The Haselgebirge evaporitic mélange in central Northern Calcareous Alps (Austria): Part of the Permian to Lower Triassic rift of the Meliata ocean?

For the reconstruction of Alpine tectonics of the Eastern Alps, the evaporitic Permian to Lower Triassic Haselgebirge Formation plays a key role in (1) the origin of Haselgebirge bearing nappes, (2) the inclusion of magmatic and metamorphic rocks revealing tectonic processes not preserved in other units, and (3) the debated mode of emplacement of the nappes, namely gravity-driven or tectonic. Within the Moosegg quarry of the central Northern Calcareous Alps gypsum/anhydrite bodies are tectonically mixed with lenses of sedimentary rocks and decimeter- to meter-sized tectonic clasts of plutonic and subvolcanic rocks and rare metamorphics. We examined various types of (1) widespread biotite-diorite, meta-syenite, (2) meta-dolerite and rare ultramafic rocks (serpentinite, pyroxenite) as well as (3) rare metamorphic banded meta-psammitic schists and meta-doleritic blueschists. The apparent 40Ar/39Ar biotite ages from three biotite-diorite, meta-dolerite and meta-doleritic blueschist samples with variable composition and fabrics range from 248 to 270 Ma (e.g., 251.2 ± 1.1 Ma) indicating a Permian age of cooling after magma crystallisation or metamorphism. The chemical composition of biotite-diorite and meta-syenite indicates an alkaline trend interpreted to represent a rift-related magmatic suite. These, as well as Permian to Jurassic sedimentary rocks, were incorporated during Cretaceous nappe emplacement forming the sulphatic Haselgebirge mélange. The scattered 40Ar/39Ar white mica ages of a meta-doleritic blueschist (of N-MORB origin) and banded meta-psammitic schist are ca. 349 and 378 Ma, respectively, proving the Variscan age of pressure-dominated metamorphism. These ages are similar to detrital white mica ages reported from the underlying Rossfeld Formations, indicating a close source-sink relationship. According to our new data, the Haselgebirge bearing nappe was transported over the Lower Cretaceous Rossfeld Formations, which include many clasts derived from the Haselgebirge Formation and its exotic blocks deposited in front of the incoming nappe comprising the Haselgebirge Formation.

Introduction

The Eastern Alps and their extension in south-eastern Europe, particularly in the Western Carpathians, comprise the Austroalpine domain of continental affinity (Fig. 1a and b), which is characterised by a Middle Triassic passive continental margin succession, which opened towards the Meliata ocean (Channell and Kozur, 1997, Lein, 1987, Neubauer et al., 2000, Schmid et al., 2004, Schmid et al., 2008, Stampfli and Mosar, 1999). However, not much data exist on the initial Permian to Lower Triassic rift development, which finally formed the Meliata ocean (e.g., Thöni, 2006). Many researchers proposed that Alpine tectonic evolution started with Early Permian rifting immediately following the Variscan orogeny and after deposition of Late Carboniferous molasse. Rifting may have resulted from continuous dextral transtensional shear between Gondwana and Laurussia (e.g., Muttoni et al., 2003, Muttoni et al., 2005). Evidence for strong Early to Late Permian tectonic subsidence and extension has been reported from the eastern Southalpine units where a carbonate platform formed during the Permian and transgression of the Paleotethyan Sea took place towards NW (within present-day coordinates). Further evidence of divergence and extension of the lithosphere was the emplacement of tholeiitic gabbros, low-pressure metamorphism due to unroofing of metamorphic core complexes, and magmatic underplating during the Permian (Schuster and Stüwe, 2008, Schuster et al., 2001, Thöni, 1999).

Fig. 1

(a) Overview of Austroalpine units in the central Eastern Alps and (b) geological map of the central NCA (modified after Leitner et al., 2011 and Schorn and Neubauer, 2011). NCA — Northern Calcareous Alps; GWZ — Greywacke zone. Locations of the existing age data are shown in Fig. 1 (a) and (b).

The Meliata unit exposed in the Northern Calcareous Alps (NCA) of the Eastern Alps comprises distal continental margin deposits and oceanic sedimentary rocks of Middle Triassic to Doggerian age (exposed in the Florianikogel; Kozur, 1991, Mandl, 2000; Mandl and Ondrejiĉková, 1991 and references therein). These include Middle to Upper Triassic pelagic carbonates and Upper Triassic radiolarites recording a subsiding and deep-sea tectonic environment and the Doggerian Florianikogel Formation with shales, volcanogenic greywackes and ashfall tuffs (Kozur and Mostler, 1992, Neubauer et al., 2007). Late Jurassic and Cretaceous tectonic events of the central NCA have been related to the closure of the Meliata ocean (e.g., Faupl and Wagreich, 2000, Gawlick et al., 1999 and references therein). The enigmatic very low- to low-grade metamorphic overprint of the structural base of the NCA at ca. 149–135 Ma argues for a major tectonic event at that time (Missoni and Gawlick, 2011, Spötl et al., 1996, Spötl et al., 1998a, Spötl et al., 1998b, Vozárová et al., 1999). This event likely represents the onset of collisional tectonics but needs further confirmation (see also Frank and Schlager, 2006).

The Haselgebirge Formation of central sectors of the NCA (Salzkammergut, Figs. 1c, 2) is the uppermost Permian to Lower Triassic evaporitic succession (Klaus, 1965, Leitner et al., 2011, Schauberger, 1986), which formed as a rift sequence close to the lithostratigraphic base of the Permian to Eocene succession of the NCA (Spötl, 1989). The Haselgebirge Formation is poorly exposed at the surface, except in gypsum quarries. A number of operating salt mines provide subsurface exposures that are also rich in sulphates (anhydrite, gypsum). Halite, shale and subordinate anhydrite, gypsum and polyhalite form an evaporitic mélange (Leitner and Neubauer, 2011, Leitner et al., 2011, Schauberger, 1986). The average halite content ranges between ca. 30 and 65 volume percent (Schauberger, 1986). The stronger the brecciation, the better the “maturity” of the halite-shale mélange called “haselgebirge” (nomenclature after Schauberger, 1986).

Fig. 2

Geological map of the central southern part of the Osterhorn Tirolic nappe and overlying units (modified after Geological Map, scale 1:50,000, sheet Hallein (Plöchinger, 1987) updated by own observations; modified after Schorn and Neubauer, 2011).

The aim of this study is to describe well exposed blocks of various magmatic and metamorphic rocks within the sulphatic evaporitic mélange of the Moosegg gypsum quarry in the central NCA. These blocks and their country rocks enable the addition of further details to the reconstruction of the Late Permian and Mesozoic history of the rift and its closure during Early Cretaceous tectonic events. The study also provides new evidence for the hitherto unknown origin of detrital minerals exposed in Lower Cretaceous synorogenic sedimentary successions (von Eynatten et al., 1996).

Geological setting

The Upper Permian to Lower Triassic Haselgebirge Formation occurs mainly in Juvavic units of the central and eastern NCA (Fig. 1b). The classic division within the NCA defines the Bajuvaric, Tirolic and Juvavic nappe complexes (Fig. 1, Fig. 2). The age of formations in the NCA ranges from Late Carboniferous (?) or Early Permian to Eocene. During the Middle and Late Triassic, the Upper Juvavic nappes comprise mostly reefs and deposits next to reefs, the Tirolic and Bajuvaric nappes comprise mainly lagoonal facies types and the Lower Juvavic nappe unit represents solely an outer shelf respectively deep-sea facies type. Rocksalt deposits are mostly found in the Lower Juvavic unit, and in a few cases associated with the Lower Triassic Werfen Formation. Middle to Upper Triassic sedimentation of the Lower Juvavic unit occurred in basins with basinal limestones (Pötschen Limestone) and on intrabasinal ridges, with reduced sedimentary thickness (Hallstatt Limestone). The ridges were suggested to relate to salt diapirism in Triassic times (Mandl, 1984, Mandl, 2000, Plöchinger, 1984).

The westernmost part of the expanding Triassic Tethys ocean is called Hallstatt–Meliata ocean (Meliata ocean in the further text), which comprises rare deep-sea (ophiolitic?) sequences in the eastern parts of the NCA (Faupl and Wagreich, 2000, Neubauer et al., 2000). Most authors interpret the Hallstatt Limestone as an outer shelf deposit (Mandl, 2000, Tollmann, 1987). Others proposed a depositional position between Upper Juvavic and Tirolic paleogeographic domains (Schweigl and Neubauer, 1997). The Meliata ocean was closed in the Late Jurassic, and Upper Jurassic blueschists in the Western Carpathians are interpreted as evidence for the subduction of the Meliata ocean (Dallmeyer et al., 2008, Faryad, 1999 and references therein). Coevally, the sea floor drowned and reached maximum water depths with the formation of radiolarites. Gravitational sliding is reported from various places (Mandl, 1982, Plöchinger, 1990), and this concept was developed until recent years (Missoni and Gawlick, 2011 and references therein). These authors argue for a Late Jurassic age of shortening and thrusting.

At the transition from Early to Late Cretaceous, nappe stacking of Austroalpine units began due to the subduction of Austroalpine continental crust (e.g., Thöni, 2006). Thrusting prograded from south to north respectively from ESE to WNW (Linzer et al., 1995, Mandl, 2000, Neubauer et al., 2000, Ratschbacher, 1986). The mechanism and the time of emplacement of the Juvavic units is still a matter of controversy. The classic hypothesis assumes that both Juvavic nappes took their position during the eo-Alpine deformational event by means of thrust tectonics (Kober, 1955, Pichler, 1963, revived and adapted by Schweigl and Neubauer, 1997). Another model explains the emplacement of all Juvavic units by gravity sliding since Late Jurassic times (e.g., Missoni and Gawlick, 2011), as Haselgebirge clasts of various sizes have been found in the Upper Jurassic Oberalm and Lower Cretaceous Rossfeld Formations (e.g., Plöchinger, 1984). This concept was extended to large mountain-like blocks also explained by emplacement due to simple gravity sliding (Gawlick and Lein, 2000, Missoni and Gawlick, 2011 and references therein).

In Eocene times, the second paroxysm of Alpine orogeny occurred, when continental basement slices (“Middle Penninic”) and parts of the North Penninic ocean (including the Rhenodanubian Flysch) were subducted below the NCA at the leading edge of the Austroalpine-Adriatic microcontinent. The NCA nappe stack as we know it today was detached from its basement and thrust over the Rhenodanubian Flysch and Helvetic domains resulting in a wide thin-skinned tectonic nappe complex (Linzer et al., 1995, Neubauer et al., 2000). The familiar rocksalt deposits, which are all located in the interior of the NCA, mostly within the Lower Juvavic unit (Fig. 1b), were considered to be only slightly affected by these Cenozoic deformation stages, since detachment of the NCA nappe stack occurred beneath the lowermost unit, the Bajuvaric nappe (Fig. 1b). Deformation of Upper Cretaceous to Eocene Gosau basins deposited on uppermost nappes (Tirolic and Juvavic nappes) suggests significant deformation in the Late Eocene to Early Miocene (Linzer et al., 1997).

Work on volcanic blocks incorporated into the Haselgebirge mélange was done by Kirchner, 1979, Kirchner, 1980a, Kirchner, 1980b, Kralik et al. (1984) Gruber et al. (1991) and Vozárová et al. (1999). For a few samples, mainly from Wienern, Bad Ischl, and Moosegg, the composition of amphiboles, pyroxene, and white mica in suggested blueschists was studied. But in most cases, no reliable age dating was performed due to the lack of datable minerals or the minerals being too fine-grained. All these ages from low-grade metamorphic volcanics range from 98 ± 8 to 118 ± 9 Ma (Kirchner, 1980a, Kirchner, 1980b, Kralik et al., 1984; all previous geochronological data from the region under consideration are compiled in Table 1, for locations of the examined samples see Fig. 1a and b).

Table 1

Compilation of age dating, which was performed on magmatic and carbonatic rocks of the Northern Calcareous Alps and its surroundings. Locations of the existing age data are shown in Fig. 1 a and b.

