricted and the intermediate compositions are
represented by the intergrowths of the end members (both
rhombohedral) hematite and ilmenite.
182 ORLICKÝ
Two main alteration processes can determine the state of
the Fe-Ti oxides in volcanic rocks: deuteric oxidation, which
is active between 800
o
and 500
o
C during initial cooling, and
regional hydrothermal alteration, acting between 0
o
and
300
o
C, during post-eruptive burial of younger material (Ade
Hall et al. 1971). The true TMs are presumably rare in nature,
they are mostly in near-stoichiometric Fe-Ti oxides state. The
degree of non-stoichiometry is limited at high temperature
(
≥
400
o
C) and the products of such deuteric oxidation beyond
the monophasis limit, are intergrowths containing spinel
components. The monophasis spinel products of low temper-
ature oxidation are refered to as titanomaghemites and oxida-
tion process itself as maghemitization (ODonovan &
OReilly 1976). Kropáèek (1986) found that the oxidation
process at temperatures up to 400
o
C is a diffusive process
during which the cation-deficient titanomagnetites (tita-
nomaghemites) are formed, at the temperatures over 500
o
C
the titanomagnetites undergo spontaneous disintegration and
hematite-ilmenites, pseudobrookites and rutiles are formed.
Readman & OReilly (1970) studied the alterations of the
TMs in detail. They revealed that an original TM was in-
verted into two-phase intergrowth (spinel and rhombohedral
phases) after heating to 700
o
C and successive cooling. The
spinel phase comprised a mineral close to magnetite (in
composition) containing small quantity of Ti and vacancies
and a mineral richer in iron than the original TM. The rhom-
bohedral phase comprised a mineral near to ilmenite (less Ti
rich in composition than ilmenite), a mineral near to hema-
tite (in composition), pseudobrookite (Fe
2
TiO
5
) and anatose
(TiO
2
). The presented knowledge has proved that the Fe-Ti
oxides within the rocks are very variable in composition,
magnetic state and grain sizes as well as in other character-
istics. Though only a very concise description of the Fe-Ti
oxides and their possible alterations has been presented
above, one can anticipate a high degree of intricacy in the
detection and study of natural Fe-Ti minerals in the rocks.
Short outline of geology
Lexa et al. (1993) have distinguished four essential
groups of neovolcanic rocks, according to their composi-
tional characteristics and spatial distribution. Only the rocks
of two of them have been investigated:
Areal type andesite volcanic activity including differ-
entiated rocks (this also involves a short episode of acidic
rhyolite activity). It lasted since the Early Badenian until the
Early Pannonian time. Its spatial distribution was strongly
influenced by back-arc extension tectonics associating with
diapiric uprising of the mantle. Geochemistry indicates sub-
duction influenced mantle source magmas with variable
crustal components.
Alkali olivine basalt/nepheline basanite volcanic activi-
ty in the north-western part of the Pannonian Basin as well as
in the southern part of Slovakia. This volcanism was active
during the Pannonian to Quaternary periods. Basalts of this
type indicate continuing extension accompanied by diapiric
uprising in the mantle, which has not been affected by sub-
duction processes.
Shortly about the petrography of the Neogene volcanics:
Alkaline basalts (according to Mihaliková & imová
1989). The alkaline basalts have been divided into the fol-
lowing types: olivine basalts, plagioclase basalts, limburgit-
ic basalts and basanites. The basanites have been divided
into the plagioclase basanites, limburgitic basanites,
nepheline basanites, amphibole basanites and trachytic
basanites. Other dominant types of basalts are the tephrites
and trachybasanites. The ore minerals (magnetite, Ti-mag-
netite, maghemite, ilmenite; in the basanites also ulvospinel
and hematite) have been found among the phenocrysts as
well as in the matrix of the rocks.
The products of the areal type andesite volcanic activi-
ty (according to Lexa et al. 1997) the main types of the
effusive and extrusive volcanic activity: basaltic andesites,
pyroxene andesites, hornblende-pyroxene andesites, pyrox-
ene-hornblende andesites, hornblende andesites, biotite-
hornblende andesites to dacites, rhyodacites, plagioclase
rhyolites, plagioclase-sanidine rhyolites. The ore minerals
(Ti-magnetite, magnetite, ilmenite) have been found among
the phenocrysts as well as in the matrix of the rocks. The
main types of the intrusive rocks: diorite, granodiorite,
aplite, diorite porphyry, basic siliceous-diorite porphyry,
acid siliceous diorite porphyry, granodiorite porphyry Zlat-
no type, granodiorite porphyry Kozí potok type, granite por-
phyry. The ore minerals (magnetite, Ti-magnetite, ilmenite)
have been found among the phenocrysts as well as in the
matrix of the rocks.
The contours of individual volcanic formations and com-
plexes are presented in Figs. 1, 2. The individual volcanic
formations and complexes including the petrographical
characteristics of volcanic rocks are described below Fig. 1.
Experimental techniques
Transmission optical microscopy and reflected light
microscopy of the samples were performed by A. Mihalí-
ková and J. Beòka, respectively, in the Geological Survey,
Bratislava.
Microprobe analyses, Mössbauer spectroscopy, X-ray
diffraction analysis and measurements of magnetic suscep-
tibility (
κ
) change, as well as electric voltage change of
samples influenced by temperature (in low and high temper-
ature intervals) were used to study the magnetic minerals of
rocks. The first five methods were performed within the
time period 19821989. Microprobe analyses were carried
out by F. Caòo in the Geological Survey, Bratislava. The
compositions of Fe-Ti oxides were studied using the JEOL
instrument equipped with the EDAX system. Microprobe
analyses were carried out on the compact polished samples
(29 samples were observed; 4 or more individual grains of
Fe-Ti oxides for each sample were analysed).
The Mössbauer spectroscopy was realized by I. Toth and
interpreted by J. Lipka in the laboratory of the Nuclear
Physics Dept. of the Slovak Technical University, Bratisla-
va (Lipka et al. 19821988). The Mössbauer spectra were
recorded using a constant acceleration spectrometer with a
source of 1.5 GBq
57
Co in rhodium. Isomer shifts have been
THE CARRIERS OF MAGNETIC PROPERTIES IN THE NEOVOLCANIC ROCKS 183
given relative to that of the
α
-Fe absorber at 27
o
C. Ca. 72
samples were analysed. The spectra were obtained at ab-
sorber laboratory temperature, but seven samples of mag-
netic fraction from basalts were also measured at liquid ni-
trogen temperature where the hopping among the octahedral
Fe
2+
and Fe
3+
ions in the Fe-Ti oxides does not occur.
X-ray powder diffraction analyses were performed by B.
