GEOLOGICA CARPATHICA, 53, 5, BRATISLAVA, OCTOBER 2002
295 —301
MESOZOIC ALKALI LAMPROPHYRES IN VARISCAN GRANITOIDS
OF THE MALÉ KARPATY AND NÍZKE TATRY MOUNTAINS –
GEOCHRONOLOGY AND GEOCHEMISTRY
JÁN SPIŠIAK
1
and KADOSA BALOGH
2
1
Geological Institute, Slovak Academy of Sciences, Banská Bystrica, Severná 5, 974 01 Banská Bystrica,
Slovak Republic; spisiak@savbb.sk
2
Institute of Nuclear Research, Hungarian Academy of Sciences, Bemtér 18/c, H-4026 Debrecen, Hungary; balogh@moon.atomki.hu
(Manuscript received June 16, 2001; accepted in revised form June 18, 2002)
Abstract: Mesozoic alkali lamprophyres from the Malé Karpaty Mts and Nízke Tatry Mts granitoids have a similar
petrographic pattern. The textures are phyric, with amphibole and clinopyroxene (Cpx) (and/or olivine) phenocrysts.
Cpx are zonal and correspond to diopside. Amphibole are zoning too and correspond to kaersutites. On the basis of
chemical composition they can be ranked with alkaline lamprophyres. The K/Ar age (approx. 100 Ma) of these dykes
corresponds to the age of the Cretaceous alkaline basalt/basanite in the Krížna Nappe of the Central Western Carpathians.
Key words: Central Western Carpathians, Mesozoic, geochronology, geochemistry, alkali lamprophyres.
Introduction
In the Mesozoic complexes of the Central Western Car-
pathians, Cretaceous alkaline basalts/basanites form part of the
Krížna Nappe, however less frequently, they also occur in cov-
er sequences. Due to the basalts often being synchronous with
the host sediments the influence of volcanic activity on the
surrounding rocks can be observed frequently (Hovorka &
Spišiak 1988). Stratigraphic data indicate the age of these
rocks to be Berriasian to Albian (see Hovorka & Spišiak l.c.).
Beside the dominating effusive and extrusive rock types in the
Mesozoic sequences, dykes of basalts/lamprophyres are also
locally present in the Variscan granitoids. Such dykes have
been reported from the area of the Malé Karpaty Mts (Hovorka
et al. 1982a) and from the Nízke Tatry Mts (Fig. 1) (Hovorka
et al. 1982b; Spišiak et al. 1991). It is difficult to rank them
stratigraphically on the basis of geological criteria, which has
led us to use geochemical and geochronological methods to
date them more precisely.
Method of K/Ar dating
Measurement of K/Ar ages was performed in the Institute of
Nuclear Research of the Hungarian Academy of Sciences
(ATOMKI), Debrecen. The samples were first crushed to 0.3—
0.1 mm according to the grain size of the minerals. Whole
rock samples and amphibole + pyroxene mineral concentrates
were prepared by heavy liquids and magnetic separation. It
was assumed that K was hosted mostly by amphibole, so the
ages measured on the mineral concentrates were regarded as
values close to the amphibole ages. Part of each sample was
pulverized for K determination. An argon extraction line and a
mass spectrometer, both designed and built in the ATOMKI,
were used for argon measurement. The rock was degassed by
high frequency induction heating, the usual getter materials
(titanium sponge, getter pills of SAES St707 type and cold
traps) were used for cleaning and transporting Ar. The
38
Ar
spike was introduced to the system from a gas-pipette before
the degassing was started. The purified Ar was directly intro-
duced into the mass spectrometer. The mass spectrometer was
a 90° magnetic sector type of 150 mm radius and was operated
in the static mode. Recording and evaluation of the Ar spec-
trum was controlled by a microcomputer. Potassium was de-
termined by flame photometry with a Li internal standard and
Na buffer.
The interlaboratory standards Asia 1/65, HD-B1, LP-6 and
GL-0 as well as atmospheric Ar were used for controlling and
calibration of the analyses. Details of the instruments, the ap-
plied methods and results of calibration have been described
elsewhere (Odin et al. 1982; Balogh 1985). The K/Ar ages
were calculated using the constants proposed by Steiger &
Jäger (1977).
