Metamorphic Conditions of Neotethyan Meliatic Accretionary Wedge Estimated by Thermodynamic Modelling and Geothermobarometry (Inner Western Carpathians)

Abstract

Metamorphic evolution of an accretionary wedge can be constrained by a reconstructed P–T conditions of the oceanic and continental margin fragments. This paper deals with the metamorphic overprinting of the Inner Western Carpathians (IWC) Meliatic Triassic–Jurassic paleotectonic units after the closure of the Neotethyan Meliata Basin. Medium to high-pressure and lower temperature conditions were estimated by Perple_X pseudosection modelling, combined with garnet–phengite, calcite–dolomite and chlorite thermometers and chlorite–phengite and phengite barometers. The Late Jurassic subductional burial to a maximum 50 km depth was estimated from the Bôrka Unit continental margin fragments at 520 °C and 1.55 GPa. This is compatible with the metamorphic peak garnet–glaucophane–phengite assemblage of blueschist facies in metabasites. The Jaklovce Unit oceanic fragments were subducted to maximum 35–40 km at 390–420 °C and 1.1–1.3 GPa. Metabasalts and metadolerites contain winchite, riebeckite, actinolite, chlorite, albite, epidote and phengite. A glaucophane-bearing metabasalt recorded an intra-oceanic subduction in blueschist-facies conditions. Rare amphibolite-facies metabasalts of this unit indicate the base of an inferred oceanic crust sliver obducted onto the continental margin wedge. The Meliata Unit oceanic/continental margin flysch calciclastic and siliciclastic metasediments suggest the burial to approximately 15–20 km at 250–350 °C and 0.4–0.6 GPa. This is indicated by a newly formed albite, K-feldspar, illite–phengite and chlorite associated with quartz and/or calcite and dolomite in these rocks. Magnesio-hastingsite to magnesio-hornblende bearing metagabbro with newly formed metamorphic magnesio-riebeckite and actinolite is an inferred detached Meliatic block tectonically emplaced in a Permian salinar mélange in the Silica Nappe hanging wall. Reconstructed P–T paths indicate variable metamorphic conditions from the medium-pressure to high-pressure subduction of the Bôrka and Jaklovce units to the Meliata Unit shallow burial in an accretionary wedge during Late Jurassic to Early Cretaceous Meliaticum evolution. Mélange blocks of Meliaticum incorporate different juxtaposed Meliatic paleotectonic units exposed in nappe outliers overlying the IWC Gemeric and Veporic superunits.

1. Introduction

The subduction-related accretionary wedges [1] have variable metamorphic P–T conditions of the oceanic and continental margin fragments [2,3,4,5,6,7]. Therefore, the high-pressure rocks in orogenic belts are reliable markers of paleosubduction zones. Reconstructed P–T conditions provide useful information on the burial depths of the original paleotectonic units in an accretionary wedge.

The Meliatic Superunit, or Meliaticum, of the Inner Western Carpathians (IWC; Figure 1) originated in a NW Neotethys oceanic and continental margin [8,9,10,11,12,13,14,15,16,17] as an embayment separating the Eurasian and Gondwanian parts of Pangea [13,17,18,19,20,21]. Some authors reported that the Meliata Basin is a back-arc basin above a Paleotethys subduction zone [19,22,23,24]. The Meliaticum mélange blocks record a closure of the Neotethyan Middle Triassic to Late Jurassic Meliatic Basin due to the subduction of its oceanic and continental margin crust during the Late Jurassic [8,11,12,13,14,15,16]. Hence, the Meliaticum occurs in the form of exhumed kilometre-size blocks overlying the inferred Gemericum northern continental margin (Figure 2). This implies a breakdown of the Meliatic Late Jurassic–Early Cretaceous subduction-related accretionary wedge during the Cretaceous orogenic processes; a transformation model to an orogenic wedge was proposed by [15].

Equilibrium thermodynamics has proven powerful in geology in recent decades. Thermobarometers are progressively accompanied by thermodynamic modelling [26,27,28,29,30,31]. These techniques had a great impact on petrological studies even when samples were only partly equilibrated [32]. Widely used sets of activity–composition (a–x) relationships originally included those developed for metapelitic or ultramafic rock modelling based on Holland and Powell datasets [28,33,34,35,36].

However, it remained difficult to model in metabasic lithologies because of the lack of the a–x relationships suitable for modelling partial melting equilibria in metabasic rocks. The metabasite set is a part of the new HPx-eos thermodynamic models introduced in 2016 [37]. It has since been used and tested by several authors, e.g., [38,39,40,41]. Thermobarometry is very challenging, and a special Chlorite–Mica database was developed for low-grade metamorphic rocks lacking indexing minerals [42,43,44]. This was mostly used as a chlorite thermometer which enabled XFe³⁺Chl estimation at fixed pressure [43,45,46]. A similar approach was employed by [47] for K-white mica thermobarometry. This enabled P–T derivation by combining the Chl-Qtz-H₂O thermometer and K-white mica Qtz-H₂O barometer [43].

This paper collects new results from the assessment of P–T data from the Meliaticum using Perple_X pseudosection modelling and geothermobarometry methods. The main issue herein is to test the new evolutionary model of Meliaticum proposed by [48] and define the metamorphic overprinting grade of Meliatic paleotectonic units incorporated in the Neotethyan Late Jurassic–Early Cretaceous accretionary wedge. The applied methods determined the precise metamorphic conditions of Meliaticum, despite this unit being incorporated in the Cretaceous orogenic wedge of the IWC.

2. Geological Setting and Review of Previous Results

Meliaticum was traditionally subdivided into the unsubducted Meliata and subducted Bôrka units [8,9,11,15,51,52,53,54,55]. The Meliatic Superunit (~Meliaticum) comprises, however, three principal paleotectonic units. These are the Bôrka Unit derived from the continental margin, the transitional Meliata Unit and the Jaklovce Unit oceanic margin crust [48].

2.1. Lithostratigraphy and Geochemistry

The Bôrka Unit (Figure 2 and Figure 3) was defined as the Meliatic continental margin composed of a deeper shelf to slope facies of Middle to Upper Triassic/Lower Jurassic carbonatic and siliciclastic sediments interlayered with calc-alkaline basalts. The age of carbonates was confirmed by conodonts [11]. These are overlying the Permian–Lower Triassic siliciclastics associated with trachyrhyolites, trachyandesites, calc-alkaline rhyolites, dacites, and basalts developed on the Early Paleozoic (Gemeric type) basement rocks [8,9,10,12,25,51,53]. Metamorphosed rocks of this succession are incorporated in the Bôrka Nappe [25,51,56].

The Meliata Unit s.s. (Figure 4) was defined as a Middle Jurassic deep-water turbiditic siliciclastic to cherty succession interlayered with radiolarites [9]. This contains olistoliths of the Middle to Upper Triassic continental margin carbonates, rare mid-Triassic radiolarites [57] and OIB-type metabasalts [48] which build the Jurassic olistostromatic formations near Meliata and Čoltovo villages [9,52,58,59]. We recommended the use of the Meliata Unit for this part of Meliaticum and other equivalent remnants of sedimentary olistostromatic formations, where the metamorphic overprinting of the sedimentary matrix and olitoliths is nearly the same (see Section 2.2).

Quite different turbiditic sediments occur at Dobšiná and Jaklovce (Figure 3 and Figure 5), where the carbonatic clastogeneous material (Cal, ±Dol) clearly predominates an admixture of the siliciclastic one (Qtz, Ms, Chl). Due to tradition, we call both types of turbiditic sediments as siliciclastic or calciclastic flysch, respectively [48], also in this paper.

The Jaklovce Unit (Figure 5) is the most characteristic oceanic or ophiolitic sedimentary–magmatic succession of the Meliaticum composed of pelagic cherty sediments to radiolarites, N-MORBs and rare alkaline OIBs associated with serpentinised and rodingitised, mostly abyssal harzburgitic, mantle fragments [9,11,14,15,53,60,61,62]. The oceanic Jaklovce Succession was more precisely defined using our new biostratigraphic data from radiolarites and cherty carbonates which distinguished the Lower (Ladinian), Middle, and Upper (Carnian to Norian?) Beds [48]. The SIMS U/Pb detrital Zrn ages from pelagic sediments revealed Permian and Anisian magmatic zircon sources from a destructed continental margin [48]. Therefore, we recommended the use of the Jaklovce Unit for this unique oceanic, despite the incomplete ophiolitic paleotectonic Meliatic domain [48].

In addition to Triassic carbonates, the MOR type basalts and mid-Triassic radiolarites were considered to be large olistoliths in the Jaklovce Jurassic olistostromatic formation [11,12]. However, the grade of metamorphic overprinting of the inferred flysch matrix and the Middle to Upper Triassic olistoliths strongly differs ([48]; see Section 2.2). This does not match the Meliata Unit s.s. at the Meliata village type locality which contains pre-metamorphic Triassic olistoliths in the Jurassic flysch. Therefore, we acknowledge an accretionary wedge mélange at Jaklovce rather than an olistostromatic formation. Meta-ophiolitic fragments of the Jaklovce Unit achieved a variable degree of MP to HP/LT metamorphic overprinting which clearly occurred before they were tectonically juxtaposed with the Jurassic flysch VLT–LT/LP metasediments in the mélange [48]. The Jaklovce Unit typically occurs around the Jaklovce village, but also as a mélange block south of Dobšiná town (Figure 3 and Figure 5).