Toman in the Geological Institute of the Slovak Academy of
Fig. 1. An outline of the lithostratigraphic units of the volcanics of central Slovakia. (The map has been combined from individual maps, ac-
cording to V. Koneèný et al. 1983). Products of andesite (and short episode of rhyolite) volcanic activity (2nd group). Explanations of
symbols in the map: Undivided rocks of the tiavnica stratovolcano; I Undivided rocks of the first stage; Zs Zlatá Studòa Forma-
tion (, I, ZS propylitized andesite and andesite porphyry, diorite porphyry, undivided complex of propylitized effusions and intrusions,
hornblende-pyroxene, unspecified pyroxene and hypersthene pyroxene andesites). T Turèok Formation (feldsparic, pyroxene and basal-
tic andesites); P Pleina Formation (extrusive domes and subordinate volcanoclastic rocks of hyperstene-hornblende andesites); Si
Sielnica Formation, Vt Vtáènik Formation, Jb Jabloòovývrch Effusive Complex, R Remata Formation, Md Flochová Forma-
tion, Tu Turová Formation, Vd Ve¾ká Detva Formation (Si, Vt, Jb, R, Md, Tu, Vd pyroxene andesites); Sb Sebechleby Forma-
tion, Sk Sitno Effusive Complex, Pr Priesil Formation, A Abèina Formation, Ja Javorie Formation, IV Undivided rocks of the
fourth stage (Sb, Sk, Pr, A, Ja, IV hornblende pyroxene andesites); Bd Baïan Formation, In Inovec Formation (Bd, In glassy py-
roxene and feldspharic andesites); St Studenec Formation, Kr Krahule Formation (St, Kr biotite-hornblende andesites ); K
Kremnický tít Formation (pyroxene-hornblende, pyroxene and biotite-hornblende andesites); Ro Rohy Formation, B Neresnica For-
mation (Ro, B hornblende-pyroxene, hyperstene-hornblende andesites ); Kl K¾akovská dolina Formation, By Blýskavica Forma-
tion (Kl, By pyroxene and basaltic andesites); v ibenièný vrch Complex, Vv Vlèí vrch Formation (v, Vv basaltic andes-
ites); J Jastrabá Formation, Hr Hliník rhyolites (J, Hr rhyolites and rhyodacites); Ib Beluj Intrusive Complex, i
Hodrua-tiavnica Intrusive Complex, Bi Banisko Intrusive Complex, Ki Kalinka Intrusive Complex (Ib, i, Bi, Ki intrusions
andesite porphyry, diorite, diorite-porphyry). Bz Basalts (the basalts belong to the alkali olivine basalt/nepheline basanite volcanic activi-
ty. B, C, D, F, G, I, J (in circuit) distinguished groups of Fe or Fe-Ti magnetic minerals).
184 ORLICKÝ
were studied by this method. The powdered samples were
prepared by grinding, subsequent magnetic separation, (most-
ly by bar permanent magnet; but several samples were sepa-
rated by Cook, or Kaldrovich magnetic separators). Some
samples were separated by the flotation method by M. abka
at the Geological Institute of the Slovak Academy of Scienc-
es, Bratislava. We also tried to separate individual magnetic
components from each other, but this procedure was almost
ineffective due to the mutual intergrowth of magnetic grains
within the rocks.
Results and the contribution of individual methods
The results of the transmission optical microscopy have
been mainly used for the more precise petrographical de-
scription of the rocks.
The results obtained by all methods have been presented
in Tables 1, 2, 3. We see from Tables13 that 3 types of
magnetic oxides were detected in the rocks using the re-
Sciences, Bratislava. The Philips PW 1420 X-ray spectrom-
eter and PW 1150 diffractometer were used to perform the
powder diffraction analyses of samples. Co-K
α
, Cu radia-
tion using the Fe filter was applied. A total of 52 samples
were analysed.
Measurements of the change of electric voltage of sam-
ples of the magnetic fraction influenced by temperature
(from liquid helium temperature to room temperature) were
performed by A. Zentko in the Institute of Experimental
Physics of the Slovak Academy of Sciences, Koice.
Measurements of magnetic susceptibility (
κ
) change in
samples influenced by temperature were performed by the
author of this article. The description of the apparatus and
laboratory procedure have been published by Orlický (1990).
This method is fully automated. It is able to detect all subtle
magnetic phases and their tendency to change due to the in-
fluence of temperature (in the presence or absence of oxygen)
on the rocks. The measurements by this method were per-
formed with the presence of air oxygen (except the sample
presented in Fig. 4). The samples from about 650 outcrops
Fig. 2. Scheme of relicts of alkali basalt volcanism of southern Slovakia (according to Vass & Eleèko 1992). 1 lava flows of Podreèany
Basalt Formation; 2 maars of the Podreèany Basalt Formation; 3 lava flows of the Cerová Basalt Formation; 4 cinders cones;
5 agglomerates; 6 lapilli tuffs; 7 maars of the Cerová Basalt Formation; 8 feeding systems of the Cerová Basalt Formation:
a) diatremes, b) necks; 9 frontiers between Slovakia and Hungary. 631 near of dots-numbers of localities. B, C, D and ~G (in cir-
cuit) selected groups of Fe-Ti magnetic minerals.
THE CARRIERS OF MAGNETIC PROPERTIES IN THE NEOVOLCANIC ROCKS 185
Group Number
Type of
Geographical Reflected Curie
temperature
Mössbauer X-ray
diffraction Microprobe analyses
of
samples
rock
coordinates
light
of magnetic
spectroscopy
analyses
Grain
FeO TiO
2
jL(
°)
lL(
°) microscopy
phases
size (mm) (%) (%)
148a/7
Basaltic
T
C1
» 130 °C
TM
25
72.49
25.78
B
andesite
48.451
18.81
T
C2
» 570 °C
15
73.35
25.07
10
73.41
24.58
7
72.99
25.53
Brehy
Nepheline
48.409 18.650
T
C1
» 220 °C
TM
20
76.64
22.42
B2/16
basanite
T
C2
» 570 °C
Pbr
10
74.36
23.77
B
8
75.84
23.20
7
74.26
24.57
6
73.48
25.63
.V.6/1
Aphanitic
48.593 18.879
T
C1
» 210 °C
TM
20
71.73
26.16
basaltic
T
C2
» 575 °C
Mag
10
75.97
23.25
andesite
Hem
8
71.86
25.84
Ilm
7
75.61
23.08
C
.V.3/2
48.593 18.879
T
C1
» 210 °C
60
73.23
24.63
T
C2
» 575 °C
8
74.44
23.83
8
74.44
23.83
8
73.49
24.58
7
75.61
23.08
Bd-256/2
Glassy
48.280 18.750
T
C1
» 480 °C
pyroxene
T
C2
» 590 °C
feldsparic
andesite
DVt-45/11
Pyroxene
48.550 18.600
T
C1
» 480 °C
TM(35%)
100
78.90
17.34
andesite
Tc
2
» 590 °C
Mag(40%)
50
78.26
18.56
Magh(6%)
10
82.75
14.51
6
82.33
13.69
Kr. Vr.-
Hyperstene
48.757 18.817
T
C1
» 420 °C
26/1
augite
T
C2
» 600 °C
andesite
F
AF-329-B2
Pyroxene
48.653 19.344
T
C1
» 530 °C
Mag(57%)
Mag
30
83.32
15.43
hornblende
T
C2
» 590 °C
Hem(6%)
Magh
15
80.35
18.88
andesite
600 % °C
Magh(10%)
Rutile
6
84.94
14.68
I-104/1
Propylitized 48.483 18.750
T
C
» 580 °C
Mag(100%)
Mag
100
93.16
4.43
pyroxene
Tv
» 153 °C
Rutile
70
94.86
3.86
andesite
50
94.05
3.25
G
15
0.82
99.18
I-181/4
48.439 18.849
T
C
» 580 °C
Tv
» 153 °C
St-156/1
Biotite-
48.451 18.966
T
C1
» 580 °C
Mag(13%)
Mag
100
79.03
20.60
hornblende
T
C2
» 620-630 °C
Hem(48%)
Hem
40
89.35
8.65
andesite
Magh(27%)
12
97.67
0.29
I
7
98.35
0.68
St-215/4
48.412 18.723
T
C1
» 580 °C
T
C2
» 620630 °C
Tv
» 153 °C
3-IV-B1/1 Hornoblende- 48.518 18.743
T
C
» 630 °C
Mag(30%)
Mag
60
76.60
23.40
pyroxene
Hem(30%)
Magh
70
89.24
9.52
andesite
Ilm
Hem
10
93.91
5.04
10
56.19
43.81
J
10
88.72
11.28
7
91.30
8.70
7
95.08
0.00
6
53.64
45.40
6
78.81
20.41
TR-24
Hyperstene
48.456 18.947
Hem
T
C
» 640 °C
Mag(16%)
Magh
45
84.40
14.53
J
-hornblende
Hem(22%)
Hem
30
55.10
44.12
-biotite
Mag
Magh(14%)
20
93.38
5.34
andesite
Ilm
7
90.20
8.40
Magmagnetite; Hemhematite; Maghmaghemite; Ilmilmenite; Usulvospinel; Brbrookite; Pbrpseudobrookite; TMtitanomagnetite.