Fig. 1. Localization of dykes.
296 SPIŠIAK and BALOGH
N. anal.
1Py
2Py
3Pr
5c
6c-r
7r
8Pr
10Py
SiO
2
48.90
47.90
45.02
49.04
47.10
46.29
41.67
45.15
TiO
2
3.05
2.87
3.85
2.03
2.55
3.51
5.45
3.75
Al
2
O
3
5.92
5.47
8.17
4.73
4.98
7.62
9.95
8.23
Cr
2
O
3
0.00
0.00
0.39
0.21
0.22
0.45
0.04
-
FeO
+
6.71
6.59
6.62
5.45
6.13
6.32
7.77
7.10
MnO
0.10
0.14
0.07
0.09
0.08
0.12
0.06
0.09
MgO
13.82
14.31
13.05
15.21
15.13
13.32
11.60
12.95
CaO
21.73
23.10
23.27
23.09
23.23
23.43
23.01
23.00
Na
2
O
0.34
0.34
0.32
0.30
0.33
0.34
0.46
0.42
K
2
O
0.00
0.02
0.00
0.00
0.00
0.00
0.00
0.00
TOTAL
100.57 100.74 100.76 100.15
99.75 101.40 100.01 100.69
Formula based on 6 oxygens
Si
IV
1.80
1.78
1.68
1.82
1.77
1.71
1.58
1.68
Al
IV
0.20
0.22
0.32
0.18
0.23
0.29
0.42
0.32
Al
VI
0.06
0.02
0.04
0.03 -
0.04
0.03
0.04
Ti
0.09
0.08
0.11
0.06
0.07
0.10
0.16
0.11
Cr
- -
0.01
0.01
0.01
0.01
-
-
Fe
2+
0.21
0.20
0.21
0.17
0.19
0.20
0.25
0.22
Mn
-
- - - - -
-
-
Mg
0.76
0.79
0.72
0.84
0.84
0.73
0.66
0.72
Ca
0.86
0.92
0.93
0.92
0.93
0.93
0.94
0.92
Na
0.02
0.02
0.02
0.02
0.02
0.02
0.03
0.03
K
- - - - - -
-
-
FeO+ — total Fe as FeO, c = core, r = rim, Pr = prizmatic sector, Py = pyramidal sector
Geology
A dyke 50—80 cm thick occurs in the area of the Malé Kar-
paty Mts, in the Modra granodiorite massif (approx. 3 km
NNW from the quarry in the Cajlanská dolina Valley, Hovorka
et al. 1982b). The dyke is subvertically orientated and can be
traced as far as 200 m. There are rare amygdales (up to 2 mm)
with chlorite filling, especially in the marginal parts of the
dyke.
Two alkali lamprophyre dykes have been reported in leuko-
crate middle-grained strongly altered granites from the area of
Liptovská Dúbrava, Nízke Tatry Mts (Hovorka et al. 1982a;
Spišiak et al. 1991). Both the dykes are rather thin, between
30—50 cm. In general, the contact of the dykes with the sur-
rounding granites is sharp and no wider contact zones can be
observed here. This proves that the melt was moving and cool-
ing quickly.
Mineralogy and petrology
Mineral compositions (Tables 1, 2) were determined with
the use of a JEOL Superprobe 733 (operated with a beam cur-
rent of 15 kV at 5nA) in the Slovak Geological Survey, Brat-
islava (analyst I. Holický). The data were reduced by ZAF cor-
rections.
The petrographic patterns of the dykes from the Malé Kar-
paty and Nízke Tatry Mts are very close to each other and this
is why we will describe them together.
The dykes show aphanitic, very rarely amygdaloidal struc-
tures. The textures are typically porphyric, with amphibole
and clinopyroxene (Cpx) (and/or olivine) phenocrysts. In the
dykes from the Nízke Tatry Mts, Cpx and olivines are totally
replaced by chlorite-carbonate aggregates and nothing but
pseudomorphoses after these minerals can be observed. The
original vitreous matrix has been strongly devitrified and con-
tains microlites of Cpx, amphibole and dark mica. Cpx from
the dyke of the Malé Karpaty Mts are zonal (sectorial and os-
cillation zoning) and often form glomerophyric aggregates.
Table 1: Selected analyses of clinopyroxenes.