2.2. Metamorphism

The Bôrka Nappe metabasites [63,64,65,66] underwent boundary greenschist to epidote-blueschists P–T conditions at 380–460 °C and 1.0–1.3 GPa. Similar P–T estimates at 400–460 °C and 1.05–1.2 GPa or 360–400 °C at 0.8 GPa were reported for glaucophane, pyroxene and chloritoid-bearing metapelitic to metapsammitic rocks [67]. These estimates are based on equilibrium conditions and calculations by using the Geo-Calc and Thermo-Calc software packages [68,69,70].

Further petrological and mineral chemistry study enabled to estimate P–T conditions from basal parts of the Bôrka Nappe in a quantitative phase diagram (PT pseudosections) contoured by mineral composition, H₂O mode isopleths, and with garnet–phengite thermometry [71]. The pseudosection modelling in Thermo-Calc software [72] estimated peak blueschist-facies conditions at 520–620 °C and 1.1–1.4 GPa [71].

The 600 MPa pressure was estimated by [73] for Mrb, Fwn in Jaklovce MORB-type metabasalts [13,60] by the empiric geobarometer Al^IV vs. Na^B of [74].

The Meliata Unit s.s. has a relatively weaker metamorphic overprinting at approximately 250–350 °C and 350–540 MPa according to Kübler´s index and chlorite–phengite geothermobarometry [54].

The oceanic slivers of the inferred Meliaticum in northeastern Hungary are embedded in Permian sediments of Perkupa Formation at the base of the Silica Nappe (Figure 2). These Bódva Valley ophiolitic metagabbros provided minimum pressures of 700–800 MPa at 350–500 °C and almost isothermal decompression of 400–600 MPa in the greenschist facies. The following metamorphic event in the albite–epidote–amphibolite facies was characterised by a temperature increase up to 500–600 °C in isobaric conditions [75,76]. Similar fragments of serpentinites, as well as gabbroic and doleritic rocks embedded in Permian salinar formation of the Silica Nappe hanging wall, were found in the Držkovce (DRŽ-1) borehole and in the area of Bohúňovo and Gemerská Hôrka areas in Slovakia (Figure 2) [77].

2.3. Tectonic Evolution and Geochronology

The Meliata Ocean closure and subduction of the continental and inferred oceanic crust was constrained in Bôrka Nappe to 160–150 Ma by ⁴⁰Ar–³⁹Ar [78,79,80,81,82] and K–Ar 155–152 Ma ages [82] of “phengitic” white micas from blueschist facies rocks. The Meliata Unit s.s. metasediments in Meliata village area have younger ⁴⁰Ar–³⁹Ar ages than the Bôrka Unit at 150–115 Ma [54,78,79,80,81,82] following the accretionary wedge formation between ca. 150 and 130 Ma. The exhumation stage at approximately 135 Ma was determined by U–Pb dating of metamorphic–metasomatic perovskite in serpentinised and rodingitised harzburgites [62,83]. This age is consistent with the EPMA Mnz age from the underlying South-Gemeric Unit [84] and indicates the overloading of the Gemeric Superunit with the exhumed Meliatic accretionary wedge [15]. The (U–Th)/He zircon ages (ZHe) from the Meliata Unit fragments document the polystage low-temperature thermal history of the Meliatic accretionary wedge during overthrusting the Gemeric Unit. The oldest ZHe cooling ages of 130–120 Ma from the southern-most Bôrka Unit nappe-outliers on Gemericum (Figure 2) were interpreted as the collapse of the Meliatic accretionary wedge due to initiated southward underthrusting of the South-Veporic and Gemeric continental margin thrust sheets [15,85], the latter exhumed between ca. 105–85 Ma according to ⁴⁰Ar–³⁹Ar ages [79,80,86]. The ZHe ages from 115 to 95 Ma show the postponed exhumation and cooling of some nappe slices in the Meliatic accretionary wedge overlying the Gemeric Unit [15]. The rutile SIMS U/Pb age of ca. 100 Ma from a Jaklovce metabasite [48] falls into this interval. The Silica-type nappes reached the Gemeric and Veporic Unit at ca. 90–85 Ma according to the ⁴⁰Ar–³⁹Ar ages of phlogopite from the Silicic Nappe sole [87]. The ZHe ages from 80 to 65 Ma obtained from both the Meliatic and the underlying Gemeric Units can be interpreted as IWC orogenic wedge cooling [15]. These ages postdate Late Cretaceous compressional/transpressional burial or the infolding of the superficial Meliatic accretionary wedge fragments at ca. 100–80 Ma within the framework of the IWC orogenic wedge [15]. The exhumation and cooling of the southern Veporic Unit to ∼250–200 °C at 75–71 Ma by Zrn fission track was data-constrained [88,89].

The Meliatic accretionary wedge [15,48] is dismembered in allochthonous blocks or nappe outliers overlying the Neo-Tethyan Meliatic Basin northern continental margin Gemeric Superunit and partly also the Veporic Superunit (Figure 2). Cretaceous tectonics of the Western Carpathians is characterised by north-vergent collision [90]. This northward thrust structure originated by collision-related crustal shortening that prograded from the Late Jurassic Meliata suture in the south towards the inferred Penninic (Atlantic Tethys, [91]) sutures during the Late Cretaceous to Early Paleogene on the IWC northern margin [85,90,92,93,94]. An interval of ca. 105–48 Ma was recorded by ⁴⁰Ar–³⁹Ar ages for the Veporic and Tatric part of the IWC orogenic wedge [86].

Following the previous review of Meliaticum tectonometamorphic events documented by geochronological data, we used the D1 stage for a pre-collisional subduction-related evolutionary stage connected with a subductional burial to the MP and HP depths of the Meliatic Bôrka and Jaklovce paleotectonic units in a subduction channel. We then relate the D2 stage to the exhumation of these unit fragments into an accretionary wedge with the Meliata Unit flysch metasediments. The tectonic juxtaposition of all three metamorphosed paleotectonic units with a different metamorphic grade during the late D2 and D3 stages indicates the start of the transformation or break-up of the accretionary wedge into numerous mélange blocks which are displaced throughout the Gemeric Superunit as kilometre-size nappe outliers. The original position of the Meliatic paleotectonic units within the wedge is still under debate. Attempted reconstruction has recently been made by [48] using new litho-bio-stratigraphy, geochemistry (including the Nd isotope study), Zrn and Rt geochronology data and preliminary metamorphic grade estimates.

In describing the IWC’s orogenic wedge evolutionary stages, we used the AD1 Alpine deformation–recrystallisation stage for the first compressional stage and nappe stacking, then AD2 for the extension- or transpression-related exhumation and thrusting, AD3 for the next compression/transpression and thrusting due to a foreland basin closure, when also conjugated northwest–southeast trending dextral shearing (called the Košice–Margecany shear zone) was combined with northeast–southwest trending shearing in the Trans-Gemeric shear zone (see Supplementary Figures S1–S4 and [15,93,95,96]).

The Meliaticum preserves the internal structure after the pre-AD1 D1 to D3 stages. It then shares evolution with the underlying Gemeric and Veporic superunits towards the north within the IWC orogenic wedge during the AD1 to AD3 stages (see Supplementary Figures S1–S8 as examples).

Abbreviations of the rock-forming minerals names used in the text, tables and figures are: Ab—albite; Act—actinolite; Alm—almandine; Amp—amphibole; An—anorthite; Ap—apatite; Aug—augite; Bt—biotite; Cal—calcite; Cel-Ms—celadonite-rich Ms; Chl—chlorite; Cpx—clinopyroxene; Czo—clinozoisite; Dol—dolomite; Ed—edenite; Ep—epidote; Fwn—ferrowinchite; Gln—glaucophane; Grs—grossular; Grt—garnet; Ill—illite; Ilm—ilmenite; Kfs—potassium feldspar; Lws—lawsonite; Mhb—magnesio—hornblende; Mhs—magnesio—hastingsite; Mrbk—magnesio-riebeckite; Ms—muscovite; Ph—phengite (~Cel-Ms); Pl—plagioclase; Prg—pargasite; Py—pyrite; Qtz—quartz; Rbk—riebeckite; Rt—rutile; Sps—spessartine; Stp—stilpnomelane; Tlc—talc; Ts-tschermakite; Tr—tremolite; Ttn—titanite; Wnc—winchite; Zo—zoisite; and Zrn—zircon.

3. Methods

The field investigation was focused on the collection of representative Triassic and Jurassic rock-types of the Meliatic continental and oceanic margin [48]. We selected suitable samples of metabasites, metacherts to metaradiolarites, marbles as well as calciclastic and siliciclastic flysch metasediments, respectively, for the P–T estimates. The mineral composition and textures of the studied rocks were first investigated in polished sections by polarised light microscope.

