GEOLOGICA CARPATHICA, 48, 2, BRATISLAVA, APRIL 1997
113–121
PETROLOGY OF THE WESTERN CARPATHIANS CRETACEOUS
PRIMITIVE ALKALINE VOLCANICS
JÁN SPIŠIAK
1
and DUŠAN HOVORKA
2
1
Geological Institute, Slovak, Academy of Sciences, Bratislava; Branch: Severná 5, 974 01 Banská Bystrica, Slovak Republic
2
Department of Mineralogy and Petrology, Faculty of Sciences, Comenius University, Mlynská dolina, 842 15 Bratislava, Slovak Republic
(Manuscript received March 20, 1996; accepted in revised form December 12, 1996)
Abstract:
In several Mesozoic tectonic units (Silesian, Tatric and Fatric ones) of the Western Carpathians, different
alkaline effusive and rarely also intrusive rocks of the Cretaceous age (approx. 100 Ma) are known. Olivines,
clinopyroxenes and less frequently also amphiboles form phenocrysts, and glomerophyric accumulations of them
occur in places. Fine-grained devitrified matrix (up to 40 vol. %) is another constant rock component. The nature of
Cpx phenocrysts documents a rapid ascent of the melt which was contaminated by the resorption (mostly of carbon-
ates) of xenoliths. The variable composition of these rocks is mainly a result of fractional crystallization and xenolith
assimilation. According to their chemical composition these rocks correspond to alkaline basalts/basanites, locally
even picrites. The presence of primitive alkaline volcanics is a consequence of extending volcanic activity in their
respective units.
Key words:
Western Carpathians, Cretaceous, primitive alkaline volcanics, petrology, geochemistry.
Introduction
The products of Mesozoic volcanic activities of various
types occur in several tectonic units which are parts of the
outer, central and inner tectonic zones of the Western Car-
pathians. They have calc-alkaline, tholeiitic and alkaline
characters. Alkaline volcanics occur in the outer and central
zones. Extending volcanism took place in a relatively short
time-period in the Cretaceous. The main products of the vol-
canic activity are lava flows, dykes and mostly hyaloclastite
flows and hyaloclatites. The thickness of individual volcanic
bodies varies from several meters to tens of meters.
In this paper we deal with Cretaceous alkaline basalts,
basanites and picrites. The geological position of the prod-
ucts of Mesozoic volcanic activity as well as their diversity
in space and time, have already been described in detail (see
Hovorka & Spišiak 1989, 1993). All the available analytical
data (Mahmood 1973; Bujnovský et al. 1981; Hovorka &
Spišiak 1988; Kudělásková 1982) have been used for
geochemical interpretation.
Geology
In the Outer Western Carpathians the area of the Moravs-
kosliezske Beskydy Mts. and the adjacent areas, both in the
Czech Republic and Polish territories, are classical occur-
rences (Teschen/Těšín = type locality) of volcanics of the
teschenite, or teschenite-picrite association (Hohenegger
1861; Tschermak 1866). The volcanic activity had a polys-
tadial character; its maximum was in the Barremian-Albian
(Table 1). The prevalence of shallow subsurface sills over ef-
fusives or their volcaniclastics, is the characteristic feature
of the whole province. Volcanic activity was located in a
longitudinal zone parallel to the axis of the Silesian nappe
basin. There was no continuous (“line” type) penetration of
magmatic melts on the bottom of the basin. Volcanic activi-
ty, however, had the character of mutually isolated fissure
and sill penetrations of magma on the water-covered surface
as well as of seamounts of alkaline basalt type.
Alkaline basalts/basanites occur in the cover Mesozoic
units (in the Malé Karpaty Mts., the Tatry Mts. and the Nízke
Tatry Mts.) as well as in a unit of nappe position (the Krížna
Nappe). In all cases volcanic activity took place in the Ap-
tian to Middle Albian. The majority of volcanics in the above
mentioned units of the central zone have the character of hy-
aloclastites. In several cases volcanics occur in the form of
dykes, in the Middle Triassic carbonates.