Table 1: The results of reflected light microscopy, Curie temperature measurements, X-ray diffraction analyses, electron microprobe
analyses and Mössbauer spectroscopy of magnetic minerals.
flected light microscopy. Magnetite (Mag) was detected in
all samples, hematite (Hem) was detected in 14 samples and
ilmenite (Ilm) was detected in 5 samples of rock. These
minerals mostly intergrow each other when they are present
together in the rock.
Electron microprobe analysis
Electron microprobe analysis can detect only the chemis-
try of the respective material. The contents of FeO and TiO
2
of samples were presented in Tables 13. The compositional
186 ORLICKÝ
Group Number
Type of
Geographical
Reflected Curie tempera-
Mössbauer
X-ray
Microprobe analyses
of samples
rock
coordinates
light mic- ture of magnetic
spectroscopy
diffraction
Grain
FeO
TiO
2
j L (
o
)
lL (
o
)
roscopy
phases
analyses
size (µm)
(%)
(%)
Pyroxene
48.610
18.583
T
C1
» 600
o
C
Mag (30%)
Mag, Hem
40
50.72
49.02
I
St-4/1
andesite
T
C2
» 620
o
C
Hem (21%)
20
50.74
48.65
Magh (25%)
10
88.27
11.05
TM (11%)
5
90.36
9.11
Ilm
Pyroxene
T
C1
» 500
o
C
Mag (20%)
Mag, Magh, Ilm
DVt-16/2
andesite
48.613
18.611
T
C2
» 590
o
C
TM (59%)
Ilm
Autometa-
Mag, Hem, Magh
70
93.73
5.27
J
Vt-38/3
morphosed
48.567
18.714
Mag
T
C
» 610
o
C
70
60.54 38.94
pyroxene
30
93.60
6.00
andesite
Hem
7
92.39
6.37
Pyroxene
Mag (36%)
Mag, Hem, Ilm
J
St-43/3
andesite
48.566
18.500
T
C
» 615
o
C
Magh (21%)
Us, Pbr
Hem (25%)
Br
Ilm
Mag
T
C1
» 580
o
C
Mag (26%)
Mag, Hem
60
91.18
8.14
Hornblende
Hem (33%)
Magh
8
73.93
25.56
I
TR-13/2
pyroxene
48.548
18.670
Hem
T
C2
» 620
o
C
Magh (8%)
7
96.49
3.27
andesite
TM (11%)
7
88.40
11.12
Hyperstene
Mag (44%)
Mag, Hem, Magh
40
92.31
7.48
I
Tr-16/1
-hornblende 48.509
18.656
Mag
T
C1
» 600
o
C
Hem (21%)
30
50.90
48.64
biotite
Hem
T
C2
» 615
o
C
Magh (11%)
Ilm
15
87.41
12.34
andesite
TM
Ilm
Br
10
87.41
12.34
Mag (37%)
2 samples:
60
91.98
7.50
Hem (35%)
Hem
60
65.79
33.83
Ilm
1 sample:
15
91.73
7.67
Mag
Magh, Br
15
70.09
29.42
Hyperstene
Hem
T
C1
» 600
o
C
2 samples:
6
90.14
8.85
I
TR-16/3
hornblende- 48.509
18.656
Ilm
Mag, Hem
5
88.28
10.90
biotite
T
C2
» 620
o
C
2 samples:
andesite
Mag, Hem, Br
7 samples:
Mag, Hem, Ilm, Br
Biotite-
Mag (%)
Magh, Hem
40
92.65
7.02
J
St-102/13 hornblende
48.482
18.745
T
C
» 630
o
C
Hem (55%)
Us, Ilm
20
88.20
11.51
andesite
Magh (29%)
Br
10
81.83
17.88
Ilm
7
80.21
19.01
Pyroxene
T
C1
» 590
o
C
Mag (82%)
Mag, Hem
30
78.05
18.89
I
I-238/7
andesite
48.382
18.633
Hem (3%)
20
51.02
48.39
T
C2
» 620
o
C
TM (10%)
10
77.56
19.09
7
76.29
20.97
Hyperstene
Mag (82%)
Mag, Hem
30
85.13
13.96
G
TR-6/2
hornblende
48.578
19.345
Mag
T
C
» 580
o
C
Hem (8%)
Br
15
91.00
8.62
biotite
15
53.99
45.86
andesite
Hem
10
54.23
45.57
10
52.11
47.42
Hornblende
2 samples:
1 sample:
70
80.77
18.91
F
TR-11
pyroxene
48.550
19.331 2 samples
T
C1
» 530
o
C
Mag (70%)
Mag, Hem, Magh
10
99.05
0.12
andesite
T
C2
» 590
o
C
Hem (10, 15%)
2 samples:
7
82.11
17.47
Mag
Ilm
Hem, Ilm
7
88.47
11.39
I
Hem
T
C1
» 560
o
C
2 samples:
1 sample:
6
91.89
8.11
TM
T
C1
» 615
o
C
Mag (51, 67%)
Hem, Ilm, Magh
70
95.72
4.02
Hem (22, 17%)
4 samples:
60
52.57
46.17
3 samples
Magh (17, 8%)
Mag, Hem, Ilm
10
83.97
15.41
Ilm
2 samples:
7
93.51
5.79
Hem
1 sample:
Mag, Hem, Ilm, Us
7
97.47
1.15
Mag (42%)
2 samples:
70
95.13
4.51
Ilm
TM (36%)
Mag, Hem
60
47.83
51.45
Ilm
Us, Pbr
8
68.68
30.98
Nonmagn. fr.:
1 sample:
7
91.07
8.93
2 samples:
Mag, Hem,
7
68.53
30.84
Mag (12, 18%)
Magh, Pbr
80
46.70
52.22
Hem (28, 30%)
1 sample:
30
90.36
9.40
Ilm
Mag, Hem, Magh,
1 sample:
Ilm, Us, Pbr
Hem (42%), Ilm
Magmagnetite; Hemhematite; Maghmaghemite; Ilmilmenite; Usulvospinel; Brbrookite; Pbrpseudobrookite; TMtitanomagnetite.