The mineral element compositions were measured by electron probe microanalysis (EPMA) on a Cameca SX–100 electron microprobe at the State Geological Institute of Dionýz Štúr in Bratislava, and by JEOL Super-probe JXA 8100 at the Earth Science Institute of the Slovak Academy of Sciences in Banská Bystrica. The voltage was accelerated by 15 kV, with a beam current of 20 nA and a beam focused to 3–5 μm, and the following standards and measured lines were used: Si (TAP, Kα, wollastonite), F (LPCO, Kα, LiF), Cl (LPET, Kα, NaCl), Al (TAP, Kα, Al₂O₃), Ca (LPET, Kα, apatite), Fe (LLIF, Kα, fayalite), Ti (LLIF, Kα, TiO₂), K (LPET, Kα, orthoclase), Na (TAP, Kα, albite), Mg (TAP, Kα, forsterite), Mn (LLIF, Kα, rhodonite), Cr (LLIF, Kα, Cr), Ni (LLIF, Kα, Ni). Additionally, for carbonates and feldspars also Sr (LPET, Lα, SrTiO₃), S (LPET, Kα, barite) and Ba (LPET, Lα, barite) were used. For the carbonates Mg, Si, Al, Ca, S and Mn, the following counting times were used: 10 s on peak and 5 s on background; Fe 20 s on peak and 10 s on background; Sr 60 s on peak and 30 s on background. For the micas Na, Si, Al, Mg, F, Cl, K, Ca, Ti, Fe, Mn, and Cr, the following counting times were used: 10 s on peak and 5 s on background; Ni 20 s on peak and 10 s on background. Detection limits were within 0.01–0.05 wt.% of oxide.

Garnet and amphibole crystal–chemical formulae were calculated using Excel spreadsheets as in [97,98]. The recalculation of the crystal formulae and chlorite classification was then performed by WinCcac Microsoft Windows program [99].

The Hačava blueschist sample (Bôrka Unit) pressures and temperatures were determined by combining thermodynamic modelling, Grt–Ph thermometry [100] and Si-in-Ph barometry (error ±0.2 GPa) [101]. The HAC-1 sample P–T pseudosection was calculated at 0.5–2.0 GPa and 300–700 °C by the Perple_X version 6.9.0 computer program package released in May 2020 [30,102]. Calculations were performed using thermodynamic dataset [33].

The following solid–solution models were chosen: cAmph(G) for amphiboles, Gt(WPH) for garnet, Chl(W) for chlorite, Mica(W) for white mica, Ep(HP11) for clinozoisite–epidote and feldspar for feldspars. Pure phases included lawsonite, titanite, rutile, quartz and H₂O. The thermodynamic modelling was based on our previously published whole-rock composition and classification data [48]. This was then calculated under the 11-component MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O₂ (MnNCKFMASHTO) system. The chemical composition of Ms (Cel) and Grt (Sps–Alm–Grs) was used for the isopleths and P–T estimation.

The original rock composition was slightly modified to fit this 11-component system: (1) CaO was reduced according to the bulk-rock phosphorous content, and assuming that these elements are bound exclusively to ideally composed apatite; (2) Fe²⁺/Fe³⁺ ratio for calculation was set to molar bulk rock Fe₂O₃/(Fe₂O₃ + FeO) value of 0.1 [103,104,105]; (3) the fluid was considered to be in excess, owing to the observations outlined by [106] that hydrated metabasites contain approximately 5–6 wt.% H₂O in the blueschist facies and (4) the bulk-rock compositions used for modelling were converted from weight % oxides to molar % oxides. A similar approach was used for the JAK-30 sample (Jaklovce Unit) calculation with the following changes: the 11-component system was simplified by ommiting MnO due to the lack of any significant Mn-bearing phase. Whole-rock compositions were calculated from representative metamorphic mineral assemblage following the modal composition of 25% Act, 25% Ab, 22% Chl, 5% Ph, 10% Ep, 10% Cal and 3% Ttn.

Pseudosections were contoured with isopleths for various chemical parameters using Perple_X werami and pstable sub-programs to supply raw data. The final pseudosections and contoured P–T diagrams were redrawn, and the mineral assemblage data at specific P–T conditions were supplied by Perple_X werami. Pressure uncertainties for assemblage field boundaries are approximately ±0.1 GPa at the 2σ level [107].

The MathWorks MATLAB script created by [43] was used for Chl–Ph–Qtz–H₂O multiequilibria geothermobarometry with the Std state and solid solutions for chlorite [43] and mica [47]. Calculations were performed under the NCKFMASHO (Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O) chemical system. This employed muscovite, Mg and Fe-celadonite, α-quartz, mica end-members and clinochlore, daphnite, sudoite, Mg and Fe-amesite and pyrophyllite chlorite end-members. The water activity of H₂O = 1 was used for the calculations of all samples.

Multiequilibria geothermobarometry was followed by using a chlorite thermometer (error ±10–30 °C) [108] based on Al^VI content or Cal–Dol solvus thermometry (error ±20–25 °C) [109] combined with Si-in-Phg barometry [101]. Crystal formulae re-calculation and Chl classification and thermometry was by WinCcac Microsoft Windows program [99]. The geothermobarometry of relic magmatic amphiboles was performed by the geothermobarometer of [110].

Finally, powder X-ray diffraction (PXRD) analysis was determined by BRUKER D8 Advance diffractometer (Laboratory of X-ray diffraction SOLIPHA, Comenius University in Bratislava, Faculty of Natural Sciences) under the following conditions: Bragg–Brentano geometry (Theta–2Theta), Cu anticathode (Kα1 = 1.5406 Å) with a 40 kV accelerating voltage and 40 mA beam current. Ni Kβ filters were used for stripping Kβ radiation, and data were obtained by BRUKER LynxEye detector. The step size was 0.01° 2θ, the counting time was 3 s per step, and the measurement ranged from 2° to 65° 2θ. The quantitative analysis of mineral phases and peak-shape fitting using pseudo-Voight function were performed with DIFFRACplus TOPAS software (version 4.1).

4. Results

4.1. Petrography of Metamorphic Rocks

4.1.1. Bôrka Unit

The Bôrka Nappe metabasalts and associated rocks from the following samples; Hačava (s. HAC-1; Figure 2 and Figure 6A), Šugov Valley (s. SUG-10; Figure 2 and Figure 6B–D), the Dobšiná block north of Dobšiná town (s. DO-31, DO-12; Figure 3 and Figure 6E,F) bear signatures of blueschist-facies metamorphism. They typically contain Grt, Gln, Ph, ±Ep, ±Ab, ±Chl and ±Tlc assemblages. The Grt blueschists of the Hačava and Šugov Valley alternate with the pale Middle to Upper Triassic marbles.

Metamorphic textures of blueschists are distinctly schistose, and often preserve relic bands and lenses from the inferred peak metamorphic D1—maximum burial stage. The metamorphic schistosity of these domains is defined by Gln, Ph and Grt (Figure 6A). The superimposed post-peak D2 secondary schistosity contains fine-grained Gln, Ph/Ms, Chl, ±Bt, Ep, Ab (Figure 6C,D). Biotite replaces Ph and Gln and is often partly replaced by Chl. The boudination of competent blueschist layers in softer marble matrix is also characteristic. The blueschist lenses are rounded δ-clasts due to rotation in marble matrix during the D2 exhumation shearing, thus indicating the “top-to-the north” movement (Figure 6B). Layers of calc-alkaline blueschists often occur in marbles and Tlc–Chl–Ph–Cal schists in the Dobšiná quarry (Figure 3 and Figure 6E,F). Phengite-rich layers formed on the contact of blueschists with serpentinite (Figure 6F).

Samples DO-12 and DO-31 are lensoidal to spherical blueschist metric fragments associated with serpentinised peridotites, rodingites, marbles and Tlc–Chl–Ph–Cal schists within the soft serpentinitic matrix exposed in the Dobšiná quarry (Figure 3). The blueschist textures are weakly to strongly schistose, composed of Gln, Ph, Chl, Ab, Ep, Ap and Ttn. This large serpentinitic mélange block is in tectonic contact with an overlying sheet of Jurassic meta-calciclastic turbidites (Figure 3). In contrast, the Meliata MEL-11/19-investigated marble block sample from the inferred Bôrka Unit is located within the Meliata Unit flysch metasediments at Meliata village (see Section 4.1.3).

4.1.2. Jaklovce Unit

N-MORB type metabasalts and metadolerites alternate with cherty schists, cherty metacarbonates and metaradiolarites at Jaklovce village (Figure 5). The thickness of the metabasalt/metadolerite layers varies from a few decimetres to the first metres. Kilometre-size blocks of this metamorphosed oceanic succession lie between the Meliata Unit Jurassic flysch metasediments and a large sheet of the Bôrka Unit continental margin Kurtova skala Hill Triassic marbles. A similar oceanic succession also occurs in a mélange block south of Dobšiná town. This succession is overlain by siliciclastic turbiditic metasediments of the Meliata Unit Jurassic flysch and the Bôrka Unit Triassic marbles in the Končistá Hill area (Figure 3).

The relic magmatic ophitic and occasional amygdaloidal texture in metabasites is crosscut by metamorphic veins (Figure 7A–H). This is a unique feature of these low-temperature metamorphosed basalts (Figure 7A,B) and dolerites (Figure 7C,D) which exhibit both relic magmatic and superimposed metamorphic textures. Magmatic Cpx and lath-shape Pl are constituent minerals, and metamorphic overprinting is observed only in the networks of veins and veinlets or the metamorphic matrix composed of newly formed Chl, Ep, Cal, Ab and Amp (Act, less Wnc or Rbk) ±Qtz (Figure 7E–H).

Metabasalts to metadolerites are interlayered with cherty schists to metaradiolarites (Figure 8A–D) and rarely with reddish cherty metacarbonates (Figure 8E). Only sample MR-1 has obvious HP blueschist facies metamorphic overprinting after blue Amp-rich (Gln) aggregates (Figure 2 and Figure 8F).

