GeolCarp_Vol69_No3_237

GEOLOGICA CARPATHICA

, JUNE 2018, 69, 3, 237–253

doi: 10.1515/geoca-2018-0014

www.geologicacarpathica.com

The Oligocene Reifnitz tonalite (Austria) and its host rocks:

implications for Cretaceous and Oligocene–Neogene

tectonics of the south-eastern Eastern Alps

FRANZ NEUBAUER



, BIANCA HEBERER

, ISTVÁN DUNKL

, XIAOMING LIU

MANFRED BERNROIDER

and YUNPENG DONG

Department of Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria;



Franz.Neubauer@sbg.ac.at

Sedimentology and Environmental Geology, Geoscience Centre, University of Göttingen, Goldschmidtstrasse 3, D-37077 Göttingen, Germany

State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China

(Manuscript received August 5, 2017; accepted in revised form May 11, 2018)

Abstract: In the south-eastern Eastern Alps, the Reifnitz tonalite intruded into the Austroalpine metamorphic basement

of the Wörthersee half-window exposed north of the Sarmatian–Pliocene flexural Klagenfurt basin. The Reifnitz tonalite

is dated for the first time, and yields a laser ICP-MS U–Pb zircon age of 30.72 ± 0.30 Ma. The (U–Th–Sm)/He apatite age

of the tonalite is 27.6 ± 1.8 Ma implying rapid Late Oligocene cooling of the tonalite to ca. 60 °C. The Reifnitz tonalite

intruded into a retrogressed amphibolite-grade metamorphic basement with a metamorphic overprint of Cretaceous age

(

Ar/

Ar white mica plateau age of 90.7 ± 1.6 Ma). This fact indicates that pervasive Alpine metamorphism of Cretaceous

age extends southwards almost up to the Periadriatic fault. Based on the exhumation and erosion history of the Reifnitz

tonalite and the hosting Wörthersee half window formed by the Wörthersee anticline, the age of gentle folding of

Austroalpine units in the south-eastern part of the Eastern Alps is likely of Oligocene age. North of the Wörthersee

antiform, Upper Cretaceous–Eocene, Oligocene and Miocene sedimentary rocks of the Krappfeld basin are preserved in

a gentle synform, suggesting that the top of the Krappfeld basin has always been near the Earth’s surface since the Late

Cretaceous. The new data imply, therefore, that the Reifnitz tonalite is part of a post-30 Ma antiform, which was likely

exhumed, uplifted and eroded in two steps. In the first step, which is dated to ca. 31–27 Ma, rapid cooling to ca. 60 °C

and exhumation occurred in an E–W trending antiform, which formed as a result of a regional N–S compression.

In the second step of the Sarmatian–Pliocene age a final exhumation occurred in the peripheral bulge in response to

the lithospheric flexure in front of the overriding North Karawanken thrust sheet. The Klagenfurt basin developed as

a flexural basin at the northern front of the North Karawanken, which represent a transpressive thrust sheet of a positive

flower structure related to the final activity along the Periadriatic fault. In the Eastern Alps, on a large scale, the distribution

of Periadriatic plutons and volcanics seems to monitor a northward or eastward shift of magmatic activity, with the main

phase of intrusions ca. 30 Ma at the fault itself.

Keywords: Periadriatic magmatism, peripheral bulge, exhumation, cooling history, shortening.

Introduction

Intrusion of plutons during the late-stage orogenic processes is

of high importance for several reasons. Such plutons often

provide evidence of plate tectonic processes such as sub-

duction, break-off or delamination of the subducted oceanic

slab (e.g., von Blanckenburg & Davies 1995; von Blancken-

burg et al. 1998; Seghedi & Downes 2012) or simply decom-

pressional melting of the exhuming, previously subducted

crust (Brown 2013). Plutons are often aligned along crustal-

scale faults like the Periadriatic fault (Schmid et al. 1987, 1989;

Rosenberg 2004; Handy et al. 2015; Cao & Neubauer 2016

and references therein). This may lead to rheological decoup ling

of different portions of the orogenic crust, influen cing there-

fore, the large-scale structure of mountain belts (Fig. 1).

Finally, deciphering exhumation paths of such plu tons may

add to the reconstruction of vertical motion of the intruded

crust along these major fault zones (e.g., Rosenberg 2004 and

references therein; Cao & Neubauer 2016).

Here, we report new data (U–Pb zircon age, microprobe

data of garnet) from the hitherto undated Reifnitz tonalite

from the south-eastern part of the Eastern Alps. This tonalite

was not considered in recent geodynamic models as its age and

significance were unknown (e.g., Rosenberg 2004). The U–Pb

zircon and (U–Th)/He ages in combination with the first

Ar/

Ar white mica age from the host rock and available

regional geological data from adjacent sedimentary basins

allow us to propose a major event of gentle N–S shortening

by folding and associated erosion for this sector of

the Eastern Alps, which was not known before. We also

discuss the large-scale distribution of Oligocene to Miocene

Periadriatic plutons, which clearly shows a northward or east-

ward shift of magmatic activity, and discuss the potential

significance.

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Geological setting

In the Eastern Alps, the European plate constitutes

the lower plate subducted principally beneath the overriding

north-directed Austroalpine nappe complex and other elements

of the Alpine orogenic wedge (Fig. 1) during Late Cretaceous

to Oligocene times. The Austroalpine nappe complex is

a detached part of the Adriatic microplate and is exposed north

of the Periadriatic fault. The Southern Alps and Dinarides

have a Paleogene to recent southward and south- westward

vergency towards Adria, which is commonly explained as

back-thrusting to the principally S-directed subduction pola-

rity of the European plate (e.g., TRANSALP Working Group

2002 and a contrary view in Lippitsch et al. 2003). The pattern

is superposed by Oligocene–Miocene eastward extrusion of

the ALCAPA (Alpine–Carpathian–Pannonian) block north of

the Periadriatic fault (Kázmér & Kovács 1985; Ratschbacher

et al. 1989, 1991), which is associated with Periadriatic plu-

tons (Rosenberg 2004 and refe ren ces therein). On a large

scale, the Periadriatic plutons are aligned along the Periadriatic

fault (Fig. 1) and allowed shear concentration by rheological

weakening of the crust.