The alkaline basalts have sharp contacts with the host rocks.
In some places only low-temperature mostly hydrothermal ef-
fects on the neighbouring rocks can be observed. Seismic ef-
fects due to volcanic activity on not yet consolidated sedi-
ments (Pl. I) have been described (Hovorka & Sýkora 1980).
Concluding the geological problems of the alkaline basalts
of the Central Western Carpathian zone it should be stressed
that the cover units on one side, and the Krížna Nappe on the
other one, represent spatially clearly different tectonic units.
Their alkaline basalts are more-or-less identical.
Besides alkaline basalt/basanites there are also picrites in
the central zone. They are known from the area of Banská
Bystrica as hidden bodies, found in boreholes. These picrites
appear in two tectonic units — the Krížna and Chočƒ nappes
— we suppose the emplacement of the picrites after the
settlement (Upper Cretaceous) of these geological units in
their present position.
114 SPIŠIAK and HOVORKA
Petrology and mineralogy
The alkaline basalts/basanites of the outer as well as the
central zones occur in the form of massive lava flows, volca-
nic (chimney) breccias and hyaloclastites. Olivines, py-
roxenes and less frequently amphiboles form phenocrysts;
locally glomerophyric accumulations of these phases are
present. Most lava flows have a fine-grained devitrified ma-
trix, forming as much as 40 per cent of the rock.
The picrites have pronouncedly phyric (Ol, Phl) fabrics.
Their matrix is fine-grained passing gradually to the original-
ly glassy fabric. Generally a fresh appearance of picrites in
thin sections is characteristic.
There are common amygdaloidal types with amygdales
filled up with carbonates, chlorites and zeolites. Apart from
amygdales, there are varying amounts of assimilated xeno-
liths (especially of carbonate rocks). For petrological and
geochemical interpretations we have chosen rock types not
affected by assimilation and metasomatism, i.e. without
amygdales and xenoliths (all the analysed samples have been
microscopically checked).
Olivines
in phyric form are present especially in picrites
and basanites (more magnesian). They are strongly altered
and in most cases only olivine pseudomorphs have been pre-
served; they are filled up with serpentine-group minerals,
chlorite and saponite. In the olivines there are rare Cr-spinel
enclosures (they mostly occur in picrites). Mg/Mg+Fe
2+
ratio
in the olivine varies in a narrow range from 0.86 to 0.87,
which corresponds to the olivines from equivalent rocks (Do-
bosi l987; Bédard et al. l988; Trommsdorff et al. l990).
Clinopyroxenes
are quantitatively the most abundant and
genetically the most significant minerals in all rock types.
Beside phenocrysts of variable shape and size they also form
microlites in devitrified matrix. Phenocryst forming clinopy-
roxenes are characteristic for sector and oscillatory zoning.
Sector zoning (hourglass structure) is expressed through two
very different sectors: pyramidal and prismatic. They differ
optically (the pyramidal one has a higher birefringence and a
lower refraction index) and chemically (Table 2). Pyramidal
sectors (011, 111) are rich in Mg, Si and depleted in Fe, Al,
Ti, as opposed to prismatic sectors (100, 110). Genetically,
sector zoning is related to different speed of the growth of in-
dividual crystal planes and to partial balance between the
crystal surface and the melt (Hollister & Gancarz l97l; Leung
l974; Nakamura 1974). Oscillatory zoning is common. Rims
enriched in Ti, Al
IV
and Fe and depleted in Mg, Al
VI
are
abundant. Sometimes there are Fe-enriched rims around Ti-
augite crystals (Fe-augite, Mahmood l973). The composition
of Cpx microlites corresponds to that of phenocrysts rims.
Following Cpx classification (IMA; Morimoto et al. l988)
these Cpx correspond to diopside (Fig. 1); the differences in
composition are expressed by appropriate different adjec-
tives (titanian, aluminian, calcian, ferroan, etc.). According
to Poldervaart & Hess (l95l) most clinopyroxenes correspond
to salite. Cpx from picrites have lower Ca and/or higher Fe
Table 1:
Survey of the Western Carpathian Mesozoic volcanic activity.