The Bretka locality mélange block contains metabasalts associated with serpentinites. Some metabasalt fragments have alternating dark carbonatic schists which highlight the greenschist facies metamorphic overprinting assemblage of Chl, Act, Ab, Ep/Czo and Cal. Other metabasalt fragments composed of Mhb, Ep, Czo, Ab-Pl, Ap and Ttn are metamorphosed in epidote-amphibolite facies. Amphibolites are crosscut by veinlets with greenschist facies mineral assemblages (s. BRT-1; Figure 4 and Figure 8G,H).

The inferred Jaklovce paleotectonic unit MEL-15 and COL-1 samples OIB type basaltic blocks and the Bôrka paleotectonic unit MEL-11/19 sample-type Triassic carbonate blocks occur as olistoliths in the Jurassic siliciclastic and cherty flysch metasediments of the Meliata Unit at Meliata and Čoltovo villages (Figure 2 and Figure 4).

4.1.3. Meliata Unit

The investigated blocks of metabasalts and metaradiolarites of the Bôrka and Jaklovce units are tectonically juxtaposed with Jurassic calciclastic (Figure 9A) or siliclastic (Figure 9B) flysch metasediments of the Meliata Unit in the Jaklovce mélange (Figure 5). The main part of the Jaklovce Unit oceanic thrust-sheet tectonically overlies the Meliata Unit flysch metasediments. The small metric-size sedimentary matrix exposures of siliciclastic flysch of a sample type JAK-204C in Figure 5 are rarely present along contacts of the oceanic crust rigid mélange blocks. Calciclastic flysch metasediments from Jaklovce (Figure 5, Figure 9A and Figure 10A,B; s. JAK-202A,B) petrographically closely resemble those from the Dobšiná quarry (Figure 3 and Figure 10C; s. DO-F1,F2).

Different slightly metamorphosed Jurassic dark clayey to cherty shales or siliciclastic flysch (Figure 9 and Figure 10D; s. MEL-2/19) with dark (Figure 10E; s. MEL-14/19) and green (Figure 10F; s. MEL-17B/19) radiolarite layers prevail at Meliata village. This type of siliciclastic flysch, typical of Meliata locality, only locally occurs at Dobšiná–Končistá (Figure 3; s. DO-K11) and Jaklovce (Figure 5; s. JAK-204C) areas.

4.1.4. Silica Nappe Hanging Wall Mélange

Rare metagabbroic blocks occur in a salinar mélange in the Silica Nappe hanging wall at Gemerská Hôrka (Figure 4). The mafic rocks with well preserved mineral relics of coarse-grained Hbl and albitised Pl most likely have magmatic origin. These rocks’ textures reveal a younger mineral assemblage of bluish Amp, Ep, Ab, Chl, ±Cal, ±Qtz. Finally, a newer Amp generation replaces the brownish Amp along the rims or in crosscutting veinlets (Figure 11A,B).

4.2. Mineral Chemistry

4.2.1. Clinopyroxene

Metabasites and metadolerites of the Jaklovce Unit have well preserved magmatic textures composed of augitic Cpx and Pl (Figure 12A–D and Figure 13).

The JAK–30 sample Aug in the fine-grained basalt has very little variation in the En_45–54Fs_9–18Wo_35–44 composition (Figure 13). In addition, the JAK–6A Aug in dolerite is similar, but has a greater variation in the Fe–Mg content (En_32–39Fs_14–30Wo_31–39, Figure 13). The decreased Al from 7.63 to 3.23 wt.% and Ti from 1.67 to 0.63 wt.% from the core to rim is obvious in the basalt porphyric Aug. There is also a small decrease in dolerite porphyric Aug from 3.8 to 2.2 wt.% Al₂O₃ and from 1.8 to 0.5 wt.% TiO₂ (

Table 1. Representative analyses of augitic clinopyroxene from the Jaklovce Unit.

Sample:	JAK-30	JAK-30	JAK-30	JAK-30	JAK-30	JAK-30	JAK-30	JAK-6A	JAK6-A	J6-A
Mineral	Aug	Aug-(c)	Aug-(r)	Aug	Aug	Aug	Aug	Aug-(c)	Aug-(r)	Aug
An. N.:	3	4	5	3	6	7	18	3	2	4
Tectonic U.:	Jaklovce Unit
SiO2	52.56	49.95	49.12	47.97	52.05	50.15	49.41	51.55	48.28	51.08
TiO2	0.97	0.83	1.40	1.83	0.82	1.25	0.01	1.00	1.82	1.17
Al2O3	7.37	4.53	5.49	7.09	2.79	5.20	5.06	3.05	3.84	2.13
Cr2O3	0.21	0.00	0.06	0.06	0.12	0.13	0.02	0.21	0.03	0.00
Fe2O3 *	0.00	3.27	2.39	1.86	0.86	1.33	5.89	0.90	3.67	0.62
FeO	5.53	7.66	6.27	7.12	6.85	6.73	13.16	8.38	11.63	14.05
MnO	0.15	0.29	0.23	0.19	0.21	0.19	0.44	0.20	0.37	0.40
MgO	12.43	14.89	15.53	13.86	16.50	16.46	12.67	15.42	14.10	12.36
CaO	18.10	17.45	18.79	19.60	19.71	18.59	11.95	19.46	15.97	18.53
Na2O	2.44	0.76	0.37	0.40	0.26	0.22	1.02	0.34	0.39	0.41
Total	99.79	99.68	99.66	99.98	100.18	100.27	100.67	100.52	100.10	100.76
Si4+	1.919	1.860	1.820	1.781	1.913	1.840	1.862	1.902	1.824	1.926
Al3+	0.081	0.140	0.180	0.219	0.087	0.160	0.138	0.098	0.171	0.074
Σ	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00
Ti4+	0.027	0.023	0.039	0.051	0.023	0.035	0.000	0.028	0.052	0.033
Al3+	0.236	0.058	0.060	0.092	0.034	0.065	0.087	0.035	0.000	0.020
Fe3+	0.000	0.092	0.067	0.052	0.024	0.037	0.167	0.025	0.104	0.017
Cr3+	0.006	0.000	0.002	0.002	0.003	0.004	0.000	0.006	0.001	0.000
Fe2+	0.056	0.000	0.000	0.036	0.013	0.000	0.033	0.058	0.049	0.234
Mg2+	0.676	0.827	0.832	0.767	0.904	0.860	0.712	0.848	0.794	0.695
Mn2+	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Σ	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Fe2+	0.113	0.238	0.194	0.185	0.198	0.206	0.382	0.200	0.319	0.209
Mn2+	0.005	0.009	0.007	0.006	0.006	0.006	0.014	0.006	0.012	0.013
Mg2+	0.000	0.000	0.025	0.000	0.000	0.041	0.000	0.000	0.000	0.000
Ca2+	0.708	0.696	0.746	0.780	0.776	0.731	0.482	0.769	0.646	0.749
Na+	0.173	0.055	0.027	0.029	0.019	0.016	0.075	0.024	0.028	0.030
Σ	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Total	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00
Wo	0.65	0.58	0.61	0.61	0.71	0.61	0.35	0.70	0.53	0.71
En	0.68	0.83	0.86	0.77	0.90	0.90	0.71	0.85	0.79	0.69
Fs	0.17	0.24	0.19	0.22	0.21	0.21	0.41	0.26	0.37	0.44

The pyroxene analyses calculations are based on 4 cations. Fe₂O₃ *—ferric iron recalculated back to oxide from a.p.f.u. values.

). The Aug intergrown with Pl also has a lower Al and Ti content. This most likely reflects the final magmatic crystallisation. The Cr₂O₃ content approaches 0.7 wt.% in all samples.

Augitic Cpx is partly preserved in metamorphic veinlets (Figure 14A–F). Its remnants are enclosed in metamorphic Act which has a small sodium content—most likely inherited from Aug (Figure 14C–F). The composition of Aug in veinlets mostly overlaps with porphyric Aug (En_48–55Fs_8–14Wo_34–41) (Figure 13). Al₂O₃ varies from 2.8 to 7.0 wt.% and TiO₂ from 0.8 to 1.8 wt.%, and the Cr₂O content reaches 0.5 wt.%. (Table 1). Irregular Aug relics in metamorphic Act (Figure 14E,F) contain a small amount of Na₂O up to 1.0 wt.% and generally a have lower CaO content up to 12.0 wt.% (Figure 13).

4.2.2. Garnet

Garnet belongs to the D1 assemblage of blueschists (Figure 15A,B;

Table 2. Representative analyses of the garnet from the Bôrka Unit.