Fig. 3. Sector zoning of clinopyroxene. Loc. Cajla, Magn. 35
×
, X polars.
Fig. 2. Oscilation zoning of clinopyroxene. Loc. Cajla, Magn.
45
×
, X polars.
Fig. 4. Sector zoning of clinopyroxene, around clinopyroxene dark
kaersutite. Loc. Cajla, Magn. 65
×
, X polars.
MESOZOIC ALKALI LAMPROPHYRES IN GRANITOIDS 297
Sector zoning can be seen through two clearly different sec-
tors: pyramidal and prismatic (Figs. 2, 3, 4). There are optical
and chemical differences between the sectors. Mostly the py-
ramidal sector is enriched with Si and Mg, and/or depleted in
Al, Ti, Fe when compared to the prismatic one. With oscilla-
tion zoning, the central part of the crystal rather than the rim is
enriched with Si and Mg and depleted in Ti, Al, Fe. With re-
gard to crystal structure stability, zoning is a non-equilibrium
state and later diffusion processes caused its wiping out.
Whether it is preserved or not depends on the speed of crystal-
lization and diffusion in the crystal. Due to this, sector zoning
is usually preserved in rapidly cooling rocks. Another pyrox-
ene type, which is characteristic of rapidly cooling basic rocks,
are microlites in the matrix. They have irregular shapes and
with their compositions they are close to prismatic sectors,
and/or marginal parts of Cpx in the case of oscillation zoning.
They represent the final phase of crystallization during the as-
cent of magma to the surface, that is they reflect decreasing
pressure and rather quick cooling.
On the basis of Cpx classification (Morimoto et al. 1988),
they correspond to diopsides (Fig. 5), and/or part of the analy-
ses are shifted towards higher Ca values (especially grain rims,
prismatic sectors). In comparison to Cpx from Mesozoic alka-
line rocks of the Tatric Unit and Fatric Unit of the Western
Carpathians, they show a striking coincidence of composition.
The dependence of Cpx compositions on those of the melts
they originated from, was used (Le Bas 1962; Letterrier et al.
1977 and others) for the determination of Cpx types. In these
diagrams the Cpx from the studied dykes correspond to the
Cpx from alkaline rocks. Cpx from the Mesozoic alkaline
rocks of the Tatric Unit and Fatric Unit of the Western Car-
pathians have a similar position.
Amphiboles are typical minerals of the dykes. Like Cpx
they are zonal (Fig. 6) and by their compositions they corre-
spond to kaersutites (Table 2, Fig. 7). Zoning is not so clear
Table 2: Selected analyses of amphiboles.
1
2
3
4
5r
5c
1r
1c
2r
2c
3
4
Loc.
Cajla (Malé Karpaty Mts)
Liptovská Dúbrava (Nízke Tatry Mts)
SiO
2
38.92
37.79
36.61
39.55
37.02
38.26
37.73
39.61
38.10
40.95
38.58
38.01
TiO
2
5.72
6.11
5.68
5.59
6.22
5.76
5.42
5.07
5.52
4.78
5.41
5.22
Al
2
O
3
13.65
14.51
14.61
12.06
13.65
14.18
14.08
13.91
14.49
13.02
14.42
14.97