Fig. 1.
Classification diagrams of clinopyroxenes (Morimoto et al.
1988). 1 — analyses of clinopyroxenes from basanites, Outer
Western Carpathians, 2 — analyses of clinopyroxenes from basan-
ites and picrites, Central Western Carpathians; A — augite, D —
diopside.
OUTER WESTERN
CARPATHIANS
CENTRAL WESTERN CARPATHIANS
Tectonic Unit
Silezic Unit
Tatric "envelope" Units
Krina Nappe
Choè Nappe
Association
Teschenite-Picrite Association
Alk. Basalts
Alk. Basalts Picrites
Picrites
Age
Berriasian-Aptian
Berriasian-Aptian
Valanginian-Albian
volcanics within the Mesozoic
sequences
Magma Series
Alk
Alk
Alk
Alk(?)
Volcanic Products
Sills, Lava Flows,
Hyaloclastites
Sills, Hyaloclastites, Lava Flows
Sills(?)
Geotectonic Position
WP
WP
WP
WP(?)
Lithostratigraphic Unit
Vývra M.
Sasková AB;
Stráe Picrites
Mlynná Dolina Valley AB;
Beckov Castle;
Kamenný ¾ab M.
Hyaloclastites;
Koeca M.;
Jed¾ovina M.;
Nolèovo M.;
Zemianska Dolina Valley M.;
Horný Diel Picrites
M - members, AB - Alk. Basalts
PETROLOGY OF THE WESTERN CARPATHIANS CRETACEOUS PRIMITIVE ALKALINE VOLCANICS 115
and Mg content. There is a good correlation between Al, or
Al
IV
and Ti. Pyroxene phenocrysts from the studied basanite
samples plot in both the “igneous clinopyroxene” and “inclu-
sion in basalts” fields of the Al
VI
versus Al
IV
diagram (Aoki
& Shiba 1973, Fig. 2). Cpx zoning (rimward enrichment in
Al
IV
, Ti and Fe and Mg and Al
VI
depletion) may be explained
in three ways (Bédard et al. l988): (1) it represents a kinetic
effect, (2) it reflects a differentiation of the melt as it cools
and crystallizes, or (3) it reflects changes in pressure during
crystallization. With regard to all possibilities and presented
data (zoning character, Cpx composition, rock composition,
etc.) we suppose that the dominant process of the Cpx gener-
ation were polybaric conditions and fractional crystallization
(Fig. 3). Rimward Ti-Al
IV
enrichment is a result of polybaric
crystallization during the ascent of the magma. As pointed
out by Wass (l979) data on solubility of Ti in Cpx in depen-
dence on pressure and temperature are often controversial. A
relation between Ti + Al
IV
: Si ratio and pressure has been
found, but fractionation trends can strongly influence the ra-
tio. The ratio of Al
IV
: Al
VI
in Cpx seems to be the most suit-
Table 2:
Selected analyses of clinopyroxene.
Fig. 2.
Al
VI
vs. Al
IV
in pyroxenes. Field of “Eclogites”, “Granulites
& inclusions in basalts” and “Igneous rocks” are from Aoki & Shi-
ba (1973). 1 — analyses of clinopyroxenes from basanites, Outer
Western Carpathians, 2 — analyses of clinopyroxenes from basan-
ites and picrites, Central Western Carpathians; c — core, r — rim.
(Data sources: Hovorka & Spišiak 1988; Spišiak et al. 1991; un-
published data). Py — pyramidal sector, Pr — prismatic sector.