Table 2: The results of reflected light microscopy, Curie temperature measurements, X-ray diffraction analyses, electron microprobe
analyses and Mössbauer spectroscopy of magnetic minerals.
THE CARRIERS OF MAGNETIC PROPERTIES IN THE NEOVOLCANIC ROCKS 187
Group Number
Type of
Geographical
Reflected Curie tempera-
Mössbauer
X-ray
Microprobe analyses
of samples
rock
coordinates
light mic- ture of magnetic
spectroscopy
diffraction
Grain
FeO
TiO
2
j L (
o
)
lL (
o
)
roscopy
phases
analyses
size (mm) (%)
(%)
Hornblende
Mag (52%)
Mag, Hem
J
TR-15/1
-pyroxene
48.544 18.947
Mag
T
C
»
610
o
C
Hem (12%)
Ilm,TM
andesite
Magh (9%)
Hem
TM (8%), Ilm
T
C1
»
520
o
C
Mag (49%)
Mag, Hem
40
88.65
10.31
F
TR-17/2
Biotite
48.509 18.973
Mag
TM (51%)
20
87.95
10.17
hornblende
T
C2
»
570
o
C
10
83.70
14.76
andesite
7
88.30
10.00
Pyroxene
Mag (74%)
Mag
J
TR-19/1
andesite
48.461 18.971
Mag
T
C
»
610
o
C
TM (4%)
Ilm
Hornblende
Mag (30%)
Hem, Ilm
J
TR-20/2
biotite
48.462 18.971
Mag
T
C
»
612
o
C
Hem (35%)
Magh, Br
andesite
Hem
Magh (12%), Ilm
Hornblende
Mag (47%)
Mag, Hem
I
TR-22/1
-biotite
48.457 18.941
Mag
T
C1
»
570
o
C
Hem (22%)
Ilm, Br
andesite
T
C2
»
620
o
C
Magh (9%), Ilm
Hornblende 48.427 18.898
Mag
T
C
»
625
o
C
Mag (53%)
Mag
15
82.27
15.64
J
TR-23/2
-biotite
Hem
Hem (24%)
8
90.13
8.60
andesite
Ilm
6
87.69
10.37
Biotite
Mag (55%)
Mag, Hem,
J
Tr-25/2
-hornblende 48.450 18.965
Mag
T
C1
»
625
o
C
Hem (23%)
Br
andesite
Magh (8%), Ilm
Pyroxene
Mag
40
0.41
99.59
J
I-174/3
andesite
48.445 18.883
T
C
»
620
o
C
15
3.15
96.05
(propylized)
10
1.38
98.62
7
2.19
96.98
Pyroxene
T
C1
»
580
o
C
Mag (78%)
Mag, Hem
I
AF-314A1
andesite
48.665 19.392
T
C2
»
600
o
C
Hem (12%)
Ilm
Ilm
Augite
Mag (16%)
Hem, Magh
100
63.87
34.79
J
AF-323/1 -hyperstene 48.660 19.400
T
C
»
630
o
C
Hem (20%)
30
50.47
49.00
andesite
Ilm
10
94.19
3.64
6
60.93
38.38
Pyroxene
Mag (59%)
50
87.50
11.71
I
VD-331B1
-biotite
48.650 19.392
T
C1
»
565
o
C
Hem (28%)
15
86.17
13.42
andesite
T
C2
»
605
o
C
Magh
10
88.35
10.73
6
87.04
12.73
Pyroxene
T
C1
»
575
o
C
Mag (43%)
Mag, Hem
40
51.87
47.70
I
VD-335A3
-biotite
48.647 19.380
T
C2
»
605
o
C
Hem (33%)
40
91.69
8.31
andesite
Magh (12%)
15
93.01
6.99
Ilm
7
92.43
7.57
Pyroxene
Mag (37%)
Mag, Hem
90
86.97
11.50
I
Ro-399
-hornblende 48.583 19.373
T
C1
»
570
o
C
Hem (51%)
Magh
30
46.17
52.31
hyperstene
T
C2
»
620
o
C
Magh (5%)
15
46.96
51.12
andesite
Ilm
6
54.95
44.24
Pyroxene
Mag, Hem
F
Ro-404B1 -hornblende 48.575 19.397
T
C1
»
520
o
C
andesite
T
C2
»
610
o
C
Pyroxene
F
Ro-405C1 -hornblende 48.573 19.387
T
C1
»
530
o
C
Mag (92%)
Mag, Hem
andesite
T
C2
»
590
o
C
Ilm
Ilm
Pyroxene
F
Ro-427A1 -hornblende 48.550 19.390
T
C1
»
520
o
C
Mag (69%)
Mag, Magh
andesite
T
C2
»
590
o
C
TM (23%)
Pyroxene
I
Ja-450
-hornblende 48.485 19.400
T
C1
»
590
o
C
Mag (87%)
Mag, Hem
andesite
T
C2
»
610
o
C
Hem (8%)
Ilm
Pyroxene
Mag (67%)
F
Ja-451D1 -hornblende 48.477 19.347
T
C1
»
520
o
C
TM (14%)
Mag, Magh
andesite
T
C2
»
600
o
C
Magh (6%)
Magmagnetite; Hemhematite; Maghmaghemite; Ilmilmenite; Usulvospinel; Brbrookite; Pbrpseudobrookite; TMtitanomagnetite.
Table 3: The results of reflected light microscopy, Curie temperature measurements, X-ray diffraction analyses, electron microprobe
analyses and Mössbauer spectroscopy of magnetic minerals.
188 ORLICKÝ
parameter x for TM was calculated using the Ti/Fe ratio ac-
cording to Furuta (1993). The first magnetic phase of basalts
and basaltic andesites (Table1) contains quasi homogeneous
or partly oxidized TMs of a composition Fe
2.35
Ti
0.65
O
4
Fe
2.5
Ti
0.5
O
4
. Several samples of andesitic rocks have pointed
out also rather homogeneous contents of FeO or TiO
2
in most
of individual grains (see Tables13), but the Ti/Fe ratio of in-
dividual grains is significantly lower compared with that for
basalts and basaltic andesites. Oxidized-cation deficient TMs
are present in these rocks. The general formula for oxidized
TM is Fe
3+
8/3-2x
Fe
2+
x
Ti
4+
x
¨
1/3
O
2-
4
, when oxidation is com-
plete (¨denotes the lattice vacancies, Stacey & Banerjee
1974). Because the oxidation parameter z (or a degree of
oxidation) of the TMs has not been determined the composi-
tional parameter x for cation deficient TMs has not been de-
rived. The samples of rock I-104/1 (Table 1) or I-174/3 (Table
3) do reflect quite uniform dominant contents of FeO (I-104/
1), or uniform dominant volumes of TiO
2
(I-174/3), among
individual grains. A dominant portion of Mag and minor por-
tion of rutile is present in sample I-104/1, and a dominant por-
tion of rutile and minor portion of other Fe-Ti oxides is
present in sample I-174/3. In samples of rocks of variable-
heterogeneous contents of FeO and TiO
2
quantities (Tables
13), a presence of ilmenite (Ilm) in respective grain has been
predicted on the basis of FeO and TiO
2
contents, compared
with the data (FeO = 46.54 %, TiO
2
= 45.70 %), published by
Lawson & Gordon (1987) for the ilmenite from the Ilmen
Mountains, USSR.