FeO
+
11.09
10.03
10.74
11.75
14.68
11.49
10.76
9.65
10.53
9.37
12.41
12.56
MnO
0.18
0.17
0.18
0.19
0.35
0.16
0.22
0.17
0.15
0
0.22
0.13
MgO
12.81
13.62
13.07
13.03
10.48
12.84
12.18
13.70
11.90
13.85
10.59
10.05
CaO
11.62
11.27
11.62
11.39
11.62
11.55
11.94
11.39
11.97
11.34
11.85
11.86
Na
2
O
2.06
1.94
1.99
2.04
1.93
1.90
2.45
2.43
2.23
2.39
2.43
2.43
K
2
O
1.61
1.69
1.78
1.47
1.63
1.77
1.10
1.55
1.06
1.29
1.16
1.16
TOTAL
97.66
97.13
96.28
97.07
97.58
97.91
95.88
97.48
95.45
96.99
97.07
96.39
Formula based on 23 oxygens
Si
5.79
5.63
5.55
5.89
5.64
5.70
5.72
5.85
5.75
6.04
5.80
5.76
Al
IV
2.21
2.37
2.45
2.11
2.36
2.30
2.28
2.15
2.25
1.96
2.20
2.24
Al
VI
0.19
0.18
0.16
0.10
0.09
0.19
0.24
0.28
0.32
0.31
0.36
0.44
Ti
0.64
0.69
0.65
0.63
0.71
0.64
0.62
0.56
0.63
0.53
0.61
0.60
Fe
2+
1.38
1.25
1.36
1.47
1.87
1.43
1.36
1.19
1.33
1.16
1.56
1.59
Mn
0.02
0.02
0.02
0.03
0.04
0.02
0.03
0.02
0.02
0
0.03
0.02
Mg
2.84
3.02
2.95
2.89
2.38
2.85
2.75
3.02
2.68
3.05
2.37
2.27
Ca
1.85
1.80
1.88
1.82
1.90
1.84
1.94
1.80
1.93
1.79
1.91
1.93
Na
0.59
0.56
0.59
0.59
0.57
0.55
0.21
0.29
0.20
0.24
0.22
0.22
K
0.31
0.32
0.35
0.28
0.32
0.34
0.72
0.70
0.65
0.68
0.71
0.71
FeO+ — total Fe as FeO, c = core, r = rim
Fig. 6. Oscillation zoning of kaersutite. Loc. Liptovská Dúbrava,
Magn. 25
×
, X polars.
Fig. 5. Classification diagram of clinopyroxenes (according to
Morimoto et al. 1988). 1 – analyses of clinopyroxenes from Ta-
ble 1; 2 – analyses of clinopyroxenes from Mesozoic alkali ba-
salt/basanites (Hovorka & Spišiak 1988).
298 SPIŠIAK and BALOGH
Sample
D-51
D-56
MV-77
MV-78
MV-79
MV-64
MV-66
MV-69
LAM-1
LAM-2
LAM-3
Locality
Dúbrava
Dúbrava
Dúbrava
Dúbrava
Dúbrava
Cajla
Cajla
Cajla
Cajla
Cajla
Cajla
SiO
2
38.96
38.97
38.94
40.21
41.33
40.36
37.22
39.38
39.45
38.40
41.24
TiO
2
3.40
3.38
3.64
3.72
3.73
3.47
3.23
3.28
3.17
3.27
3.72
Al
2
O
3
12.61
12.57
12.64
13.48
13.29
13.32
10.74
11.83
13.34
10.71
13.61
Fe
2
O
3
6.46
6.07
14.03*
14.16*
13.76*
13.26*
12.89*
12.78*
4.80
4.48
5.07
FeO
7.22
7.43
7.85
8.34
7.29
MnO
0.20
0.19
0.18
0.18
0.17
0.17
0.19
0.19
0.18
0.17
0.17
MgO
7.71
7.97
8.15
7.30
7.66
7.45
11.15
10.93
10.08
9.86
7.68
CaO
8.41
8.63
8.57
7.63
8.79
10.49
14.12
12.34
12.12
13.90
9.40
Na
2
O
2.17
2.00
2.00
2.34
2.25
2.59
1.55
1.45
1.48
2.03
3.01
K
2
O
2.41
2.54
2.48
2.40
2.40
2.26
0.85
1.75
1.88
1.01
2.46
P
2
O
5
0.97
0.99
0.98
1.03
1.03
0.99
0.79
0.85
0.49
0.48
0.55
LOI
8.94
8.85
8.20
7.60
5.70
5.50
6.60
4.60
4.95
7.02
5.66
Total
99.46
99.59
99.81
100.05
100.11
99.86
99.33
99.38
99.79
99.67
99.86
Cr
106.1
177.3
105.0
87.0
104.0
180.0
481.0
402.0
330.0
309.0
118.0
Ni
65.6
69.5
99.0
77.0
79.0
91.0
245.0
199.0
160.0
171.0
84.0
Co
40.8
44.3
51.0
43.0
43.0
40.0
54.0
51.0
39.0
42.0
32.0
V
147.2
158.7
249.0
261.0
249.0
296.0
277.0
273.0
226.0
200.0
237.0
Pb
24.6
18.1
