GEOLOGIJA 39, 159-191 (1996), Ljubljana
Lithofacies characteristics of the Smrekovec volcaniclastics,
northern Slovenia
Litofacialne značilnosti smrekovških vulkanoklastitov
(severna Slovenija)
Polona Kralj
Geološki zavod Ljubljana
Inštitut za geologijo, geotehniko in geofiziko
Dimičeva 14, 1000 Ljubljana, Slovenija
Key words: andésite volcaniclastics, volcaniclastic turbidites, zeolites
Ključne besede: andezitni vulkanoklastiti, vulkanoklastični turbiditi, zeoliti
Abstract
The Smrekovec mountains are characterised by a widespread occurrence of
volcanic rocks of the Upper Oligocene age. Their development is closely related to
volcanic activity which resulted in the formation of a submarine stratovolcano
complex, emplaced onto pre-Tertiary carbonate basement and locally, on Upper
Oligocene marine marls and silts. Magma composition varied with time during
volcanic activity. The original tholeiitic magmas very likely underwent a differen-
tiation due to low pressure crystal fractionation, resulting in the development of
andesitic and finally rhyodacitic magmas. The early stage of volcanic activity was
dominantly non-explosive; the main style of fragmentation was autoclastic, relat-
ed to chill and quench processes that affected lavas and high-level intrusive bod-
ies. During the late-stage of volcanic activity, explosive volcanism was also pre-
sent, being most probably related to magmatic and combined magmatic-hydrovol-
canic activity. Explosions also seem to have generated or triggered volcaniclastic
debris flows and turbidity ash flows.
Shallow intrusive bodies (syn-volcanic sills and feeder dykes) were a local
source of heat that generated hydrothermal/geothermal conditions in the enclos-
ing, water-saturated volcaniclastic sediments. Consequently laumontite, analcime,
clinoptilolite, heulandite, thomsonite, yugawaralite, prehnite, pumpellyite, albite,
apophyllite, epidote, sphene, chlorite and mixed-layered clay minerals developed
as replacements of the primary constituents, interstitial fillings and vein minerals.
Kratka vsebina
Smrekovško podgorje grade vulkanske kamnine zgornjeoligocenske starosti.
Njihov nastanek je vezan na razvoj vulkanskega masiva, sestavljenega iz enega ali
več stratovulkanov, ki so delovali v morskem okolju. Podlaga sestoji iz mezozoj-
skih karbonatnih kamnin, ponekod tudi iz zgornjeoligocenskih laporjev in meljev-
cev. Sestava magme se je med vulkanskim delovanjem spreminjala. Prvotna sesta-
160_Polona Kralj
va magme je bila toleitna, vendar se je, najverjetneje zaradi kristalne frakciona-
cije, diferencirala, sprva v andezitno in nato v riodacitno. V zgodnjem obdobju je
prevladovala neeksplozivna vulkanska dejavnost. Tedaj je bil najpomembnejši na-
čin fragmentacije avtoklastičen, vezan na procese nenadnega ohlajanja lave v vod-
nem mediju oziroma magme ob intruzijah v plitvo ležeče vlažne sedimente. V po-
znejšem obdobju vulkanskega delovanja so se pojavile tudi magmatske in mag-
matsko-hidrovulkanske eksplozije. Najverjetneje so le-te povzročile tudi nastanek
vulkanoklastičnih debritnih in turbiditnih tokov.
Plitvi intruzivi (sin-vulkanski siili in dyki) so predstavljali lokalni izvor toplo-
te, zaradi katere so v okolnih, z morsko vodo prepojenih sedimentih iz pornih vod
nastajale tople raztopine s povečano vsebnostjo raztopljenih mineralnih snovi. Za-
radi njihovega delovanja so začeli kristalizirati zeoliti laumontit, analcim, klinop-
tilolit, heulandit, thomsonit, yugawaralit in avtigeni silikati: prehnit, pumpellyit,
albit, apofilit, epidot, sfen, klorit in glineni minerali z zmesno strukturo vrste
klorit/montmorillonit. Avtigeni minerali nadomeščajo prvotne sestavine kamnin
ali pa zapolnjujejo pore in razpoklinske sisteme v kamnini.
Introduction
The Smrekovec mountains, located in northern Slovenia (fig. 1), are characterised
by a widespread occurrence of coherent volcanic rocks and volcaniclastic deposits.
The complex encompasses an area of approx. 15 sq.km and includes three major
mountain peaks, Komen, Krnes and Smrekovec, reaching of 1684 m, 1613 m and 1577
m respectively. The Smrekovec volcanic complex represents a part of a wider vol-
canic belt, named the "Smrekovec series", extending along a distance of about 100
km towards the southeast (Mioc, 1978, 1983; Mioč et al., 1986). The Smrekovec
volcanics are of Upper Oligocene stratigraphie age, as determined on the basis of
foraminifera fauna, encountered in locally underlying marine marls and siltstones
(Rijavec, 1966).
An early publication on the Smrekovec volcanics appeared at the end of the previ-
ous century, when Teller (1898) elaborated the first geological map of the area. Fol-
lowing works are mainly related to the period after the Second World War
(Hinterlechner-Ravnik; Plenicar, 1967; Mioč, 1978, 1983; Mioč et al., 1986;
Osterc, 1976; Kovic&Krošl-Kuščer, 1986;Kovič, 1988).
The basement consists mainly of Mesozoic carbonates, occurring as tectonically
uplifted blocks on the NW and SE margins of the Smrekovec volcanic complex. A
NW-SE trending deep-seated fault of the peri-Adriatic lineament separates this com-
plex from the Karavanke tonalité (Mioč, 1983), which is in "sensu stricto" quartz
diorite (Zupančič, 1994).
The present, rather complicated geological situation in northern and north-east-
ern Slovenia is closely associated with global tectonic processes of subduction and
collision of the continental African and oceanic European plates and their segmented
parts, Apulia and the Pannonian fragment (Oberhauser, 1980; Roy den, 1988;
Dercourt et al., 1986). In early Tertiary, Apulia and Europe collided in south-north
direction. In early Miocene the Pannonian fragment separated from Apulia and
began to escape eastward from the collision zone, whereas the movements of Apulia
were directed westwards. The plate movements were accomodated by the peri-Adri-
atic lineament (Roy d en, 1988).
The details about the extent and directions of displacements along the peri-Adri-
atic lineament in the territory of Slovenia are still uncertain of Slovenia. It also
remains undefined whether the Smrekovec volcanism is related to an active conti-
nental margin or to one of the collision combinations: island arc - active continental
Lithofacies characteristics of the Smrekovec volcaniclastics
161
Fig. 1. The Smrekovec volcanic complex: geologic sketch map (after Mioč, 1983)
SI. 1. Poenostavljena geološka karta smrekovškega podgorja (po Mioču, 1983)
margin - passive continental margin. Andesitic volcanism may continue during the
collision and after its separation from a trench, dipping seismic zone and the
geophysical characteristics associated therewith (Gill, 1981).
Magma composition gives rather good indications of the tectonic environment. In
the Smrekovec volcanic complex, coherent volcanic rocks mainly occur as high-level
intrusive bodies and only subordinately as lava flows. Both, coherent and volcani-
clastic rocks have undergone appreciable alteration, mainly upon hydrothermal con-
ditions (Kovic & Krošl-Kuščer, 1986). The alteration undoubtedly puts severe
constraints particularly on geochemical reliability of alkaline elements and alkaline
earth abundances. Prior to a description of lithofacieses encountered in volcaniclas-
tic deposits, I shall provide some general information on the chemical composition of
magma and indicate some problems related to its interpretation.
162
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Chemical composition of coherent rocks
Magma composition varied with time during of the Smrekovec volcanic activity.
Basalts were the early volcanic products, occurring as submarine lavas and high-
level intrusive sills and dykes. Later, andésites predominated and although both,
basic and acid varieties are encountered, acid andésites seem to be more common.