Location	Formation	Examined minerals	Method	Age ± error (Ma)	Reference
Webing (Rigaus, Abtenau)	Haselgebirge	Na-amphibole (crossite)	K–Ar	103 ± 9, 118 ± 9	Kirchner, 1980a, Kirchner, 1980b
S Hochkönig	Permian–Lower Triassic and Carnian Fms	white mica	K–Ar	96 ± 9, 117–134	Kralik et al. (1987)
S Hochkönig	Permian–Lower Triassic Fms	white mica	Rb–Sr isochron	135 ± 5 (isochron age)	Kralik (1983)
E Tennengebirge	Permian–Lower Triassic Fms	white mica	K–Ar	120, 136–141	Kralik et al. (1987)
Annaberg/Lower Austria	Werfen	diabase whole rock	K/Ar isochron	99 ± 8	Kralik et al. (1984)
Moosegg	Haselgebirge	apatite	apatite fission track	143 ± 21 (142 ± 22)	Hejl and Grundmann (1989)
Central and western NCA	Rossfeld	detrital muscovites and phengites	40Ar/39Ar	320–360	Von Eynatten et al. (1996)
Grundlsee (Wienern)	Haselgebirge	authigenic K-feldspar	40Ar/39Ar	145 ± 1, 144 ± 1	Spötl et al. (1996)
Grundlsee (Wienern)	Haselgebirge	authigenic K-feldspar	Rb/Sr	152–140, isochron: 147 ± 6.4	Spötl et al. (1996)
Moosegg, Wienern, Webing, Wolfbauer, Tragöß, Pfennigbach	Haselgebirge	authigenic K-feldspar	40Ar/39Ar	90–97, 145–154	Spötl et al. (1998a)
S and E Tennengebirge	Permian–Lower Triassic Fms	sericite	40Ar/39Ar	98–102, 114–122	Frank and Schlager (2006)

Data related to the diagenetic to very low-grade metamorphic overprint of the Haselgebirge Formation was recently compiled by Leitner et al. (2011). The central sectors of the NCA underwent high diagenetic to very low-grade metamorphic conditions during the Late Jurassic to early Late Cretaceous. Maximum temperatures were estimated at around 200–300 °C (Gawlick et al., 1994, Götzinger and Grum, 1992, Kralik et al., 1987, Rantitsch and Russegger, 2005, Spötl, 1992, Spötl and Hasenhüttl, 1998, Spötl et al., 1996, Spötl et al., 1998a, Spötl et al., 1998b, Wiesheu, 1997). Maximum temperatures of country rocks increase to the south as indicated by mineral assemblages (Kralik et al., 1987), fluid inclusions studies, vitrinite reflection studies, microfabrics observations and a few apatite fission track analyses (Hejl and Grundmann, 1989). In the north, apatites maintained their detrital signature, i.e. are composed of mixed age populations, whereas samples from the south are completely reset (Hejl and Grundmann, 1989). In contrast, the temperature of the Haselgebirge mélange was also high in the north. In detail, the Haselgebirge mélange experienced temperatures of 180 °C in Hallstatt (Spötl and Hasenhüttl, 1998) and over 250 °C in Bad Ischl, Altaussee (Wiesheu, 1997) and Berchtesgaden (Kralik et al., 1987). Similar temperatures were found in gypsum/anhydrite deposits of the central NCA (Spötl et al., 1998a, Spötl et al., 1998b). One of the most reliable temperature estimates from fluid inclusions in quartz from Moosegg yielded temperatures of 220–260 °C (Spötl et al., 1998b). Primary fluid inclusions in anhydrite, calcite and dolomite from Moosegg range from 150 °C to over 300 °C (Wiesheu, 1997).

Geochronological ages (mainly K–Ar white mica ages and a single K-feldspar 40Ar/39Ar age) range between 150 Ma and 96 Ma (Table 1; Kirchner, 1980b, Kralik et al., 1984, Kralik et al., 1987, Spötl et al., 1998a, Spötl et al., 1998b, Rantitsch and Russegger, 2005, Frank and Schlager, 2006). Authigenic K-feldspar from Wienern/Grundlsee (Fig. 1b) yielded 40Ar/39Ar ages of 144 ± 1 to 145 ± 1 Ma (Spötl et al., 1996) and authigenic K-feldspar (mainly low to intermediate microcline) from several other deposits (e.g., Moosegg) showed 40Ar/39Ar ages of 145/146–154 Ma (Spötl et al., 1998a, Spötl et al., 1998b) and 90–94 Ma (Spötl et al., 1998a). Na-amphiboles (crossites) from metabasic rocks, which are tectonically incorporated in the gypsum deposit of Webing quarry/Rigaus were dated at 103 ± 9 Ma and 118 ± 9 Ma (Kirchner, 1980a, Kirchner, 1980b). Hejl and Grundmann (1989) found a cooling age of 143 ± 21 Ma by means of apatite fission-track dating for an altered metabasalt from the Moosegg quarry, which is older than the Na-amphibole age. Interestingly, apatite fission track ages in Cretaceous sedimentary units from the Tirolic nappes underlying the Haselgebirge mélange are in part older than the age of deposition and indicate that the maximum temperature reached (< 120 °C) is significantly lower than in the overlying Haselgebirge mélange (Hejl and Grundmann, 1989).

Kralik et al. (1984) obtained a K–Ar isochron age of 99 ± 8 Ma (whole rock) for an albite-chlorite diabase of Erzgraben/Annaberg (Lower Austria), which is incorporated in rocks of the Werfen Formation.

Regional geology of the central NCA

The study area is located in the central NCA (Fig. 1, Fig. 2). The Tirolic units are widespread and nearly subhorizontal within the so-called Tirolic arc (Tollmann, 1985). The Juvavic units are subdivided into the Lower Juvavic unit with the Haselgebirge Formation and mainly lenses and blocks of Middle-Upper Triassic pelagic limestone of the Hallstatt facies realm. These units are tectonically overlain by the Upper Juvavic units of the Untersberg and Dachstein nappes, and in the study area, by the Schwarzer Berg block (Fig. 2). In the Moosegg area, the Haselgebirge Formation is exposed in a tectonic klippe (Moosegg klippe), there overlying the Lower Cretaceous Rossfeld Formations. The Lower and Upper Rossfeld Formations comprise synorogenic clastic sediments (mainly sandstones and subordinate conglomerates; Faupl and Tollmann, 1978, von Eynatten et al., 1996).

Lithologies of the Moosegg klippe

The gypsum mine Grubach at Moosegg (GPS-coordinates 47°36′56.41N13°13′00.50 E) (Fig. 2, Fig. 3) was first documented in 1613 and was mapped in detail in terms of its geology and geological structure (Fig. 3). A syncline of light-coloured massive gypsum with lenses of anhydrite in the centre (Petraschek, 1947) is surrounded by more or less foliated dark gypsum breccia (Fig. 4a). Furthermore, some decimeter-to meter-sized blocks of exotic rocks including different types of plutonic rocks, greenstones and various claystone/mudstones as well as dolomite lenses are of great importance. A detailed description can be found in Schorn and Neubauer (2011). The quarry levels are numbered I-X with increasing altitude.

Fig. 3

Geological map of Moosegg quarry, JN — Juvavic nappe. I–X — quarry levels with increasing altitude (modified after Schorn and Neubauer, 2011).

Fig. 4

Field photographs: (a) Overview of Moosegg quarry, note the lenses of brown, banded dolomite (BBD), green and dark clayey mudstone (GM), light-brownish claystone (BC), dark anhydrite with fibrous blue Na-amphibole (NA) and red and green claystone (RGC) on the left side and light-coloured white gypsum (G) with small lenses of anhydrite (A) on the right side, embedded in dark, foliated gypsum breccia (DGB). (b) Biotite–diorite block within gypsum breccia with two types of dark components. (c) and (d) Well-foliated carbonate and anhydrite mylonites at level I of the Moosegg quarry. (e) Scan of the thin section II-A (banded meta-psammitic schist) showing recrystallisation throughout, various types of millimeter thick layers, foliation and an isoclinally folded banding. Long edge of the photomicrograph corresponds to (~ 40 millimeter).

A breccia with a groundmass of gypsum (Fig. 4a and b) makes up the bulk of the quarry, and components vary in size between 1 cm and 1 m. Fibrous gypsum of the Moosegg quarry, which was dated by sulphur-isotope measurements, yielded a Late Permian age (Pak, 1978). Apart from gypsum and anhydrite clasts, it consists of several different types of magmatic rocks. These include biotite–diorites (Fig. 4b), meta-syenite, then meta-doleritic blueschists, ultramafitites, and heavily altered, carbonatic volcanic rocks, the latter not further considered here, and rare banded meta-psammitic schist. Ultramafitite is also only exposed as a small lens within the red and green claystone of level VI. Besides serpentine, few brownish pyroxene grains can be observed.

Brown, banded dolomite (of levels II and III) shows a dark brown lamination and the anhydrite is partly quite rich in extension joints filled with blue Na-amphibole (riebeckite according to microprobe data). Their origin is likely due to rock/hydrothermal brine interaction. In the south-eastern part of level I ductile structures related to thrusting of the Haselgebirge Formation over the Lower to lowermost Upper Cretaceous rocks are preserved close to the structural base of the Moosegg klippe in folded, nearly vertically dipping anhydrite and carbonate mylonites (Fig. 4c and d).

Petrography and mineral composition

We selected a number of unaltered plutonic and metamorphic blocks for detailed petrographic work, geochemistry and Ar–Ar mineral dating. The principal magmatic rock types include: (1) biotite–diorite, (2) meta-dolerite, (3) meta-syenite, (4) meta-doleritic blueschist, and (5) ultramafitite. The banded meta-psammitic schist is also described as it was used for 40Ar/39Ar age dating. For all samples, the first term gives the level in the quarry according to the map shown in Fig. 3.

Petrography

In the following, a representative sample from each group of rocks is described, which was also used for geochemical investigations. The main emphasis is on preservation of relictic magmatic minerals, the degree and nature of secondary alteration of primary magmatic rocks, and the metamorphic neocrystallisation.

The biotite–diorite (sample IV-E, similar to samples IV-F and III-F) comprises mostly brown-coloured biotite (Fig. 5a), which has marginally transformed to leucoxene or a fine-grained aggregate of chlorite and white mica. The more common secondary peripheral change to green biotite is important for the age interpretation. The xenomorphic or lath-shape ore grains (0.1–0.5 mm) are often overgrown by brown biotite. Furthermore, the rock contains titanium-rich brown amphibole (kaersutite), which is well preserved in relicts, primarily intergrown with biotite, marginally intergrown with other minerals and fragmented. Some margins are transformed to a fine-grained aggregate (with grains sizes of 0.02 mm) of chlorite, white mica and possibly epidote. Fragments of colourless to pale green actinolite occur, which are also in part marginally frayed. Larger aggregates of plagioclase — presumably oligoclase (15–20% anorthite) — are sometimes nearly completely transformed to sericite. Nevertheless, they partly still show polysynthetic twinning. Moreover, pseudomorphs composed of chlorite, secondary green biotite, green actinolite and much clinozoisite and epidote (slightly Ca- and Fe-enriched in the cores) are quite common. The average grain sizes of these minerals vary between 0.05 and 0.1 mm.

Fig. 5

Photomicrographs: (a) Brown biotite (bt) with peripheral transformation to green biotite (gbt) of thin section IV-E (biotite–diorite), parallel polarisers. (b) Amphibole (actinolithe — act), overgrown by secondary, blue Na-amphibole (riebeckite — rie) of II-A (banded meta-psammitic schist), parallel polarisers. (c) Back-scattered electron image showing fabrics the meta-doleritic blueschist III-T with relictic cpx-cores with blue amphibole rims (winchite-ferro winchite), strong exsolution phenomena in magmatic minerals and celadonite-rich white mica and carbonate pseudomorphs after plagioclase; amph — amphibole, car — carbonate, cpx — clinopyroxene, plag — plagioclase, sph – sphene, wm – white mica. (d) Quartz-muscovite-biotite schist layer of II-A (banded meta-psammitic schist), crossed polarisers; ms – muscovite.