337.0
405.0
141.0
ND
ND
ND
ND
ND
ND
Zn
ND
ND
147.0
160.0
148.0
106.0
106.0
115.0
ND
ND
ND
Rb
ND
ND
82.0
86.0
61.0
68.0
28.0
58.0
30.0
16.0
54.0
Ba
581
700
589
605
689
1318
1286
1578
1620
1290
1470
Sr
1770
3000
877
814
1001
990
684
746
930
720
1070
Ta
ND
ND
ND
4.25
ND
ND
ND
4.44
ND
ND
ND
Nb
ND
ND
85.00
113.50
92.00
95.00
70.00
105.20
ND
ND
ND
Hf
ND
ND
ND
10.16
ND
ND
ND
6.19
ND
ND
ND
Zr
419
440
396
457
423
308
262
313
267
216
276
Y
29.50
37.90
32.00
32.00
33.00
28.00
23.00
25.00
26.00
22.00
28.00
Th
ND
ND
12.00
7.56
9.00
8.00
6.00
6.06
ND
ND
ND
U
ND
ND
7.00
7.00
3.00
ND
ND
ND
ND
ND
ND
La
62.80
77.20
44.00
69.23
92.00
74.00
56.00
67.30
87.00
75.00
96.00
Ce
131.00
160.50
155.00
143.13
156.00
144.00
90.00
129.44
ND
ND
ND
Pr
15.30
20.20
ND
17.19
ND
ND
ND
14.79
ND
ND
ND
Nd
68.20
76.30
71.00
68.27
64.00
65.00
49.00
56.86
ND
ND
ND
Sm
11.80
14.00
ND
12.94
ND
ND
ND
10.31
ND
ND
ND
Eu
3.90
4.90
ND
3.98
ND
ND
ND
3.17
ND
ND
ND
Gd
10.20
12.50
ND
10.88
ND
ND
ND
8.27
ND
ND
ND
Tb
ND
ND
ND
1.43
ND
ND
ND
1.10
ND
ND
ND
Dy
7.40
8.70
ND
7.74
ND
ND
ND
5.76
ND
ND
ND
Ho
1.22
ND
ND
1.37
ND
ND
ND
1.03
ND
ND
ND
Er
2.93
3.82
ND
3.41
ND
ND
ND
2.54
ND
ND
ND
Tm
0.30
0.46
ND
0.42
ND
ND
ND
0.32
ND
ND
ND
Yb
2.07
3.17
ND
2.46
ND
ND
ND
1.81
ND
ND
ND
Lu
0.28
0.40
ND
0.34
ND
ND
ND
0.26
ND
ND
ND
* Total Fe as Fe
2
O
3
and is manifested through increasing Ti, Al and Fe contents
and/or decreasing Si and Mg contents from core to rim.
Ti-biotites, plagioclases, apatites, chlorites and carbonates
are also present in accessory amounts. Tiny (X mm), different-
ly resorbed xenoliths, mostly of granite composition are also
typical of the dykes.
Geochemistry
Major elements were analysed by X-ray fluorescence in the
Geological Institute of the Slovak Academy of Sciences in
Bratislava, some trace elements and REEs were analysed by
ICP in the Slovak Geological Survey, Analytical Laboratory at
Spišská Nová Ves and in the Geochemical Centre, Saint
Mary’s University in Halifax, Nova Scotia.
The analyses for major and rare earth element contents were
used to solve the petrogenesis and geotectonic position of the
Cretaceous alkaline volcanics. Although the rocks from the
dykes underwent secondary alterations to different degrees,
most major elements, HSFE, REE, Th, as well as transition el-
ements were not significantly mobilized.
On the whole, Cretaceous lamprophyres from granites are
characterized (Table 3) by low SiO
2
contents (ca. 39 weight
%), enhanced contents of TiO
2
and P
2
O
5
(3.2, and/or
Fig. 7. Classification diagram of amphiboles (according to Leake et
al. 1988). 1 – analyses of kaersutites from Liptovská Dúbrava, 2 –
analyses of kaersutites from Cajla; 3 – analyses of kaersutites
from Mesozoic alkali basalt/basanites (Hovorka & Spišiak 1988).
Table 3: Chemical composition of rocks.