Acid andésites are mostly vitrophyric and sometimes show perlitic texture. The latest
magmas were dacitic and rhyodacitic in composition. They mainly extruded as lava
flows and locally underwent extensive autoclastic fragmentation, leading to the for-
mation of in situ hyaloclastites. The chemical composition of coherent volcanic rocks
(tables 1,2,3) indicates the existence of a volcanic suite which evolved during the the
Smrekovec volcanism.
A hydrothermal alteration moderately modified the bulk chemical composition of
the Smrekovec volcanics. It is known already that the alteration very likely affects
the content of alkali metals, alkaline earths (mainly Na, K, Rb, Ba, Sr), light REE and
iron oxydes (Thompson, 1973; Honnorez, 1978; Furnes, 1980; Furnes &
El-Anbaawy, 1980). For this reason, the diagram using immobile elements SÌO2,
Ti and Zr (Winchester & Floyd, 1977) was recognised as reliable for the classifi-
cation of the Smrekovec volcanics (fig. 2).
The Smrekovec volcanics show anomalous abundances of potassium and rubidi-
um. The anomalies can be traced by a diagram using K/Rb ratio vs KgO content (fig.
3). K/Rb ratio commonly decreases with an increasing KgO content (Gill, 1981) and
Fig. 2. The Zr/TiO, ratios vs SiOg contents (after Winchester & Floyd,
1977) for the Smrekovec volcanics
SI. 2. Diagram odvisnosti med razmerjem Zr/Ti02 in vsebnostjo SiOg (po
Winchester & Floyd, 1977) za preiskane vzorce neeksplozivnih predornin
smrekovškega podgorja
Lithofacies characteristics of the Smrekovec volcaniclastics
163
Table 1. Chemical composition of the Smrekovec lavas and high-level intrusives.
Major elements in wt.%
Tabela 1. Kemična sestava smrekovških predornin. Glavne prvine v masnih odstotkih
1. - basalt, northern slopes of Komen (sample Ко-3); 2.- basalt, northern slopes of Smrekovec
(sample Sm 34a); 3. - rhyodacite lava flow, southern slopes of Komen (sample Sm 81/96C); 4. -
basic andésite, southern slopes of Krnes (sample Sm 83/96C); 5. - acid andésite, southern slopes
of Krnes (sample Sm 83/96A); 6. - acid andésite, the top of Krnes (sample Sm 16/88); 7. - acid
andésite lava flow, southern slopes of Krnes (sample Sm 74/88); 8. - hyaloclastite, southern
slopes of Krnes (sample Sm 76/88); Analysed in XRAL Activation Services., Ann Arbor, Michigan
164
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Table 2. Chemical composition of the Smrekovec lavas and high-level intrusives. Trace elements
in ppm
Tabela 2. Kemična sestava smrekovških predornin. Sledne prvine v mg/g
Lithofacies characteristics of the Smrekovec volcaniclastics
165
Table 3. Chemical composition of the Smrekovec lavas and high-level intrusives. Rare earth
elements in ppm
Tabela 3. Kemična sestava smrekovških predornin. Prvine redkih zemelj v mg/g
usually lies above, but parallel to Shaw's main trend (Gill, 1981). Values for K/Rb
ratios vs KgO content of the Smrekovec volcanics mostly lie under Shaw's main trend
(Shaw, 1968), except in two samples. They even show an inverse trend compared to
that observed in several suites of orogenic andésites.
E wart (1982) reported that the abundances of Ce and the corresponding Ce/Y
ratios are systematically related to the K abundances in many volcanic series from
the south-western Pacific subregion. The data of Ce/Y ratios vs Ce abundances for
Fig. 3. The K/Rb ratios vs K2O contents (after Gill, 1981) for the Smrekovec volcanics
SI. 3. Diagram odvisnosti med razmerjem K/Rb in vsebnostjo K2O (po Gillu, 1981) za preiskane
vzorce neeksplozivnih predornin smrekovškega podgorja
166_Polona Kralj
Fig. 4. The Ce abundances vs Ce/Y ratios for the Smrekovec vol-
canics
SI. 4. Diagram odvisnosti med vsebnostjo Ce in razmerjem Ce/Y
za preiskane vzorce neeksplozivnih predornin smrekovškega
podgorja
The diagram using FeO*/MgO ratio vs SiOg content (FeO* is total iron recalculat-
ed as FeO) is widely used to discriminate between tholeiitic and calcalkaline charac-
ter of volcanic rocks (Gill, 1981). The FeO*/MgO vs SiOg values of the Smrekovec
volcanics (fig. 5) are arranged in a suite which predominantly lies on the line separat-
ing tholeiitic and calcalkaline fields. The Smrekovec suite trend compared with the
data by Gill (1981) shows an affiliation with either low-K calcalkaline suites or
medium-K tholeiitic suites.
Other geochemical criteria useful for the recognition of tectonic setting include
Ba/Ta, Ba/La and La/Nb ratios (Gill, 1981). These ratio values were also tested for
the Smrekovec volcanics (table 4). According to Gill (1981), a Ba/Ta ratio greater
than 450 is the single diagnostic geochemical characteristic of arc magmas, whereas
Ba/La, La/Th and La/Nb seem to be less significant. The Ba/La ratios of the
Smrekovec volcanics are very low, ranging from 100 - 380. As Ba and many other
LIL-elements can be mobile during alteration (Thompson, 1973), and on the other
hand. Ta is assumed to be a fairly immobile trace element, the Ba/Ta ratios for the
Smrekovec volcanics might have been modified by hydrothermal processes. The
La/Nb ratios are consistent with the values characteristic of orogenic andésites.
the Smrekovec volcanics (fig. 4) do not show such anomalously scattered values as
the K/Rb ratios vs K2O contents. As cerium and yttrium are assumed to be immobile
upon zeolite facies conditions, and potassium being mobile and readily incorporated
into the zeolite lattice, the anomalous K/Rb ratios vs KgO content can be at least par-
tially ascribed to the rock alteration.
In orogenic andésites, Th/U ratios likewise tend to increase with KgO, being <2, 2
to 4 and >4 in low, medium and high-K suites, respectively (Gill, 1981). Th/U ratios
in the Smrekovec volcanics range from 2.3 to 3.5 in spite of the relatively low K^O
abundances measured, but do not show any positive correlation with the increasing
KgO content.
Lithofacies characteristics of the Smrekovec volcaniclastics
167
Fig. 5. The FeOVMgO ratos vs SÍO2 abundances (after Gill, 1981) for the      ;
Smrekovec volcanics '
SI. 5. Diagram odvisnosti med razmerjem FeO*/MgO in vsebnostjo SiOg
(po Gillu, 1981) za preiskane vzorce neeksplozivnih predornin smre-
kovškega podgorja
Table 4. Some trace element ratios in the Smrekovec lavas and high-level intrusives '
Tabela 4. Razmerja nekaterih slednih prvin v smrekovških predorninah
1. - basalt, northern slopes of Komen (sample Ко-3); 2 - basalt, northern slopes of
Smrekovec (sample Sm 34a); 3. - rhyodacite lava flow, southern slopes of Komen
(sample Sm 81/96C); 4. - basic andésite, southern slopes of Krnes (sample Sm
83/96C); 5. - acid andésite, southern slopes of Krnes (sample Sm 83/96A); 6. - acid
andésite, the top of Krnes (sample Sm 16/88); 7. - acid andésite lava flow, southern
slopes of Krnes (sample Sm 74/88); Analysed in XRAL Activation Services., Ann
Arbor, Michigan
The distribution of rare earth elements, normalised to chondritic values by N a k a-
m u r a (1974), shoves only moderate enrichment (fig. 6): for the basalt sample, LREE
20-12 X chondritic level, HREE 16-12 x chondritic level; for dacite and rhyodacite
samples, LREE 50-17 x chondritic level, HREE 22-10 x chondritic level, and for
andésite samples, LREE 62-16 x chondritic level, HREE 30-10 x chondritic level. The
168
Polona Kralj
Fig. 6. The chondrite normalised (after Nakamura, 1974) REE patterns of the Smrekovec vol-
canics
SI. 6. Razporeditev prvin redkih zemelj normalizirana na vsebnosti v hondritih (po Nakamuri,
1974) za preiskane vzorce neeksplozivnih predornin smrekovškega podgorja
REE distribution is very consistent for the whole suite and shows pronounced nega-
tive Eu anomaly (table 4). La/Yb ratios (table 4) are very low compared with the val-
ues for orogenic andésites (Gill, 1981; Lopez- Escobar et al., 1977; Poka, 1988;
Panto, 1981), indicating limited REE fractionation.