The south-eastern Austroalpine nappe complex north of

the Periadriatic fault (Fig. 2) is composed mostly of partly

retrogressed and potentially polymetamorphic micaschists

of the metamorphosed Middle Austroalpine basement (“Alt-

kristallin” in the older terminology) covered by the Stangalm

Permo–Mesozoic cover unit (von Gosen 1989). This unit is

overridden by the Gurktal nappe complex, which contains two

major subunits with Ordovician to Lower Carboniferous

successions, the lower Murau nappe with mainly phyllites and

the upper Stolzalpe nappe with mainly slate and mafic volca-

nics and subordinate thin limestones and dolomites. This unit

is covered by unmetamorphic to very low-grade Permian to

Triassic successions, such as the Eberstein Permo–Triassic

(Fig. 2) (Appold & Pesch 1984). The boundary between

the Middle Austroalpine unit and the Gurktal nappe complex

is a top-WNW ductile thrust fault overprinted by a Late

Cretaceous top-ESE ductile normal fault causing retrogression

of micaschists along the ductile normal fault (e.g., Ratschbacher

et al. 1989; Koroknai et al. 1999). Normal faulting was

associa ted with the formation of the Santonian to Eocene

Krappfeld Gosau basin (Koroknai et al. 1999; Willingshofer et

al. 1999).

The overall structure of the southernmost sectors of Austro-

alpine units is less clear, particularly along the south-eastern

portion within the study area south of Lake Wörthersee

(Figs. 2, 3), which has been described as the Klagenfurt (or

Fig. 1. Simplified geology of the Alps (after Pfiffner 2014 and Neubauer 2014) showing the distribution of Eocene to Miocene Periadriatic

plutons, dykes and volcanics (modified after Rosenberg 2004).

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Wörthersee) half-window (e.g., Claasen et al. 1987; von Gosen

1989). There, amphibolite-grade, in part retrogressed mica-

schists are exposed (Schwaighofer 1965; von Gosen 1989).

These units also extend north of Lake Wörthersee (Homann

1962) in ca. E–W striking tectonic windows underneath

the Gurktal nappe complex (Kleinschmidt et al. 2008).

It has been known for a long time, that small scattered

bodies of tonalite are exposed within the “Altkristallin” base-

ment north of the not well studied E–W trending Keutschach

fault over a length of about eight kilometres (e.g., Kahler 1931,

1953, 1962; Meixner 1949; Heritsch 1964, 1971; Schwaighofer

1965). Along the Keutschach fault, low-grade Permo–

Mesozoic units are exposed including the Viktring Permo–

Mesozoic (Schünemann et al. 1982) and the Rossegg

Permo– Mesozoic units (Claasen et al. 1987) (Figs. 2, 3),

which correlate either with the Stangalm Permo–Mesozoic

underneath the Gurktal nappe system or with the Eberstein

Permo–Mesozoic above it. Further to the east, small remnants

of Permo–Mesozoic formations are exposed between

Klagenfurt and Völkermarkt (Fig. 2). The Viktring and

Rossegg Permo–Mesozoic units have mostly undergone

Cretaceous low-grade metamorphism (von Gosen et al. 1987).

In spite of their metamorphic overprint, Claasen et al. (1987)

suggested that these units belong to the cover of the Gurktal

nappe complex rather than being a correlative unit of

the Stan galm Permo–Mesozoic unit.

All these units are overlain (Fig. 3) by the uppermost Middle

Miocene to Pliocene Sattnitz Conglomerate, which is over-

lying, at Penken, the potentially Middle Miocene “Ground

Seam” Formation (“Grundflöz” strata composed of terrestrial

mudstone and coals (Kahler 1929; Griem et al. 1991). Kahler

(1929, 1931) found Middle Miocene agglutinated foramini-

fera within basal mudstones implying a short marine ingression.

However, this observation was not confirmed later because of

the lack of exposures since cessation of coal mining.

Eocene to Miocene (42–14 Ma) plutons, dykes and volca-

nics of mainly intermediate and rare mafic composition are

widespread along the Periadriatic fault (Fig. 1; Deutsch 1984;

Dal Piaz et al. 1988; von Blanckenburg et al. 1998; Rosenberg

2004; D´Adda et al. 2011; Bergomi et al. 2015). It was pro-

posed that they comprise two age groups: ca. 42–30 Ma old

plutons and dykes in the west, and ca. 30–14 Ma old volcanics

Fig. 2. Geological map of the south-eastern Alps (modified after Bigi et al. 1990) and apatite fission track and (U–Th)/He ages. A–A´and

B–B´are locations of N–S sections shown in Figure 11. Sources for apatite fission track ages (AFT) and (U–Th)/He (AHe) ages: Hejl (1997),

Sachsenhofer et al. (1998), Wölfler et al. (2010), Kurz et al. (2011), Legrain et al. (2014) and Heberer et al. (2017). The orientation of lettering

of various synforms and antiforms gives fold orientation.

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and subordinate plutons in the east (Fodor et al. 1998, 2008;

Hanfland et al 2004; Kralj 2012, 2013). Based on the wide-

spread occurrence of these plutons, Late Eocene to Oligocene

slab break-off of the subducted oceanic lithosphere from

the subducted European continental plate during plate collision

and uprise of hot asthenosphere through the slab window of

the broken subducted plate has been postulated (von Blancken-

burg & Davies 1995; von Blanckenburg et al. 1998). The main

period of magmatism occurred at ca. 34–30 Ma. In the Eastern

Alps, however, much younger periods of magmatism (18–14 Ma,

ca. 11–1.6 Ma) are well known north of the Periadriatic fault

implying younger magma-producing mantle processes (e.g.,

Lippolt et al. 1975; Deutsch 1980, 1984; Handler et al. 2006;

Fodor et al. 2008; Trajanova et al. 2008 and references therein)

independent from the classical 34–30 Ma slab-break off event

sensu von Blanckenburg et al. (1995) and Davies & von

Blanckenburg (1995). The second magmatic phase ranging

from ca. 18–14 Ma (e.g., Ebner & Sachsenhofer 1995; Fodor

et al. 2008; Trajanova et al. 2008) is not well explained in

the slab break-off model (von Blanckenburg et al. 1998).

Fodor et al. (2008) interpreted the Pohorje pluton as intruded

in an E–W extensional setting related

to strike-slip deformation along the Peri -

adriatic fault.

Thermochronology can constrain

the post-magmatic cooling of intru-

sions and post-metamorphic cooling

of crust in mountain belts. Sparse

apatite fission track (AFT) and few

(U–Th–Sm)/He (AHe) ages are avai-

lable from the Austroalpine nappe

complex north of the Periadriatic fault

(Hejl 1997, 1999; Heberer et al. 2017;

Fig. 2), and only a few AFT and

AHe ages are available from the eas-

tern Periadriatic fault (Nemes 1997;

Heberer et al. 2017; Fig. 2). An AFT

age of the Villach granite gneiss is

29.8 ± 2.1 Ma (Hejl 1997). AFT ages

adjacent to the eastern Periadriatic

fault mainly range from 15 to 25 Ma

with an age of 23.1 ± 1.5 Ma for

the Finkenstein tonalite (Hejl 1997;

Nemes 1997; Fodor et al. 2008) and

(U–Th–Sm)/He ages from 6.3 ± 1.0 to

11.4 ± 1.1 Ma (Heberer et al. 2017).