SAMPLE
1Pr
2Pr
3c
3r
4m
5m
6r
6c
7c
7r
8r
8c
9Pr
9Py
rock
P
P
F
F
B
B
B
B
B
B
B
B
B
B
SiO
2
39.84
40.80
46.68
41.43
46.77
46.68
41.67
43.98
45.29
41.95
45.90
49.15
42.72
46.35
TiO
2
5.01
4.31
2.49
5.39
2.84
2.71
5.45
4.31
2.85
4.00
3.22
1.94
5.50
3.63
Al
2
O
3
10.39
9.81
5.87
10.09
5.17
4.98
9.95
9.25
6.46
8.99
6.57
4.70
11.51
7.65
Cr
2
O
3
0.00
0.00
0.00
0.00
0.00
0.03
0.04
0.05
0.65
0.41
0.00
0.00
0.00
0.00
FeO*
7.52
7.75
6.17
7.35
7.31
7.25
7.77
7.28
5.87
7.20
7.77
5.98
10.91
8.73
MnO
0.16
0.15
0.11
0.14
0.07
0.10
0.06
0.09
0.05
0.10
0.18
0.08
0.22
0.15
MgO
12.32
12.54
13.14
11.34
13.48
13.52
11.60
12.65
14.20
13.13
13.19
14.66
8.80
12.95
CaO
23.97
23.81
24.44
24.16
22.17
22.00
23.01
23.13
24.14
21.87
22.64
22.59
19.11
19.10
Na
2
O
0.57
0.59
0.45
0.57
0.42
0.40
0.46
0.46
0.45
0.49
0.46
0.47
0.60
0.51
K
2
O
0.21
0.22
0.34
0.34
0.00
0.01
0.00
0.00
0.00
0.09
0.00
0.00
0.05
0.30
TOTAL
99.99
99.98
99.69 100.81
98.23
97.68 100.01 101.20
99.96
98.23
99.93
99.57
99.42
99.37
Formula based on 6 oxygens
Si
1.53
1.56
1.76
1.57
1.78
1.79
1.58
1.64
1.70
1.61
1.73
1.83
1.63
1.74
Al
IV
0.47
0.44
0.24
0.43
0.22
0.21
0.42
0.36
0.29
0.39
0.27
0.17
0.37
0.26
Al
VI
0.00
0.00
0.02
0.02
0.02
0.01
0.03
0.04
0.00
0.02
0.02
0.04
0.14
0.08
Ti
0.14
0.12
0.07
0.15
0.08
0.08
0.16
0.12
0.08
0.12
0.09
0.05
0.16
0.10
Cr
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.01
0.00
0.00
0.00
0.00
Fe
3+
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Fe
2+
0.24
0.25
0.19
0.23
0.23
0.23
0.25
0.23
0.18
0.23
0.24
0.19
0.35
0.27
Mn
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.00
0.01
0.00
Mg
0.70
0.71
0.74
0.64
0.77
0.77
0.66
0.70
0.80
0.75
0.74
0.81
0.50
0.73
Ca
0.98
0.98
0.99
0.98
0.91
0.90
0.94
0.92
0.97
0.90
0.91
0.90
0.78
0.77
Na
0.04
0.04
0.03
0.04
0.03
0.03
0.03
0.03
0.03
0.04
0.03
0.03
0.04
0.04
K
0.01
0.01
0.02
0.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.01
FeO* - total Fe as FeO, Pr -prismatic sector, Py - pyramidal sector, c - core, r - rim, m - microlites, P -pyroxenites, F - fourchites, B - basanites,
l-3 - Outer Western Carpathians, 4-9 - Central Western Carpathians. Data sources: Kudìlásková l982, Hovorka & Spiiak et al. 1991,
original analyses.
116 SPIŠIAK and HOVORKA
able indicator of relative pressure (Thompson l974; Wass
l979). Following the Cpx composition in the Cretaceous al-
kaline basalts/basanites of the Western Carpathians we can
summarize:
— the ratio of Al
IV
: Al
VI
in Cpx cores is close to 1, which in-
dicates their crystallization originating under high pressures
and high temperatures (ca. 20 kbar, 1300
o
C);
— Cpx rims (with a high Al
IV
: Al
VI
ratio) crystallized under
much lower pressures, i.e. during the ascent of the melt;
— the ratio of Al
IV
: Al
VI
in the matrix microlites is similar to
that of phenocryst rims (the microlites crystallized during the
magma ascent).