MESOZOIC ALKALI LAMPROPHYRES IN GRANITOIDS 299
0.8 weight %) and elevated contents of Cr (280 ppm) and Ni
(190 ppm), elevated contents of incompatible elements such as
Ba (650 ppm), Sr (700 ppm) and L REE as well as those of Nb
(78 ppm), V (245 ppm) and Zr (305 ppm). The rocks of the
dykes were ranked either as alkaline, and/or calc-alkaline ones
on the basis of a ternary diagram by Rock (1987; Fig. 8). In
this diagram the projection points of the analyses of the rocks
from the dykes in granites are plotted in the field of alkaline
lamprophyre rocks. A generally negative correlation Al
2
O
3
/
CaO vs. Mg* (MgO/[MgO+FeO] in mole %) suggests that the
rocks underwent clinopyroxene dominated fractionation. Al-
though lamprophyre dykes penetrate through continental crust
complexes, no significant crustal contamination can be ob-
served. This is proved by a low Th/La ratio which is close to
the ratios in primitive mantle (Sun & McDonough 1989). Cre-
taceous lamprophyres from granites do not satisfy the compo-
sitional criteria for identifying primary upper mantle partial
melts (Green 1971; Sato 1977). They were evidently derived
by a certain degree of fractional crystallization from more
primitive magma. A high concentration of strongly compatible
elements (including Ni and Cr; Table 3) and the presence of
olivine phenocrysts indicated that the rocks are relatively
primitive. Similar trace element characteristics of lampro-
phyres of the two localities under consideration suggest that
they could be formed by similar degrees of partial melting of a
common/similar mantle source.
For a more precise geotectonic classification of the rocks
from dykes we used different ternary diagrams (Fig. 9a,b,c). In
the diagram MnO—TiO
2
—P
2
O
5
(Fig. 9a) the projection points
of analyses of the studied lamprophyres lie in the OIA (ocean-
ic island alkali) field and most points coincide with the field of
Mesozoic alkaline basalts from the Central Western Car-
pathians. Three of the points are shifted to the TiO
2
peak due
to lower values for this oxide in the analyses. In the following
diagram Ti —Zr —Y (Fig. 9b) projection points of the analysed
lamprophyres are plotted in the field or on the boundary of the
WPB (within-plate basalts) field. In the last diagram Zr —Nb —
Y (Fig. 9c) within-plate basalts are divided into alkaline and
tholeiite ones. The lamprophyres under study as well as Meso-
zoic alkaline basalts of the Central Western Carpathians being
compared are plotted in WPA (within-plate alkali) field. Simi-
larly, the course of the normalized REE curve (Fig. 10) is
clearly declined in the direction of low HREE contents with-
Fig. 8. Classification ternary diagram CaO—SiO
2
/10—TiO
2
*4 for
lamprophyric rocks (according to Rocks 1987). 1 – analyses of
rocks from Liptovská Dúbrava; 2 – analyses of rocks from Cajla,
ALK – alkaline lamprophyres; CAL – calc-alkaline lampro-
phyres.
Fig. 9. Discrimination diagram for basalts: a – MnO
×
10—TiO
2
—P
2
O
5
×
10 (Mullen 1983); b – Zr—Ti/100—Y.3 (Pearce & Cann 1973); c –
Zr/4—2Nb—Y (according to Meschede 1986). 1 – analyses of rocks from Liptovská Dúbrava, 2 – analyses of rocks from Cajla, 3 –
analyses of Mesozoic alkali basalt/basanites (Hovorka & Spišiak 1988; Spišiak & Hovorka 1997; Hovorka et al. 1999). OIT = oceanic
island tholeiites, OIA = oceanic island alkali basalts, CAB = calc-alkaline basalts of volcanic arcs, IAT = island arc tholeiites, MORB =
middle oceanic ridge basalts, WPB = within plate basalts, WPA = within-plate alkali basalts, E-MORB = E-type middle oceanic ridge
basalts, N-MORB = N-type middle oceanic ridge basalts, VAB = volcanic arc basalts, WPT = within-plate tholeiites.