The thin section also comprises relicts of primary pyroxene, which have transformed to chlorite and actinolite. In addition, there are also abundant leucoxene and apatite grains. The latter are mostly idiomorphic and hexangular but also occur in unusual prolate shapes or as inclusions in plagioclase.

The fabric of the meta-syenite (sample I-J) is principally consistent with the other meta-dolerites (like I-G and I-H, I-N). Furthermore, it contains, apart from abundant brown biotite, up to 0.2 mm long brown amphibole (kaersutite) with rims of greenish amphibole and some K-feldspar.

The meta-dolerite (sample I-N, similar to samples I-G and I-H) is a quite fine-grained amphibole-rich rock type, which contains abundant 0.1 to 0.3 mm large brown amphibole (kaersutite) showing a greenish rim, many Ti-mineral inclusions and a partial overgrowth by fine-grained white mica. The thin section also comprises brown biotite with many ore segregations. It is transformed peripherally to green biotite, which is in turn altered marginally to white mica. Furthermore, some rutile grains, large aggregates of epidote and relicts of plagioclase and pyroxene are found. Very fine-grained aggregates are composed of a mixture of fine-grained ore minerals, chlorite, leucoxene and white mica.

The meta-doleritic blueschist (sample III-T, similar to sample III-Q and III-O) comprises a strongly altered bluish amphibole with a doleritic, subvolcanic fabric, which is characterised by intergrown 0.3–0.7 mm long and 0.5 mm wide laths of plagioclase and pseudomorphs after plagioclase. They have mainly been altered to fine-grained sericite, with average grain sizes of 0.01–0.02 mm, and maximum lengths of 0.1 mm, and carbonate (Fig. 5c). Pseudomorphs of other minerals are less frequent and can be classified into two different types: (1) Dark pseudomorphs are completely decomposed and consist of leucoxene with boundaries diffusely intergrown by ore grains and fine-grained relicts of pyroxene (probably orthopyroxene). (2) The second type is characterised by relicts of actinolitic amphibole, epidote and clinopyroxene. Furthermore, the rock partly contains well preserved green amphibole and brown biotite, both minerals sometimes transformed to green biotite, isometric ore grains (probably titanium-magnetite), apatite and secondary chlorite.

The ultramafitite (sample IV-B) comprises relicts of olivine, which is predominantly serpentinized. Furthermore, relicts of well preserved clinopyroxene showing cleavage and twinning and few box-shaped orthopyroxene grains also occur.

The banded meta-psammitic schist (sample II-A) represents one of the few foliated metamorphic clasts and was found within the brown, banded dolomite. The sample is essential for the (white mica) dating of a metamorphic event in the source rocks of the block embedded within the gypsum breccia and shows a highly ductile metamorphic fabric including foliation and exemplarily well developed isoclinal folding (Fig. 4e). There are three different types of layers: (1) The light-coloured layers represent a quartz-muscovite-biotite schist (Fig. 5d) and are composed of slightly stretched, 0.05–0.10 mm long quartz grains with amoeboid grain boundaries and much chlorite. Furthermore, white mica with grain sizes from 0.1 to 0.3 mm occurs, as well as brown biotite, which is very often intergrown with chlorite, 0.02 mm long ore grains and rare chloritoid. (2) The dark layers are polymineralic and rich in amphibole, strongly corroded, and largely transformed to other minerals. Some relicts of colourless to light green amphibole are zoned. The green/brown amphibole (kaersutite) is overgrown by secondary, blue Na-amphibole (riebeckite) (Fig. 5b). (3) The carbonatic layers are intergrown with chlorite. They contain approximately 10–15 modal % of chlorite with ore inclusions indicating an origin from biotite and some white mica. The protolith is probably a quartz-rich sandstone with carbonatic layers.

Composition of magmatic minerals in biotite–diorite

We selected a few samples with well preserved magmatic minerals from the biotite–diorite, meta-dolerite, meta-syenite and meta-doleritic blueschist for microprobe work. We investigated various minerals of the biotite–diorite and here only report data from the kaersutitic amphiboles and their rims and from clinopyroxene (Figs. 5c and 6a), which are important for the interpretation of the tectonic setting of the magmatic suite. The analytical methods are described in Appendix A. Representative analytical results are given in Table 2 and are graphically shown in Fig. 6.

Fig. 6

Composition of (a) clinopyroxene, (b) kaersutitic amphibole and (c) actinolite of biotite–diorite and meta-dolerite.

Table 2

Representative microprobe analyses of various magmatic and metamorphic minerals from the Moosegg quarry. Cpx — clinopyroxene.

Sample	AS-III-L		AS-III-T	AS-III-L		AS-III-T	AS-III-T	AS-I-G		AS-I-N	AS-II-A		AS-III-W
Point-no.	586	587	563	511	8687		8626	8620	8599	2508	2487	1655	8830
Mineral	kaer-sutite	kaer-sutite	ferro-winchite	winchite	actinolite	actinolite	cpx	cpx	celadonite	phengite	phengite	phengite	biotite
SiO2	41.67	41.34	51.59	54.68	54.94	55.85	51.56	51.96	52.47	48.16	50.59	47.16	36.11
TiO2	4.63	4.60	1.33	0.27	0.06	0.09	1.06	0.99	0.09	0.05	0.02	0.39	6.26
Al2O3	11.41	11.12	3.13	3.33	0.61	0.75	1.97	3.37	18.54	26.05	24.42	32.56	12.89
Cr2O3	0.00	0.04	0.06	0.01	0.00	0.00	n.m.	n.m.	n.m.	0.00	0.03	0.01	n.m.
FeO⁎	11.97	12.01	20.14	17.98	9.70	9.17	11.14	7.93	7.56	3.53	2.75	1.40	17.33
MnO	0.16	0.16	0.14	0.12	0.15	0.17	0.35	0.22	0.09	0.07	0.21	0.00	0.13
MgO	12.86	12.63	8.32	11.08	17.64	18.33	14.15	15.57	5.68	4.66	5.02	1.90	11.68
CaO	11.42	11.37	4.60	4.11	12.59	12.72	18.48	19.41	0.06	0.00	0.07	0.00	0.03
Na2O	2.80	2.77	5.51	4.95	0.14	0.22	0.45	0.37	0.03	0.05	0.13	0.78	0.62
K2O	1.01	0.98	0.00	0.00	0.00	0.00	0.00	0.00	10.13	11.30	11.23	10.17	8.61
Cl	0.00	0.00	0.00	0.00	0.02	0.00	0.01	0.01	0.01	n.m.	n.m.	n.m.	0.02
Total	97.93	97.02	94.82	96.53	95.85	97.30	99.17	99.83	94.66	93.87	94.47	94.37	93.68
Formula on the basis of
			23 O				6 O			22 O
Si	6.141	6.158	7.827	7.925	7.929	7.913	1.944	1.918	7.248	6.637	6.880	6.336	5.573
Ti	0.513	0.515	0.152	0.029	0.007	0.010	0.030	0.027	0.009	0.005	0.002	0.039	0.726
Al (IV)	1.859	1.842	0.173	0.075	0.071	0.087	0.026	0.055	0.752	1.363	1.120	1.664	2.427
Al-tot	1.982	1.952	0.560	0.569	0.104	0.125	0.088	0.147	3.018	4.230	3.913	5.157	2.344
Al(VI)	0.123	0.110	0.387	0.494	0.033	0.038	0.062	0.092	2.266	2.867	2.793	3.493	0.000
Cr	0.000	0.005	0.007	0.001	0.000	0.000	0.000	0.000	0.000	0.000	0.003	0.002	0.000
Fe3 + ⁎	0.200	0.180	0.356	0.626	0.043	0.054	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Fe2 +	1.275	1.316	2.200	1.553	1.128	1.032	0.351	0.245	0.873	0.406	0.313	0.157	2.237
Mn	0.020	0.020	0.018	0.015	0.018	0.020	0.011	0.007	0.011	0.008	0.024	0.000	0.017
Mg	2.825	2.805	1.882	2.394	3.796	3.872	0.795	0.857	1.170	0.957	1.019	0.381	2.687
Ca	1.803	1.815	0.748	0.638	1.947	1.931	0.747	0.768	0.009	0.000	0.010	0.000	0.006
Na	0.800	0.800	1.621	1.391	0.039	0.060	0.033	0.026	0.007	0.014	0.035	0.204	0.186
K	0.190	0.186	0.000	0.000	0.000	0.000	0.000	0.000	1.785	1.986	1.949	1.743	1.695
sum cat	15.749	15.752	15.370	15.143	15.010	15.018
cl	0.000	0.000	0.000	0.000	0.005	0.000	0.001	0.001	0.002	0.000	0.000	0.000	0.005
Ti	0.513	0.515
Mg/(Mg + Fe2)	0.689	0.681	0.461	0.607	0.771	0.790
CaB	1.803	1.815
CaB + NaB	2.000	2.000	1.999	1.887	1.976	1.976
NaB	0.190	0.185	1.251	1.249	0.029	0.043
NaA + KA	0.793	0.801	0.370	0.143	0.010	0.018

Fe3 + calculation after Holland and Blundy (1994).

Clinopyroxene occurs in the core of partly well preserved grains or in shape relicts, which are surrounded by a fine-grained mixture of blue amphibole rims (winchite–ferro-winchite). Celadonite-rich white mica and carbonate pseudomorphs after plagioclase are abundant. In the same rock type, brownish kaersutitic amphibole is observed (Fig. 5c). Clinopyroxene is mostly augite (Fig. 6a). The brownish amphibole is kaersutite and the rims are composed of actinolite (Fig. 6b and c).

Geochemistry

The samples of magmatic blocks incorporated within the gypsum breccia were analysed by Acme Analytical Laboratories Ltd.. The rock types can be found in Table 3. The chemical analytical details are described in Appendix B, the results are shown in Table 4. The graphs of nomenclature, magmatic series and tectonic discrimination diagrams were drawn with the program PetroGraph2beta (Petrelli et al., 2005), the multi-element variation diagrams with PetroPlot (Su et al., 2002) and the Harker diagrams (not shown) with Microsoft Excel 2003.

Table 3

Mineralogical composition and fabric of investigated rock samples. Abbreviations: pl — plagioclase, kf — k-feldspar, fs — feldspar, px — pyroxene, cpx — clinopyroxene, opx — orthopyroxene, amph — amphibole, ol — olivine, mt — magnetite, chl — chlorite, act — actinolithe, kae — kaersutite, rie — riebeckite, ser — sericite, ms — muscovite, ap — apatite, an — anhydrite, car — carbonate, qz — quartz, ctd — chloritoide, ti — titanium mineral, tm — titanium magnetite, py - pyrite, ore — unknown opaque ore mineral, ep — epidote, cz — clinozoisite, lx — leucoxene, ru — rutile, PA — plateau age, o. SSA — older single step age, y. SSA — younger single step age.