Sample:	HAC-2	HAC-2	HAC-2	HAC-2	HAC-2	HAC-2	HAC-2
Mineral	Grt-(r)	Grt-(t)	Grt-(c)	Grt-(c)	Grt-(c)	Grt-(t)	Grt-(r)
An. N.:	1	2	3	5	7	10	3
Tectonic U.:	Bôrka Unit
SiO2	37.61	36.89	36.82	37.23	37.38	37.09	37.30
TiO2	0.09	0.18	0.19	0.17	0.19	0.13	0.09
Al2O3	20.21	19.85	19.65	19.65	19.96	19.90	20.30
Cr2O3	0.00	0.02	0.03	0.01	0.04	0.01	0.00
FeO	24.28	21.47	19.26	18.54	19.16	20.51	23.97
MnO	8.82	12.69	16.35	16.55	15.87	14.52	8.62
MgO	0.32	0.23	0.21	0.16	0.18	0.19	0.38
CaO	9.15	8.55	7.45	8.12	7.98	8.14	9.15
Na2O	0.12	0.00	0.02	0.04	0.03	0.00	0.02
Total	100.59	99.87	99.99	100.47	100.79	100.51	99.83
Si4+	3.015	2.992	2.993	3.007	3.008	2.993	3.012
Ti4+	0.005	0.011	0.012	0.010	0.011	0.008	0.005
Al3+	1.910	1.897	1.882	1.870	1.893	1.893	1.933
Cr3+	0.000	0.001	0.002	0.001	0.003	0.001	0.000
Fe3+	0.067	0.096	0.110	0.101	0.070	0.104	0.035
Fe2+	1.561	1.360	1.198	1.152	1.220	1.280	1.584
Mg2+	0.039	0.028	0.025	0.018	0.022	0.023	0.046
Mn2+	0.599	0.872	1.125	1.132	1.082	0.993	0.590
Ca2+	0.786	0.743	0.649	0.703	0.688	0.704	0.792
Na+	0.018	0.000	0.003	0.006	0.004	0.000	0.003
Total	8.00	8.00	8.00	8.00	8.00	8.00	8.00
Alm	0.55	0.48	0.43	0.41	0.43	0.46	0.55
Sps	0.21	0.31	0.40	0.40	0.38	0.35	0.20
Grs	0.24	0.21	0.17	0.19	0.19	0.19	0.25

Garnet analyses calculations are based on 8 cations. (c)—crystal core; (r)—crystal rim; (t)—a transitional area between the crystal core and the rim.

) and has a typical Sps/Alm-rich composition (Alm_39–55Sps_20–41Grs_17–25) (Figure 16A).

Garnet in metabasalts exhibits prograde zoning, however, this is not observable on BSE images (Figure 16B). The Mn content in Grt decreases (MnO 16.35–8.82 wt.%, Sps_41–20) and the Fe content increases (FeO 19.26–24.35 wt.%, Alm_39–55) from the core towards the crystal rim (Figure 16A,C; Table 2). While Ca shows less variation, there is a gradual increase in Ca content (CaO 7.45–9.15 wt.%, Grs_17–25) towards the crystal rim (Figure 16D; Table 2). The Grt Mg content is typically very low at up to 0.32 wt.%, with an indistinct rim to core variation (Figure 16E; Table 2).

4.2.3. Amphiboles

Composition of the Bôrka Unit blueschist amphiboles (Figure 15A,B and Figure 17A) mainly corresponds to Gln and Rbk, but extends into Wnc and Act fields (Figure 18A–E;

Table 3. Representative analyses of amphibole from the Bôrka, Jaklovce and Silica units.

Sample:	HAC-1	HAC-1	HAC-1	SUG-10	DO-31	DO-31	DO-31	DO-31	JAK-30	J-7A	J-6	J-6	MR-1	BRT-1	BRT-1	SA-6	SA-6	SA-6	SA-6
Mineral	Gln(c)	Gln(r)	Rbk	Gln	Gln	Mrbk	Fwn	Act	Act	Rbk	Fwn	Act	Gln	Mhb	Act	Mrbk	Act	Mhs	Mhb
An. N.:	10	11	9	1	1	2	3	4	1	5	3	1	1	10	11	2	5	8	10
Tectonic U.:	Bôrka Unit								Jaklovce U.	Jaklovce Unit						Silica Unit
SiO2	54.90	56.54	54.56	54.02	59.02	57.39	56.14	55.25	53.39	54.39	54.55	53.66	57.58	49.20	54.64	56.04	54.58	43.51	51.15
TiO2	0.00	0.02	0.00	0.02	0.09	0.04	0.00	0.05	0.00	0.00	0.05	0.00	0.02	0.09	0.00	0.02	0.14	2.05	0.33
Al2O3	5.88	7.83	4.79	8.08	5.57	2.18	2.33	0.47	1.43	0.83	1.58	0.57	8.58	4.93	0.14	3.15	1.24	9.09	4.94
Cr2O3	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.02	0.02	0.01	0.00	0.00	0.00	0.02	0.00	0.03
FeO	26.12	20.14	26.80	24.49	12.76	15.22	12.36	14.35	12.04	25.79	13.61	24.20	13.48	18.61	14.05	20.50	10.61	15.27	9.34
MnO	0.50	0.06	0.53	0.13	0.02	0.12	0.10	0.32	0.19	0.28	0.24	0.51	0.12	0.26	0.24	0.16	0.28	0.22	0.28
MgO	3.72	6.11	3.94	2.98	13.18	14.11	16.01	14.81	15.80	7.50	14.78	8.22	10.01	10.87	14.90	9.65	17.20	12.79	19.01
NiO	0.00	0.00	0.00	0.04	0.00	0.01	0.02	0.04	0.00	0.00	0.05	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
CaO	0.23	0.53	0.21	0.67	1.43	2.51	6.25	11.57	12.51	2.68	12.74	5.42	0.65	12.25	13.04	1.32	12.59	10.75	9.59
Na2O	6.59	6.42	6.58	6.50	6.58	5.98	4.18	0.96	0.35	5.72	0.28	4.54	6.84	0.41	0.01	6.29	0.49	3.37	2.62
K2O	0.00	0.02	0.00	0.03	0.04	0.04	0.10	0.07	0.00	0.03	0.03	0.03	0.01	0.12	0.00	0.00	0.02	0.25	0.12
Cl	0.00	0.00	0.00	0.02	0.00	0.05	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.00	0.01	0.00	0.04	0.14	0.07
Total	97.94	97.68	97.41	96.97	98.69	97.64	97.49	97.89	95.79	97.25	97.93	97.17	97.32	96.82	97.06	97.12	97.19	97.39	97.45
Si4+	8.000	8.000	8.000	7.948	8.000	7.96	7.913	7.972	7.816	8.000	7.862	7.993	7.999	7.352	7.969	8.000	7.818	6.505	7.225
Ti4+	0.000	0.002	0.000	0.003	0.009	0.004	0.000	0.005	0.000	0.000	0.005	0.000	0.002	0.010	0.000	0.002	0.015	0.231	0.035
Al3+	1.012	1.321	0.831	1.402	0.893	0.356	0.387	0.08	0.246	0.144	0.268	0.100	1.405	0.869	0.023	0.530	0.210	1.601	0.824
Cr3+	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.002	0.002	0.001	0.000	0.000	0.000	0.002	0.000	0.003
Fe3+	0.814	0.271	0.986	0.547	0.761	1.316	0.469	0.067	0.06	1.366	0.000	0.864	0.432	0.300	0.000	1.203	0.077	0.214	0.561
Fe2+	2.378	2.14	2.313	2.466	0.69	0.45	0.988	1.665	1.414	1.807	1.640	2.150	1.134	2.026	1.714	1.246	1.194	1.694	0.542
Mg2+	0.81	1.303	0.864	0.653	2.673	2.918	3.364	3.186	3.448	1.645	3.175	1.825	2.073	2.421	3.240	2.054	3.673	2.850	4.002
Mn2+	0.062	0.008	0.067	0.016	0.002	0.014	0.012	0.039	0.023	0.035	0.029	0.064	0.014	0.033	0.03	0.019	0.034	0.027	0.033
Ca2+	0.036	0.082	0.033	0.106	0.208	0.373	0.944	1.789	1.962	0.422	1.967	0.865	0.097	1.96	2.037	0.202	1.932	1.722	1.451
Ni2+	0.000	0.000	0.000	0.004	0.003	0.002	0.000	0.000	0.006	0.000	0.006	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Na+	1.867	1.783	1.877	1.855	1.735	1.608	1.142	0.268	0.099	1.632	0.078	1.311	1.843	0.117	0.004	1.742	0.135	0.976	0.716
K+	0.000	0.004	0.001	0.005	0.007	0.007	0.018	0.013	0.001	0.006	0.006	0.006	0.002	0.023	0.000	0.000	0.003	0.048	0.021
Total	15.00	15.00	15.00	15.00	15.01	15.01	15.24	15.09	15.08	15.06	14.97	15.12	15.31	15.49	15.13	15.00	15.05	15.22	15.03
Cl−	0.00	0.00	0.00	0.01	0.00	0.01	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.04	0.00	0.03
OH−	2.00	2.00	2.00	1.99	2.00	1.99	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	1.99	1.96	1.98
Fe2+/(Fe2+ + Mg)	0.75	0.62	0.73	0.79	0.21	0.13	0.23	0.34	0.30	0.52	0.34	0.54	0.35	0.46	0.35	0.38	0.25	0.37	0.12

Amphibole analyses calculations are based on 15 cations.

). Amphibole chemical analyses create a trend almost parallel with the Tr–Gln joint (Figure 18D,E). This documents high-pressure Gln to Rbk, medium-pressure Wnc or lower-pressure Act.