Mössbauer spectroscopy
In principle, Mössbauer absorption spectra of magnetic
spinels and their paramagnetic and ferrimagnetic states
should provide useful information about the valence state of
the cations, their distribution between octahedral and tetrahe-
dral sites, and deviations from perfect cubic symmetry. In
practice, however, only the normal spinel data, where each
site contains only one kind of cation can be interpreted with a
high degree of confidence. In inverse spinels complications
can arise in interpretation of the results (Banerjee et al. 1967).
Basically linewith, isomer shift (IS), quadrupole splitting
(QS) and hyperfine field of the spectrum are characteristics
for respective Fe or Fe-Ti minerals. Unfortunately, in Fe-Ti
oxides we can find some difficulties in these parameters. For
example ilmenite (FeTiO
3
) and pseudobrookite (Fe
2
TiO
5
)
have rather the same range of QS and IS. Room temperature
spectra with increasing portions of Ti
4+
ions in TM also in ti-
tano-hematites become progressively more difficult to ana-
lyze because of broadening and overlapping of the peaks of
the spectrum (Warner et al. 1972). Such a result is not inter-
pretable according to standard procedures. Fe-Ti oxides of
basaltic rocks (Table 1) were measured at room temperature
as well as at the liquid nitrogen temperature. While the spec-
tra at room temperature were broad (non Lorentzian lines), on
cooling to 196
o
C, one set of six lines was sharpened dra-
matically. The parameters of the spectra correspond rather to
magnetite, but with relatively broad lines. Similar results
have been published by Banerjee et al. (1967). According to
their suggestion the results suggest that at 196
o
C there is no
hopping of the electrons among the octahedral Fe
2+
and Fe
3+
ions, so that the observed spectrum is the sum of that from
Fe
2+
, which is broad and similar to that of Fe
2
TiO
4
, and Fe
3+
,
which is an almost spherically symmetrical ion and gives
sharp lines as it is not so sensitive to the random environ-
ment. We know that individual magnetic minerals are present
in different grain size in the sample. The Mössbauer spectros-
copy is very sensitive to the grain size of the studied sample.
For example while Hem of about 18 nm has a typical sextets
spectrum, Hem of about 5 nm appears as a typical doublets,
paramagnetic spectrum.
Most of the Mössbauers spectra of the Fe-Ti oxides from
the andesitic rocks were interpreted despite the above de-
scribed difficulties. The interpretation of Ilm is considered
problematic. Its presence has been only predicted in respec-
tive rocks. Most andesitic rock samples contain Mag, Hem,
Magh, in some samples also TM or Ilm, according to Tables
13. Their relation is very different.
X-ray powder diffraction analysis
We can use the results of analyses to make only a rough
image about the composition of the Fe-Ti oxides. We know
that the unit cell size increases with the amount of the
Fe
2
TiO
4
within the titanomagnetite (from 8.39 Å for pure
Fe
3
O
4
to 8.53 Å for pure Fe
2
TiO
4
, McElhinny 1973). Similar-
ly the unit cell parameter (a
rh
) increases with the amount of il-
menite (FeTiO
3
) within the hematite-ilmenite (from 5.42 Å
for pure
α
-Fe
2
O
3
to 5.54 Å for pure ilmenite, McElhinny
1973). This means that the composition of the Fe-Ti oxide
might have been determined very effectively on the basis of
the unit cell parameters. Due to intricate interferences, the X-
ray diagrams were not suitable for deriving the unit cell sizes
of the Fe-Ti oxides. Only a qualitative interpretation of the X-
ray diagrams were made. (We derived the lattice constants of
some samples of the TMs using the equation of Hamano
(1989), for basalts for the temperature 20
o
C in the past, Orlic-
ký et al. (1992); they are: d = 8.4558.489 Å, for x = 0.30.73).
Measurements of the magnetic susceptibility change
of samples influenced by temperature
The method can use the following effects for the detection
of different magnetic phases within the magnetic material:
The Curie temperature (T
C
) which is a characteristic
constant for both, ferromagnetic or ferrimagnetic materials.
The Curie temperatures of TMs are dependent primarily on
the concentration of cations found on the octahedral and tet-
rahedral lattice sites and are dependent in only a subordinate
way on the cation distribution (OReilly 1984).
The Verwey transition temperature (T
V
) of magnetite
at about 155
o
C (magnetite undergoes a cubic-to-orthorom-
bic crystallographic transition on cooling through 155
o
C,
Stacey & Banerjee 1974). This effect is accompanied by the
THE CARRIERS OF MAGNETIC PROPERTIES IN THE NEOVOLCANIC ROCKS 189
presence of magnetic susceptibility (
κ
, or other magnetic
parameters) peak at about 155
o
C; it is the so-called iso-
tropic point. However, the isotropic point itself is very sen-
sitive to departures from stoichiometry of the magnetite and
generally will be lowered for impure samples (Syono & Ish-
ikawa 1963). The presence of a well defined isotropic peak
in magnetite constitutes a diagnostic feature of the multido-
main state (Radhakrishnamurty et al. 1981).
A decreasing of the
κ
of the titanomagnetites from
room temperature down to liquid nitrogen temperature. This
effect was studied by Senanayake & McElhinny (1982) on
the magnetic fraction of basaltic rocks, and by Radhakrish-
namurty & Likhite (1993) on synthesized titanomagnetites.
A decreasing of the
κ
of maghemitized magnetite over
280
o
C due to transformation of maghemitized part of mag-
netite (if any) into hematite influenced by temperature. This
effect appears more conspicuous with decreasing of the
grain size of magnetic particles.
The Morin transition of hematite. In hematite, the spin
moments above 10
o
C are oriented in the c plane, but in-
stead of being precisely antiparallel, they are slightly cant-
ed, resulting in a weak spontaneous magnetization within
the c plane, but normal to the spin-axis. Below 10
o
C, due
to change in the sign of the magnetocrystalline anisotropy,
the c-axis becomes the spin axis (Stacey & Banerjee 1974).
This effect is accompanied by a sharp decreasing of the
κ
,
or other magnetic parameter of hematite, being cooled e.g.
from room temperature to below 10
o
C. This effect de-
pends very strongly on the stoichiometry of hematite, in
some non-stoichiometric hematites it is completely missing.
The Néel temperature (T
N
) for the detection of the sto-
ichiometric ilmenite at about 218
o
C. In the hematite-ilmeni-
tes the Néel temperature ranges in the 218
o
C (ilmenite) to
675
o
C (for hematite) temperature interval, depending on the
content of ilmenite in hematite (Nord & Lawson 1989; McEl-
hinny 1973). Several samples of hornblende pyroxene andes-
ite of locality 3-IV-B1 (group J) were studied by the method
of electric voltage change of a sample influenced by tempera-
ture, in the interval from laboratory temperature down to liq-
uid helium temperature.