Sample No.	Rock type	Primary minerals	Metamorphic/secondary minerals	Remarks to fabric	Age dating (Ma)
IV-B	ultramafitite	relicts of cpx and opx	serpentinized ol	magmatic fabric, static recrystallisation	–
I-H	meta-dolerite	kf, bt, ms, plag	ser, ore, lx pseudomorphs, an, ore	magmatic fabric, static recrystallisation	270.9 ± 0.7 (o.SSA)263.1 ± 0.7 (y.SSA)
I-G	meta-dolerite	bt marginally altered to green bt or chl,plag	ser, ore, lx pseudomorphs, an, ap	magmatic fabric, static recrystallisation	263.3 ± 0.7
I-N	meta-dolerite	kae, bt marginally altered to green bt or chl orms, plag, px	ti, ore, ms, chl, lx, ru, ep,	magmatic fabric, static recrystallisation	–
I-J	meta-syenite	bt marginally altered to green bt or chl, plag, kae	amph, ser, ore, lx pseudomorphs, an, ap	magmatic fabric, static recrystallisation	–
IV-E	biotite–diorite	bt marginally altered to green bt or chl, plag, px, kae	ms, chl, ore, lx, ep, act, ap, ser,cz	magmatic fabric, static recrystallisation	251.2 ± 1.1 (PA)
IV-F	biotite–diorite	bt marginally altered to green bt or chl, plag, kae, px,	tm, amph, ep, cz, ap	magmatic fabric, static recrystallisation	254.4 ± 3.1
IV-G	biotite–diorite	bt marginally altered to green bt or chl, plag, px, kae	ms, chl, ore, lx, ep, act, ap, ser, cz	magmatic fabric, static recrystallisation	–
III-W	meta-dolerite	bt marginally altered to green bt or chl, plag, px, kae	ms, chl, ore, lx, ep, act, ap, ser, cz	magmatic fabric, static recrystallisation	259.0 ± 0.8 (o.SSA)252.0 ± 0.7 (y.SSA)
III-O	meta-doleritic blueschist	plag, amph, px (opx?), act, cpx, bt marginally altered to green bt or chl	ser, chl, lx, ep, ore (tm?), ap	magmatic fabric, doleritic, subvolcanic fabric	248.3 ± 2.9 Ma
III-Q	meta-doleritic blueschist	plag, amph, px (opx?), act, cpx, bt marginally altered to green bt or chl	ser, chl, lx, ep, ore (tm?), ap	magmatic fabric, doleritic, subvolcanic fabric	253.6 ± 2.9
III-T	meta-doleritic blueschist	amph, px, fs, qz, bt	ms, kae, car	magmatic fabric, doleritic, subvolcanic fabric	252.3 ± 3.1 (bt)
349 ± 15 (wm)
III-F	biotite–diorite	bt marginally altered to green bt or chl, plag, cpx	ms, chl, ep, ti, py	magmatic fabric, doleritic, subvolcanic fabric	253.1 ± 3.2
II-A	banded meta-psammitic schist	ms, bt, qz, amph, kae	chl, ctd, rie, car, ore	highly ductile metamorphic fabric including foliation and exemplarily well-developed isoclinal fold	378.4 ± 0.9

Table 4

Results of geochemical analysis of 15 samples, performed through ICP mass spectrometry by Acme Analytical Laboratories Ltd., Canada. LOI, loss of ignition; MDL, minimum detection limit, for all samples: Rock pulp type.

Analyte	Unit	MDL	III-W	IV-G	IV-B	I-H	I-N	III-I	III-H	I-J	I-G	IV-E	IV-F	III-O	III-Q	III-T	III-F
SiO2	%	0.01	46.28	46.73	38	52.13	46.98	3.3	2.54	53.1	48.74	47.38	46.98	43.89	46.71	47.09	45.88
Al2O3	%	0.01	17.91	16.8	2.72	18.99	17.71	1.22	0.84	18.39	18.3	17.41	16.78	16.17	14.91	13.66	16.56
Fe2O3	%	0.04	8.09	9.12	7.96	4.94	4.1	0.98	0.83	4.25	4.04	9.56	9.47	10.15	12.05	12.66	9.42
MgO	%	0.01	7.56	8.04	34.89	4.49	4.43	19.97	20.45	5.38	3.86	5.98	7.32	9.63	8.42	7.04	8.69
CaO	%	0.01	6.45	6.69	0.24	1.09	4.35	28.55	28.62	0.94	4.98	5.65	6.45	4.07	2.96	6.99	6.25
Na2O	%	0.01	3.35	3.47	< 0.01	0.3	0.08	0.03	0.02	0.13	1.53	3.85	3.56	1.12	1.76	3.67	3.2
K2O	%	0.01	2.57	2.26	0.03	12.53	11.94	0.73	0.59	12.76	10.1	3.43	2.81	6.58	5.87	2.02	2.58
TiO2	%	0.01	1.65	2.08	0.07	0.7	0.66	0.04	0.03	0.56	0.65	2.49	2.31	1.83	2.1	2.04	2.28
P2O5	%	0.01	0.39	0.43	0.01	0.24	0.24	0.01	< 0.01	0.05	0.2	0.65	0.55	0.3	0.25	0.16	0.41
MnO	%	0.01	0.07	0.11	0.08	0.1	0.13	0.09	0.09	0.07	0.11	0.09	0.11	0.17	0.14	0.2	0.08
Cr2O3	%	0	0.025	0.03	0.533	0.012	0.012	< 0.002	< 0.002	0.013	0.011	0.015	0.026	0.025	0.02	0.022	0.035
Ni	ppm	20	115	123	2431	28	37	< 20	< 20	< 20	< 20	53	96	102	68	55	138
Sc	ppm	1	18	24	17	10	16	1	1	19	21	27	26	32	38	46	23
Ba	ppm	1	179	116	185	390	168	11	12	130	212	154	140	57	90	104	137
Be	ppm	1	2	2	< 1	8	12	< 1	< 1	11	8	2	2	1	2	< 1	2
Co	ppm	0.2	32.8	33.2	113.9	6.5	9.1	1.5	1.3	3	5	25.5	28.1	40	37.6	38.7	35.6
Cs	ppm	0.1	7.1	3.2	0.6	9	6.2	0.2	< 0.1	4.2	7.2	6.5	5.2	10	8.9	2.5	6.9
Ga	ppm	0.5	16	15.9	2.5	26.3	23.4	1.4	1.1	23.2	24.3	16.3	16.6	17.4	17.7	18.5	16
Hf	ppm	0.1	4	4.8	< 0.1	3.3	2.8	0.3	0.2	3	3.2	5.1	5.2	4	3.6	3.3	4.5
Nb	ppm	0.1	24.5	27.4	0.1	17	14.8	0.8	0.6	17.9	20.8	30.3	29.2	13.7	7.5	2.6	27.4
Rb	ppm	0.1	47.2	29.9	1.4	382.2	263.3	8.1	5.1	188	263	50.4	39.5	63.6	53.2	26.1	46.6
Sn	ppm	1	2	2	< 1	6	10	< 1	< 1	7	10	2	2	2	2	1	2
Sr	ppm	0.5	1187.9	759.9	1614	1125	298.4	257.4	548.3	136.8	276.5	1502.3	926.2	358.1	156.2	130.4	998.6
Ta	ppm	0.1	1.7	1.9	< 0.1	1.3	1.4	< 0.1	< 0.1	1.2	1.4	2.1	2.1	1	0.5	0.2	1.8
Th	ppm	0.2	3	2.7	< 0.2	14.2	14.2	0.7	1	28.8	13.7	3	2.7	0.7	0.5	0.4	2.8
U	ppm	0.1	1.2	1.1	0.7	2.3	3	2.6	2.4	2	2.3	1.1	1	0.5	0.3	0.1	1.2
V	ppm	8	140	172	73	81	92	26	25	96	80	222	193	225	319	374	165
W	ppm	0.5	< 0.5	< 0.5	< 0.5	0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5
Zr	ppm	0.1	193.2	207.6	1.7	100.1	93.7	12.6	8.8	92.1	96.3	224.9	223.8	157.6	146	116.9	207.8
Y	ppm	0.1	21.3	24.1	1	63.6	68.5	1.9	1.7	33.7	105.6	28.8	27.8	28.1	35.8	38.7	24.6
La	ppm	0.1	21	21.5	0.4	50.5	39	1.9	2	32	193.1	26.1	24.7	12.3	8.6	4.8	21.6
Ce	ppm	0.1	44.8	47.8	0.5	122.2	105	4	4.2	70.8	297.8	59	55.3	29.9	22.4	15	47.5
Pr	ppm	0.02	5.32	5.71	0.07	13.9	13.46	0.53	0.47	7.46	25.33	7.16	6.66	3.9	3.31	2.45	5.61
Nd	ppm	0.3	21.4	23	0.3	54	52	2	1.9	26.4	80.1	29	27.6	17.5	16.4	12.3	22.2
Sm	ppm	0.05	4.18	4.93	0.05	9.33	10.34	0.38	0.34	5	13.09	6.24	5.87	4.21	4.49	4.09	4.87
Eu	ppm	0.02	1.55	1.66	0.03	1.71	2.06	0.08	0.07	1.07	2.29	2.05	1.93	1.56	1.65	1.57	1.66
Gd	ppm	0.05	4.21	4.8	0.1	8.78	9.28	0.35	0.34	4.68	12.17	6	5.67	5.01	5.74	5.8	4.89
Tb	ppm	0.01	0.69	0.8	0.03	1.46	1.56	0.06	0.06	0.84	2.28	0.99	0.92	0.86	1.02	1.07	0.79
Dy	ppm	0.05	3.8	4.57	0.11	8.65	8.92	0.27	0.28	4.96	13.51	5.7	5.28	4.98	6.18	6.47	4.77
Ho	ppm	0.02	0.76	0.87	0.04	1.68	1.85	0.07	0.06	1.04	2.7	1.08	0.99	1.02	1.3	1.41	0.89
Er	ppm	0.03	2.15	2.49	0.12	5.17	5.7	0.16	0.17	3.18	8.39	3.05	2.87	2.79	3.78	4.23	2.38
Tm	ppm	0.01	0.33	0.37	0.03	0.8	0.89	0.03	0.03	0.51	1.23	0.45	0.43	0.41	0.58	0.61	0.37
Yb	ppm	0.05	2	2.2	0.13	4.62	5.35	0.16	0.17	3.32	6.71	2.66	2.63	2.64	3.54	3.74	2.26
Lu	ppm	0.01	0.28	0.33	0.02	0.51	0.71	0.03	0.03	0.45	0.69	0.39	0.36	0.39	0.53	0.56	0.33
TOT/C	%	0.02	0.09	0.14	0.36	0.19	0.24	12.6	11.51	0.04	0.12	0.16	0.13	0.11	0.06	0.13	0.08
TOT/S	%	0.02	0.96	0.21	0.13	0.52	2.52	0.45	0.32	0.5	2.11	0.2	0.11	0.79	0.26	0.35	1.23
Mo	ppm	0.1	2.8	2.5	< 0.1	0.2	0.3	1	0.9	0.8	0.3	2.2	2.5	0.9	0.4	0.2	1.6
Cu	ppm	0.1	25.5	27.8	12.4	3.3	6.3	6.8	4.3	2.6	2.3	17.4	16.9	3	4.9	8.2	11.3
Pb	ppm	0.1	1.1	3.6	< 0.1	< 0.1	1.5	4.1	2.5	< 0.1	0.7	2.9	5.6	5.1	2.4	0.8	1.9
Zn	ppm	1	28	46	24	125	160	12	13	129	95	21	30	111	69	51	32
Ni	ppm	0.1	92.7	101.5	2380	4.7	32.4	1.5	1.5	6.6	13.7	38.5	72	72.9	44.2	29.6	110.8
As	ppm	0.5	1.3	4.6	1.5	9.1	5.1	< 0.5	< 0.5	13.2	2.9	1.2	3.6	9.1	5.7	2.6	3.4
Cd	ppm	0.1	< 0.1	0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Sb	ppm	0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	0.2	< 0.1	0.1	0.7	0.3	0.2	< 0.1
Bi	ppm	0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Ag	ppm	0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Au	PPB	0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	3.4	2	< 0.5	0.6	0.5	0.8	1
Hg	ppm	0.01	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01	0.02	0.02	0.01	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01
Tl	ppm	0.1	0.3	0.2	< 0.1	0.3	0.3	0.1	< 0.1	0.2	< 0.1	< 0.1	< 0.1	0.1	< 0.1	< 0.1	< 0.1
Se	ppm	0.5	< 0.5	< 0.5	0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5

We used the TAS (total alkalies-silica) graph for plutonics after Cox et al. (1979) (Fig. 7a). One of the meta-dolerites plots near the Ijolite field, the others plot close to the gabbro field just as the biotite–diorites and one of the meta-dolerites. The meta-dolerites are located near the meta-syenite within the nepheline–syenite field. We also used the Q'(F')-ANOR discrimination diagram for plutonics of Streckeisen and LeMaitre (1979; not shown). The meta-dolerites are located in the fields of foid-syenite, foid-monzonite, foid-monzodiorite and foid-monzogabbro. The biotite–diorite samples plot in the foid-monzodiorite and foid-monzogabbro fields. The meta-dolerites show a broad distribution: they plot in the monzo-gabbro/diorite field as well as on the border of foid-syenite to foid-monzonite and together with the meta-syenites in the foid-syenite fields.