Relatively flat REE chondrite-normalised patterns and a pronounced negative Eu
anomaly (>10%) are not common in andésites (Gill, 1981; Lopez-Escobar et al.,
1977), but are rather characteristic of tholeiites (Herrmann, 1972; Condie, 1982;
Kay&Hubbard, 1978).
Although a petrogenesis of the Smrekovec volcanics is far beyond the scope of this
work, and the available data rather insufficient, some general statements can be sug-
gested. As plagioclases in residue mainly deplete the melt in Sr and Eu (Hanson,
1978), this model can be applied as an option in the case of the Smrekovec volcanics.
Some dykes encountered in the Smrekovec volcanic complex are composed almost
exclusively of feldspars and could therefore represent late-stage emplacements of the
mentioned residual magmas. Some additional fractionation of potassium feldspar
would, besides Sr and Eu, contribute to a depletion of K and Ba in the melt relative
to the parent. Since REE distributions are very similar for the whole Smrekovec vol-
canic suite, the above mentioned feldspar fractionation would explain the anomalous
K/Rb, Ba/Ta and Ba/La ratios observed.
Lithofacies characteristics of the Smrekovec volcaniclastics__169
Lithofacieses of autoclastic deposits and resedimented hyaloclastite deposits
Autoclastic fragmentation is closely related to chill and quench processes when
lavas enter an aqueous medium or move on a surface composed of water-saturated
sediments (Cas & Wright, 1987; Fisher & Schmincke, 1984). Through such
non-explosive fragmentation, autobreccias are formed (Mc Phie et al., 1993).
Another group of autoclastic rocks are hyaloclastites, encompassing clastic aggre-
gates developed by non-explosive fracturing and disintegration of quenched lavas
(Honnorez & Kirst, 1975; Yamagishi, 1987), or parts of intrusions on contacts
with wet, unconsolidated host sediments, the so-called intrusive hyaloclastites (Mc
Phie et al., 1993).
Lithofacies Hb - hyaloclastite breccia
Marginal parts of the the Smrekovec coherent volcanic bodies were commonly
affected by non-explosive fragmentation. Hyaloclastite breccias are related to frag-
mented lava flows - lithofacies Hb(l), and high-level intrusives - lithofacies Hb(i).
Lavas were readily fragmented when extruded into the submarine environment
(plate 1, fig.l). The lava-sediment basal contacts, observed on a microscopic scale,
show smooth and curviplanar boundaries; very frequently no obvious mixing of lava
and sediment is present. Brecciated lateral and frontal parts of lava flows are com-
posed mainly of larger hyaloclasts, amounting up to 20 cm in diameter. This juvenile
lava hyaloclasts are blocky, with curviplanar and sometimes resorbed surfaces; vesic-
ulation is very uncommon.
In the upper parts of lava flows, autobreccias might be developed. Autoclasts are
locally slabby, flow foliated and have jagged ends.
Description of lithofacieses
Recognition of lithofacieses in the Smrekovec volcaniclastic deposits is far from
simple. One of the reasons is the scarcity of outcrops due to an abundant vegetation
cover, and a furtheron the complex fragmentation and resedimentation process going
on in submarine depositional environment.
Mioč et al. (1986) already stated, that stratified sequences of volcaniclastic rocks
encountered in the Smrekovec volcanic complex, actually represent turbidity current
deposits. Field observation and detailed microscopic inspection encompassed in the
present study indicate that volcaniclastic turbidite deposits vastly predominate in
the area.
During the recognition, description and classification of the Smrekovec volcani-
clastic deposits contemporary approaches from the works of F i s h e r and S c h m i n-
cke (1984), Cas and Wright (1987) and Me Phie et al. (1993) were taken into
account. The lithofacieses of volcaniclastic deposits were subdivided into four main
groups:
lithofacieses of autoclastic deposits and resedimented hyaloclastite deposits
lithofacieses of pyroclastic deposits (?)
lithofacieses of volcaniclastic debris flow and turbidite ash flow deposits
lithofacieses of reworked turbidite ash flow deposits
170_Polona Kralj
Lithofacies Hv - hyaloclastites
Quench fragmentation of lavas and high-level intrusive bodies due to chilling
effects of cooling marine water or water-saturated enclosing sediments may be very
efficient producing sand- and granule-sized grains. Hyaloclasts are essentially non-
vesicular glassy particles with a distinctly angular shape and curviplanar surfaces
(Fisher & Schmincke, 1984; Cas & Wright, 1987; Mc Phie et al., 1993). Hya-
loclastites developed "in situ" are strictly monomict and are neither internally
organised nor stratified (Yamagishi, 1987; Honnorez & Kirst, 1975). Resedi-
mented hyaloclastites may be internally graded and polymict.
In situ hyaloclastites developed in the Smrekovec volcanics are localised in close
vicinity of lava flows and high-level intrusives. They are mainly monomict, although
they may contain very small amounts (up to 8 vol.%) of lithics and pumice. Hyalo-
clasts are angular (plate 2, fig. 1), with curviplanar surfaces, glassy with very scarce
plagioclase phenocrysts and predominanty non-vesicular. A texture of flow foliation
in individual hyaloclasts is not uncommon. In many examples the glass is perlitic.
Reworked hyaloclastites occur in some cm to a few dm thick, ungraded layers, but
they differ from in situ hyaloclastites in much higher content of the admixted compo-
Lateral and front parts of lava flows may contain minor amounts of matrix, con-
sisting of finer-grained hyaloclastites and admixed underlying volcaniclastic sedi-
ment. Alteration upon zeolite facies conditions is common. Ocassionally, perlite frac-
turing is developed due to early hydration processes in the glassy groundmass. Pla-
gioclases of hyaloclasts are readily replaced by fine-grained aggregates of albite and
the groundmass is altered to microcrystalline quartz, chlorite, mixed-layered clay
minerals and opaque oxides. Zeolites, predominantly laumontite, occur as interstitial
fillings and vein minerals, rarely they also replace fine-grained clayey matrix of hya-
loclastite breccias.
High-level intrusive bodies are appreciably more abundant among the Smrekovec
coherent rocks. They commonly occur in subaqueous settings when the lithostatic
pressure of sedimentary cover exceeds the confining pressure of ascending magma
(Cas & Wright, 1987; M c Phi e et al., 1993). In such case, magma intrudes into the
pile of sedimentary cover as syn-volcanic sill or feeder dyke. Sudden and intensive
heat transfer leads to autoclastic fragmentation, which is particularly pronounced in
marginal parts of intrusive bodies.
Hyaloclastite breccias related to high-level intrusive bodies are encountered on
the top of Komen, as well as in its southern and northern slopes. Autoclasts range in
sizes from a few dm to some tenths of mm. The sandy fraction, along with an exten-
sively developed interstitial cement, forms the matrix of hyaloclastite breccias (plate
1, fig. 2). Autoclasts are blocky and commonly show curviplanar surf ces similar to
those produced in frontal and lateral parts of lava flows.