The preceding findings are also proved by the composition
and the character of Cpx zoning in individual rock types. In
the case of rock bodies of great thickness, or well-crystal-
lized bodies, mineral zoning is insignificant and the Al
IV
: Al
VI
ratio low, close to 1. In thin dykes, Cpx zoning is well ex-
pressed, and the ratio (Al
IV
: Al
VI
) is high. On the basis of the
position of the analyzed Cpx in various discriminant dia-
grams (Le Bas l962; Leterrier et al. l982) they have the char-
acter of the Cpx of the alkaline (peralkaline) rock types.
Amphiboles.
A number of amphiboles vary in different
rock types, and/or depend on their evolution. The highest
modal contents are in thin basanite dykes. Similar to Cpx,
amphibole forms phenocrysts (usually smaller than Cpx)
with observable zoning. Apart from rare sector zoning there
is typical oscillatory zoning with increasing Ti, Al and Fe,
and decreasing Si and Mg rimwards. The other elements do
not show significant changes (K-depletion of the rims), or
there is no zoning. Zoning in Cpx and Hbl is identical. The
identical Hbl zoning has been described in similar alkaline
rock types (Mokhtari & Velde l987). Locally amphibole re-
placement of Cpx can be observed. The amphiboles under
study have high Ti and low Si contents. In the IMA amphib-
ole classification (Fig. 4, Leake l978) they correspond to
kaersutite, or subsilicic kaersutite. The composition of am-
phibole rims, or microlites, along with their occurrences (re-
placement of Cpx, concentrated occurrences in the spaces of
resorbed xenoliths) point out their origin from the melt hav-
ing been affected by xenolith assimilation (especially car-
bonatic rock).
Dark micas
(flakes smaller than 1 cm ) mostly occur in pi-
crites - here their composition corresponds to phlogopites,
and in thin basanite dykes, where they form tiny flakes of Ti-
biotite. In dark micas, too, there is zoning with increasing Ti
and Mg, and decreasing Fe and K from core to rim. The spe-
cific composition of the discussed micas reflects the compo-
sitions of the parental melt (high Ti, Mg, etc. contents).
In the matrix of primitive alkaline volcanics studied here,
there are also other minerals according to the rock type
namely: nepheline, analcime, plagioclase, leucite, ore min-
erals, spinel and others.
Geochemistry
Although the Cretaceous alkaline rocks of the central
West-Carpathian zone show considerably different modal
compositions, their chemical compositions are similar (Ta-
Fig. 4.
Classification diagram of amphiboles (Amph; IMA, Leake
1978). 1 — Amph from basanites, Outer Western Carpathians,
2 — Amph from basanites, Central Western Carpathians, 3 — se-
lected analyses, c — core, r — rim.
Fig. 3.
Al
IV
vs. Mg/(Mg + Fe) in pyroxenes from Western Car-
pathians Cretaceous alkali basalts/basanites. 1 — Cpx from basan-
ites, Outer Western Carpathians, 2 — Cpx from basanites and pi-
crites, 3 — Cpx from thin basanite dykes, 2, 3 — Central Western
Carpathians, r — rims; D — decompression, F — fractionation.
(Data sources: Hovorka & Spišiak 1988; Spišiak et al. 1991, un-
published data).