300 SPIŠIAK and BALOGH
out a considerable Eu-anomaly. Such a course of normalized
curve is typical of ocean island (OIB), continental alkaline
volcanic suites of Central and Western Europe (Wilson &
Downes 1991; Wedepohl et al. 1994) as well as of Mesozoic
alkaline rocks from different parts of Europe (Moravian alkali
rocks; Dostal & Owen 1998, North-Pyrenean rift zone; Azam-
bre et al. 1992, Northern Calcareous Alps; Trommsdorff et al.
1990, etc.). Studies of Cenozoic alkali basalts in Europe
showed that these magmas were derived from a HIMU-type
(mantle with high U/Pb ratio, Zidler & Hart 1986) mantle
source (Wilson & Downes 1991). This source was interpreted
as mainly of sub-lithospheric origin and results of a three-com-
ponent mixing primary between a HIMU component and the
DM (depleted mantle) with a subordinate addition of an en-
riched mantle component (EM, Wilson & Downes 1991). A
similar development is considered by Dostal & Owen (1998)
in the case of Moravian Cretaceous lamprophyres and
a similar source is very likely in the case of these rocks.
Geochronology
It was a problem to determine the ages of the given rocks. It
was possible only on the basis of a comparison of geochemical
characteristics, and the similarity to Cretaceous volcanics sug-
gested a Cretaceous age (Hovorka & Spišiak 1988; Spišiak et
al. 1991). Two fresh samples from each mountain range were
analysed for K /
40
Ar contents (Table 4). The results offered
rather coherent values for the Malé Karpaty Mts 93.4 ± 3.4
Table 4: Age of the lamprophyres.
Sample
Locality
K weight %
40
Ar(rad) 10
-6
cm
3
/g
40
Ar(rad) %
Age Ma
± σ
MV-56
Cajla
1.340
4.982
72.0
93.2
± 3.6
MV-56*
Cajla
1.280
4.777
65.9
93.4
± 3.4
MV-69
Cajla
0.736
3.397
73.4
115.0
± 4.5
MV-69*
Cajla
0.696
3.229
69.1
115.6
± 4.5
MV-76
Liptovská Dúbrava
2.390
9.623
79.4
100.7
± 3.8
MV-79
Liptovská Dúbrava
2.220
9.114
84.6
102.6
± 3.8
Separates marked with * are more dense than bromoform and nonmagnetic. So amphiboles and pyroxenes should concentrates in them. Since they resulted similar
ages, the ages are likely original ones.
Ma, and/or 115 ± 4.5 Ma and in case of Liptovská Dúbrava
(Nízke Tatry Mts) 100.7 ± 3.8 Ma, and/or 102.6 ± 3.8 Ma.
Geochronological settings show a good correlation between
chemical and mineral compositions and the age of the dykes in
Variscan granites and Cretaceous alkaline basalts/basanites in
the Krížna Nappe of the Western Carpathians.
Conclusion
Cretaceous lamprophyres from granites are similar to Meso-
zoic alkali rocks from the Tatric Unit and Fatric Unit of the
Western Carpathians. The detected ages (approx. 100 Ma)
prove that. These data correspond to the new geochronological
data pointing to the K/Ar age of approx. 110 Ma (Grabowský
– unpublished data) or
40
Ar/
39
Ar 122 Ma (Lucińska-Anczk-
Fig. 10. Chondrit-normalized REE abundance (normalized accord-
ing to Sun 1982) of the studied lamprophyres (analyses from Ta-
ble 3) and TES – teschenite (Rossy et al. 1992).
iewicz et al. 2002). On the basis of their mineral and chemical
compositions they can be ranked with alkaline lamprophyres.
Their trace element composition is similar to that of oceanic
island basalts (intra-plate provenience), which suggests an
analogous deep-seated mantle source (HIMU). Continental
within-plate basalts with the given signs are often interpreted
as a result of mantle diapirs (Weaver 1991). A low volume of
lamprophyres on the whole does not suggest their binding to
mantle diapir. This magmatic activity is likely to have been
synchronous with Cretaceous volcanism in the Westen Car-
pathians and was bound to fault systems connected with form-
ing basins. This idea counts on melting due to a passive up-
welling of a mantle material caused by lithosphere depletion
during an extensional tectonic regime.
Acknowledgement: This study represents a partial output from
the grants No. 2/7091/00 VEGA. Finally, we would like to
thank Mrs. N. Halašiová for computer processing of the data.
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