Dunkl et al. (2005) reported several

populations of apatite fission track

ages (36 ± 14 Ma, 30 ± 1 Ma, and

20 ± 4 Ma) from two Miocene sand-

stones of the Klagenfurt basin inter-

preted as reflecting the denudation

history of the source regions.

Analytical methods

Electron microprobe analytical technique

Well preserved garnet grains were analysed in polished thin

sections by using a fully automated JEOL 8600 electron

microprobe at the Dept. of Geography and Geology, University

of Salzburg, Austria. Point analyses were obtained using

a 15 kV accelerating voltage and 40 nA beam current.

The beam size was set to 5 μm. Natural and synthetic oxides

and silicates were used as standards for major elements. We

used the Mathematica package based software (PET) (Dachs

2004) for mineral formula calculation.

U–Pb dating

The U–Pb analytical techniques largely follow those

described in Liu et al. (2008). The zircon concentrate was

prepared at the University of Salzburg. Zircons were dated

in-situ on an excimer (193 nm wave length) laser ablation

inductively coupled plasma mass spectrometer (LA-ICP-MS)

at the State Key Laboratory of Continental Dynamics,

Fig. 3. Simplified geological map of the Wörthersee region with location of the study area

(modified after Kahler 1962). Red-yellow arrows indicate westernmost and easternmost

exposures of the Reifnitz tonalite.

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Northwest University, Xi´an, China. The ICP-MS used is

an Agilent 7500a (with shield torch). The unique shield

torch increases analytical sensitivity by a factor of >10,

(for example, 4500 cps/ppm for

238

U at a spot size of 40 µm

and laser frequency of 10 Hz), which is important for

LA-ICP-MS. The GeoLas 200M laser ablation system

(MicroLas, Göttingen, Germany) was used for the laser

ablation experiments. Helium was used as carrier gas.

The used spot size and laser frequency were 40 µm and 10 Hz,

respectively. The data acquisition mode was peak jumping

(20 ms per isotope each cycle). Raw count rates were measured

for

Si,

204

Pb,

206

Pb,

207

Pb,

208

Pb,

232

Th and

238

U. U, Th and

Pb concentrations were calibrated by using

Si as an internal

standard and NIST SRM 610 as the reference standard.

Each analysis consists of 30 s gas blank and 40 s signal

acquisition. High-purity argon was used together with

a custom helium filtration column, which resulted in

204

and

202

Hg being less than 100 cps in the gas blank. Therefore,

the contribution of

204

Hg to

204

Pb was negligible and no

cor rection was made.

207

Pb/

206

Pb,

206

Pb/

238

207

Pb/

235

U and

208

Pb/

232

Th ratios, calculated using GLITTER 4.0 (Macquarie

University), were corrected for both instrumental mass bias

and depth- dependent elemental and isotopic fractionation

using Harvard zircon 91500 as the external standard. The ages

were calculated using ISOPLOT 3 (Ludwig 2003). Our

measurement of TEMORA 1 as an unknown yielded

a weighted

206

Pb/

238

U age of 415 ± 4 Ma (MSWD = 0.112,

n = 24) (Yuan et al. 2004), which is in good agreement with

the recommended ID-TIMS age of 416.75 ± 0.24 Ma (Black et

al. 2003). Analytical details for age and trace and rare earth

element determinations of zircons are reported in Yuan et

al. (2004). Common Pb corrections were made following

the method of Andersen (2002). Because measured

204

usually accounts for <0.3 percent of the total Pb, the correction

is insignificant in most cases.

Ar/

Ar analytical technique

Ar/

Ar techniques largely follow descriptions given in

Handler et al. (2004) and Rieser et al. (2006). Preparation of

the samples before and after irradiation,

Ar/

Ar analyses,

and age calculations were carried out at the ARGONAUT

Laboratory of the Department of Geography and Geology at

the University of Salzburg. The white mica concentrate was

packed in aluminium-foil and placed in a quartz vial. For cal-

culation of the J-values, flux-monitors were placed between

each 4–5 unknown samples. The sealed quartz vials were

irradiated in the Řež reactor (Prague, Czech Republic) for

16 hours. Correction factors for interfering isotopes were

calculated from 45 analyses of two Ca-glass samples and 70

analyses of two pure K-glass samples and are:

Ar/

(Ca)

0.000225,

Ar/

(Ca)

= 0.000614,

Ar/

(Ca)

= 0.011700 and

Ar/

(K)

= 0.0266. Variations in the flux of neutrons were

monitored using the DRA1 sanidine standard for which

Ar/

Ar plateau age of 25.26 ± 0.05 Ma is reported

(van Hinsbergen et al. 2008).

Ar/

Ar analyses were carried out using a UHV

Ar-extraction line equipped with a combined MER-

CHANTEKTM UV/IR laser system, and a VG-ISOTECHTM

NG3600 mass spectrometer. Isotopic ratios, ages and errors

for individual steps were calculated following suggestions by

McDougall & Harrison (1999) and Scaillet (2000) using decay

factors reported by Renne et al. (2011). Definition and calcu-

lation of plateau ages was carried out using ISOPLOT/EX

(Ludwig 2003).

Results from the Reifnitz tonalite

Petrography

All investigated samples of the Reifnitz tonalite show

a strong low-temperature alteration, mostly sericitization and

carbonatization. The grain size of porphyric minerals ranges

from 1.5 to 5 mm, whereas feldspar and subordinate inter-

stitial quartz of the matrix are ca. 0.1 mm in size. Dominant

euhedral plagioclase, subordinate K-feldspar and rare rounded

quartz phenocrysts are observed. Quartz phenocrysts show

resorption embayments, feldspar some garnet inclusions.

Phenocrystic and matrix feldspars are heavily sericitized,

transformed to sericite or clay minerals and are in part replaced

by carbonate (Fig. 4a, b). In very few cases, relics of oscilla-

tory normal zoning of plagioclase could be observed indica-

ting andesine and oligoclase compositions. Biotite phenocrysts

with a length of 0.7 to 1.5 mm are generally transformed into

chlorite, leucoxene and carbonate. In places, elongated

xenocrystic garnet grains in the matrix and as inclusions

within feldspar are common, ranging in size from 1–2 mm,

rarely up to 4 mm. Further minerals include euhedral zircons,

apatite and opaque minerals. Alteration of samples was too

strong to carry out geochemical investigations except for well

preserved garnet.