Authigenic mineralisation under zeolite facies conditions is particularly pro-
nounced in hyaloclastite breccias (plate 1, fig 2), related to high-level intrusions. Pri-
mary constituents may be completely replaced by secondary minerals: plagioclases
by albite, prehnite, laumontite, pumpellyite or analcime, and the glassy groundmas
most commonly by chlorite or interlayered chlorite/smectite, microcrystalline quartz,
sphene and albite. Laumontite, prehnite, analcime and thomsonite are fairly abun-
dant minerals infilling pore space and crack systems.
Lithofacies characteristics of the Smrekovec volcaniclastics_171
nent. Pumice may be particularly abundant attaining up to 40 vol.% of the bulk rock.
Resedimented hyaloclastites are fairly eroded. Some scarce, erosional remnants are to
be found on the top of the mountain range from Komen to Smrekovec, but also along
the southern and northern slopes of the mountain range, at a distance of about 1 km
from the mountain peaks. The layers have a declination angle of approx. 25°. Most
commonly, resedimented hyaloclastites originate from glassy acid andésite lava flows
(table 1, sample 8). Pumice lapilli of similar composition, encountered in resediment-
ed hyaloclastites indicate the lavas possibly followed explosive eruptions, producing
pyroclastic deposits.
In situ hyaloclastites are commonly altered upon hydrothermal and contact meta-
morphic conditions to contain laumontite, albite and quartz are the most pronounced
new-formed minerals. In resedimented hyaloclastites clinoptilolite and heulandite
are abundantly developed; along with smectite and crystobalite they replace volcanic
glass in hyaloclasts, pumice and fine-grained matrix.
Lithofacies Bp - peperitic breccias
Upon an intrusion of magma into wet, unconsolidated sediments, quenched debris
may be dynamically mixed with the enclosing sediment. As interstitial water in sedi-
ments boils due to magma intrusion, the dispersal of hyaloclasts by fluidisation
occurs (Kokelaar, 1982; Cas & Wright, 1987; Mc Phie et al., 1993). Such mix-
tures of quenched debris with the enclosing sediments are called peperites or peperit-
ic breccias (Cas&Wright, 1987).
Peperitic breccias developed in the Smrekovec volcanic complex are related to
intrusions of high-level intrusives. They outcrop on the southern flanks of Krnes, W
of the farmhouse Kugovnik and somewhat southwards, near the farmhouse Atelšek.
The interpretation of rock formation was given by Jocelyn McPhie and Ray Cas (pers.
comm.) during their visit to the Smrekovec mountains in September 1996.
Peperitic breccias consist of blocky clasts, characteristic of hyaloclastites, and
matrix, composed of fine-grained volcaniclastic sediments (plate 1, fig. 3; plate 2,
figs. 2, 3). The blocky clasts are composed of glassy acid andésite, with a fairly com-
mon perlitic texture (plate 2, fig. 3). The contacts of blocky clasts and sediment local-
ly indicate that resorption and alteration processes were not uncommon. Clasts are
essentially non-vesicular and sometimes show the texture of flow foliation.
The alteration mainly affected blocky clasts whereas the matrix remained poorly
altered. Zeolites - most abundantly laumontite - replace volcanic glass and infill
microfissures. The associated authigenic minerals are albite, prehnite, sphene, quar-
tz, chlorite and interlayered clay minerals.
Lithofacies Vp - peperites
Peperites are mixtures of lavas and the enclosing sediment (plate 3, figs. 1, 2).
Autoclasts commonly have patchy or globular forms and are very commonly altered
to such an extent that their origin became obscured. The alteration is related to
hydration reactions and intensive heat transfer from still hot autoclast to the sur-
rounding sediment. It is characteristic of this type of alteration that it affected only
autoclasts whereas the sediment remained fairly unaltered. Very common secondary
minerals replacing autoclasts in peperites are zeolites.
172
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Lithofacieses of pyroclastic deposits
Pyroclastic deposits should have both, distinct pyroclastic composition and the
mode of transport (Cas & Wright, 1987). In the Smrekovec volcanic complex,
pumice-rich tuffs of acid andesitic to dacitic composition are locally encountered
(plate 3, fig. 3). However, there is no clear evidence of pyroclastic mode of transport
and sedimentation, and the abundance of pumice lapilli only is not an evidence suffi-
cient for the recognition of the origin of rocks. Some pumice-rich deposits occur in
the sequences of volcaniclastic turbidity flow deposits (fig. 7). In comparison with a
typical pyroclastic flow deposit, they lack of cross-bedded fine-grained unit; the
coarse-grained unit can be massive or fainty stratified. The upper unit consists of a
Fig. 7. Pyroclastic flow deposits (?) sealed in a sequence
of volcaniclastic turbidity flow deposits, southern
slopes of Krnes. Pyroclastic flow unit (?) can be seen in
the lower left half of the photo
SI. 7. Piroklastiti (?) med zaporedjem vulkanoklasti-
čnih turbiditov z južnega pobočja Krnesa. Plasti piro-
klastitov se vidijo na spodnji levi polovici slike
Lithofacies characteristics of the Smrekovec volcaniclastics
173
Fig. 8. Disturbed, fine-grained, horizontally an vaguely laminated tuffs, the upper
pyroclastic flow (?) unit. A detail from the previous photo
SI. 8. Porušeni, vzporedno in vijugavo laminirani drobnozrnati tufi v vrhnjem de-
lu piroklastitov. Detajl iz prejšnje slike
fine-grained tuff, horizontally or vaguely laminated (fig. 8). The coarse-grained tuff
contains tube pumice of coarse sand- to granule-size; the matrix is subordinate in
occurrence and glass shards can not be recognised due to alteration processes. The
deposit does not show lenticular geometry. It closely resembles subaqueous volcani-
clastic mass-flow deposits (after McPhie et al., 1993). The flow very possibly start-
ed as a pyroclastic flow, and was converted to a volcaniclastic mass-flow during its
movement in the submarine environment.
Lithofacieses of volcaniclastic debris flow and turbidity ash flow deposits
Volcaniclastic deposits formed by the settling of volcaniclastic debris flows and
turbidity ash flows are particularly widespread on the southern slopes of the moun-
tain range. Turbidity ash flow deposits overlie volcaniclastic debris flow deposits and
are internally stratified, building fining-upward sedimentary sequences. In the
vicinity of Komen, Krnes and Smrekovec peaks, volcaniclastic deposits comprise a
considerably larger proportion of volcaniclastic debris flow deposits - often over 75
percent of the total sequence. At a distance of about 2-4 km from the top of the
mountain range, volcaniclastic debris flow deposits become much thinner and may
even be absent. The proportion of volcaniclastic debris flow deposits decreases to 50
percent or less of the total sequence. In these more distal settings, reworked turbidite
deposits are also encountered.
174
Polona Kralj
The material contained in volcaniclastic deposits is mainly of autoclastic, subor-
dinately of pyroclastic origin, and may be rather heterogenous according to the tex-
ture, composition and stage of alteration.
Lithofacies Bx - polymict volcaniclastic breccia with mud clasts
Polymict volcaniclastic breccia is abundantly encountered in the vicinity of the
present outcrops of coherent volcanic rocks near the top of the Komen-Krnes-
Smrekovec mountain range. It commonly occurs in the form of tabular bodies,
attaining a thickness of a few metres to over ten metres.
The deposits are massive, containing angular fragments of coherent volcanics and
rounded or angular clasts of mudstone, set in a coarse-grained tuffaceous matrix (fig.
9). The largest fragments may attain up to 5 dm in diameter, but usually they do not
exceed 2 dm. The shape and size of larger coherent rock clasts indicate that they
probably originate from hyaloclastite breccias and autobrecciated lavas. Juvenile
material is very scarce in occurrence.