The presence of non-stoichiometric ilmenite was detected
by this method.
Moreover, if the Curie temperatures of synthetic TMs of
defined composition are known, the compositional parame-
ter (x) of a respective sample of natural Fe-Ti oxide can be
derived (e.g. magnetic phases of samples 148a/7 and B2/16,
with the range T
C
≈
130220
o
C, Table 1, correspond to the
composition of Fe
2.3
Ti
0.7
O
4
Fe
2.4
Ti
0.6
O
4
, and magnetic
phases of samples Kr.Vr.-26/1 and Bd-256/2 with the range
T
C
≈
420480
o
C, Table 1, correspond to the compostion of
Fe
2.7
Ti
0.3
O
4
Fe
2.8
Ti
0.2
O
4
, comparing our results with those
published by Radhakrishnamurty et al. (1981) for synthetic
TMs of defined parameter x). The composition of Ti
4+
in
TM derived by this procedure is supposed to be rather high-
er compared with that derived from the Ti/Fe ratio accord-
ing to Furuta (1993). (The data presented by Radhakrishna-
murty et al. 1981 were obtained on synthetic, stoichiometric
T
M
, whereas the data presented by Furuta (1993), were de-
rived from the results of natural Fe-Ti oxides; other discrep-
ancy can result from a different oxidation of TM; e.g. a TM
of x = 0.6 could have T
C
≈
175
o
C for oxidation parameter
z = 0.0, but T
C
≈
490
o
C for z = 1.0, according to Néel
Chevallier theoretical calculation; in Moskowitz 1987).
Fig. 5. Thermomagnetic curves of sample No. V-6/1 (aphanitic ba-
saltic andesite). The sample contains two magnetic phases T
C1
≈
210
o
C; T
C2
≈
575
o
C.
Fig. 4. Thermomagnetic curves of sample No. B2/16 (nepheline
basanite). Sample contains two magnetic phases T
C1
≈
220
o
C; T
C2
≈
570
o
C. Curve 1 measurements of the sample in air; Curve 2
measurements in a vaccuum (
≈
10
5
Torr). Only one phase with T
C1
≈
170
o
C has been detected after heating of the sample to 700
o
C and
successive cooling in a vacuum.
Fig. 3. Thermomagnetic curve of sample No. 148a/7 (basaltic
andesite). The sample contains two magnetic phases T
C1
≈
130
o
C; T
C2
≈
570
o
C;
κ
T
magnetic susceptibility of the sample
at temperature T,
κ
Max
maximum magnetic susceptibility of the
sample among all the data within the whole applied temperature
interval. T
C
Curie temperature of concrete magnetic phase. T
temperature.
→
heating of sample,
←
cooling of sample. The ex-
planations of T,
κ
Max
,T
C
,T,
→
,
←
, are also valid for Figs. 410.
190 ORLICKÝ
tite has pointed out very clear, reproducible Curie tempera-
ture of T
C
≈
675
o
C, Hopkinsons peak (Hp
≈
650
o
C) and the
Morin transition temperature of about T
M
≈
20
o
C (Orlický
1994). No case of detection of Curie temperature of T
C
≈
675
o
C, Morin transition of T
M
≈
20
o
C or Hopkinsons peak
of about 650
o
C was found in these volcanic rocks. It means,
no clear stoichiometric hematites occurred in the above
mentioned rocks, but hematite-ilmenites should be present
in these rocks. The presence of the hematite-ilmenites can
be interpreted on the basis of their Curie (or Néel) tempera-
tures, taking into account the theoretical linear dependence
of T
C
on the portion of ilmenite within hematite; T
C
≈
675
o
C
corresponds to pure hematite and T
C
≈
218
o
C corresponds
to pure ilmenite (Stacey & Banerjee 1974; McElhinny 1973;
Nord & Lawson 1989). So, the compositional parameter
x
≈
0.090.04 has been derived for Fe-Ti oxides of Curie
temperatures within the range T
C
≈
585640
o
C. This is sup-
posed to be within the range of the hematite-rich compo-
nents, which are as a consequence of slow cooling of titano-
hematites (Fe
2-x
Ti
x
O
3
), according to the above mentioned
statements.
We see from Tables 13 and in Figs. 310, that most of the
rocks contain two magnetic phases, but some of them contain
only one magnetic phase. The characteristic representative
thermomagnetic curves of Fe-Ti oxides (Figs. 310) have
been chosen on the basis of a comparison of the results of all
the samples studied by this method (670 individual samples
were studied; the T
C
of the magnetic phase on each presented
graph is inferred where the projected steepest part of the de-
scending curve intersects the temperature axis; only the re-
sults during heating of the sample were considered for the de-
tection of different magnetic phases on the basis Curie
temperatures). We see from Figs. 37 and Fig. 9 that a rela-
tion between the magnetic phase of lower Curie temperature
and that of higher T
C
is different. In Figs. 8, 10, only one
magnetic phase of Fe-Ti oxide was detected within the stud-
ied samples of rock.
Interpretation of the results
Seven dominant groups of magnetism carriers have been
chosen on the basis of thermomagnetic curves and the rela-
tion of magnetic phases within the rocks. The mentioned
groups have been designated B, C, D, F, G, I, and J (Tables
13 and in Figs. 310). The following characteristics of the
individual groups are presented below.
Group B: the Fe-Ti oxides of the group contain two mag-
netic phases (Figs. 3, 4); a dominant phase (T
C1
≈
130
220
o
C) containing quasi homogeneous to partly oxidized
TMs with a composition of Fe
2.35
Ti
0.65
O
4
Fe2.5Ti
0.5
O
4
, and
the second- less abundant magnetic phase (T
C2
≈
570
o
C)
which contains oxidized TMs.
Group C: Fe-Ti oxides contain two magnetic phases
(Fig. 5): the first magnetic phase (T
C1
≈
210
o
C) corresponds
to quasi homogeneous to partly oxidized TMs of composi-
tion Fe
2.5
Ti
0.5
O
4
, and the second-phase T
C2
≈
575
o
C, which
corresponds to oxidized TMs. The share of both phases is
supposed to be equal in the rocks.
Fig. 6. Thermomagnetic curves of samples of magnetic fraction.
Curve 1 sample No. Bd-256/2 glassy pyroxene-feldsparic
andesite. The sample contains two magnetic phases T
C1
≈
480
o
C;
T
C2
≈
590
o
C. Curve 2 sample No. Vt-45/11 pyroxene andesite.
The sample contains two magnetic phases T
C1
≈
480
o
C; T
C2
≈
590
o
C.
Fig. 7. Thermomagnetic curves of samples of magnetic fraction.
Curve 1 sample No. 329-B2 pyroxene-hornblende andesite. The
sample contains two magnetic phases T
C1
≈
530
o
C; T
C2
≈
590
600
o
C. Sample No. KrVr-26/1 hyperstene-augite andesite. The
sample contains two magnetic phases T
C1
≈
420
o
C; T
C2
≈
600
o
C.
Fig. 8. Thermomagnetic curves of samples of magnetic fraction.
Curve 1 sample No. I-104/1 propylized pyroxene andesite.