Fig. 7

(a) TAS (Total Alkalies-Silica) graph for plutonic rocks according to Cox et al. (1979). (b) Ta/Yb–Th/Yb discrimination diagram according to Pearce (1982); VAB — volcanic arc basalt, SHO — shoshonite, CA — calcalkaline, TH — tholeiitic, MORB — mid ocean ridge basalt, TR — trachytic, ALK — alkaline, WPB — within plate basalt. (c) Spider diagram normalised to: CI chondrite (McDonough and Sun, 1995). (d) Multi-element variation diagram All Trace P mantle (Sun and McDonough, 1989), m.-d. blueschist — meta-doleritic blueschist.

In Harker diagrams (not shown), according to their variable chemical composition, the geochemical data analysis shows a broad distribution in the classical diagrams. The major elements Al2O3 and K2O increase with rising SiO2 contents, while Na2O, TiO2 and Fe2O3 decrease. The trace elements Th, Ga and Rb show a positive and Zr, Ni, Cu, Pb and Rb a negative correlation with SiO2. Particularly the high contents in FeOtot (ca. 4–14%) and TiO2 (> 1%) as well as unusually high contents of Zr (ca.100–250 ppm) are typical for alkaline rocks.

Several diagrams were proposed to distinguish between various magmatic series. For example in the SiO2-F/M diagram after Miyashiro (1974) (not shown), all meta-dolerites, biotite–diorites and three meta-dolerites plot in the tholeiitic field. One meta-dolerite sample and the meta-syenite are situated in the calcalkaline field. In the K2O–SiO2 diagram after Middlemost (1975) (not shown), one meta-doleritic blueschist as well as all biotite diorites and one meta-dolerite are assigned to the alkaline rock field.

In the following multi-variation diagram analysis, we distinguish five different rock types. The REE (normalised CI chondrite after McDonough and Sun, 1995) (Fig. 7c) of meta-dolerite and meta-syenite are extremely enriched (thousandfold) with light rare earth elements, which is typical for alkaline magmatites (e.g., from rifts). Furthermore, they show a high La/Lu ratio and a characteristic negative Eu anomaly, which is caused by a plagioclase fractionation in the melt. The meta-doleritic blueschist shows a plain pattern with low enrichment in elements and no Eu-anomaly, which means that plagioclase was never removed from the melt. The La concentration is lower than that of Ce, which is particular for N-MORB (normal mid-ocean ridge basalt) or T-MORB (transitional MORB) rocks. Together, these samples are very meaningful and surely indicate an N-MORB-origin of meta-doleritic blueschists.

The biotite–diorite samples show a significant enrichment in REEs but no negative Eu-anomaly. Both facts are representative for alkaline rocks. The ultramafitite sample shows a flat pattern and is notably less enriched in all elements than the previous rocks. It also has no Eu-anomaly, which is typical for ultramafic rocks. This rock represents a cumulate, which probably developed from the parent melt of the meta-doleritic blueschist protolith.

In the multi-element-variation diagram of trace elements versus primitive mantle composition using normalisation values of Sun and McDonough (1989), all samples show more or less flat patterns with partially very distinct anomalies (Fig. 7d). They are all enriched with Cs and Rb and show, except for the blue meta-dolerite samples, a prominent negative Ba anomaly.

We suggest that both the blue meta-dolerites and biotite–diorites derived from a primitive mantle melt. The meta-doleritic blueschists show an affinity to MOR basalts while the biotite–diorites originate from the alkaline milieu of a shallow magma chamber without any influence of a subduction zone. In detail, the results are as follows: The meta-dolerites and the meta-syenite show positive anomalies of Cs, Rb, Th, La/Ce, Pr, Nd, Sm, Y and negative ones for Nb, Ta and Ba. The meta-doleritic blueschist bears positive anomalies in Cs, Rb and Pb as well as a slightly negative one in Ba. Biotite–diorites exhibit positive anomalies for Cs, Rb, Pb and Sr. The ultramafitite shows positive anomalies for U, Pb, Sr and negative ones for Nb, Sm and Hf.

In the Ta/Yb–Th/Yb discrimination diagram after Pearce (1982) (Fig. 7b), the meta-doleritic blueschist plots in the MORB field, the biotite–diorites and one meta-dolerite in the alkaline transition zone. The remaining meta-dolerites are assigned to the shoshonite–calkalkaline field and the meta-syenite to the volcanic arc basalts.

In the Nb-Y discrimination diagram after Pearce et al. (1984), the meta-doleritic blueschist and one meta-dolerite are located in the VAG and syn-COLG fields (volcanic arc granites and syn-collisional granites) (figure not shown). The biotite–diorite samples are assigned to the WPGs (within-plate granites). The remaining meta-dolerites plot in a transition zone between the WPG and ORG (ocean ridge granite) field, the meta-syenite plot on the boundary between the VAG and syn-COLG fields.

The Ta–Yb discrimination diagram of Pearce et al. (1984) allows discrimination of granitoids (not shown). The meta-dolerites and the meta-syenite are assigned to the VAGs (volcanic arc granites), the biotite–diorites and one meta-dolerite to the syn-COLG (syncollisional granites). The remaining meta-dolerites plot in the transition zone between the WPG (within plate granites) and ORG fields.

In the Th-Hf-Ta discrimination diagram for basaltic rocks after Wood (1980) (not shown), one meta-doleritic blueschist is assigned to the E-type MORBs and within-plate tholeiites, one to the N-type MORBs and another one as well as three meta-dolerites and the meta-syenite to the volcanic arc basalts. The biotite–diorites and one meta-dolerite plot in the alkaline within-plate basalt field.

40Ar/39Ar age dating results

Laser-probe step-heating 40Ar/39Ar experiments have been performed on multi-grains of the 200–350 μm fraction. Details of the mineral separation and analytical procedure for 40Ar/39Ar dating can be found in Appendix C. 40Ar/39Ar analytical results are presented in Table 5 and are graphically shown in Fig. 8, Fig. 9. Two samples (III-T and II-A) yielded fine-grained metamorphic white mica of a sufficiently large grain size, nine samples (III-T, III-O, III-Q, I-G, I-H, III-W, IV-E, IV-F, III-F) contain well preserved magmatic biotite for 40Ar/39Ar dating.

Table 5

40Ar/39Ar analytical data of all mineral concentrates from magmatic and metamorphic blocks enclosed within the Haselgebirge mélange of the Moosegg quarry. Errors of ratios, J-values, and ages are at 1-sigma level. 37Ar is corrected for post-irradiation decay of 37Ar; %40Ar*: non atmospheric 40Ar. Mu — muscovite respectively white mica; Bt — biotite.