The following contents were noted: the Na₂O sodium amphibole content ranges from 4.2 to 7.8 wt.% with the lower values linked to up to 4.9 wt.% Fwn in the sample DO-31; the Al₂O₃ content varies between 2.2 and 8.1 wt.% with lower values in Rbk/Mrbk (up to 5.1 wt.%, s. HAC-1, DO-31); Fwn (up to 2.8 wt.%, s. DO-31); the MgO varies between 3.0 and 17.4 wt.% with higher values for Mrbk, Fwn (s. DO-31) and lower for Gln (up to 6.2 wt.%, s. HAC-1) (Table 3); the FeO content in sodium amphiboles is relatively high in all samples, between 12.8 and 26.8 wt.%. Figure 16A shows that Hačava glaucophane samples have prograde zoning with an increased content of FeO in the crystal core up to 26.5 wt.% (Table 3), there is up to 7.8 wt.% Al₂O and up to 6.2 wt.% MgO increase towards the crystal rim. Amphiboles with an Act composition were identified in samples from Dobšiná (s. DO-31, Table 3) with a CaO content up to 12.4 wt.% and generally low content of Al₂O₃ and Na₂O content up to 0.80 wt.%. Finally, FeO in Act approaches 8.2 wt.% (Table 3).

Figure 18D,E then highlights that the Jaklovce Unit samples (Figure 17B–F) amphibole composition creates a similar trend parallel to the Tr–Gln joint. In addition, the amphiboles chemical analysis mainly plots into the Act (Tr) and Wnc fields (Figure 18A,B,D,E). The glaucophane occurs only in sample MR-1 from Malý Radzim at Brdárka. The Na₂O concentration in the sodium amphiboles reaches 8.0 wt.%. Glaucophane has increased Al₂O₃ up to 8.7 wt.%, and this contrasts with the rest of the sample’s lower value up to 2.65 wt.% (Figure 17B and Figure 18C–E; Table 3).

Amphiboles with Act and Wnc composition occur in greenschist facies metabasites (s. J-6,7A, Figure 17C,D; s. BRT-5) and in the greenschist overprint minerals assemblage of Bretka metabasalts (s. BRT-1, BRT-2, Figure 17E,F). Almost all Wnc and Act amphiboles have an increased content of FeO up to 26 wt.%, and the Act CaO reaches 12.7 wt.% (Table 3). Analyses that plot into the Mhb field (Figure 18B) belong to an amphibolite facies mineral assemblage of Bretka metabasalts (s. BRT-1, BRT-2, Figure 17E,F). Here, the Al₂O ranges up to 10.5 wt.% while the TiO₂ content is relatively low, at up to 0.5 wt.%.

The amphibole composition in the Silica Unit samples is very variable. Analyses which plot along the entire Tr–Gln joint in Figure 18D,E mirror the transition from sodium-rich Mrbk composition to Ca-rich Act amphiboles. The Na₂O content in sodium amphiboles reaches 6.3 wt.% (Table 3). In addition, the Silica Unit metagabbro contains magmatic Mhs relics with Al₂O up to 9.1 wt.% and TiO₂ to 2.1 wt.% Mhs to Mhb transition towards the crystal rim is accompanied by decreased Al₂O₃ up to 4.9 wt.% and TiO₂ to 0.3 wt.% (Figure 18A,B and Figure 19A,B, Table 3).

4.2.4. White Mica

Celadonite-rich Ms (Ph) is typical HP white mica in the Bôrka Unit blueschists and marbles (Figure 15A,B and Figure 17A;

Table 4. Representative analyses of white mica from the Bôrka, Jaklovce, Meliata and Silica units.

Sample:	HAC-1	HAC-1	SUG-10	DO-12	DO-12	DO-31	DO-31	MEL-11/19	JAK-6/19	JAK-204B	JAK-30	JAK-30	JAK-30	DO-K2	DO-K2	SA-6	JAK-204C	JAK-204C
Mineral	Ph	Ph	Ph	Cel-Ms	Ph	Ph	Ph	Cel-Ms	Ph	Ph	Cel-Ms	Ph	Ph	Ph	Ph	Ph	Cel-Ms	Cel-Ms
An. N.:	5	16	2	1	2	6	2	1	6	1	1	4	5	2	4	3	2	3
Tectonic U.:	Bôrka Unit								Jaklovce U.	Jaklovce Unit						Silica U.	Meliata Unit
SiO2	51.61	50.19	52.50	49.17	50.38	53.37	50.48	47.17	50.58	50.79	47.05	54.55	55.74	52.22	55.29	49.32	48.97	47.56
TiO2	0.16	0.09	0.17	0.51	0.08	0.11	0.14	0.13	1.25	0.22	0.04	0.00	0.00	0.13	0.06	0.12	0.23	1.04
Al2O3	23.37	24.60	26.59	30.76	27.37	24.05	24.71	23.14	24.76	29.38	32.01	24.04	22.18	24.04	24.32	23.21	30.99	30.32
FeO	6.01	5.76	6.20	3.86	2.91	2.93	2.77	4.95	4.17	2.43	1.13	3.31	3.31	5.32	4.86	5.70	1.92.	3.23.
MnO	0.03	0.07	0.06	0.05	0.00	0.01	0.02	0.06	0.02	0.03	0.05	0.12	0.05	0.02	0.03	0.04	0.01	0.04
MgO	3.11	2.91	1.91	2.12	2.69	4.90	5.39	6.16	3.43	1.91	1.54	3.30	4.52	6.18	5.65	3.54	1.94	2.65
CaO	0.02	0.03	0.05	0.05	0.23	0.02	0.34	2.12	0.19	0.08	0.02	0.46	0.29	0.09	0.12	0.06	0.04	0.07
Na2O	0.09	0.12	0.11	0.11	0.12	0.08	0.20	0.08	0.15	0.23	0.35	0.03	0.03	0.08	0.04	0.34	0.08	0.12
K2O	10.86	11.09	5.97	9.47	10.48	10.67	9.66	8.17	7.85	9.73	10.84	10.76	10.66	9.15	8.24	10.64	10.33	9.40
Total	95.28	94.89	93.58	96.09	94.29	96.16	93.73	92.23	92.41	94.83	93.93	96.58	96.80	97.30	98.62	93.04	92.59	91.2
Si4+	3.513	3.440	3.513	3.256	3.404	3.534	3.428	3.301	3.460	3.379	3.194	3.599	3.662	3.441	3.544	3.464	3.277	3.205
IVAl3+	0.487	0.560	0.487	0.744	0.596	0.466	0.572	0.699	0.540	0.621	0.806	0.401	0.338	0.559	0.456	0.536	0.723	0.795
∑T	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00
Ti4+	0.008	0.005	0.009	0.025	0.004	0.005	0.007	0.007	0.064	0.011	0.002	0.000	0.000	0.007	0.003	0.006	0.012	0.053
VIAl3+	1.389	1.427	1.610	1.657	1.584	1.411	1.406	1.209	1.456	1.684	1.755	1.468	1.380	1.308	1.381	1.385	1.72	1.61
Fe2+	0.342	0.330	0.347	0.214	0.165	0.162	0.157	0.290	0.238	0.135	0.064	0.183	0.182	0.293	0.261	0.335	0.107	0.182
Mn2+	0.002	0.004	0.004	0.003	0.000	0.001	0.001	0.003	0.001	0.001	0.003	0.007	0.003	0.001	0.002	0.002	0.001	0.002
Mg2+	0.316	0.297	0.190	0.209	0.271	0.484	0.546	0.643	0.349	0.189	0.156	0.325	0.443	0.607	0.540	0.371	0.194	0.267
∑M	2.06	2.06	2.16	2.11	2.03	2.06	2.12	2.15	2.11	2.02	1.98	1.98	2.01	2.22	2.19	2.10	2.04	2.12
Ca2+	0.002	0.002	0.003	0.003	0.017	0.001	0.025	0.159	0.020	0.006	0.001	0.032	0.082	0.006	0.008	0.004	0.003	0.005
Na+	0.012	0.016	0.014	0.014	0.016	0.010	0.026	0.011	0.685	0.029	0.046	0.003	0.004	0.010	0.005	0.047	0.010	0.016
K+	0.943	0.970	0.509	0.800	0.903	0.901	0.837	0.730	0.870	0.826	0.939	0.906	0.894	0.769	0.673	0.953	0.882	0.808
I□	0.04	0.01	0.47	0.18	0.06	0.09	0.11	0.10	0.28	0.14	0.01	0.06	0.08	0.21	0.31	0.00	0.11	0.17
∑I	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Total	7.06	7.06	7.16	7.11	7.03	7.06	7.12	7.15	7.11	7.02	6.98	6.98	7.01	7.22	7.19	7.10	7.04	7.12
OH−	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00	2.00

White mica analyses calculations are based on 11 oxygens: ΣT—sum of tetrahedral (T) site; ΣM—sum of octahedral (M) site; ΣI—sum of interlayer cations; □—vacancy.

). It is closely associated with the Gln and Grt of the D1 peak metamorphic assemblage. White mica from metabasites has SiO₂ content from 49.2 to 53.4 wt.% (3.26–3.64 a.p.f.u). The marble SiO₂ content reaches 47.2 wt.% (3.3 a.p.f.u.) and the K₂O values in mica vary between 8.2 and 11.1 wt.%; with the lowest values bound to marbles in sample MEL-11/19. Sample HAC-1 from Hačava exhibits increased FeO content 5.8–6.0 wt.%, accompanied by a lower MgO up to 3.1 wt.%. In direct contrast, however, the Dobšiná and Šugov samples generally have lower FeO up to 3.9 wt.% and higher MgO up to 5.4 wt.% (Table 4).