PETROLOGY OF THE WESTERN CARPATHIANS CRETACEOUS PRIMITIVE ALKALINE VOLCANICS 117
ble 3). In the Outer Western Carpathians there is a wider
range of rock types (from picrites to syenites); in the Central
Western Carpathians rock composition generally corre-
sponds to basanites. In the TAS diagram the volcanics are
concentrated in the field of basanites, and/or picrobasalts
(Hovorka & Spišiak l988). Following a more detailed classi-
fication of alkaline rocks (Le Bas l989, Fig. 5; Rock 1987,
Fig. 6) they correspond to basanites - melanephelinites, and/
or alkaline lamprophyres. In general, the rocks have low
SiO
2
(ca. 4l %) and high TiO
2
and P
2
O
5
contents (3.2 and
0.8 % respectively). Characteristic features of these rocks
are: elevated Cr (280 ppm) and Ni (l90 ppm) contents; ele-
vated contents of incompatible elements such as Ba
(650 ppm), Sr (700 ppm) and LREE; also high Nb (78 ppm),
V (245 ppm) and Zr (305 ppm) are detected. On the other
hand, the contents of Y (24 ppm) and HREE are relatively
low (all data in Hovorka & Spišiak l988, Nb = unpublished
data). Different discrimination diagrams (Pearce & Cann
1973; Mullen 1983; Meschede 1986 etc.) assign these rocks
to alkaline basalts (WPA, OIA; Hovorka & Spišiak 1993).
The standardized REE pattern (Fig. 7) shows a slight posi-
tive Eu anomaly. The REE contents and their normalized pat-
terns are equal in similar alkaline rocks in Europe (Wedepohl
l985; Mertes & Schmincke l985; Trommsdorff et al. 1990).
Several authors (e.g. Frey et al. l978) calculated mantle
sources for various basanite and nephelinite types on the basis
of REE abundances. They conclude that a single source (lher-
zolite pyrolite) modal composition can yield the observed
REE contents by 4–7 % melting provided that the source re-
gion was already relatively enriched in LREE prior to the par-
tial melting event. Their findings are also proved by data on
the abundances of other trace elements and at the same time
support the assumption on similar mantle sources and similar
melting characteristics for the alkaline rocks studied.
Table 3:
Chemical composition of representative rocks types.
SAMPLE
1
2
3
4
5
6
7
8
9
10
11
12
Rock
P
T
F
F
B
B
B
B
B
B
B
B
SiO
2
39.12
39.54
38.80
38.90
42.55
39.72
40.36
37.51
38.96
38.97
39.35
36.82
TiO
2
1.6
2.3
2.49
1.5
3.46
2.84
3.47
2.8
3.4
3.38
2.89
2.58
Al
2
O
3
11.99
14.16
13.27
12.48
12.83
13.19
13.32
10.88
12.61
12.57
14.08
9.81
Fe
2
O
3
5.52
6.32
8.06
6.3
13.47* 10.77* 12..26* 10.83*
6.46
6.07
11.46*
1.97
FeO
5.57
4.55
5.53
4.16
7.22
7.43
8.66
MnO
0.13
0.01
0
0.05
0.13
0.11
0.17
0.14
0.2
0.19
0.17
0.15
MgO
16.55
6.13
6.53
12.55
7.99
9.75
7.45
8.28
7.71
7.97
5.77
8.57
CaO
14.13
13.36
16.87
15
11.49
10.66
10.49
13.92
8.41
8.63
11.82
15.01
Na
2
O
1.4
3.29
3.02
1.76
3.21
1.46
2.59
2.66
2.17
2
2.1
2.64
K
2
O
0.8
1.77
0.65
0.68
0.17
1.56
2.26
0.76
2.41
2.54
4.05
0.75
P
2
O
5
0.45
1.54
0.62
1
1.12
0.58
0.99
0.78
0.097
0.99
1.02
0.76
LOI
2.65
7.58
3.19
5.71
4.1
9.2
5.5
11.5
9.76
9.47
6.7
13.3
TOTAL
99.91 100..55
99.03 100.09 100.52
99.95
98.86 100.06
99.407 100.21
99.41 101.02
Cr
460
3
4
320
193
343
180
316
106
177
57
288
Co
42
10
5
44
71
40
39
41
44
33
30
Ni
300
35
70
110
133
155
91
185
66
70
40
170
V
28
300
280
520
255
263
296
225
147
159
245
101
La
50
98
82
83
44
74
59
62.8
77.2
65
30
Ce
102
235
160
160
117
144
109
131
160.5
141
78
Nd
43
135
78
60
36
65
45
68.2
76.3
59
Sm
7.3
22
13
9.2
5.4
11.8
14
5.6
Eu
2.6
7
4.4
3.2
2.5
3.9
4.9
2.5
Gd
12
20.6
10.6
10.2
12.5
Tb
0.92
2.9
1.58
2.4
0.92
1.2
Ho
0.95
2.8
2.1
1.22
Yb
2.2
3.8
0.35
2.7
2
2.07
3.17
1.9
Lu
0.31
1.3
0.32
0.28
0.4
0.22
*
- total Fe as Fe
2
O
3
, P - picrites, T - teschenites, F - fourchites, B - basanites, l-4 - Outer Western Carpathians, 5-12 - Central Western
Carpathians. Data Sources: Kudìlásková 1982, Hovorka & Spiiak 1988, Spiiak et al.1991, original analyses.