Step	36Ar/39Ar	± 36Ar/39Ar	37Ar/39Ar	± 37Ar/39Ar	40Ar/39Ar	± 40Ar/39Ar	36Ar/40Ar	± 36Ar/40Ar	39ArK/40Ar*	± 39ArK/40Ar*	%40Ar*	%39Ar	Age [Ma]	± [Ma]
	Meas.	1-sigma abs.	Irrad. corr.	1-sigma abs.	Meas.	1-sigma abs.	Meas.	1-sigma abs.	Calculated	1-sigma abs.				1-sigma abs.
	Sample	AS-II-A Mu		200–250 μm		10	Grain(s)				J‐value	0.00869	+/−	0.00002
1	0.06996	0.01187	0.00003	0.08033	40.160	1.244	0.001742	0.000291	19.464	3.505	48.5	0.1	282.0	47.0
2	0.01773	0.00331	0.07361	0.01650	22.432	0.258	0.000791	0.000147	17.174	0.997	76.6	0.6	251.0	13.6
3	0.00522	0.00041	0.02624	0.00196	24.794	0.063	0.000211	0.000016	23.228	0.135	93.8	4.2	331.7	1.9
4	0.00477	0.00039	0.01030	0.00339	27.382	0.167	0.000174	0.000014	25.951	0.196	94.9	3.0	366.9	2.6
5	0.00064	0.00006	0.00000	0.00029	27.065	0.030	0.000024	0.000002	26.851	0.035	99.3	33.0	378.4	0.9
6	0.00071	0.00005	0.00260	0.00037	27.215	0.029	0.000026	0.000002	26.980	0.032	99.2	28.8	380.0	0.9
7	0.00560	0.00047	0.01804	0.00608	29.439	0.161	0.000190	0.000016	27.761	0.206	94.4	3.4	389.9	2.7
8	0.00188	0.00019	0.00533	0.00120	27.837	0.158	0.000067	0.000007	27.260	0.164	98.0	7.8	383.6	2.2
9	0.00077	0.00024	0.00000	0.00255	28.585	0.185	0.000027	0.000009	28.333	0.197	99.2	5.3	397.1	2.6
10	0.00498	0.00059	0.02502	0.00549	28.370	0.190	0.000175	0.000021	26.878	0.251	94.8	2.4	378.7	3.3
11	0.00204	0.00034	0.00424	0.00287	27.667	0.142	0.000074	0.000012	27.039	0.172	97.8	4.9	380.8	2.3
12	0.00129	0.00029	0.00497	0.00238	26.941	0.091	0.000048	0.000011	26.537	0.125	98.6	6.4	374.4	1.8
	Sample	AS‐III‐T Mu		160–355 μm		7 gr	Grain(s)				J‐value	0.00602	+/−	0.00002
1	0.00576	0.00142	0.31393	0.03716	27.599	0.230	0.000209	0.000051	25.892	0.472	93.9	3.6	261.5	4.5
2	0.00009	0.00030	0.02037	0.00607	34.662	0.092	0.000002	0.000009	34.607	0.127	99.9	18.9	341.6	1.7
3	0.00090	0.00074	0.01527	0.02324	38.901	0.280	0.000023	0.000019	38.604	0.353	99.3	5.3	377.2	3.4
4	0.00024	0.00018	0.00000	0.00308	36.195	0.060	0.000007	0.000005	36.093	0.080	99.8	31.1	354.9	1.5
5	0.00031	0.00024	0.00000	0.00399	33.212	0.149	0.000009	0.000007	33.089	0.164	99.7	24.0	327.9	1.9
6	0.00458	0.00210	0.00000	0.03690	40.610	0.506	0.000113	0.000052	39.225	0.791	96.7	2.6	382.7	7.1
7	0.00131	0.00046	0.01293	0.00792	37.623	0.163	0.000035	0.000012	37.205	0.211	99.0	11.7	364.8	2.3
8	0.00131	0.00233	0.00002	0.04583	36.177	0.324	0.000036	0.000065	35.759	0.760	98.9	2.7	351.9	6.9
	Sample	AS‐III‐T Bt		160–355 μm		10	Grain(s)				J‐value	0.00601	+/−	0.00002
1	0.08857	0.00456	0.04341	0.04901	46.955	0.622	0.001886	0.000094	20.754	1.333	44.2	0.4	212.0	12.9
2	0.01409	0.00080	0.02301	0.01235	30.515	0.128	0.000462	0.000026	26.323	0.262	86.3	2.1	264.9	2.6
3	0.00324	0.00011	0.00869	0.00173	25.859	0.028	0.000125	0.000004	24.870	0.042	96.3	16.6	251.2	1.0
4	0.00004	0.00008	0.00880	0.00105	25.111	0.022	0.000001	0.000003	25.070	0.032	100.0	24.1	253.1	1.0
5	0.00000	0.00025	0.00000	0.00370	25.355	0.057	0.000000	0.000010	25.324	0.092	100.0	5.9	255.5	1.3
6	0.00000	0.00005	0.00000	0.00130	24.333	0.063	0.000000	0.000002	24.302	0.064	100.0	19.4	245.8	1.1
7	0.00000	0.00009	0.04326	0.00238	24.860	0.076	0.000000	0.000003	24.833	0.080	100.0	11.1	250.8	1.2
8	0.00002	0.00016	0.06279	0.00504	25.049	0.065	0.000001	0.000006	25.017	0.080	100.0	7.1	252.6	1.2
9	0.00060	0.00011	0.04313	0.00221	25.637	0.084	0.000024	0.000004	25.430	0.089	99.3	12.5	256.5	1.2
10	0.01031	0.00222	0.00002	0.03348	29.105	0.286	0.000354	0.000076	26.027	0.703	89.5	0.7	262.1	6.7
11	0.15372	0.04647	0.00051	0.81978	74.242	8.578	0.002071	0.000581	28.787	13.197	38.8	0.0	287.8	121.9
	Sample	AS‐III‐O Bt		200–355 μm		12	Grain(s)				J‐value	0.00599	+/−	0.00002
1	0.08688	0.00338	0.20234	0.04018	43.077	0.292	0.002017	0.000077	17.387	0.995	40.4	0.4	178.8	9.8
2	0.02486	0.00152	0.11101	0.01532	32.960	0.177	0.000754	0.000046	25.592	0.468	77.7	0.9	257.3	4.5
3	0.00565	0.00025	0.02509	0.00234	25.929	0.054	0.000218	0.000010	24.232	0.090	93.6	6.6	244.5	1.2
4	0.00129	0.00007	0.01165	0.00090	25.598	0.046	0.000050	0.000003	25.187	0.050	98.5	15.9	253.5	1.0
5	0.00037	0.00005	0.00969	0.00062	24.534	0.036	0.000015	0.000002	24.394	0.038	99.6	20.7	246.1	0.9
6	0.00033	0.00070	0.02637	0.00651	26.881	0.241	0.000012	0.000026	26.754	0.317	99.6	1.7	268.2	3.1
7	0.00042	0.00007	0.02636	0.00118	24.500	0.034	0.000017	0.000003	24.347	0.039	99.5	12.6	245.6	0.9
8	0.00020	0.00005	0.01640	0.00086	24.292	0.045	0.000008	0.000002	24.204	0.048	99.8	18.0	244.3	0.9
9	0.00036	0.00006	0.01185	0.00142	25.070	0.049	0.000014	0.000002	24.935	0.051	99.6	13.8	251.2	1.0
10	0.00049	0.00028	0.01094	0.00611	24.639	0.069	0.000020	0.000011	24.463	0.107	99.4	3.3	246.7	1.3
11	0.00000	0.00022	0.00000	0.00596	25.156	0.050	0.000000	0.000009	25.124	0.083	100.0	3.5	252.9	1.2
12	0.00225	0.00030	0.00058	0.00750	25.267	0.079	0.000089	0.000012	24.571	0.117	97.4	2.5	247.7	1.4
	Sample	AS‐III‐Q Bt		160–200 μm		20	Grain(s)				J‐value	0.00600	+/−	0.00002
1	0.05800	0.00401	0.04703	0.07671	36.189	0.457	0.001603	0.000109	19.022	1.190	52.6	0.3	194.9	11.6
2	0.01329	0.00073	0.12659	0.01600	28.898	0.140	0.000460	0.000025	24.950	0.247	86.4	1.7	251.6	2.5
3	0.00183	0.00020	0.03441	0.00248	26.259	0.025	0.000070	0.000008	25.691	0.064	98.0	7.1	258.6	1.1
4	0.00128	0.00011	0.01632	0.00165	25.494	0.024	0.000050	0.000004	25.087	0.041	98.5	14.7	252.9	1.0
5	0.00000	0.00018	0.00000	0.00476	25.265	0.073	0.000000	0.000007	25.233	0.091	100.0	5.2	254.3	1.2
6	0.00062	0.00009	0.00931	0.00155	25.000	0.025	0.000025	0.000004	24.785	0.037	99.3	13.5	250.1	0.9
7	0.00070	0.00016	0.01288	0.00369	25.085	0.051	0.000028	0.000006	24.847	0.070	99.2	7.7	250.7	1.1
8	0.00000	0.00038	0.00000	0.00691	25.633	0.074	0.000000	0.000015	25.601	0.135	100.0	3.0	257.7	1.6
9	0.00009	0.00005	0.00955	0.00073	25.513	0.039	0.000004	0.000002	25.456	0.041	99.9	24.5	256.4	1.0
10	0.00009	0.00006	0.00551	0.00084	25.022	0.024	0.000004	0.000002	24.964	0.029	99.9	21.8	251.8	0.9
11	0.00116	0.00254	0.00000	0.02660	29.505	0.345	0.000039	0.000086	29.131	0.825	98.8	0.6	290.6	7.7
	Sample	AS‐IV‐E Bt		200–355 μm		7	Grain(s)				J‐value	0.00603	+/−	0.00003
1	0.03136	0.00239	0.10999	0.03731	29.557	0.282	0.001061	0.000080	20.269	0.729	68.6	0.4	208.1	7.1
2	0.00660	0.00025	0.28274	0.00338	27.621	0.118	0.000239	0.000009	25.662	0.133	93.0	4.1	259.7	1.6
3	0.00170	0.00010	0.00448	0.00136	25.268	0.044	0.000067	0.000004	24.735	0.053	98.0	9.5	250.9	1.1
4	0.00087	0.00009	0.00401	0.00167	24.944	0.042	0.000035	0.000004	24.654	0.050	99.0	11.3	250.1	1.1
5	0.00000	0.00004	0.00767	0.00106	24.844	0.029	0.000000	0.000002	24.813	0.032	100.0	12.6	251.6	1.0
6	0.00000	0.00009	0.02352	0.00129	24.694	0.044	0.000000	0.000004	24.664	0.051	100.0	12.6	250.2	1.1
7	0.00025	0.00008	0.00418	0.00128	24.897	0.027	0.000010	0.000003	24.793	0.035	99.7	12.0	251.5	1.0
8	0.02219	0.00028	0.00642	0.00206	31.236	0.051	0.000710	0.000009	24.649	0.094	79.0	6.0	250.1	1.3
9	0.00009	0.00007	0.01411	0.00075	25.019	0.043	0.000004	0.000003	24.961	0.048	99.9	19.1	253.0	1.1
10	0.00054	0.00038	0.00000	0.00410	25.136	0.076	0.000021	0.000015	24.946	0.135	99.4	3.0	252.9	1.6
11	0.00097	0.00072	0.00221	0.00989	26.096	0.082	0.000037	0.000028	25.779	0.228	98.9	1.3	260.8	2.4
12	0.00027	0.00012	0.00648	0.00151	25.139	0.024	0.000011	0.000005	25.029	0.044	99.7	8.6	253.7	1.1
	Sample	AS‐IV‐F Bt		200–355 μm		7 gr	Grain(s)				J‐value	0.00604	+/−	0.00003
1	0.21953	0.01357	0.25269	0.05442	86.966	1.578	0.002524	0.000150	22.084	3.872	25.4	0.2	225.9	37.2
2	0.02323	0.00141	0.20611	0.01442	30.461	0.181	0.000762	0.000046	23.583	0.438	77.5	1.3	240.3	4.3
3	0.00602	0.00020	0.03721	0.00289	26.381	0.038	0.000228	0.000007	24.572	0.068	93.3	7.9	249.7	1.2
4	0.00107	0.00004	0.01518	0.00097	25.403	0.041	0.000042	0.000001	25.057	0.042	98.8	21.5	254.3	1.1
5	0.00028	0.00003	0.01075	0.00088	25.236	0.048	0.000011	0.000001	25.123	0.049	99.7	20.8	254.9	1.1
6	0.00000	0.00027	0.00000	0.00253	26.079	0.066	0.000000	0.000010	26.047	0.105	100.0	5.2	263.6	1.4
7	0.00173	0.00096	0.01969	0.01356	26.189	0.115	0.000066	0.000037	25.646	0.306	98.0	1.1	259.9	3.1
8	0.00049	0.00004	0.01600	0.00054	24.844	0.031	0.000020	0.000002	24.669	0.033	99.4	30.0	250.6	1.0
9	0.00241	0.00042	0.03860	0.00651	25.812	0.086	0.000094	0.000016	25.071	0.151	97.2	3.1	254.4	1.7
10	0.00138	0.00034	0.01330	0.00580	25.850	0.078	0.000053	0.000013	25.411	0.127	98.4	2.8	257.6	1.6
11	0.00286	0.00027	0.00028	0.00238	26.113	0.050	0.000109	0.000010	25.238	0.092	96.8	6.1	256.0	1.3
	Sample	AS‐III‐F Bt		200–355 μm		10 gr	Grain(s)				J‐value	0.00598	+/−	0.00002
1	0.23620	0.01871	1.23490	0.21474	95.027	2.507	0.002486	0.000186	25.298	5.270	26.6	0.0	254.2	49.4
2	0.02723	0.00228	0.15918	0.03408	31.729	0.238	0.000858	0.000072	23.666	0.694	74.7	0.3	238.9	6.6
3	0.00795	0.00048	0.04228	0.00594	27.780	0.131	0.000286	0.000017	25.404	0.186	91.5	2.1	255.2	1.9
4	0.00131	0.00011	0.03115	0.00267	25.675	0.044	0.000051	0.000004	25.259	0.054	98.5	4.7	253.9	1.0
5	0.00090	0.00010	0.02356	0.00190	25.556	0.049	0.000035	0.000004	25.261	0.057	99.0	7.1	253.9	1.0
6	0.00061	0.00009	0.01457	0.00279	25.389	0.040	0.000024	0.000004	25.179	0.048	99.3	5.1	253.1	1.0
7	0.00027	0.00003	0.01983	0.00065	25.030	0.020	0.000011	0.000001	24.921	0.021	99.7	14.9	250.7	0.9
8	0.00030	0.00004	0.01691	0.00110	25.857	0.032	0.000012	0.000001	25.739	0.034	99.7	11.0	258.4	0.9
9	0.00024	0.00004	0.01252	0.00106	26.204	0.052	0.000009	0.000001	26.103	0.053	99.7	10.7	261.8	1.0
10	0.00011	0.00003	0.01919	0.00106	24.888	0.042	0.000005	0.000001	24.825	0.043	99.9	10.4	249.8	0.9
11	0.00024	0.00009	0.01123	0.00175	25.090	0.093	0.000010	0.000003	24.988	0.096	99.7	6.8	251.3	1.2
12	0.00000	0.00006	0.00000	0.00131	25.309	0.056	0.000000	0.000002	25.278	0.059	100.0	9.0	254.0	1.0
13	0.00020	0.00004	0.00850	0.00100	25.002	0.028	0.000008	0.000001	24.912	0.030	99.8	13.0	250.6	0.9
14	0.00054	0.00013	0.00791	0.00337	24.928	0.070	0.000022	0.000005	24.739	0.080	99.4	4.6	249.0	1.1
15	0.00910	0.00169	0.08404	0.05188	28.174	0.210	0.000323	0.000060	25.460	0.534	90.5	0.3	255.8	5.1
	Sample	AS-I-G Bt		200–250 μm		15	Grain(s)				J-value	0.00865	+/−	0.00002
1	0.02309	0.00211	0.15414	0.04438	20.757	0.130	0.001112	0.000102	13.921	0.630	67.1	0.9	205.1	8.8
2	0.00337	0.00009	−0.00944	−0.00186	17.351	0.030	0.000194	0.000005	16.331	0.038	94.2	15.4	238.4	0.7
3	0.00047	0.00007	−0.01591	−0.00173	17.169	0.030	0.000028	0.000004	17.005	0.037	99.2	11.8	247.6	0.7
4	0.00045	0.00003	0.00000	0.00063	17.703	0.022	0.000025	0.000002	17.548	0.023	99.3	42.8	255.0	0.6
5	0.00037	0.00009	−0.00486	−0.00262	17.718	0.044	0.000021	0.000005	17.583	0.051	99.4	13.0	255.4	0.9
6	0.00002	0.00005	0.00000	0.00135	18.120	0.031	0.000001	0.000003	18.089	0.033	100.0	14.2	262.3	0.7
7	0.00065	0.00026	0.00003	0.00490	18.304	0.052	0.000035	0.000014	18.088	0.093	99.0	3.9	262.3	1.4
	Sample	AS-I-H Bt		200–250 μm		15	Grain(s)				J-value	0.00864	+/−	0.00002
1	0.02631	0.00169	0.11229	0.04761	20.032	0.165	0.001313	0.000084	12.242	0.508	61.2	0.4	181.3	7.2
2	0.00908	0.00091	0.13768	0.01598	18.217	0.156	0.000499	0.000050	15.519	0.300	85.3	0.8	226.9	4.1
3	0.00893	0.00167	0.08547	0.05445	19.587	0.248	0.000456	0.000085	16.930	0.538	86.5	0.3	246.2	7.3
4	0.00292	0.00007	0.02675	0.00095	16.218	0.093	0.000180	0.000004	15.332	0.093	94.7	18.1	224.3	1.4
5	0.00085	0.00014	0.00012	0.00134	18.052	0.033	0.000047	0.000008	17.776	0.054	98.6	6.6	257.6	0.9
6	0.27420	0.00916	0.19712	0.05874	98.758	1.623	0.002776	0.000081	17.723	2.384	17.9	0.2	256.9	32.2
7	0.00046	0.00003	0.00215	0.00043	18.917	0.036	0.000024	0.000002	18.758	0.037	99.3	26.4	270.9	0.7
8	0.00041	0.00007	0.00001	0.00063	17.925	0.020	0.000023	0.000004	17.779	0.028	99.3	14.0	257.7	0.6
9	0.00000	0.00007	0.00001	0.00102	18.209	0.029	0.000000	0.000004	18.185	0.035	100.0	8.5	263.1	0.7
10	0.00010	0.00008	0.00001	0.00107	18.250	0.044	0.000005	0.000004	18.197	0.050	99.8	8.2	263.3	0.9
11	0.00000	0.00004	0.00016	0.00092	18.001	0.051	0.000000	0.000002	17.977	0.052	100.0	15.3	260.3	0.9
12	0.00074	0.00035	0.00942	0.00812	18.429	0.047	0.000040	0.000019	18.187	0.113	98.8	2.0	263.2	1.6
	Sample	AS-III-W Bt		200–250 μm		12	Grain(s)				J-value	0.00861	+/−	0.00002
1	0.04278	0.00267	0.22664	0.03703	25.491	0.263	0.001678	0.000103	12.842	0.791	50.4	0.7	189.1	11.1
2	0.00002	0.01526	1.41005	0.23992	20.838	1.028	0.000001	0.000732	20.921	4.629	100.4	0.1	298.7	60.9
3	0.00870	0.00042	0.00028	0.00524	20.107	0.063	0.000433	0.000021	17.512	0.137	87.2	4.7	253.3	1.9
4	0.00123	0.00008	0.03380	0.00103	17.800	0.023	0.000069	0.000005	17.415	0.033	98.0	22.3	252.0	0.7
5	0.00003	0.00070	0.00002	0.01329	17.574	0.082	0.000002	0.000040	17.541	0.222	99.9	2.1	253.7	3.0
6	0.00003	0.00090	0.00279	0.01725	18.092	0.135	0.000001	0.000050	18.061	0.299	100.0	1.7	260.7	4.0
7	0.00004	0.00099	0.00069	0.01882	17.853	0.101	0.000002	0.000055	17.817	0.309	99.9	1.5	257.4	4.2
8	0.00002	0.00040	0.07182	0.00704	17.849	0.041	0.000001	0.000023	17.825	0.126	100.0	3.7	257.5	1.8
9	0.00072	0.00028	0.04150	0.00455	17.574	0.030	0.000041	0.000016	17.340	0.088	98.8	7.7	250.9	1.3
10	0.00013	0.00004	0.02817	0.00073	17.995	0.040	0.000007	0.000002	17.934	0.042	99.8	44.5	259.0	0.8
11	0.00000	0.00027	0.00001	0.00317	18.666	0.097	0.000000	0.000014	18.642	0.125	100.0	9.7	268.4	1.8
12	0.00623	0.00213	0.00029	0.02969	18.830	0.168	0.000331	0.000113	16.964	0.647	90.2	1.0	245.9	8.8
13	0.00860	0.00374	0.00056	0.05681	18.851	0.212	0.000456	0.000198	16.287	1.119	86.5	0.5	236.7	15.3