The tabular geometry of polymict volcaniclastic breccias suggest that they are
deposits of cohesive volcanic debris flows or lahars. They could have been triggered
by volcanic explosions or the effects of earthquakes, gravitational instability on the
surface of repose or some larger-scale tectonic displacements. Volcaniclastic debris
flows must have been the instrumental in the generation of turbidity ash flows. In
Fig. 9. Turbidite ash deposits; southern slopes of Komen. Horizontally stratified
division - lithofacies T(h), overlain by volcaniclastic debris flow deposits,
lithofacies Bx
SI. 9. Sedimenti turbiditnega toka; južno pobočje Komna. Nad vzporedno plas-
tovito enoto litofaciesa T(h) leže sedimenti vulkanoklastičnega debritnega toka
litofaciesa Bx
Lithofacies characteristics of the Smrekovec volcaniclastics
175
volcaniclastic sequences, polymict volcanic breccia commonly overlies turbidite ash
deposits and comprises eroded clasts of mudstones from the uppermost turbidite ash
division. Due to a lower velocity of volcaniclastic debris flow in relation to the tur-
bidity current, the turbidite ash flow deposits underlie the deposits of volcaniclastic
debris flow they evolved from (fig. 9).
Lithofacies Bt - volcaniclastic tuff-breccias
The rocks of this lithofacies type are also related to basal parts of the fining-
upward sequences of turbidite ash flow deposits (fig. 10). The bed thickness varies
from under 2 dm up to 4 m, but most commonly it ranges between 3-12 dm. The rock
structure is massive and the basal contacts erosional. The main constituents are
angular fragments of coherent volcanic rocks of diverse origin whereas pumice lapilli
are subordinate in occurrence and may locally amount to up to 20% of the bulk rock
composition. The matrix is sandy and with respect to the composition closely related
to the coarser fraction. Fines are subordinate in occurrence; the rock is mainly grain-
supported.
Lithofacies Tv(h) - horizontally stratified coarse-grained tuffs
The rocks of this lithofacies type are fairly widespread in occurrence throughout
the Smrekovec volcanic complex. In well developed turbidity sequences, the division
Fig. 10. Distal volcaniclastic turbidite flow deposit; Primož, north-west of Ljub-
no. Each sedimentary cycle consists of lithofacieses Bt, T(h), F(h), F(v) and F(m)
SI. 10. Distalni sedimenti vulkanoklastičnega turbiditnega toka; Primož nad Ljub-
nim. Vsak sedimentacijski ciklus sestoji iz litofaciesa Bt, T(h), F(h), F(v) in F(m)
176_Polona Kralj
Lithofacieses F(h) and F(v) - horizontally laminated and vaguely
laminated fine-grained tuffs
The deposits of this litofacies type occupy the uppermost parts of the turbidity
sequence and are interpreted as deposits from dilute suspensions, trailing the tur-
bidity currents. The lamination is fairly commonly diffuse. In the more ideally devel-
oped sequences, the horizontally and vaguely laminated rocks may attain a thicknes
of 1-5 dm; syn-sedimentary structures of slumping and sliding occur locally.
Lithofacies F(m) - massive fine-grained tuffs
Massive fine-grained tuffs occupy the top position in turbidite ash deposits. The
thickness varies between a few mm and 25 cm. In near-source deposits they may be
absent, but in distalparts they are very common (fig. 11).
Lithofacieses of reworked turbidite ash deposits
Reworked, fine-grained turbidite ash deposits locally overlie distal, fine-grained
turbidite ash deposits. They are related to shallower, possibly shoreline environment,
indicated by cross-stratification, bioturbation, mud drapes and abundant organic
matter. Compositionally they contain some non-volcanic component, very possibly
originating from Upper Oligocene siltstones and mudstones.
Lithofacies Sv(m) -
massive tuffaceous sandstones
The occurrence of massive tuffaceous sandstones is scarce. According to their
grain-size, they range from fine-grained sandstones to silty sandstones. Locally they
are bioturbated. The composition indicates some admixture of non-volcanic material
- mainly illite and quartzite, derived from Upper Oligocene clastic sediments.
of horizontally stratified coarse-grained tuff overlies massive tuff-breccias of lithofa-
cies Bt (fig. 10). The thickness of the coarse-grained tuff division is approx. 0.1-5 m.
It may comprise several (over fifty) graded units, 1-20 cm thick. Very commonly one
bedding set is composed of distinct subsets, defined by faint stratification. Gradation
is for the most part normal. The tuffs vary, according to grain size, from very coarse,
granule-rich varieties, to tuffs comprising a fair amount of fine ash.
Coarse-grained tuffs are mainly composed of angular rock fragments of diverse
composition, texture and stage of alteration. Some sequences are characterised by
the occurrence of pumice which may amount to up to 20% of the bulk rock composi-
tion, but glass shards are fairly uncommon. The tuffs are predominantly grain-sup-
ported; fine-grained matrix, if present, is subordinate and may consist of glassy ash
or tuffitic material. Examples of pronounced cementation can be found. Zeolites are
the most common cementing minerals that infill interstitial fillings and replace fine-
grained matrix.
Lithofacies characteristics of the Smrekovec volcaniclastics
177
Fig. 11. Turbidite ash deposits alternating with reworked turbidite ash deposits;
Primož, north-west of Ljubno
SI. 11. Sedimenti turbiditnega toka, ki se menjavajo z lokalno presedimentiranimi
sedimenti turbiditnega toka; Primož nad Ljubnim
Lithofacies Sv(t) -
through-cross stratified tuffaceous sandstones
The deposits of this lithofacies type are related to distal settings. They overlie the
horizontally and vaguely laminated fine-grained tuffs of lithofacies types F(h) and
F(v). With respect to the grain-size, fine-grained sandstones and silty sandstones pre-
dominate.
The most common bedforms are antidunes and dunes (fig. 12). According to Cas
& Wright (1987) antidunes are deposited by unidirectional current flows charac-
terised by progressively increasing velocity. Many of the antidune and dune bedforms
have thin mud drapes (fig. 12).
Mineral composition of the cross-stratified division indicates a partial incorpora-
tion of non-volcanic material, characterised mainly by the presence of illite and
detritial quartz.
Lithofacies M -
massive tuffaceous mudstones
Massive tuffaceous mudstones of reworked deposits are characterised by mixed,
volcanic and non-volcanic mineralogy and local abundance of organic matter.
178
Polona Kralj
Fig. 12. Reworked turbidite ash deposits, through cross-stratified sandstone unit
- lithofacies Sv(t); Primož, north-west of Ljubno
SI. 12. Lokalno presedimentirani sedimenti turbiditnih tokov, litofacies navzkriž-
, no plastovitega peščenjaka Sv(t); Primož nad Ljubnim
The succession of volcaniclastic deposits related to the settling
from turbidite ash flows
Volcaniclastic deposits related to the settling from turbidity ash flows are organ-
ised in sequences comparable to Bouma's sequence for turbidites (Bo um a, 1962;
Cas, 1979). An ideal sequence comprises massive, coarse-grained basal layer (divi-
sion a), planar stratified coarse sand (division b), wavy and ripple cross-laminated
sand (division c), laminated mud and silt (division d) and massive mud (division e).
The development of a volcaniclastic turbidite sequence, encountered in the Smre-
kovec volcanic complex, is closely related to the distance of the deposition site from
the assumed source. The main present outcrops of coherent volcanics on the moun-
tain range top must have been located close to the source of turbidity currents. A
widespread occurrence of polymict volcaniclastic breccias deposited from volcani-
clastic debris flows or lahars in the vicinity of coherent volcanics also indicates a
position was close to the source.
Turbidite ash deposits situated closer to the source (fig. 13) comprise coarser-
grained massive tuff-breccias (lower division a, lithofacies Bt), horizontally strati-
fied, coarse-grained tuff (division b, lithofacies T(h)), and laminated mud and silt
(division d, lithofacieses F(h) and F(v)). The upper finely-grained unit (division d) is
commonly missing. The stacking of sedimentation units results in the formation of
amalgamated turbidites. Slumping and sliding structures are fairly common.
Distal turbidite deposits (located approx. 3-4 km further to the south-west are
thinner, sometimes lacking the coarser-grained layers (division a).