Garnet composition

Back-scattered electron images show the zoned nature of

garnet. The large garnet grains were formed by coalescence of

small garnet grains preserved in the core (Fig. 5a). Several

small garnet grains coalesced into an aggregate, which is

surrounded by an inner and an outer rim, which represent

almandine-rich garnets (Table 1; Fig. 5 a, b). The growth

pattern is well reflected by chemical variation of MgO,

CaO and MnO contents (Table 1; Fig. 5b). The core is

high in MgO (4.9 wt. %), poor in MnO (1.0 wt. %), and

low in CaO content (7.9 wt. %) compared to the inner

rim, which has higher MnO (2.6 wt. %), and CaO (8.4 wt. %)

and lower MgO (2.5 wt. %) contents (Fig. 5b). The outer

rim is low in MnO (1.5 wt. %) and CaO (5.2 wt. %),

but high in MgO (4.8 wt. %). The boundaries between

the three zones are diffuse (Fig. 5a). The generally high

FeO and Al

contents classify the garnet as almandine-rich

garnet.

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U–Pb dating results

Zircons of sample KAR-25 (46°35’48” N,

14°08’31” E) are generally euhedral. Cathodo-

luminescence images show either regular, some-

times complex oscillatory magmatic zoning, or

zircons are internally rather uniform (Fig. 6).

30 spots have been measured on zircons of sam-

ple KAR-25 (Table 2; Figs. 6, 7). The U contents

range from 532 to 2216 µg/g and the Th contents

are much lower, 25 to 178 µg/g. The Th/U ratio

varies between 0.025 and 0.1, which is not

typical for magmatic zircons. Typical Th/U

ratios in magmatic zircons are > 0.1 (Hoskin &

Schaltegger 2003; Kirkland et al. 2015). Most

spots plot on the concordia curve; the weighted

mean age of 22 spots is 30.72 ± 0.30 Ma

(MSWD = 2.6). One euhedral grain (spot 12) with

an oscillatory magmatic zoning at the rim and

a patchy internal pattern is significantly older,

with a

236

206

Pb age, 107.3 ± 1.4 Ma, and is

explained as an inherited potentially metamor-

phic core within that grain.

Fig. 4. a and b — Photomicrographs of thin sections of the Reifnitz tonalite (sample KAR-25). a — Garnet grains within altered feldspar

phenocryst surrounded by fine-grained matrix. b — Chloritized biotite surrounded by a fine-grained matrix of feldspar and quartz, which

includes calcite and sericite as alteration products. c and d — Mylonitic, sheared quartzite from the basement complex (sample KAR-24).

Abbreviations: Bt-Chl — chloritized magmatic biotite, Cb — calcite, Gt — garnet, Wm — white mica.

Fig. 5. Garnet composition of the Reifnitz tonalite. a — Back-scattered electron

image of a composite garnet grain and measured points. b — Compositional variation

along the garnet profile.

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(U–Th–Sm)/He dating results

Three apatite grains from sample KAR-25 were measured.

Data were included in Heberer et al. (2017) but not discussed

and interpreted in detail with respect to the local geology.

One grain is older (38.9 ± 5.7 Ma) than the U–Pb zircon age.

Consequently, we consider that the age result of this grain

unreliable, and might have its cause in undetected inclusions

of a U-rich phase. The other two grains have similar ages and

the average of the two grains yields an age of 27.6 ± 1.8 Ma

(Heberer et al. 2017).

Spot

SiO

MgO

CaO

TiO

FeO

MnO

NiO

Total

37.84

21.19

4.87

0.03

5.22

0.35

29.82

1.48

0.04

0.00

100.87

37.41

21.09

2.51

0.03

8.47

0.24

28.25

2.61

0.01

0.00

0.03

0.04

0.00

100.71

37.74

21.01

4.93

0.02

7.95

0.59

27.08

1.00

0.02

0.00

0.01

0.09

0.00

100.42

Spot

Sum

5.94

3.92

1.14

0.01

0.88

0.04

3.92

0.20

0.01

0.00

24.00

40.06

5.94

3.94

0.59

0.01

1.44

0.03

3.75

0.35

0.00

0.01

24.00

40.06

5.92

3.88

1.15

0.01

1.33

0.07

3.55

0.13

0.00

0.01

24.00

40.06

Table 1: Representative garnet composition of the three zones of the composite garnet grain graphically shown in Figure 5.

Metamorphic host rocks: microfabrics and

Ar/

Ar white mica age

The foliation of the metamorphic host rocks is gently

south-dipping and the stretching lineation trends E–W. We

examined a few thin sections of the metamorphic rocks, which

mainly comprise garnet-bearing micaschist and subordinate

lenses of garnet-amphibolite, epidote-amphibolite and thin

marble lenses, variably retrogressed by chloritization under

greenschist facies metamorphic conditions. For

Ar/

white mica dating, we selected a strongly sheared quartzite

Fig. 6. Cathodoluminescence images of dated zircons.

238

206

Pb ages are given. Ages in brackets are discordant outside of 90 –110 percent.

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Table 2:

U–Pb zircon analytical data of the Reifnitz tonalite (sample KAR-25).