Fig. 8

40Ar/39Ar release pattern of white mica from metamorphic rocks (samples II-A and III-T). Laser energy increases from left to right (FSA — first step age, MA — mean age, SSA — single step age).

Fig. 9

40Ar/39Ar release pattern of biotite from magmatic rocks (samples III-T, III-O, III-Q, IV-E, IV-F, III-F, I-G, I-H and III-W). Laser energy increases from left to right (FSA = first step age, MA = mean age, PA = plateau age, o.SSA = older single step age, y.SSA = younger single step age).

40Ar/39Ar ages of the meta-psammitic schist

The white mica concentrate (10 grains, grain size 200–250 μm) of sample II-A (Fig. 8), a banded meta-psammitic schist, yields a highly disturbed staircase-type age pattern. The first meaningful step (step 2) yields an age of 251.0 ± 13.6 Ma. Steps 4–13 vary in age between 331.7 and 397.1 Ma and the mean age of steps 2–12 is 376.3 ± 9.7 Ma. Step 5 includes 33.0% of 39Ar and yields an apparent age of 378.4 ± 0.9 Ma. We interpret this best age step as geologically significant for dating the approximate age of white mica growth during a thermal event of the Variscan orogeny. We also think that the age of step 2 of 251.0 ± 13.6 Ma represents a geological event likely due to a low-temperature thermal overprint (according to models reviewed in Villa, 1998).

40Ar/39Ar ages of the meta-doleritic blueschists and the meta-dolerites

The white mica concentrate (7 grains, grain size 160–355 μm, mainly at lower size limit) of sample III-T (Fig. 8), a meta-doleritic blueschist, yields a highly disturbed staircase-type age pattern. The first step yields an age of 261.5 ± 4.5 Ma. Steps 2–8 vary in age between 341.6 and 382.7 Ma. The mean age of steps 2–7 is 349 ± 15 Ma. Despite the large scatter, we also interpret this mean age as geologically significant, and as suitable to date the approximate age of white mica growth during a thermal event of the Variscan orogeny. As thin section observations reveal, this thermal event likely resulted in the decomposition of feldspar to a mixture of carbonate and white mica.

We think that the first step age of III-T of 261.5 ± 4.5 Ma, as well as the age of step 2 of sample II-A of 251.0 ± 13.6 Ma, represents a significant geological event dating the age of cooling through the argon retention temperature in white mica at ca. 425 ± 25 °C (Harrison et al., 2009). Both ages lie within error close to the Permian-Triassic-boundary (like all of the biotite-mean ages, see below).

We dated biotite from two further meta-dolerite blueschist samples (Fig. 9). The first step of the biotite concentrate of sample III-T (Fig. 9) (10 grains, grain size 160–355 μm, mainly at lower size limit) yields an age of 212 ± 12.9 Ma. Steps 2–11 vary in age between 245.8 and 287.8 Ma. The mean age of steps 2–11 is 252.3 ± 3.1 Ma. The isochron age is 253.5 ± 8.0 Ma. We interpret, therefore, the mean age of 252.3 ± 3.1 Ma as geologically significant and as the age of reheating and subsequent cooling through the appropriate argon retention temperature of biotite at ca. 300 °C.

The first step of the biotite concentrate of sample III-O (12 grains, grain size 200–355 μm, mainly at lower size limit) yields an age of 178.8 ± 9.8 Ma. Steps 2–12 vary in age between 244.3 and 257.3 Ma. The mean age of steps 2–12 is 248.3 ± 2.9 Ma (MSWD = 14). The isochron age is 251.5 ± 6.6 Ma. The first step of the biotite concentrate of sample III-Q (20 grains, grain size 160–200 μm) yields an age of 194.9 ± 11.6 Ma. Steps 2–11 vary in age between 290.6 and 250.1 Ma. The mean age of steps 2–10 is 253.6 ± 2.9 Ma (MSWD = 7.9) and the isochron age is 258.3 ± 9.2 Ma. In both cases, we consider the mean ages as geologically significant and as the age of reheating or cooling through the appropriate argon retention temperature in biotite, ca. 300 °C.

Furthermore, we dated three biotite concentrates of meta-dolerite samples. The biotite concentrate of sample I-G (Fig. 9) (15 grains, grain size 200–250 μm), a meta-syenite, yields a highly disturbed staircase-type age pattern. The first meaningful step (step 1) yields an age of 205.1 ± 8.8 Ma. Steps 2–7 vary in age between 238.4 and 262.3 Ma, showing a continuous increase in age from steps 2–7. We consider the last two steps 6 and 7 with an apparent age of 263.3 ± 0.7 Ma as geologically significant.

The biotite concentrate of the meta-dolerite sample I-H (Fig. 9) (15 grains, grain size 200–250 μm) also yields a highly disturbed staircase-type age pattern. The first step yields an age of 181.3 ± 7.2 Ma. Steps 2–12 vary in age between 224.3 and 270.9 Ma. Due to the large scatter, we suggest that this sample comprises two different biotite populations and that it has probably also been overprinted by a secondary thermal event. While the older biotite population (older single step age — o. SSA in Fig. 9) is represented by step 7 and an age of 270.9 ± 0.7 Ma the younger one (younger single step age — y.SSA in Fig. 9) yields an age of 263.1 ± 0.7 Ma (step 9).

The biotite concentrate of sample III-W (Fig. 9) (12 grains, grain size 200–250 μm), a biotite-rich meta-dolerite, yields a highly disturbed staircase-type age pattern. The first step of the biotite concentrate yields an age of 189.1 ± 11.1 Ma. Steps 2–13 vary in age between 298.7 and 236.7 Ma. The mean age of steps 1–13 is 254.9 ± 2.9 Ma. Because of the large variance in age, we think that this biotite concentrate is not uniform and comprises two different age populations. The older one (older single step age — o. SSA: Fig. 9), which is represented best by step 10, yields an age of 259.0 ± 0.8 Ma. The younger one (younger single step age — y. SSA in Fig. 9) is dated by step 4 with an age of 252.0 ± 0.7 Ma.

40Ar/39Ar ages of the biotite–diorites

We dated three biotite concentrates from biotite–diorite samples. The first step of the biotite concentrate from sample IV-E (7 grains, grain size 200–355 μm) yields an age of 208.1 ± 7.1 Ma. Steps 2–12 vary in age between 250.1 and 260.8 Ma. The mean age of steps 2–12 is 252.2 ± 1.8 Ma. The plateau age (Fig. 9) is 251.2 ± 1.1 Ma (including 85.6% of 39Ar released). The isochron age is 254.1 ± 6.3 Ma, within error similar to the plateau age. We consider, therefore, the plateau age as geologically significant and as the age of cooling through the appropriate argon retention temperature in biotite at ca. 300 °C. The first step of the biotite concentrate of sample IV-F (Fig. 9) (7 grains, grain size 200–355 μm) yields an age of 225.9 ± 37.2 Ma. Steps 2–11 vary in age between 240.3 and 263.6 Ma. The mean age of steps 2–11 is 254.4 ± 3.1 Ma. The isochron age is 255.2 ± 4.3 Ma. The initial 40Ar/36Ar value is 278 ± 18. Steps 1–15 of the biotite concentrate from sample III-F (Fig. 9) (10 grains, grain size 200–355 μm) exhibit some scatter and steps vary in age between 238.9 and 261.8 Ma. The mean age of steps 1–15 is 253.4 ± 2.1 Ma. The isochron age is 253.1 ± 3.2 Ma with an initial 40Ar/36Ar value of 291 ± 16. We consider, therefore, the isochron ages of both samples as geologically significant and as the age of cooling through the appropriate argon retention temperature in biotite.

In summary, the mean biotite ages of all biotite, well-preserved biotite–diorites and meta-dolerites are similar, within error, and date the age of cooling through the argon retention temperature in biotite at ca. 300 °C. This is an important, hitherto undetected geological event within the Haselgebirge unit. Furthermore, nearly all biotites have a lower age in the first step representing the maximum age of a secondary thermal and/or hydrothermal overprint.