Lithofacies characteristics of the Smrekovec volcaniclastics
179
Fig. 13. Simplified graphic log of the Smrekovec volcaniclastic debris flow and turbidite ash
deposit: A, proximal deposits and B, distal deposits interbedded with reworked turbidite
deposits
SI. 13. Shematski profil prek skladovnice sedimentov vulkanoklastičnega debritnega toka in
vulkanoklastičnih turbiditnih tokov: A, sedimenti proksimalnih območij in B, sedimenti distal-
nih območij, mešani s presedimentiranimi turbiditi
Facies model of the Smrekovec volcaniclastics
The Upper Oligocene Smrekovec volcanic activity is recorded by the occurrence of
coherent volcanic rocks, autoclastic deposits, volcaniclastic deposits and rev^orked
volcaniclastic deposits. Among recently outcropping volcanics, volcaniclastic debris
flow and turbidity ash flow deposits predominate. Among coherent volcanic rocks,
high-level intrusive bodies are far more abundant than lavas.
Early magmas were of basaltic composition, extruding as submarine lava flows or
forming high-level intrusive bodies. The chemical composition of trace elements,
particularly of rare earths, indicates that basaltic magma most probably underwent a
differentiation due to crystal fractionation. Consequently, basaltic andésites, acid
andésites and finally rhyodacites evolved in time, forming a volcanic suite. Major
element composition is slightly modified due to hydrothermal activity, but trace ele-
ment proportions and REE distribution in the Smrekovec coherent volcanics of inter-
mediate composition are not very characteristic of orogene andésites. For this reason
the tectonic setting still remains ambiguous and may also be related to a setting dif-
ferent from convergent plate boundaries. The andésite and dacite occurrence in cen-
tral California (Dickinson & Snyder, 1979 a, b) was attributed to local extension
180_Polona Kralj
Conclusions
The Upper Oligocene Smrekovec volcanic activity is recorded by the occurrence of
coherent volcanic rocks, autoclastic deposits, volcaniclastic deposits and reworked
volcaniclastic deposits. Besides extrusive rocks, settled in a submarine environment,
high-level intrusive bodies were emplaced into unconsolidated, water-saturated vol-
caniclastic sediments.
at the plate boundary. The proximity of the peri-Adriatic lineament and the migra-
tory junction of Apulia, Europe and the Pannonian fragment could have resulted in
local extension and leakage at the plate boundary.
The early stage of volcanic activity was dominantly non-explosive. Basalts and
basaltic andésites were emplaced as submarine lavas or high-level intrusive bodies.
The style of fragmentation was mainly autoclastic, related to chill and quench
processes. The late-stage of volcanic activity is characterised not only by non-explo-
sive volcanism of acidic andesitic to rhyodacitic composition, but also by explosions,
either combined magmatic and hydrovolcanic, or solely magmatic. Juvenile material,
chiefly pumice and glass shards, became relatively abundant. Volcanic activity built
an edifice of submarine stratovolcano(es) with a significant positive relief, composed
of lavas, high-level intrusive bodies, autoclastic deposits, pyroclastic deposits and
syn-eruptive resedimented volcaniclastic deposits.
Syn-eruptive volcaniclastic resedimentation is rather effective in submarine envi-
ronments. Presently outcropping volcanics in the Smrekovec mountains are in fact
only erosional remnants of the former, broader volcanic complex and are composed
mainly of syn-eruptive resedimented volcaniclastic rocks (fig. 14). Volcaniclastic
debris flows and turbidity ash flows may have been generated due to gravitational
instability of material resting on steep slopes of strato volcano edifices, and also by
volcanic explosions. However, the distinction between deposits of submarine pyro-
clastic flows and volcaniclastic turbidity flows is very difficult in general. When pyro-
clastic flows enter an aqueous media, they actually behave like volcaniclastic tur-
bidity flows (Cas & Wright, 1987). Unlike most turbidite sequences, the lower mas-
sive division forms 50 percent or more of the total sequence (Fisher & Schminke,
1984). As single pyroclastic flow deposit commonly reaches several tenths to several
hundred metres in thickness (Cas & Wright, 1987; Fisher & Schmincke, 1984).
The composition of Smrekovec volcaniclastic rocks is characteristically polymict.
The main constituents are lithics which show strong affinity to the Smrekovec coher-
ent volcanics and their autoclastic deposits, although textural and compositional dif-
ferences may occur in the same sample; sometimes there is also a difference in their
state of alteraton. For instance, it is possible to encounter in the same volcaniclastic
rock sample relatively unaltered glassy fragments and lithics of high-level intrusive
bodies with pumpellyite, prehnite, epidote or laumontite as authigenic minerals.
Tuffs, comprising predominantly juvenile material are, very rare, and since they are
fairly overgrown, it can not be established whether they have both, a demonstrable
pyroclastic mode of fragmentation and transport.
In distal parts of the Smrekovec volcanic complex, turbidite ash deposits under-
went a reworking process in a shallow-marine environment, in addition to minor
admixtures of non-volcanic material, cross-stratification, bioturbation and mud
drapes are also characteristic of rocks of this lithofacies.
Lithofacies characteristics of the Smrekovec volcaniclastics
181
Fig. 14. Idealised facies model for the Smrekovec volcanics
SI. 14. Idealizirani facialni model smrekovških vulkanitov
182_Polona Kralj
Acknowledgements
I am much obliged to the Institute of Geology, Geotechnics and Geophisics for
having enabled me to work on this problem. The study was supported by the Ministry
of Science and Technology of the Republic of Slovenia.
I express my cordial thanks to Prof. Dr. Josip Tišljar from The University of
Zagreb, Croatia, for revision of the manuscript and many helpful comments.
The chemical composition of coherent volcanics indicates that magmas varied
with time from basaltic, basaltic andesitic and acidic andesitic to dacitic, forming a
volcanic suite. Major element composition is slightly modified due to hydrothermal
alteration, but trace element proportions and the REE distribution in the volcanics of
intermediate composition are not very characteristic of orogene andésites. I believe
that the Smrekovec volcanism must be related to the local extension and leakage at
the migratory junction of Apulia, Europe and the Pannonian fragment.
During the Smrekovec volcanic activity, extruded lavas, high-level intrusive bod-
ies and pyroclastic deposits built a volcanic complex of submarine stratovolcano(es)
with significantly elevated relief. The extruded lavas and high-level intrusives
underwent quench fragmentation on their contacts with seawater or enclosing water-
saturated sediments. In situ hyaloclastites, resting on gravitationaly unstable slopes
of the stratovolcano were easily resedimented and consequently resulted in the for-
mation of resedimented hyaloclastites. Volcanic debris flow deposits and turbidity
ash flow deposits are the most widespread rock type of the Smrekovec volcanic com-
plex. Their generation could also be related to the late-stage period of explosive
activity. Turbidite ash deposits are locally reworked in a shallow-marine environ-
menk___........_____________________________________________.............._............^____... .........„......______,_____
Litofacialne značilnosti smrekovških vulkanoklastitov_     183
Litofacialne značilnosti smrekovških vulkanoklastitov
(severna Slovenija)
Uvod
Smrekovško podgorje grade zgornjeoligocenske vulkanske kamnine. Raztezajo se
na površini približno petnajstih kvadratnih kilometrov in predstavljajo osrednji del
obsežnejšega vulkanskega pasu, imenovanega tudi smrekovška serija (Mioč, 1978,
1983; Mioč et al., 1986). Najvišje se vzpno vrhovi Komen (1684m), Krnes (1613m) in
Smrekovec (1577 m). Zgornjeoligocenska starost predornin je določena na osnovi bio-
stratigrafskih raziskav foraminiferne favne, vsebovane v meljastih sedimentih pod-
lage (Rij avec, 1966).
Prvo geološko delo s tega področja datira iz konca prejšnjega stoletja, ko je Teller
(1898) objavil geološko karto lista Prassberg. Po drugi svetovni vojni so tod delovali
številni slovenski geologi, bodisi v okviru projekta Osnovne geološke karte I (Hinter-
lechner-Ravnik & Pleničar, 1967; Mioč, 1978, 1983; Mioč et al., 1986) kakor
tudi raziskav zeolitov (O s t ere, 1976; Kovic & Krošl-Kuščer, 1986; Kovic,
1988).