Spot #

Isotope ratios

Ages

207

/Pb

206

207

235

206

238

208

/Th

232

207

/Pb

206

207

235

206

238

208

/Th

232

concordia

Th/U

0.084

0.00338

0.051

0.00148

0.00441

0.00007

0.01466

0.00041

1292

76.5

50.5

1.4

28.3

0.43

294.3

8.2

178.4

0.03

0.0471

0.00159

0.03196

0.00065

0.00492

0.00007

0.0019

0.00004

54.3

31.9

0.6

31.7

0.43

38.4

0.9

100.6

0.07

0.0533

0.00193

0.03507

0.00084

0.00478

0.00007

0.00217

0.00006

341.2

79.96

35.0

0.8

30.7

0.43

43.8

1.2

114.0

0.08

0.0503

0.00178

0.03371

0.00077

0.00487

0.00007

0.00151

0.00005

206.5

80.04

33.7

0.8

31.3

0.43

30.4

107.7

0.05

0.0453

0.00152

0.03025

0.00061

0.00485

0.00007

0.00151

0.00005

0.1

37.3

30.3

0.6

31.2

0.42

30.5

97.1

0.04

0.0503

0.00214

0.03241

0.00105

0.00468

0.00007

0.00194

0.0001

207.2

95.67

32.4

30.1

0.44

39.2

107.6

0.05

0.0474

0.00169

0.03035

0.0007

0.00464

0.00006

0.00167

0.00006

70.5

83.28

30.4

0.7

29.9

0.41

33.8

1.3

101.7

0.04

0.0458

0.00161

0.03054

0.00069

0.00484

0.00007

0.00148

0.00004

0.1

70.7

30.5

0.7

31.1

0.42

29.9

0.9

98.1

0.07

0.0477

0.00169

0.031

0.00071

0.00473

0.00007

0.0022

0.00007

84.6

82.8

31.1

0.7

30.4

0.42

44.4

1.3

102.3

0.05

0.0458

0.0015

0.03028

0.00057

0.0048

0.00006

0.00169

0.00003

0.1

64.75

30.3

0.6

30.8

0.42

34.2

0.7

98.4

0.09

0.0472

0.00158

0.03095

0.00062

0.00476

0.00006

0.00173

0.00004

59.5

78.58

30.9

0.6

30.6

0.42

35.0

0.8

101.0

0.07

0.0523

0.00171

0.12096

0.00225

0.01678

0.00023

0.00278

0.00008

299.5

72.73

115.9

107.3

1.44

56.1

1.5

108.0

0.10

0.0494

0.00174

0.03078

0.0007

0.00452

0.00006

0.0014

0.00004

166.3

80.5

30.8

0.7

29.1

0.4

28.4

0.8

105.8

0.08

0.0454

0.00149

0.02954

0.00056

0.00472

0.00006

0.00141

0.00003

0.1

44.41

29.6

0.6

30.4

0.41

28.5

0.5

97.4

0.15

0.046

0.0015

0.02939

0.00055

0.00463

0.00006

0.00136

0.00003

0.1

75.48

29.4

0.5

29.8

0.4

27.5

0.6

98.7

0.06

0.0453

0.00159

0.02993

0.00067

0.0048

0.00007

0.00167

0.00005

0.1

40.66

29.9

0.7

30.9

0.43

33.7

96.8

0.06

0.0492

0.00159

0.03171

0.00057

0.00468

0.00006

0.00257

0.00006

155.6

73.81

31.7

0.6

30.1

0.41

51.9

1.1

105.3

0.04

0.0554

0.00205

0.03838

0.00097

0.00503

0.00007

0.00366

0.00012

429.4

80.4

38.2

32.3

0.46

73.9

2.3

118.3

0.04

0.0461

0.00165

0.03062

0.00072

0.00482

0.00007

0.00173

0.00007

3.4

83.06

30.6

0.7

31.0

0.43

34.9

1.3

98.7

0.04

0.0464

0.0016

0.03139

0.00068

0.00491

0.00007

0.0016

0.00004

17.1

79.61

31.4

0.7

31.6

0.44

32.2

0.8

99.4

0.09

0.0461

0.00155

0.03153

0.00064

0.00497

0.00007

0.00179

0.00004

0.1

78.99

31.5

0.6

32.0

0.44

36.2

0.9

98.4

0.07

0.0372

0.00132

0.02551

0.0006

0.00498

0.00007

0.00169

0.00004

0.1

25.6

0.6

32.0

0.44

34.1

0.7

80.0

0.08

0.0462

0.00161

0.03043

0.00067

0.00478

0.00007

0.00169

0.00004

7.7

80.82

30.4

0.7

30.7

0.43

34.1

0.8

99.0

0.09

0.0478

0.00179

0.03033

0.00079

0.0046

0.00007

0.00197

0.00007

89.8

87.47

30.3

0.8

29.6

0.42

39.8

1.4

102.4

0.06

0.0471

0.00161

0.0319

0.00067

0.00492

0.00007

0.00159

0.00004

53.2

79.83

31.9

0.7

31.6

0.44

32.2

0.9

100.9

0.07

0.0453

0.00156

0.03046

0.00066

0.00487

0.00007

0.00172

0.00004

0.1

43.7

30.5

0.7

31.3

0.44

34.7

0.9

97.4

0.08

0.051

0.00173

0.03292

0.00069

0.00468

0.00007

0.00201

0.00005

243.5

76.37

32.9

0.7

30.1

0.42

40.6

109.3

0.06

0.0557

0.00183

0.03658

0.0007

0.00476

0.00007

0.00243

0.00005

441.6

71.35

36.5

0.7

30.6

0.42

49.1

0.9

119.3

0.10

0.0514

0.00168

0.03354

0.00064

0.00473

0.00007

0.00198

0.00004

259.4

73.52

33.5

0.6

30.4

0.42

40.0

0.8

110.2

0.08

0.0475

0.00156

0.03074

0.00059

0.0047

0.00007

0.00149

0.00005

71.9

77.21

30.7

0.6

30.2

0.42

30.0

0.9

101.7

0.04

245

THE OLIGOCENE REIFNITZ TONALITE AND ITS HOST ROCKS (EASTERN ALPS, AUSTRIA)

GEOLOGICA CARPATHICA

, 2018, 69, 3, 237–253

(sample KAR-24; 46°36’33” N, 14°08’52” E) with a ca. E–W

trending stretching lineation, showing S–C fabrics and shear

bands (Fig. 4c, d). The S-foliation is formed by strongly elon-

gated quartz grains, showing a shape preferred orientation,

whereas the C-foliation is formed by white mica (Fig. 4c, d).

In this peculiar case, the shear is top to the west. Grain boun-

daries of quartz show bulging, which is typical for tempera-

tures lower than ca. 400 °C (Stipp et al. 2002). Small white

mica occurs as mica-fish with a grain-size of 0.05 to 0.2 mm.

Further minerals are abundant zircon and rare apatite deco-

rated by fine opaque minerals. The ductile S–C fabric is some-

times overprinted or cut at high angle by small semiductile

to cataclastic micro-shear zones (Fig. 4c), which deflect

the earlier S–C fabric. The micro-shear zones consist mainly

of fine-grained quartz and sericite.

We selected white mica (grain size fraction of 125–200 µm)

for

Ar/

Ar analysis from an orthoquartzite (Table 3 for

results). In the resulting Argon release pattern (Fig. 8), indi-

vidual steps 1 to 8 scatter around 80 to 100 Ma and have

a large individual error, whereas steps 9 to 13 show a plateau

age of 90.7 ± 1.6 Ma comprising 69.5 percent of

Ar released.

Discussion

Distribution of Upper Eocene to Oligocene magmatism

along the Periadriatic fault

The new data indicate that the Reifnitz tonalite belongs to

the Eocene–Oligocene Periadriatic plutons. It represents one

of the northernmost plutonic bodies, relatively distant from

the Periadriatic fault. It also represents the easternmost

Oligocene Periadriatic pluton north of the Periadriatic fault.

Major plutons north of the Periadriatic fault are the Biella,

Bergell (Oberli et al. 2004; Rosenberg 2004) and Rieserferner

(Romer & Siegesmund 2003; Wagner et al. 2006) ). However,

many younger dykes (20–14 Ma) are present, which stretch

from the Kreuzeck Mts. (Deutsch 1980, 1984) and may be

correlative, as a zone, with volcanics and volcanic necks in

the Lavant Valley area (Kollnitz in Fig. 2; Lippolt et al. 1975)

and in the Styrian basin (Ebner & Sachsenhofer 1995; Handler

et al. 2006). The Pohorje pluton with its age of ca. 18 Ma is

the only major pluton of that zone (Fodor et al. 2008; Trajanova

et al. 2008).