The sample contains only one magnetic phase of T
C
≈
580
o
C and
Verwey transition temperature T
V
≈
153
o
C. The sample showed
very strong maghemitization in the interval 220530
o
C. Curve 2
sample No. I-181/4-propylitized pyroxene andesite. The sample
contains only one magnetic phase of T
C
≈
580
o
C and Verwey transi-
tion temperature T
V
≈
153
o
C.
We see from Tables 13, that quite frequently a presence
of hematite in respective rocks has been interpreted on the ba-
sis of ore microscopy, Mössbauer spectroscopy and X-ray
diffraction analysis. We know that pure stoichiometric hema-
THE CARRIERS OF MAGNETIC PROPERTIES IN THE NEOVOLCANIC ROCKS 191
Group D: Fe-Ti oxides contain two magnetic phases
(Fig. 6); the first dominant magnetic phase of T
C1
≈
480
o
C and the second magnetic phase of T
C2
≈
590
o
C,
which is in a minor portion in the sample. Both magnetic
phases correspond to oxidized TMs of unknown composi-
tion. Hematite-ilmenites can be present in these minerals.
Group F: Fe-Ti oxides contain two magnetic phases
(Fig. 7); the first magnetic phase of T
C1
≈
420
o
C and T
C1
≈
530
o
C, and the second magnetic phase of T
C2
≈
600
o
C and
T
C2
≈
590600
o
C. Both magnetic phases correspond to oxi-
dized TMs with presence of hematite-ilmenites.
The magnetic minerals of groups B to F show a characteris-
tic decreasing of
κ
from laboratory temperature down to liq-
uid nitrogen temperature (Figs. 37). This behaviour reflects
a presence of either quasi homogeneous or oxidized TMs.
Group G: The magnetic minerals of this group contain
only one magnetic phase of T
C
≈
580
o
C (and Verwey transi-
tion temperature of T
V
≈
153
o
C (Fig. 8)). This magnetic
phase corresponds to pure multi domain magnetite (a small
portion of hematite-ilmenites can be present in these mag-
netic minerals).
Group I: The magnetic minerals of this group contain two
magnetic phases, both of them with comparatively high Cu-
rie temperatures (Fig. 9; T
C1
≈
580
o
C, T
C2
≈
620630
o
C).
The first phase corresponds to magnetite (mostly non-sto-
ichiometric), the second phase contains hematite-ilmenites.
Group J: The magnetic minerals contain only one magnet-
ic phase of Curie temperatures in the range T
C
≈
620640
o
C.
Hematite-ilmenites are present in the rocks of the group J. Il-
menites are frequently present in both I and J groups (see Ta-
bles 13). The composition of the hematite-ilmenites is sup-
posed to be within the range of x
≈
0.090.04 for magnetic
phases with Curie temperatures of T
C
≈
585640
o
C.
Magnetic minerals of the first phase of lower T
C
of rocks
of the D and F groups correspond to oxidized TMs, the sec-
ond magnetic phase of higher T
C
correspond probably also
to oxidized TMs with a presence of hematite-ilmenites. Ac-
cording to McElhinny (1973) the composition of naturally
occurring spinels tend to be displaced towards the ilmenite-
hematite series in the direction of increased oxidation. So,
we can predict that the hematite-ilmenites can also be
present there in the rocks of the B, C, groups, despite not
having been detected by applied methods. The composi-
tions of oxidized TMs have not been derived due to lack of
information about the degree of oxidation.
The occurrences of the above mentioned dominant groups
of magnetism carriers have been delineated in the geologi-
cal schemes (Figs.1, 2).
The Fe-Ti oxides of groups B and C (Figs. 35) have been
revealed dominantly within the basalts and basaltic andesites
(Figs.1, 2). Oxidized TMs of group D were revealed in pyrox-
ene andesites, glassy pyroxene feldspharic andesites (Fig. 1)
and olivine basalts, as well as in basaltic andesites (Figs.1, 2).
Fe-Ti oxides of C and D groups were revealed mostly within
the smaller individual lava flows, basaltic diatremes, volcanic
cones, dykes and necks. Fe-Ti oxides of group F are frequent-
ly present in basaltic andesites, pyroxene andesites of the
Kremnické vrchy Mts., in pyroxene and basaltic andesites as
well as in hornblende and hyperstene hornblende andesites of
the Po¾ana and Javorie Mts. (Fig. 1). Magnetites of group G
were revealed mostly within the propylitized andesites and
the most of intrusive rocks (Fig. 1; e.g. diorites, monzodior-
ites from borehole Kon-1, within the interval from ca. 1000
to 1800 m contain dominantly magnetite of the group G).
The basalts of several localities contain minerals near to
magnetite (Figs.1, 2). These types of Fe-Ti oxides were
found mostly in basaltic bodies of different shapes (lava
flows, volcanic cones and agglomerates together).
While the Fe-Ti oxides of the group I have been revealed
very frequently in andesites of variable petrographic types,
as well as in several localities of rhyolites, the Fe-Ti oxides
of the group J occurred mostly within biotite-hornblende
andesites, hornblende pyroxene andesite, hyperstene-horn-
blende andesites, as well as in most of rhyolites and rhyo-
dacites (Fig. 1). TMs or oxidized TMs have never been
found in rhyolites or rhyodacites.
Acknowledgements: I thank RNDr. J. Beòka, CSc., RNDr.
A. Mihalíková who performed respectively the ore and trans-
mission microscopy, RNDr. F. Caòo, who realized the elec-
Fig. 10. Thermomagnetic curves of samples of magnetic fraction.
Curve 1 sample No. 3-IV-B1/1 hornblende-pyroxene andesite.
Curve 2 sample No. St-201/4 biotite-hornblende andesite.
Curve 3 sample No. St-TR-24/23 hyperstene-hornblende-bi-
otite andesite. All three samples contain only one magnetic phase of
high Curie temperature-from T
C
≈
620
o
C (curve 2) to T
C
≈
640
o
C
(curve 3). Sample 3-IV-B1/1 is highly maghemitized.
Fig. 9. Thermomagnetic curves of samples of magnetic fraction.
Curve 1 sample No. St-215/3; Curve 2 sample No. St-156/1
both samples are biotite-hornblende andesites. The samples contain
two magnetic phases of T
C1
≈
580
o
C and T
C2
≈
620630
o
C. The first
phase of sample showed theVerwey transition temperature as well.
192 ORLICKÝ
tron microprobe analysis, Prof. Ing. J. Lipka, DrSc., and Ing.
I. Tóth who performed the laboratory measurements and the
interpretation of the Mössbauer spectroscopy, RNDr. B. To-
man, who realized the laboratory measurements and the inter-
pretation of the X-ray diffraction analysis, and Doc. RNDr. A.
Zentko, DrSc., who studied the change of electric voltage of
samples influenced by temperature in the interval from labo-
ratory temperature down to liquid helium temperature.
Many
thanks Doc.RNDr.I.Rojkoviè,DrSc., and RNDr.J.Lexa,CSc.,
for stimulating discussions and very appreciable improvement
of early version of the manuscript.
References
Ade Hall J.M., Palmer H.C. & Hubbard T.P., 1971: The magnetic
and petrological response of basalts to regional hydrothermal
alteration. Geophys. J. Roy. Astron. Soc., 24, 13717.