Tektonsko okolje nastanka smrekovškega vulkanizma ostaja še vedno nedorečeno.
Globalni tektonski procesi, katerih posledica je sedanja zapletena geološka zgradba
ozemlja, so nedvomno vezani na zgornjejursko subdukcijo oceanske evropske plošče
pod kontinentalno afriško, ki pa je že v začetku terciarja prešla v kolizijo, usmerjeno
od juga proti severu (Oberhauser, 1980; Royden, 1988; Dercourt et al., 1986).
Konec oligocena sta za tektonsko dogajanje na današnjem ozemlju Slovenije pomem-
bni predvsem dve manjši litosferni plošči, imenovani Apulija in Panonija, ki sta na-
stali z drobljenjem in spajanjem tako afriške kakor tudi evropske plošče. Gibanje
Apulije je bilo usmerjeno proti severozahodu, gibanje Panonije pa sprva proti severo-
vzhodu in nato proti vzhodu. Gibanje obeh manjših litosfernih plošč se je uravnavalo
v peri-adriatski prelomni coni (Royden, 1988).
Dosedanji maloštevilni podatki o kemizmu smrekovških predornin ne dovoljujejo
dorečenih sklepov o njihovem izvoru, geokemični pripadnosti in tektonskem okolju.
Vendar je na osnovi vsebnosti glavnih in slednih prvin v preiskanih vzorcih vendarle
mogoče reči, da njihov kemizem ni značilen za orogene andezite. Predvsem razpore-
ditev prvin redkih zemelj je zelo podobna tako bazaltnim kot tudi andezitnim in da-
citnim različkom smrekovškega vulkanskega niza in je zelo netipična za orogene
andezite. Najverjetneje je nastanek andezitov in dacitov posledica kristalne frakcio-
nacije neke bazaltne magme. Znano je, da se lahko vulkanska aktivnost andezitnega
značaja nadaljuje tudi med kolizijo litosfernih plošč in po njej (Gill, 1981), ali pa
njen pojav sploh ni neposredno vezan na subdukcijo litosfernih plošč, temveč na lo-
kalno ekstenzijo, kakor je to v osrednji Kaliforniji (Dickinson & Snyder, 1979a,
1979 b). Menim, da je smrekovški vulkanizem posledica lokalne ekstenzije med odd-
vajanjem Apulije od Panonije oziroma prepustnosti peri-adriatskega lineamenta.
Opis litofaciesov vulkanoklastičnih kamnin
Smrekovške vulkanoklastične kamnine so bile razporejene v štiri glavne skupine
litofaciesov:
184_Polona Kralj
Litofaciesi avtoklastičnih kamnin in lokalno presedimentiranih hialoklastitov
Avtoklastična fragmentacija je vezana na procese nenadnega ohlajanja, ko se lave
izlijejo v vodo ali gibajo po površini vlažnih sedimentov (Cas & Wright, 1987; Fi-
sher & Schmincke, 1984). Takšna neeksplozivna fragmentacija pa se pojavlja tudi
na stikih plitvo ležečih intruzivov vulkanskega nivoja z okolišnimi vlažnimi sedimen-
ti (Mc Phie et al., 1993). Plitvo ležeči intruzivi vulkanskega nivoja se pogosto poja-
vljajo v morskih okoljih tedaj, ko je teža sedimentnega pokrova in vodnega stebra
večja od tlaka dvigujoče se magme (Mc Phie et al., 1993). Fragmentirani deli plitvo
ležečih intruzivov vulkanskega nivoja se imenujejo intruzivni hialoklastiti.
Avtobrečirane lave (tabla 1, si. 1) so med smrekovškimi predominami sorazmerno
redke. Mnogo pogosteje je mogoče najti avtoklastične kamnine intruzivnega porekla.
Bolj debelozrnati različki so hialoklastične breče (tabla 1, si. 2), ki vsebujejo hialok-
laste z značilnimi, ukrivljenimi ploskvami. Osnova hialoklastičnih breč sestoji iz
hialoklastičnega materiala velikosti 0.063-2.0 mm.
Hialoklastiti smrekovškega podgorja sestoje iz hialoklastov velikosti drobnih
lapilov in vulkanskega pepela. Hialoklasti se od juvenilnih piroklastov ločijo pred-
vsem po tem, da skorajda ne vsebujejo votlinic plinskih mehurčkov, oblike zrn so po-
gosto zelo oglate, ploskve pa ukrivljene in le malo nazobčane (tabla 2, si. 1). Presedi-
mentirani hialoklastiti niso strogo monomiktni, temveč vsebujejo primes plovca, ki
znaša ponekod do 40 vol.%. Prav tako je v nasprotju razliko od pravih hialoklastitov,
ki so notranje neorganizirani, v presedimentiranih hialoklastitih opazna plastovitost.
Hialoklastične breče, vezane na stike plitvo ležečih intruzivov z okolnimi vlažnimi
sedimenti, prehajajo bočno v mešane sedimente, imenovane peperitne breče in peper-
iti. Peperitne breče sestoje iz hialoklastov, ki so pomešani z okolnim sedimentom
(tabla 1, si. 3; tabla 2, si. 2, 3). Mešanje nastaja zaradi fluidizacije osnove okolnih
vlažnih sedimentov, v katerih se porne vode zaradi bližine vročega intruziva močno
segrejejo. Fluidizacija osnove tako omogoči disperzijo hialoklastov v okolni sediment
(MC Phie et al., 1993). Hkrati s fluidizacijo in segrevanjem pornih raztopin v okolnih
sedimentih se pričenjajo ustvarjati lokalni hidrotermalni sistemi, ki povzročajo nas-
tanek zeolitov. Peperiti (tabla 3, si. 1, 2) se od peperitnih breč razlikujejo po nepravil-
ni, krpasti ali kroglasti obliki hialoklastov (Mc Phie et al., 1993).
Litofaciesi piroklastitov (?)
Piroklastiti morajo vsebovati juvenilni material, hkrati pa morajo tudi jasno od-
ražati piroklastični način transporta (Cas & Wright, 1987). Med smrekovškimi vul-
kaniti se pojavljajo plasti, bogate s plovcem (tabla 3, si. 3), vendar pa teksture niso
dovolj značilne, da bi jih lahko z gotovostjo opredelili kot piroklastite. S plovcem bo-
gate plasti izdanjajo med zaporedjem vulkanoklastičnih turbiditov (si. 7). V primer-
javi z značilno zgradbo in zaporedjem sedimentov piroklastičnega toka v plasteh do-
mnevnih piroklastitov smrekovškega vulkanskega kompleksa manjkajo spodnji, nav-
litofaciesi avtoklastičnih kamnin in lokalno presedimentiranih hialoklastitov
litofaciesi piroklastitov (?)
litof aciesi vulkanoklastičnih debritov in turbiditov,
litof aciesi lokalno presedimentiranih vulkanoklastičnih turbiditov.
Litofacialne značilnosti smrekovških vulkanoklastitov__185
Litofaciesi vulkanoklastičnih debritov in turbiditov
Vulkanoklastiti, nastali s sedimentaci]o iz debritnih in turbiditnih tokov, so naj-
bolj razširjena zvrst kamnin smrekovškega podgorja. Posebno razprostranjeni so na
južnih pobočjih Smrekovca, Krnesa in Komna. Te vulkanoklastične kamnine grade
skladovnice z zmanjševanjem velikosti zrn navzgor. V bližini omenjenih vrhov sestoje
te skladovnice iz masivnih debritov v njihovih spodnijh delih ter iz plastovitih in
laminiranih turbiditov v zgornjih delih. Debriti grade skoraj 75% celotne sekvence. V
razdalji 2-4 km od gorskega grebena vrhov Smrekovca, Krnesa in Komna se zmanjša
delež debritov v vulkanoklastični turbiditni sekvenci na manj kot 50%, pojavijo pa se
tudi drobnozrnati sedimenti, ki so bili lokalno presedimentirani v plitvem morskem
okolju.