The distribution of (1) Upper Eocene to Oligocene plutons

and rare volcanics (Smrekovec) (42–28 Ma) and the younger

Miocene (20–14 Ma) plutons and volcanics is quite interes-

ting and shows a hitherto unexplained phenomenon (Fig. 1;

Rosenberg 2004). In the western PP segment (to the west of

the Adamello pluton; Fig. 1), Oligocene magmatic rocks

including dykes are widespread both in the Southalpine unit

as well as in Austroalpine units. In the central PP segment,

the Adamello (42–30 Ma; Brack 1983; Schoene et al. 2012;

Bergomi et al. 2015) and Bergell plutons and associated dykes

indicate the largest N–S-extent of Periadriatic plutons across

the Periadriatic fault dominated by the huge Adamello body

and many dykes. In the eastern PP segment, plutons and dykes

are only present along and north of the Periadriatic fault (e.g.,

Pomella et al. 2011, 2012). This distribution cannot be

explained by a simple slab break-off model alone, which

would imply an along strike-strike younging of magmatism

(Wortel & Spakman 2000) according to the lateral progression

of the slab window. The oldest pluton (Adamello with an age

extending from 42 to 30 Ma) occurs in the central segment and

its age distribution shows that the Oligocene magmatic rocks

occur south of the Periadriatic fault in the western segment, in

the eastern segment to the north. This feature could be tenta-

tively explained by initiation of magmatism in the central

segment and potential post-30 Ma dextral displacement of

the segments north of and shearing along the Periadriatic fault.

The eastern segment is then overprinted by Miocene magma-

tism (Fig. 1), which seems to be independent of Oligocene

Fig. 7. a — U–Pb zircon concordia age plot of the Reifnitz tonalite, sample KAR-25. b — Weighted mean age.

246

NEUBAUER, HEBERER, DUNKL, LIU, BERNROIDER and DONG

GEOLOGICA CARPATHICA

, 2018, 69, 3, 237–253

Sample: KAR-24 Mu 125–200 µm 12 grains J-V

alue: 0.010717± 0.000046

step

±σ

Ar*/

± σ

Ar*

age [Ma]

± [Ma]

meas.

decay corr

meas.

decay corr

meas.

1σ abs.

2.5874E+00

7.60E+00

3.9627E+01

5.32E+01

1.2555E+01

1.88E+01

1.8263E+03

8.72E+01

1.0795E+04

2.84E+01

5.49

1.26

92.9

0.9

103.2

23.0

9.5487E+00

7.31E+00

3.5671E+01

3.1

1E+01

4.0759E+01

1.88E+01

3.6736E+03

5.95E+01

2.0306E+04

5.06E+01

4.76

0.59

86.1

1.8

89.7

10.9

3.6454E-01

1.14E+01

4.4321E+01

5.32E+01

8.7755E+01

1.50E+01

4.6279E+03

5.40E+01

3.0453E+04

7.58E+01

6.56

0.73

99.6

2.2

122.5

13.2

1.6586E+01

1.1

1E+01

2.3902E+00

5.73E+01

1.1508E+02

9.87E+00

8.7171E+03

3.33E+01

6.0623E+04

1.14E+02

6.39

0.38

91.9

4.2

119.5

6.8

1.7896E+01

1.16E+01

8.3173E+01

5.14E+01

1.5759E+02

1.47E+01

9.6721E+03

3.28E+01

5.7560E+04

6.29E+01

5.40

0.35

90.8

4.7

101.6

6.5

1.8696E+01

1.22E+01

2.4501E+00

5.54E+01

2.2282E+02

1.94E+01

1.3947E+04

4.1

1E+01

7.5686E+04

4.01E+01

5.03

0.26

92.7

6.8

94.7

4.8

8.7185E+00

1.32E+01

1.2889E+02

4.43E+01

2.3618E+02

1.62E+01

1.8841E+04

5.81E+01

1.0096E+05

1.1

1E+02

5.22

0.21

97.4

9.1

98.2

3.8

1.7717E+01

8.73E+00

8.0799E+01

6.25E+01

4.0913E+02

2.35E+01

2.9660E+04

5.86E+01

1.5016E+05

1.31E+02

4.88

0.09

96.5

14.4

92.1

1.7

2.0966E+01

1.05E+01

1.6429E+01

4.09E+01

4.3093E+02

2.12E+01

3.4327E+04

5.69E+01

1.7312E+05

1.19E+02

4.86

0.09

96.4

16.6

91.6

1.7

1.8873E+01

1.03E+01

8.4137E+01

4.61E+01

5.0616E+02

2.72E+01

3.9788E+04

5.51E+01

1.9501E+05

1.34E+02

4.76

0.08

97.1

19.3

89.8

1.5

6.2432E+01

1.06E+01

4.9194E+01

4.92E+01

4.0075E+02

2.44E+01

3.1794E+04

5.50E+01

1.6823E+05

1.01E+02

4.71

0.10

89.0

15.4

88.8

1.8

7.9445E+01

1.29E+01

6.1

102E+00

4.60E+01

1.0147E+02

1.70E+01

7.931

1E+03

5.56E+01

6.7367E+04

5.99E+01

5.53

0.48

65.1

3.8

103.9

8.8

Table 3:

Ar/

Ar analytical data of a white mica concentrate from a mylonitic quartzite from the basement (sample KAR-24).

magmatism and was either related to the polarity reversal of

the subduction zone (Lippitsch et al. 2003; Handy et al. 2015)

or with a second stage of post-collisional slab break-off mag-

matism starting in the south-eastern Alps and progressing

along the Carpathian arc (Wortel & Spakman 2000).

Significance of garnet in the tonalite

A peculiar feature is the occurrence of garnet in the Reifnitz

tonalite, which is typical for S-type granites and rare but

present in some I-type granitoids(e.g., Pe-Piper 2000; Harangi

et al. 2001; Samadi et al. 2014 and references therein). René &

Stelling (2007) summarized potential models for the occur-

rence of garnet in granitoids, which is more common in S-type

granitoids and rare in I-type granitoids (see also Harangi et al.

2001): (1) garnet could represent a refractory restite phase

transported within the magma from the area of partial melting,

or (2) a refractory xenocryst phase from high-grade meta-

sedimentary country rocks, or (3) could have crystallized in

the marginal facies of a granitic intrusion as a result of reaction

between granitic melt and pelitic xenoliths rich in Al and Mn

compared to the melt. Because of strong alteration particularly

of feldspars in the investigated samples, no equilibrium of gar-

net and plagioclase or biotite could be observed, which would

allow us to estimate the P–T conditions of garnet crystalli-

zation at depth. However, because of the high CaO content of

ca. 8 percent in core and inner rim we can conclude that

the almandine-rich garnet cores likely represents either refrac-

tory xenocrysts incorporated at lower/middle levels of the crust

into the magma or represent garnet grown in a magma. These

garnet aggregates likely interacted with magma forming

the outer rim with a CaO content of ca. 5 percent implying

crystallization at middle crustal level. The almandine-rich

garnet outer rim composition with ca. 5 percent CaO is very

similar to magmatic garnet, which crystallized in an I-type

Fig. 8.