118 SPIŠIAK and HOVORKA
Experiments with basanite-like melts (Green l973; Ulmer
et al. 1989 in Trommsdorff et al. l990) determined a rather
narrow temperature and pressure ranges of their generation
(25–30 kbar, 1200–1300
o
C). The composition and zoning
of Cpx in the Cretaceous alkaline rocks of the Western Car-
pathians document similar conditions of the generation (ap-
prox. 23 kbar and approx. 1260
o
C). A very low magma vis-
cosity and suitable geotectonic conditions caused a rapid
ascent of the melt and its further evolution.
The contents of the main and trace elements, including
REE in the rocks under consideration, are specific and have
no equivalent among the West-Carpathian volcanics. Their
compositions, however, correspond very well to the compo-
sitions of the Mesozoic alkaline rocks of the Northern Cal-
careous Alps (Trommsdorff et al. l990), and/or some Meso-
zoic alkaline rocks in Hungary (Bükk Mts., Mecsek Mts.,
Velence Mts., Buda Hills: Dobosi l986; Dobosi & Horváth
l988).
As it was presented before, for geochemical interpretations
we have chosen rock types without amygdales and xenoliths.
The problem of composition of these rocks (especially low
Fig. 6.
(K
2
O+Na
2
O) vs. SiO
2
plot of the lampropyres. Field of
lamprophyres according to Rock (1987). 1 — basanites from Out-
er Western Carpathians, 2 — basanites from Central Western Car-
pathians.
Fig. 5.
CIPW normative ne vs. ab plot of the nephelinitic rocks
and basanites (Le Bas 1989). 1 — basanites from Outer Western
Carpathians, 2 — basanites from central Western Carpathians,
B — basanites, MN — melanephelinites, N — nephelinites.
Fig. 7.
REE pattern of the Western Carpathians alkali basanites/ba-
salts normalized to chondrites (Haskin et al. 1968). 1 — basanites
from Central Western Carpathians, 2 — basanites from Outer
Western Carpathians, 3 — basanites (Ehrwaldite) from Northern
Calcareous Alps (Trommsdorff et al. 1990), 4 — Average compo-
sition of the alkali basalts (Wedepohl 1975), 5 — composition of
the basanites in Neogene European rift systems (Chauvel-Jahn
1984; Wedepohl 1985).
Plate I. Fig. 1.
Intimate contact of limy mud (aphanitic) with basal-
tic lava. The Ve ká Fatra Mts. — Biely potok brook (Hovorka &
Sýkora 1979). Enlarg. 27
×
. Fig. 2. Plastic deformation of unconsoli-
dated limy mud by moving basaltic lava — filling of epigenic
cracks by calcite. The Ve ká Fatra Mts. — Biely potok brook (Hov-
orka & Sýkora 1979). Enlarg. 1.4
×
. Fig. 3. Hyaloclasts of alkali ba-
salt in limestone. The Strážovské vrchy Mts. — Soblahov. Enlarg.