Banerjee S.K. & OReilly W., 1967: Mössbauer-effect measure-
ments in Fe-Ti spinels with local disorder. J. of Apl. Phys., 38,
3, 12891290.
Ehlers E.G. & Blatt H., 1980: Petrology, Igneous, Sedimentary and
Metamorphic. W.H. Freeman and Company, San Francisco.
Furuta T., 1993: Magnetic properties and ferromagnetic mineralo-
gy of oceanic basalts. Geophys. J. Int., 113, 95114.
Hamano Y., 1989: Lattice constants of titanomagnetites at high
temperatures. J. Geomag. Geoelectr., 41, 6575.
Hargraves R.B. & Petersen N., 1971: Notes on the correlation be-
tween petrology and magnetic properties of basaltic rocks. Z.
Geophys., 37, 367382.
Koneèný V., Lexa J. & Planderová E., 1983: Stratigraphy of the Cen-
tral Volcanic Fields. Západ. Karpaty, Sér. Geol., 9 (in Slovak).
Kropáèek V., Laovièková M. & Bochníèek J., 1981: Magnetic
and electrical properties of basaltic rocks from South-Eastern
Slovakia. Sbor. Geol. Vìd, ø. UG, 17, 87100.
Kropáèek V., 1985: Magnetic properties of young alkaline volca-
nic rocks of Central Europe. (Doctorants Thesis). Manu-
script; The Geophysical Institute of the Czechoslovak
Republic, Prague, (in Czech).
Lexa J., Koneèný V., Kalièiak M., Hojstrièová V., 1993: A space-
time distribution of volcanics in the Carpatho-Pannonian re-
gion. Geodynamic model and deep-seated pattern of the West
Carpathians. GÚD, Bratislava, 5769 (in Slovak).
Lexa J., Koneèný P., Hojstrièová V., Koneèný V. & Köhlerová M.,
1997: The petrographical model of the tiavnica Mts.´s Stra-
tovolcano. Manuscript. In the Archives of the Geological Sur-
vey of Slovak Republic, Bratislava (in Slovak).
Lawson Ch.A., Nord Jr.G.L. & Champion D.E., 1987: Fe-Ti oxide
mineralogy and the origin of normal and reverse remanent
magnetization in dacite pumice blocks from Mt. Shasta, Cali-
fornia. Phys. Earth Planet. Inter., 46, 270288.
Lipka J., Hucl M., Prejsa M., Tóth I., Cirák J., Gábri F., Sitek J.,
Grone R., Èerveò I., Seberíni M., Metko E., tubendek M., 1982-
1988: Mössbauer spectroscopy of natural minerals. (IVI stage,
Manuscripts). The laboratory of the Nuclear Physic Dept. of the
Slovak Technical University, Bratislava (in Slovak).
McElhinny M.W., 1973: Palaeomagnetism and plate tectonics.
Cambridge University Press, 1357.
Mihalíková A. & ímová M., 1989: The geochemistry and petrolo-
gy of the Miocene-Pleistocene alkaline basalts of
central
and
southern Slovakia. Západ. Karpaty, Ser. Miner., Geochem.,
Metallogen., 12, 7142 (in Slovak).
Moskowitz B.M., 1987: Towards resolving the inconsistencies in
characteristic physical properties of synthetic tita-
nomaghemites. Phys. Earth Planet. Inter., 46, 173183.
Nord Jr. G.L. & Lawson Ch.A., 1989: Order-disorder transition-in-
duced twin domains and magnetic properties in ilmenite-he-
matite. Amer. Mineralogist, 74, 160176.
ODonovan J.B. & OReilly W., 1977: The preparation, character-
ization and magnetic properties of sythetic analogues of some
carriers of the palaeomagnetic record. Adv. Earth Planet. Sci.,
1, 99112.
OReilly W., 1984: Rock and mineral magnetism. Blackie, Glas-
gow, 1222.
Orlický O., Kropáèek V. & Vass D., 1982: Palaeomagnetism and
radiometric ages of alkaline basalts of SW Slovakia. Miner.
slovaca, 14, 97116 (in Slovak).
Orlický O., 1990: Detection of magnetic carriers in rocks: results
of susceptibility changes in powdered rock samples induced
by temperature. Phys. Earth. Planet. Inter., 63, 6670.
Orlický O., 1992: Paleomagnetismtiavnické vrchy and Po-
hronský Inovec Mts., Vtáènik Mts., Kremnické vrchy Mts.,
Javorie and Po¾ana Mts. (Manuscript). Geophysical Institute
of the Slovak Academy of Sciences, Bratislava (in Slovak).
Orlický O., Caòo F., Lipka J., Mihaliková A. & Toman B., 1992:
Fe-Ti magnetic minerals of basaltic rocks: A study of their
nature and composition. Geol. Carpathica, 43, 5, 287293.
Orlický O., 1993: Palaeomagnetism and magnetic mineralogy of
selected neovolcanic rocks of the Central Slovakia. Geol.
Carpathica, 44, 6, 399408.
Orlický O., 1994: Study and detection of magnetic minerals by
means of the measurements of their low-field susceptibility
changes induced by temperature. Geol. Carpathica, 45, 113119.
Orlický O., 1996: Curie temperatures of the Fe-Ti oxides of ba-
salts: Is it possible to use Curie temperatures to assess the
source of the depth of origin of the Fe-Ti oxides and related
basalt magmas? Geol. Carpathica, 47, 1, 5158.
Orlický O., Balogh K., Koneèný V., Lexa J., Túnyi I. & Vass D.,
1996: Paleomagnetism and radiometric ages of basalts of
Central and Southern Slovakia (Western Carpathians). Geol.
Carpathica, 47,1, 2130.
Pateka V., 1991: Identification of Magnetic Minerals at Low Temper-
atures. Acta Geol. Geogr. Univ. Comen., Geol., 47/II, 121125.
Radhakrishnamurty C., Likhite S.D., Deutsh E.R. & Murthy G.S.,
1981: A comparison of the magnetic properties of synthetic ti-
tanomagnetites and basalts. Phys. Earth Planet. Inter., 26, 3746.
Radhakrishnamurty C. & Likhite S.D., 1993: Frequency depen-
dence of low-temperature susceptibility peak in some titano-
magnetites. Phys. Earth Planet. Inter., 76, 131135.
Readman P.W. & OReilly W., 1970: The synthesis and inversion
of non-stoichiometric titanomagnetites. Phys. Earth Planet.
Inter., 4, 121128.
Stacey F.D. & Banerjee S.K., 1974: The physical principles of rock
magnetism. Elsevier, Amsterdam, 1195.
Syono Y. & Ishikawa Y., 1963: Magnetocrystalline anisotropy of
xFe
2
TiO4(1-x)Fe
3
O4. J. Phys. Soc. Jpn., 18; 12301231.
Senanayake W.E. & McElhinny M.W., 1982: The effects of heating
on low-temperature susceptibility and hysteresis properties of
basalts. Phys. Earth Planet. Inter., 30, 317321.
Warner B.N., Shive P.N., Allen J.L. & Terry C., 1972: A Study of
the hematite-ilmenite series by the Mössbauer Effect. J. Geo-
mag. Geoelectr., 24, 353367.