Discussion

In this chapter, the origin and age of magmatic and metamorphic blocks encased within the gypsum breccia of Moosegg quarry is discussed in a wider context.

Origin of magmatic rocks

The geochemical analyses of plutonic and subvolcanic inclusions (meta-dolerites, meta-doleritic blueschists and biotite–diorites) show different tectonic and geochemical settings. Both the meta-doleritic blueschists and the biotite–diorites are considered to derive from a primitive mantle melt. The ultramafitites represent a cumulate, which was probably developed by extraction of melt leading to the future meta-doleritic blueschist. In rare earth elements and multi-element variation diagrams, the meta-doleritic blueschist show typical MORB patterns with an affinity to N-MOR basalts.

According to their origin in alkaline series, the meta-dolerites and meta-syenites show typical patterns of melts which formed by low-volume mantle melts within a rift zone. The biotite–diorites descend from the alkaline milieu of a shallow magma chamber without any influence of a subduction zone. This is also supported by the presence of the Ti-rich amphibole (kaersutite) and augite. We presume that the meta-dolerites, meta-syenites and biotite–diorites together indicate a rift sequence.

As no zircons have been found, the protolith ages unfortunately remain unknown, but are older than the biotite and white mica ages discussed below. Scarce occurrences of mafic volcanic rocks of alkaline affinity were described from the uppermost Permian–Lower Triassic Haselgebirge Formation and the Lower Triassic Werfen Formation (Gruber et al., 1991, Kirchner, 1979, Kirchner, 1980a, Kralik et al., 1984, Zirkl, 1957). All these occur as tectonic lenses within these formations, and no ages on protolith formation have been published. The occurrence of the Grundlsee seems to be in a primary relationship to the Haselgebirge Formation. We tentatively correlate the blocks of the plutonic suite (gabbro, syenite) with these basaltic rocks. However, more work is needed to strengthen these correlations. Note that no such Upper Permian–Lower Triassic magmatism was found up until now within Austroalpine units of Eastern Alps.

Interpretation of the 40Ar/39Ar age dating results

We dated a few white micas from metamorphic rocks and mainly biotite from biotite–diorite, meta-dolerite and meta-doleritic blueschist samples. We consider plateau respectively mean ages and the low-temperature overprint (mainly of the first step). Four different tectonic events could be derived from age dating of biotite and white mica concentrates (Fig. 10).

Fig. 10

Diagram showing the 40Ar/39Ar ages of all samples and their interpretation. For explanation, see text.

Variscan high-pressure metamorphism: The apparent ages of white mica growth of the meta-doleritic blueschist III-T (349 ± 15 Ma) and the banded meta-psammitic schist II-A (378.4 ± 0.9 Ma) indicate two different thermal events during the Variscian orogeny. As thin section observations reveal, the thermal event of the meta-doleritic blueschist (III-T) (349 ± 15 Ma) resulted from the likely decomposition of feldspar to a mixture of carbonate and white mica under static conditions (Fig. 5c). In contrast, white mica in the banded meta-psammitic schist sample II-A with the age of 378.4 ± 0.9 Ma grew along the foliation plane during a syntectonic metamorphic event (Fig. 4e).

The meta-doleritic blueschists probably formed during Variscan high-pressure metamorphism. The metamorphism of the banded meta-psammitic schist probably also occurred within a subduction zone. The Moosegg quarry comprises one of the rare outcrops of metamorphic Variscan basement in the Eastern Alps with an age of ca. 380 Ma. They are only found in the Wechsel complex (Müller et al., 1999), and the Kaintaleck complex of the Greywacke zone (Dallmeyer et al., 1998, Handler et al., 1999, Neubauer et al., 2002), the latter also representing the basement unit of major portions of the NCA. However, the lithology of the banded meta-psammite is entirely unknown both in the Kaintaleck and Wechsel complexes. Consequently, we argue for a hitherto unknown source–sink relationship between the Rossfeld Formations in the footwall and the Haselgebirge nappe in the hangingwall (see below). Interestingly, an amphibolite-grade Variscan metamorphic complex overprinted by Jurassic blueschist facies metamorphism is known from the Meliata unit of the Western Carpathians (in the north-eastern extension of Eastern Alps). The 40Ar/39Ar white mica ages in that unit range from 416 ± 6 Ma to 348 ± 3 Ma and peak amphibolite conditions are assumed between 379 and 370 Ma (Faryad and Frank, 2011, Faryad and Henjes-Kunst, 1997). The 40Ar/39Ar age range of white micas and the textural relationships of metamorphic mineral assemblages are similar to the banded meta-psammitic schist and meta-doleritic blueschist. These observations suggest a wide regional distribution of such an Early Variscan tectonic unit poorly known in the present basement of Eastern Alps and Western Carpathians.

Cooling after crystallisation within the rift zone: We dated biotite concentrates from several samples of biotite–diorites, meta-dolerites and meta-doleritic blueschists. In summary, the biotite ages of all biotites of biotite–diorite, meta-dolerite and meta-doleritic blueschist including a plateau age of 251.2 ± 1.1 Ma are similar within error and date the age of cooling through the argon retention temperature in biotite at ca. 300 °C (McDougall and Harrison, 1999). This important hitherto undetected geological event at the Permian-Triassic boundary probably represents the cooling after intrusion of magmatic rocks during a rifting event (Fig. 11a). We propose an asymmetric rift setting in the Late Permian (Fig. 11a) with a principally ductile low-angle normal fault cutting through the whole lithosphere. This resulted in the following outcome, which fits with the new observations. The initial rift resulted in the formation of halfgrabens, which are filled by clastic sediments exposed along the present-day southern margin of the NCA. We interpret this stage as the synrift phase. In an advanced stage of rifting, mantle melts were produced through an uprise of an asymmetric asthenospheric dome, which shifted towards the upper plate. A few gabbroic bodies intruded into a high level of the crust and a few volcanic successions are known, specifically from the eastern Salzkammergut area (e. g., Grundlsee; Kirchner, 1979, Vozárová et al., 1999). These volcanic rocks are in direct contact with the Haselgebirge Formation, which argues for an emplacement during the deposition of the evaporites. We interpret the time of deposition of the Haselgebirge as the post-rift phase. Internally consistent ages strongly argue for a thermal event during the late Permian and subsequent cooling at ca. the Permian/Triassic boundary. Such plutonic rocks and such a thermal event have never been described before as all dated magmatic rocks are significantly older, ca. 260–270 Ma (Thöni, 2006), than the Permian/Triassic boundary . Note however, that Permian cooling after a thermal event is widespread within the Austroalpine unit of the Eastern Alps (Liu et al., 2001, Schuster and Stüwe, 2008, Schuster et al., 2001) and Lower Permian granitic and gabbroic magmatism and even Middle Triassic granitic magmatism is also well documented (Bole et al., 2001, Schuster and Stüwe, 2008; Thöni, 2006 and references therein).

Fig. 11

Tectonic models for two steps of the tectonic evolution of the Austroalpine unit of Eastern Alps. (a) Model of an asymmetric rift setting during Upper Permian. (b) Tectonic model of the evolution of the Haselgebirge nappe (modified after Schorn and Neubauer, 2011).

Maximum age of Alpine low-temperature thermal overprint: In several samples, although the analytical error is large in each example, we found evidence for a low-temperature overprint in biotite. The Ar retention temperature of biotite is considered to be approximately 300 ± 25 °C (McDougall and Harrison, 1999). Nearly all biotites have a lower age in the first step, representing the maximum age of a secondary thermal and/or hydrothermal overprint. This event has to be younger than 178.8 Ma (± 9.8 Ma), and the temperature of this overprint should be between approximately 250 and 300 °C. Two stages of such very low-grade metamorphic events were found within the sedimentary successions of the Haselgebirge Formation and the structural base of the NCA up until now (Table 1). These include an event at ca. 140–145 Ma at the Jurassic/Cretaceous boundary (e.g., Spötl et al., 1996), particularly well constrained by authigenic growth of K-feldspar. A second, also well constrained age group includes ages of 115–105 Ma representing metamorphic growth of minerals like white mica (Frank and Schlager, 2006). We suggest that the argon loss in all our biotite concentrates is the result of the combined effects of these two low-temperature overprints, which was not sufficient to fully reset the Ar ages of biotite. We tentatively relate the final thermal overprint of the Haselgebirge to the Lower Cretaceous emplacement of the Haselgebirge-bearing nappe over the underlying Upper Rossfeld Formations within ductile conditions. This disproves previous models of purely gravity-driven emplacement of the Haselgebirge-bearing nappe during Jurassic times (for details, see Schorn, 2010; Schorn and Neubauer, 2011).

Origin of detrital white mica in the Rossfeld Formations

After von Eynatten et al. (1996), detrital white mica samples of the overthrusted Rossfeld Formations show a Variscan age of approximately 350 Ma and white mica grains of this age population are associated with bluish amphibole (von Eynatten and Gaupp, 1999). Our ages demonstrate a close relationship between ages of detrital white mica in the Rossfeld Formations and the metamorphic blocks in the Haselgebirge Formation. We interpret, therefore, the origin of Variscan detrital white mica within the base of the Haselgebirge nappe (Fig. 11b). Furthermore, they feature the Na-amphibole riebeckite, which was also encountered in some dark anhydrites of level III of the Moosegg quarry (for example samples III-C and III-D). Von Eynatten et al. (1996) also found Na-amphibole associated with their Variscan-aged detrital white mica within the Rossfeld Formations. The source–sink relationship between the Haselgebirge Formation and the Lower Cretaceous Rossfeld Formations provides evidence for a close paleogeographic relationship of these units during the Early Cretaceous. Based on the presence of mylonitic fabrics within evaporites at the base of the Haselgebirge-bearing nappe (Lower Juvavic nappe), Schorn and Neubauer (2011) argued for early Late Cretaceous emplacement of this nappe over the Lower Cretaceous Rossfeld Formations.

These facts indicate that the rocks of the Haselgebirge tectonic mélange, including detrital white micas, were eroded and later deposited in the Rossfeld flexure basin at the thrust front of the Lower Juvavic nappe (Fig. 11b). Our new data contribute this particular evidence for this model.

The greywackes, pelagic limestones and red and green claystones surely represent an abyssal depositional milieu. During the Haselgebirge thrust faulting, they could have been detached from the underlying Meliata oceanic crust and reincorporated by the tectonic mélange of the overriding Haselgebirge nappe. The possible Meliata ocean origin of these rocks has not been examined in the course of our studies but it could be subject of further work.

Conclusions

The new data from magmatic blocks add new significant constraints to the long-lasting discussion on the rifting stage of the Middle Triassic Meliata oceanic tract and paleogeographic relationships of tectonic units of Australpine domain in the Eastern Alps.

For the first time, plutonic and subvolcanic rocks and rare metamorphics were found in the Upper Permian to Lower Triassic Haselgebirge Formation.

Abundant biotite–diorite and meta-syenite of an alkaline magmatic suite are likely related to rare basaltic rocks found elsewhere, and indicate a rift-related magmatic suite.

Meta-dolerites, rare ultramafic rocks (serpentinite, pyroxenite) and meta-doleritic blueschists indicate a second source. The scattered 40Ar/39Ar white mica ages of a meta-doleritic blueschist (of N-MORB origin) and banded meta-psammitic schist are at ca. 349 and 378 Ma, respectively proving the Variscan age of pressure-dominated metamorphism, and, therefore, a pre-Alpine magmatic suite.

The 40Ar/39Ar biotite ages from three biotite–diorite, meta-dolerite and meta-doleritic blueschist samples with variable composition and fabrics range from 248 to 270 Ma (e.g., 251.2 ± 1.1 Ma) indicating a Permian age of cooling after magma crystallisation or metamorphism.

The 40Ar/39Ar ages of the banded meta-psammitic schist are similar to detrital white mica ages reported from the underlying Rossfeld Formations indicating a close source–sink relationship between the overlying Haselgebirge-bearing nappe and the Lower Cretaceous Rossfeld Formations.

Ar loss in dated biotites is related to a low-temperature overprint during Lower Cretaceous emplacement of the Haselgebirge-bearing nappe over the Lower Cretaceous Rossfeld Formations.