Ar/

Ar release pattern of white mica separated from

a mylonitic quartzite, sample KAR-24. Laser energy increases from

left to right until fusion.

247

THE OLIGOCENE REIFNITZ TONALITE AND ITS HOST ROCKS (EASTERN ALPS, AUSTRIA)

GEOLOGICA CARPATHICA

, 2018, 69, 3, 237–253

granite in Iran (Samadi et al. 2014). The CaO content requires

an elevated pressure of garnet crystallization corresponding to

middle to lower crustal depth (Harangi et all. 2001). However,

for final clarification, more detailed investigations on less

altered samples are needed, and are planned in the near future.

Similar garnets were also found in Miocene andesites of

the Western Carpathians (Harangi et al. 2001; Pécskay et al.

2006; Kohút & Danišík 2017 and references therein). These

garnets show a wide variation in composition and include

both xenocrystic garnet, similar in composition to those in

the Reifnitz tonalite, and garnets formed by growth in a deep-

seated magma chamber (Harangi et al. 2001).

Implications for Cretaceous tectonics

We interpret that the

Ar/

Ar white mica plateau age of

90.7 ± 1.6 Ma is geologically significant and dates either

(1) the age of regional cooling through ca. 425 ± 25 °C

(Harrison et al. 2009) after epidote-amphibolite facies meta-

morphic conditions or the last stage of ductile deformation.

Besides regional cooling many other factors like hydrous

fluids and deformation are influencing the resetting of the Ar

isotopic system (e.g., Villa et al. 2014; Villa 2016). Thin sec-

tion observations indicate that white mica is fully recrystal-

lized during deformation. Deformation and associated fluid

could have led to complete isotopic resetting as shown by

the well defined plateau age.

Our findings of a Cretaceous age of metamorphism have

several tectonic implications for the south-eastern Alps:

The new

Ar/

Ar age 90.7 ± 1.6 Ma of the strongly deformed

white mica of the quartzite indicates pervasive metamorphic

overprint of the micaschist and intercalated quartzite with

temperatures exceeding 425 °C (Ar retention temperature of

white mica; Harrison et al. 2009). It seems to be likely that

the micaschist reached Early Cretaceous epidote amphibolite

facies metamorphic conditions as the pelitic rocks commonly

include oligoclase as the main feldspar (Schwaighofer 1965

and own observations) and rare epidote-amphibolite lenses.

The new

Ar/

Ar white mica age in combination with previous

data on the low-grade metamorphic overprint on Permian and

Triassic cover rocks of Viktring and Rossegg Permo–Mesozoic

units (Schünemann et al. 1982; von Gosen et al. 1987;

von Gosen 1989) indicate pervasive metamorphic overprint of

rocks within the Klagenfurt half-window, which is also

supported by a Rb–Sr mica age of 84 ± 3 Ma in the Villach

orthogneiss (Göd 1976). The southern limit of Alpine meta-

morphism of Cretaceous age (SAM) is outlined in Fig. 2 and

is located much further to the south as reported by Hoinkes et

al. (1999). This also implies that there is not enough space

north of the North Karawanken thrust sheet (Fig. 2) for

a potential root zone of the Gurktal nappe complex, which was

formed at around the Early to Late Cretaceous boundary.

The Gurktal nappe complex is only the southernmost part of

the Upper Austroalpine nappe complex (e.g., Neubauer 1987

and references therein). This fact indicates that the potential

root zone of the Gurktal nappe complex is either displaced by

Eocene to Oligocene strike-slip faults like the Periadriatic

fault or subducted during Cretaceous times. This is in agree-

ment with the area further east, where the ultra-high pressure

metamorphic rocks with a Cretaceous age of the southernmost

Pohorje Mts. are also juxtaposed to very low-grade- or non-

metamorphic rocks of the Southalpine units (e.g., Placer 2009;

Janák et al. 2016; Sandmann et al. 2016). The Pohorje area

exposes the Early to Middle Miocene Pohorje pluton intruded

into metamorphic rocks of Cretaceous age and thermally over-

printed during Miocene times (Fodor et al. 2008) as well as

the area adjacent to the north (Sachsenhofer et al. 1998). Both

units were exhumed by Miocene ca. E–W extension (Fodor et

al. 2008). However, the Miocene thermal overprint did not

destroy the nappe structure of Cretaceous age. In summary,

the root zone of the Gurktal nappe complex and other Upper

Austroalpine tectonic elements is missing and likely displaced

by the Periadriatic strike-slip fault.

Implications for Oligocene and Neogene tectonics of

the Eastern Alps

The small occurrences of the Reifnitz tonalite are aligned in

an E–W direction and the entirely crystalline fabric with rela-

tively large porphyric grains (2–4 mm) show that the Reifnitz

tonalite intruded at some depth into the basement. The exact

intrusion depth is difficult to determine in the absence of

well-preserved magmatic mineral assemblages. The scattered

occurrences extending over about eight kilometres in an E–W

direction might also indicate that the Reifnitz tonalite belongs

to the plumbing system underneath a surface volcano and

might represent part of a major pluton, which widens at depth

(Fig. 9a as shown in an illustrative model). This interpretation

of the tentative relationships between surface and depth are

shown in Figs. 9 and 10.

The present-day erosional level of the “Altkristallin” base-

ment implies denudation and erosion of at least one or two

kilometres of overburden after intrusion of the Reifnitz

tonalite. The Reifnitz tonalite is located in the centre of

the Wörthersee antiform (Figs. 2 and 11). Here, we note

that both in the northern and southern sectors of this

antiform Cenozoic sedimentary units crop out. In the north, in

the Krapp feld area (Fig. 2), discontinuous sedimentary succes-

sions including Upper Cretaceous, Eocene, possible Oligocene,

then Lower Miocene (Karpatian) strata (e.g., Thiedig 1970,

1975; Thiedig et al. 1999) are exposed in a synform (Figs. 2,

10, 11). In the Krappfeld area, these sedimentary units are

sepa

rated by angular unconformities and/or sedimentary

hiatuses (Thiedig 1975; Thiedig et al. 1999). The presence of

sediments implies that this segment of the Upper Austroalpine

units has always been in a near-surface position since Late

Cretaceous times. The presence of potentially Oligocene sedi-

ments (Appold et al. 1986) implies that this area was subsiding

at the same time as the Wörthersee antiform was uprising and

the Reifnitz tonalitre was cooling. For the Krappfeld area,

Neubauer & Heberer (2011) proposed an Oligocene age of

gentle folding predating Karpatian sediment deposition of

248

NEUBAUER, HEBERER, DUNKL, LIU, BERNROIDER and DONG

GEOLOGICA CARPATHICA

, 2018, 69, 3, 237–253

the Waitschach Gravel (Figs. 9b and 10), deformation D1 in

Figure 9b. Together, the new data from the Wörthersee anti-

form indicate that the entire south-eastern Alps were affected

by gentle folding due to N–S shortening (Fig. 11). Such

late-stage folds were already postulated by Fritsch (1965)

and Neubauer et al. (2000) assigning a loosely constrained

Cenozoic age. This folding obviously affected major portions

of the Austroalpine nappe complex east of the Tauern window

(Fig. 2). The N–S D1 shortening was followed by Early

Miocene (Karpatian?) WSW–ESE extension in the Krappfeld

basin area, formation of halfgraben related to eastward lateral

extrusion (Ratschbacher et al. 1989; Neubauer & Heberer

2011; deformation stage D2 in Figure 10).