Debriti so zastopani z masivno grajenimi vulkanoklastičnimi tufskimi brečami, ki
se pojavljajo v obliki lečastih in ploskastih teles, debelih od manj kot 2 dm do največ
4 m (si. 9). Stiki s podlago so navadno erozijski. Glavna sestavina vulkanoklastičnih
tufskih breč so oglati fragmenti lave in plitvo ležečih intruzivov različne sestave,
medtem ko je plovec le maloštevilno zastopan. Drobnozrnate osnove je zelo malo, za-
to ima kamnina pretežno klastno podporo.
Med turbiditi se pojavljajo vzporedno plastoviti debelozrnati tufi, vzporedno in
vijugavo laminirani drobnozrnati tufi in masivno grajeni drobnozrnati tufi (si. 10,
11). Sestava vulkanoklastičnega materiala je heterogena, v splošnem je vsebnost
plovca nizka in le izjemoma presega 10 vol.% celotne kamnine.
Litofaciesi lokalno presedimentiranih vulkanoklastičnih turbiditov
Lokalno presedimentirani drobnozrnati turbiditi (si. 12) so vzporedno ali nav-
zkrižno plastovito grajeni, pojavljajo se drobne leče mulja (mud drapes), bioturbacija
in ponekod tudi organska snov. Sedimenti vsebujejo tudi nevulkanogeno primes, ki
najverjetneje izvira iz zgornjeoligocenskih meljevcev.
Sklep
Zgornjeoligocenski vulkanizem na Slovenskem je zapustil sledove svojega delo-
vanja tudi na smrekovškem podgorju. Vulkanizem je deloval v morskem okolju, kjer
je nastal vulkanski masiv z enim ali več stratovulkanov in izrazitim pozitivnim relie-
fom. Sestava magme se je zaradi frakcijske kristalizacije bazaltne taline s časom
spreminjala od bazaltne prek bazaltne andezitne in kisle andezitne do dacitne in tako
ustvarila vulkanski diferenciacij ski niz. Tako so se v zgodnjem obdobju vulkanskega
delovanja izlili na morsko dno bazalti in bazaltni andeziti. V poznem obdobju vul-
zkrižno plastoviti deli drobnozmatih tufov (Mc Phie et al., 1993). Debelozrnati tufi
so masivno grajeni ali pa izražajo samo nakazano vzporedno plastovitost; zgornji deli
sestoje iz vzporedno in vijugavo laminiranega drobnozrnatega tufa (si. 8). Ti sedi-
menti so najverjetneje nastali s sedimentaci]o iz tokov, ki so po izvoru piroklastični,
vendar so se zaradi gibanja v vodnem mediju kmalu spremenili v vulkanoklastične
turbiditne tokove.
186_Polona Kralj
Zahvala
Zahvaljujem se Inštitutu za geologijo, geotehniko in geofiziko, ki mi je omogočil
delo pri reševanju te problematike. Raziskave je financiralo Ministrstvo Republike
Slovenije za znanost in tehnologijo.
Prisrčna zahvala velja prof. dr. Josipu Tišljarju iz Univerze v Zagrebu za recenzijo
rokopisa in številne koristne nasvete.
kanskega delovanja so prevladovali kisli andeziti in daciti, ki so se izlili kot lava ali
pa so intrudirali v še nekonsolidirane vulkanoklastične sedimente; pojavljale so se
tudi vulkanske eksplozije magmatskega ali mešanega magmatsko-hidrovulkanskega
značaja. Robovi plitvih intruzivov in lave so se avtobrečirali in mešali z okolnim sed-
imentom, zaradi česar je nastal niz avtoklastičnih in mešanih avtoklastičnih-vulka-
noklastičnih kamnin. Vulkanski kompleks je bil podvržen nenehni eroziji in presedi-
mentaciji že med samim vulkanskim delovanjem. Kasnejša erozija in živahno tekton-
sko delovanje sta oblikovala njegovo današnjo podobo.
Lithofacies characteristics of the Smrekovec volcaniclastics_     187
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Lithofacies characteristics of the Smrekovec volcaniclastics
189
Plate 1 - Tabla 1
Fig. 1. Autobrecciated lava
flow; SW of Komen
SI. 1. Avtobrečirani lavini tok;
jugozahodno pobočje Komna
Fig. 2. Hyaloclastite breccia;
southern slopes of Krnes     ^
SI. 2. Hialoklastična breca; <
južno pobočje Krnesa *'
Fig. 3. Peperitic breccia;
southern slopes of Krnes,
westwards of the farmhouse
Kugovnik
SI. 3. Peperitna breca; južno
pobočje Krnesa, zahodno od
kmetije Kugovnik
190
Polona Kralj
Plate 2 - Tabla 2
Fig. 1. Angular hyaloclasts in
a hyaloclastite from southern
slopes of Krnes. Plane
polarised light, magnification
14.5 X
SI. 1. Oglati hialoklasti v
hialoklastitu z južnega
pobočja Krnesa. Presevna
polarizirana svetloba,
povečava 14.5 x
Fig. 2. Peperitic breccia;
southern slopes of Krnes, W of
the farmhouse Kugovnik.
Angular, locally resorbed and
flow-foliated andésite clasts
in fine-grained matrix. Plane
polarised light, magnification
14.5 X
SI. 2. Peperitna breca; južno
pobočje Krnesa, zahodno od
kmetije Kugovnik. Oglati, sem
in tja resorbirani in zaradi
tečenja poviti klasti andezita
v drobnozrnati osnovi.
Presevna polarizirana
svetloba, povečava 14.5 x
Fig. 3. Peperitic breccia;
southern slopes of Krnes, near
the farmhouse Atelšek. An
angular clast of acid andésite
composition with perlitic
texture. Plane polarised light,
magnification 14.5 x
SI. 3. Peperitna breca z
južnega pobočja Krnesa,
blizu kmetije Atelšek. Oglat
klast kislega andezita kaže
perlitsko strukturo. Presevna
polarizirana svetloba,
povečava 14.5 x
Lithofacies characteristics of the Smrekovec volcaniclastics
191
Plate 3 - Tabla 3
Fig. 1. Hyaloclasts of acid
andésite (dark-coloured areas)
set in a fine-grained matrix.
Peperite; southern slopes of
Krnes, westwards of the
farmhouse Kugovnik. Plane
polarised light, magnification
14.5 X
SI. 1. Hialoklasti kislega
andezita (temnejši deli) v
drobnozrnati osnovi. Peperit
z južnega pobočja Krnesa,
zahodno od kmetije Kugovnik.
Presevna polarizirana
svetloba, povečava 14.5 x
Fig. 2. Irregularly shaped
hyaloclasts of an acid andésite
(darker areas) set in a
fine-grained matrix. Peperite;
southern slopes of Krnes,
westwards of the farmhouse
Kugovnik. Plane polarised
light, magnification 14.5 x
SI. 2. Nepravilne oblike
hialoklastov kislega andezita
V drobnozrnati osnovi. Peperit
z južnega pobočja Krnesa,
zahodno od kmetije Kugovnik.
Presevna polarizirana
svetloba, povečava 14.5 x
Fig. 3. Resedimented(?)
pumice-rich tuff; southern
slopes of Krnes. Volcanic glass
of a tube pumice is replaced
by heulandite, quartz and
smectite. Plane polarised
light, magnification 14.5 x
SI. 3. Presedimentirani
plovčev tuf z južnega pobočja
Krnesa. Vulkansko steklo
cevastega plovca je nadome-
ščeno s heulanditom, kreme-
nom in montmorillonitom.
Presevna polarizirana
svetloba, povečava 14.5 x