SiO₂ content in white mica from Jaklovce Unit ranges from 45.0 to 55.7 wt.% (3.11–3.66 a.p.f.u.) with lower values largely represented in metaradiolarites (Figure 20A–C) up to 50.7 wt.%, except sample DO-K2 (Table 4). The variable K₂O between 7.8 and 10.8 wt.% in all metaradiolarite samples documents a transitional illite–phengite composition with a decreased Na + K or K₂O. However, contents up to 5.3 wt.% MgO and 6.2 wt.% FeO are relatively constant in all samples.

The clastogenic Ms prevails in most samples from the Meliata Unit calciclastic or siliciclastic flysch (Figure 20D–F) and is often overgrown by newly formed Chl (Figure 20F). Sample JAK-204C contains newly formed Cel-Ms aggregates beside clastogenic Ms (Figure 20E). K₂O content in newly formed celadonic (phengitic) Ms in the JAK-204C sample ranges from 9.4 to 10.3 wt.%. and the SiO₂ is 47.6 to 49.0 wt.% (3.28–3.30 a.p.f.u) (Table 4). Meliata Unit metaradiolarite and Čoltovo metabasalt contained just newly formed Chl without Cel-Ms (Figure 20G,H).

Chemical analyses of the white mica in both Bôrka and Jaklovce units rocks project along the muscovite–celadonite mixing-line in classification diagram [113] (Figure 21).

Some Ms porphyroclasts exhibit a transitional illite–phengite composition with decreased Na₂O at 1.0–0.04 wt.% and K₂O at 11.2–7.85 wt.% (Figure 20B,C,E and Figure 22A; Table 4).

Analyses of the phengitic white mica in Figure 22B mainly plots along the muscovite–phengite line but they are shifted in semi-parallel to the illite field. This is due to the small but significant deficit in interchange layer [114]. The total interlayer charge (t.i.c.) calculated for 22 oxygens is approximately 1.7 a.p.f.u.

White mica in the Gemerská Hôrka metagabbro (Figure 19A,B) shows celadonic (phengitic) composition (Figure 21) with K₂O values up to 10.6 wt.% and SiO₂ up to 49.3 wt.% (Table 4).

4.2.5. Chlorite

Chlorite from Bôrka Unit metabasites in Figure 23 and

Table 5. Representative analyses of chlorite from the Bôrka, Jaklovce, Meliata and Silica units.

Sample:	SUG-10	DO-12B	DO-31	JAK-6-19	JAK-204B	MR-1	JAK-30	JAK-6A	J-6	MEL-15	DO-K2	MEL-14-19	MEL-17-19	SA-6
Mineral	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl	Chl
An. N.:	11	15	3	1	1	2	1	3	3	1	2	5	8	10
Tectonic U.:	Bôrka Unit			Jaklovce Unit								Meliata U.		Silica U.
SiO2	24.45	26.84	30.43	27.30	26.49	28.08	29.13	27.85	28.45	25.41	29.15	26.08	24.86	27.83
TiO2	0.07	0.05	0.01	0.00	0.04	0.03	0.00	0.05	0.01	0.02	0.00	0.07	0.02	0.05
Al2O3	19.02	21.09	17.75	20.48	19.63	17.70	17.90	18.98	17.81	21.47	19.87	22.10	19.64	17.75
Cr2O3	0.00	0.03	0.00	0.00	0.00	0.08	0.00	0.00	0.00	0.02	0.02	0.01	0.03	0.06
FeO	36.84	21.29	13.96	21.26	27.25	23.70	19.57	24.26	24.24	26.54	14.46	26.98	34.65	21.26
MnO	0.59	0.02	0.11	0.07	0.33	0.37	0.25	0.30	0.38	0.17	0.27	0.09	0.95	0.29
MgO	7.05	17.48	25.09	15.49	13.04	17.15	20.24	16.28	17.32	12.70	23.63	12.43	8.27	19.22
CaO	0.07	0.00	0.09	0.14	0.08	0.13	0.07	0.55	0.00	0.04	0.03	0.02	0.02	0.11
Na2O	0.02	0.00	0.01	0.00	0.01	0.03	0.00	0.00	0.00	0.00	0.01	0.00	0.00	0.01
K2O	0.00	0.04	0.00	0.19	0.05	0.02	0.01	0.00	0.02	0.00	0.00	0.15	0.00	0.01
H2O *	10.67	11.56	12.12	11.31	11.17	11.43	11.71	11.54	11.55	11.15	12.08	11.37	10.84	11.47
Total	88.10	86.84	87.45	84.93	86.92	87.29	87.17	88.27	88.23	86.38	87.46	87.94	88.45	86.58
Si4+	2.749	2.784	3.010	2.895	2.844	2.945	2.982	2.894	2.954	2.733	2.892	2.752	2.748	2.908
IVAl3+	1.251	1.216	0.990	1.105	1.157	1.055	1.018	1.106	1.046	1.267	1.108	1.248	1.252	1.092
∑T	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00
Ti4+	0.006	0.004	0.001	0.000	0.004	0.002	0.000	0.004	0.001	0.002	0.000	0.005	0.002	0.004
Cr2+	0.000	0.002	0.000	0.000	0.000	0.007	0.000	0.000	0.000	0.002	0.002	0.001	0.003	0.005
VIAl3+	1.269	1.363	1.079	1.454	1.327	1.132	1.143	1.218	1.134	1.455	1.216	1.500	1.307	1.093
Fe2+	3.463	1.847	1.155	1.885	2.447	2.078	1.675	2.108	2.105	2.387	1.200	2.380	3.203	1.857
Mn2+	0.056	0.002	0.009	0.006	0.030	0.033	0.022	0.026	0.033	0.015	0.023	0.008	0.089	0.025
Mg2+	1.181	2.702	3.700	2.448	2.087	2.680	3.090	2.522	2.681	2.037	3.495	1.955	1.362	2.994
Ca2+	0.008	0.000	0.010	0.016	0.009	0.015	0.008	0.061	0.000	0.004	0.004	0.003	0.002	0.012
Na+	0.005	0.001	0.002	0.000	0.002	0.006	0.000	0.000	0.000	0.000	0.003	0.000	0.000	0.001
K+	0.001	0.006	0.000	0.026	0.006	0.003	0.001	0.000	0.003	0.000	0.000	0.021	0.000	0.002
M□	0.025	0.081	0.056	0.204	0.102	0.063	0.071	0.121	0.046	0.102	0.060	0.145	0.033	0.020
∑M	6.01	6.01	6.01	6.04	6.01	6.02	6.01	6.06	6.00	6.01	6.00	6.02	6.00	6.01
OH-	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00	8.00

Chlorite analyses calculations are based on 14 anions: ΣT—sum of tetrahedral (T) site; ΣM—sum of octahedral (M) site; □—vacancy; H₂O *—calculated water content based on stoichiometry.

mostly belong to the post-peak (D2) mineral association. The chlorite replaces Gln or Grt in some places and occurs in mineral assemblage with Ab, Act, Ep and Bt.

Chlorites from the metabasite samples were plotted into fields of Mg and Fe–chlorites in classification diagram of [115] (Figure 23). Fe–chlorite (chamosite) was found in the Šugov blueschist sample SUG–10 with up to 36.8 wt.% FeO and 7.0 wt.% MgO. The Fe/(Fe + Mg) ratio is 0.74 (Table 5). All chlorites from the Dobšiná blueschist were plotted into the Mg–Chl (clinochlore) field with most values between 24.9 and 25.1 wt.% MgO and 13.3–14.0 wt.% FeO as in sample DO–31. The Fe/(Fe + Mg) ratio for Dobšiná samples varies between 0.22 and 0.40. A content of ^VIAl reaches up to 1.08–1.36 a.p.f.u. in all the studied samples from the Bôrka Unit (Table 5).

Figure 23 shows that most of the Jaklovce Unit Chl projects into Mg–Chl fields in the classification diagram [115]. Exceptions to this are seen in the MEL-15 metabasalt from Meliata and the JAK–204B metaradiolarite samples. These plot into the Fe–Chl chamosite field (Figure 23). MgO content in Chl ranges from 12.7 to 21.9 wt.% with higher MgO values generally found in metabasites (Table 5). The FeO content varies between 17.3 and 27.3 wt.% with a FeO/(FeO + MgO) ratio between 0.31 and 0.54. Finally, the ^VIAl reaches up to 1.13–1.46 a.p.f.u. in all Jaklovce Unit studied samples (Table 5).

All Meliata Unit flysch chlorites plot in the Fe-Chl chamosite field in the classification diagram [115] (Figure 23). The FeO reaches 25.3–37.3 wt.% and MgO 6.3–13.9 wt.%. The Fe/(Fe + Mg) ratio is 0.51–0.78, and the ^VIAl content varies between 1.3 and 1.49 a.p.f.u. (Table 5).

Chlorite in Gemerská Hôrka metagabbro (Figure 19A,B) plots in the Mg–Chl (clinochlore) field (Figure 23). The Fe/(Fe + Mg) ratio is 0.38 and the Al^VI value is 1.09 a.p.f.u. (Table 5).

4.2.6. Carbonates

Carbonate rich layers in the Meliata Unit flysh contain Cal intergrown with Dol grains. These form part of the Cal–Dol–Ab–Chl–Kfs–Qtz assemblage of the peak D1 metamorphic stage (Figure 24A–C;

Table 6. Representative analyses of calcite and dolomite from the Bôrka and Meliata units.