South of the Reifnitz tonalite, the Sarmatian to Pliocene and

possibly Quaternary infill of the Klagenfurt basin is exposed

(Fig. 2) (Polinski & Eisbacher 1992; Nemes et al. 1997).

This basin was interpreted to represent a flexural basin

formed at the front of the N-directed Karawanken thrust

(Nemes et al. 1997). This thrust is part of a major positive

flower structure along the Periadriatic fault (Polinski &

Eisbacher 1992; Nemes et al. 1997). Structural relationships

between the Middle Miocene–Pliocene Klagenfurt basin and

the Wörthersee antiform (Fig. 9c) imply that the Reifnitz

tonalite is located on the peripheral bulge in the front of

the flexural Klagenfurt basin. This also implies N–S to

NW–SE shortening (deformation stage D3 in Figure 10), some

surface uplift in front of the Klagenfurt basin in the order

of several 100 m as the lithosphere underneath had a low

strength (Nemes et al. 1997). Dunkl et al. (2005) reported two

detrital apatite fission track age populations of (1) 30 ± 1 Ma

(or 36 ± 14 Ma in another sample) and (2) 20 ± 4 Ma from two

sandstone samples from different locations in the Klagenfurt

basin (Unterbergen and Ferlach, see Fig. 2 for locations). One

of these samples contains euhedral apatites suggesting a poten-

tially magmatic origin of grains with the age of 30 ± 1 Ma

(Dunkl et al. 2005) similar to suspected ages of volcanic mate-

rial above the Reifnitz tonalite. This age group (30 ± 1 Ma resp.

36 ± 14 Ma) is also consistent with the (U–Th–Sm)He apatite

Fig. 9. Three-stage tectonic model for the evolution of the Wörthersee area in southeastern Austria. a — Time of intrusion of the Reifnitz

tonalite with a potential volcanoe above it. b — Oligocene gentle folding and formation of antiforms and synforms. c — Formation of

the peripheral bulge by flexuring the crust in front the North Karawanken thrust (after Nemes et al. 1997) and erosion of the Wörthersee

antiform. White arrows indicate dominant vertical motion at the given time interval.

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, 2018, 69, 3, 237–253

age of the Reifnitz tonalite and with the apatite fission track

age of 29.8 ± 2.1 Ma from the Villach orthogneiss (Hejl 1997,

1999; Fig. 2). The latter is also located on the Wörthersee anti-

form within the Klagenfurt half-window.

Kahler & Papp (1968) report many Eocene limestone peb-

bles in the Sattnitz conglomerate and even in the Quaternary

Drau River sediments. Most of them have a close affinity to

Eocene limestones now exposed at the northern margin of

the Krappfeld basin (Kahler & Papp 1968). In the present

drainage basin of the Drau no such limestones are exposed.

The presence of such Eocene limestones could be taken as

evidence, that the Eocene cover was much more widespread

between Sattnitz and Krappfeld and could have been poten-

tially eroded since late Middle Miocene (Fig. 9c).

Our new data imply, therefore, that the Reifnitz tonalite

is part of a combined post-30 Ma antiform and peripheral

bulge (Figs. 9c, 10 and 11). In a first step, which is dated as

ca. 31–27 Ma, rapid cooling to ca. 60 °C and exhumation of

the Reifnitz tonalite occurred in an E–W trending antiform,

which formed as a result of regional compression that also

affected the Krappfeld area further north (Neubauer & Heberer

2011). In a second, Sarmatian–Pliocene step, final exhumation

of several 100 metres occurred in response to the lithospheric

flexure in front of the overriding North Karawanken thrust

sheet (Fig. 9c).

This later stage of deformation, Late Miocene to Pliocene

in age, coincides with approximately N–S shortening in

the eastern Alps, the Slovenian Sava fold (Fodor et al. 2002)

region and the wider Pannonian basin area (Fodor et al. 1998,

2002; Kiss & Fodor 2007).

Conclusions

The new data from the hitherto undated Reifnitz tonalite

and its metamorphic host rocks suggest the following

conclusions:

• The “Altkristallin” basement complex south of the Wörther-

see was fully affected by metamorphism of Cretaceous age.

• The laser ICP-MS U–Pb zircon age of the Reifnitz tonalite

is 30.72 ± 0.30 Ma and the tonalite intruded into the likely

epidote amphibolite-grade metamorphic Austroalpine base-

ment of Cretaceous age (

Ar/

Ar white mica: 90.7 ± 1.6 Ma)

south of the Wörthersee area.

Fig. 10. Schematic diagram showing the relationships between the Oligocene Wörthersee anticline, which also corresponds to the peripheral

bulge of Neogene Klagenfurt basin, and the adjacent Cenozoic sedimentary basins in southeastern Alps. Time scale after Ogg et al. (2008) and

Piller et al. (2007). Note that the exact onset and termination of the three mentioned deformation stages are uncertain because of the poorly

dated sedimentary rocks.

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GEOLOGICA CARPATHICA

, 2018, 69, 3, 237–253

• The (U–Th–Sm)/He apatite age of the tonalite is

27.6 ± 1.8 Ma indicates fast cooling and rapid exhumation

after intrusion. The intrusion occurred into a large-scale

antiformal structure, which initially formed during Late

Oligocene times.

• In a second step, during the Sarmatian–Pliocene time

interval, final exhumation of several hundred metres

occurred in response to lithospheric flexure in front of

the overriding North Karawanken thrust sheet, responsible

for formation of the peripheral bulge in the front of

the Klagenfurt basin.

Acknowledgements: We acknowledge valuable comments

and suggestions by László Fodor and an anonymous reviewer,

the topical editor Jaroslav Lexa, and the managing editor,

Milan Kohút. These helped to clarify ideas and presentation.

The final work has been done within the framework of project

P22110 of the Austrian Science Fund FWF.

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