48
×, ||
polars. Fig. 4. Compositionally zonal phenocryst of clinopy-
roxene in alkali basalt. The Nízke Tatry Mts. — Salatin. Enlarg.
95
×, ||
polars. Fig. 5. Glomerophyric clinopyroxenes I with clinopy-
roxenes II on the rim of alkali basalt. The Strážovské vrchy Up-
land — brook near Mraznica. Enlarg. 30
×
/polars. Fig. 6. Xenolith
(1 cm
3
) of organodetritic limestone (Lassic ?) in alkali basalt. The
Nízke Tatry Mts. — Ďumbier. Enlarg. 180
×
.
§
PLATE I 119
120 SPIŠIAK and HOVORKA
SiO
2
contents) has not been definitely solved yet. In the
rocks (mainly dykes) there is often a high amount of differ-
ently resorbed crustal xenoliths (size usually 0.5 to 10 mm,
Hovorka et al. l982; Hovorka & Spišiak l988; Spišiak et al.
l99l). Carbonate rock xenoliths (some of them with fossil
remnants) are most frequent. They are assimilated to various
degrees and in the space of the original xenoliths originate
kaersutites, in a few cases also Cpx, the compositions of
which correspond to phenocryst rims (in this case Cpx and
Hbl are only slightly zonal or even unzonal). The space of as-
similated carbonate xenoliths show a lack of ore minerals
that are abundant in the host matrix. Xenoliths of quartz-
bearing rocks are rare. Beside xenoliths, blaebs of immisci-
ble melt are likely to be contained in these rocks.
Considering the Cpx and rock composition and comparing
them with their respective equivalents we suppose that the
assimilation processes took part after the crystallization of Ol
and Cpx phenocrysts, during the ascent of magma onto the
(Earth’s) surface. As the ascent was rapid, due to a low mag-
ma viscosity and extensional conditions, there were no con-
siderable (except for SiO
2
contents) changes in chemical
composition.
Conclusion
On the basis of the fabric and composition of rock-forming
minerals (especially those of Ol, Cpx and Hbl) we could sup-
pose their origin as follows:
— olivines most probably represent high-pressure phenoc-
rysts;
— the central parts of phenocrysts, especially those of Cpx,
crystallized under high pressure conditions as products of
fractional crystallization;
— rims of Cpx and Hbl phenocrysts (but also partly dark
micas) crystallized under substantially lower pressure during
magma ascent. Under just the same conditions microliths in
the matrix and Cpx and Hbl in the space of resorbed xeno-
liths also crystallized;
— the rims of Cpx and Hbl phenocrysts (partly also mafic
micas) originated under a considerable pressure drop during
the ascent of the melt. The same conditions were applied dur-
ing crystallization of microliths in the matrix and Cpx and
Hbl in resorbed parts of xenoliths;
— the composition and zoning of Cpx in the Cretaceous al-
kaline rocks of the Outer and Central Western Carpathians
document the similar conditions of their generation (approx.
23 kbar and approx. 1260
o
C, according Al
IV
:Al
VI
ratio). A
very low magma viscosity and suitable geotectonic condi-
tions caused a rapid ascent of the melt and its further devel-
opment;
— the nature of Cpx phenocrysts documents a rapid ascent
of the melt which was contamined by a resorption of xeno-
liths (mostly of neighbouring carbonatic rocks);
— the rocks are similar to Mesozoic alkaline rocks in the
Northern Calcareous Alps and Cretaceous volcanics in the
Mecsek Mts. Hungary in composition, occurrence and age;
— the occurrences of these rocks are conditioned by an ex-
tensional tectonic regime (embryonal rifting) in their respec-
tive units (Silesian, Tatric and Fatric units). The character of
magmatism as well as its coincidence in the other parts of the
Alpine – Carpathian region prove an extensional tectonic
setting (rifting) in the whole mountain chain (Alpine — Car-
pathian segment of the Tethys).
Acknowledgements:
This work presents the results of the
studies carried out within scientific projects No. 1805/94 and
1081/95 financially suported by the Slovak Grant Agency.
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