Sample:	MEL-11/19	MEL-11/19	JAK-202A	JAK-202A	JAK-202B	JAK-202B	JAK-202B	JAK-202B
Mineral	Cal	Dol	Cal	Dol	Cal	Dol	Cal	Dol
An. N.:	2	3	1	2	3	4	26	27
Tectonic U.:	Bôrka Unit		Meliata Unit
MgO	0.58	19.48	0.55	16.62	0.58	17.22	0.58	16.52
CaO	55.05	32.05	54.74	31.99	53.14	33.20	53.01	31.63
MnO	0.64	0.44	0.21	1.64	0.11	0.33	0.16	0.70
FeO	0.32	1.33	0.48	3.19	0.46	2.81	0.40	2.65
SrO	0.00	0.00	0.06	0.01	0.07	0.03	0.01	0.00
Total	56.60	53.31	56.05	53.44	54.36	53.60	54.16	51.50
Mg2+	0.029	0.896	0.028	0.785	0.030	0.804	0.030	0.803
Ca2+	1.945	1.059	1.952	1.086	1.953	1.114	1.954	1.105
Mn2+	0.018	0.012	0.006	0.044	0.003	0.009	0.005	0.019
Fe2+	0.009	0.034	0.013	0.084	0.013	0.073	0.012	0.072
Sr2+	0.000	0.000	0.001	0.000	0.001	0.001	0.000	0.000
C	2.000	2.000	2.000	2.000	2.000	2.000	2.000	2.000
Total	4.00	4.00	4.00	4.00	4.00	4.00	4.00	4.00
%MgCO3	1.44	44.77	1.38	39.26	1.48	40.18	1.49	40.17
%CaCO3	97.23	52.94	97.60	54.31	97.63	55.67	97.69	55.25
%MnCO3	0.89	0.58	0.29	2.20	0.16	0.44	0.24	0.96
%FeCO3	0.44	1.71	0.67	4.22	0.66	3.67	0.58	3.62
%SrCO3	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00

Calcite and dolomite analyses calculations are based on 6 oxygens.

). In addition, tiny Dol grains are ingrown to Cal in the Bôrka Unit marbles due to distinct metamorphic overprinting, while the younger Cal veinlets contain no Dol (Figure 24D; Table 6).

4.2.7. Feldspars

All feldspars in the Bôrka, Jaklovce and Meliata units metabasites correspond to pure Ab with a composition of Ab_99.1–99.8An_0.1–0.6Or_0.1–0.5 (Figure 17B–F;

Table 7. Representative analyses of feldspars from the Bôrka, Jaklovce and Meliata units.

Sample:	SUG-10	DO-31	MR-1	JAK-6A	MEL-15	BRT-1A	JAK-202A	JAK-202A	JAK-202B	COL-1
Mineral	Ab	Ab	Ab	Ab	Ab	Ab	Or	Ab	Or	Ab
An. N.:	6	7	5	1	2	4	3	4	3	2
Tectonic U.:	Bôrka Unit		Jaklovce Unit				Meliata Unit
SiO2	68.59	67.07	68.26	68.29	67.93	68.09	64.94	68.39	64.98	68.68
Al2O3	19.08	18.45	19.35	19.32	19.44	19.75	19.64	19.43	19.72	18.99
FeO	0.05	0.06	0.38	0.48	0.43	0.73	0.04	0.05	0.04	0.53
MgO	0.00	0.00	0.02	0.24	0.10	0.23	0.00	0.00	0.00	0.19
CaO	0.02	0.01	0.31	0.31	0.20	0.11	0.13	0.12	0.10	0.12
SrO	0.00	0.00	0.01	0.00	0.00	0.00	0.00	0.00	0.00	0.00
BaO	0.00	0.00	0.00	0.00	0.00	0.00	0.25	0.00	0.24	0.00
Na2O	11.53	11.77	11.52	11.25	11.16	11.80	0.26	11.74	0.16	11.79
K2O	0.02	0.02	0.06	0.08	0.02	0.05	16.61	0.06	15.97	0.02
Total	99.30	97.38	101.01	99.97	100.29	100.79	99.73	99.19	100.23	100.32
Al	0.988	0.976	0.977	0.996	0.987	1.013	1.104	1.015	1.083	0.976
Si	3.012	3.010	2.923	2.987	2.927	2.962	3.098	3.031	3.027	2.996
Fe3+	0.002	0.002	0.012	0.016	0.014	0.024	0.002	0.002	0.002	0.017
Mg	0.000	0.000	0.001	0.016	0.006	0.015	0.000	0.000	0.000	0.012
Ca	0.001	0.000	0.014	0.015	0.009	0.005	0.007	0.006	0.005	0.006
Sr	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Ba	0.000	0.000	0.000	0.000	0.000	0.000	0.005	0.000	0.004	0.000
Na	0.982	1.024	0.957	0.954	0.932	0.996	0.024	1.009	0.014	0.997
K	0.001	0.001	0.003	0.005	0.001	0.003	1.011	0.003	0.949	0.001
Total	4.99	5.01	4.89	4.99	4.89	5.09	5.25	5.07	5.09	5.01
Ab (mol. %)	99.8	99.9	98.2	98.0	98.9	99.2	2.3	99.1	1.5	99.3
An (mol. %)	0.1	0.0	1.5	1.5	1.0	0.5	0.6	0.6	0.5	0.1
Or (mol. %)	0.1	0.1	0.3	0.5	0.1	0.3	97.1	0.3	98.0	0.6

Feldspars analyses calculations are based on 8 oxygens.

). Plagioclase relics with higher anorthite content are rare. Similarly, metagabbro from Gemerská Hôrka and metabasalts from Meliata and Čoltovo contain pure Ab after magmatic Pl (Figure 19A,B and Figure 20H). Finally, the carbonate-rich layers in Meliata Unit flysch also contain, besides Ab, pure orthoclase alkali feldspar with a composition of Ab_1.5–2.3An_0.5–0.6Or_97.1–98.0 (Figure 24A–C; Table 7).

4.3. PXRD Analysis

The mineral composition of calciclastic flysch metasediments was studied also with PXRD (Figure 25). The dominant phases include Qtz and feldspars, which are mostly Ab, but some samples also have a small percentage of Kfs associated with variable Chl and Ms proportions (

Table 8. Quantitative proportion of mineral phases calculated from the powder X-ray diffraction (PXRD) data by Rietveld quantitative analysis.

Phase	DO-F1	DO-F2	DO-K11	JAK-202A	JAK-202B	MEL-2/19	MEL-3/19	MEL-10/19	MEL-13/19	MEL-18/19
Albite	7.2	4.5	12.2	14.1	6.0	8.4	17.9	-	8.3	19.1
Calcite	29.7	14.4	-	69.4	35.9	-	2.6	-	-	51.4
Chlorite	12.7	18.7	23.7	2.2	11.2	26.3	15.4	38.4	32.7	15.0
Dolomite	0.1	0.2	-	0.2	-	-	1.7	-	-	0.2
Muscovite	40.7	51.2	38.7	4.3	28.0	6.8	37.7	31.7	5.6	4.0
K-feldspar	-	-	-	5.2	11.4	-	-	5.3	-	-
Paragonite	-	-	13.2	-	-	1.7	-	-	-	-
Quartz	9.7	11.1	12.1	4.7	7.5	56.9	24.7	24.5	52.3	9.8

). Samples DO-F1, DO-F2, JAK-202A, JAK-202B, MEL-3/19 and MEL-18/19 contain a significant admixture of carbonates which mainly comprise Cal and small amounts of Dol. In addition, Chl phyllosilicate has a relatively stable content at 11–38 wt.% and this is also noted in the small 2.2 wt.%. content in the JAK-202A sample. Muscovite has the following variable contents: JAK-202A, MEL-2/19, MEL-13/19 and MEL-18/19 have less than 10 wt.% and JAK-202B and MEL-3/19 have 28–32 wt.%. Finally, DO-F1, DO-F2, DO-K11 and MEL-3/19 are the most enriched in Ms with 37–51 wt.%, while DO-K11 and MEL-2/19 have an indication of another mica phase, probably paragonite.

4.4. P–T Estimates

4.4.1. Bôrka Unit

Metabasites

Perple_X pseudosection modelling determined the precise D1 stage P–T conditions of the Grt-bearing blueschist layers in Hačava marble (Figure 6A and Figure 15A,B). This was accomplished by using whole-rock analysis in

Table 9. Bulk-rock composition of HAC-1 and JAK-30 metabasites in oxide weight and molar percentages.

Weight % Oxides
Sample	SiO2	TiO2	Al2O3	Fe2O3	FeO	MgO	MnO	CaO *	Na2O	K2O	-	-
HAC-1	49.55	2.92	13.02	1.53	12.37	4.30	0.18	2.83	3.45	4.09	-	-
JAK-30	48.70	1.41	13.20	1.01	9.05	4.88	-	10.71	5.41	0.20
JAK-30 *	47.50	1.32	13.31	1.06	9.51	9.47	-	14.02	2.97	0.59	-	-
Molar % Oxides
Sample	SiO2	Al2O3	CaO	MgO	FeO	MnO	K2O	Na2O	TiO2	O2	H2O	CO2
HAC-1	56.93	8.82	3.48	7.36	13.21	0.18	3.00	3.84	2.52	0.66	Excess	-
JAK-30	52.07	8.71	9.18	15.08	9.61	-	0.50	3.08	1.28	0.48	Excess	Excess

The Fe₂O₃ contents were calculated assuming bulk-rock Fe₂O₃/(FeO + Fe₂O₃) = 0.1. * CaO was reduced according to bulk-rock phosphorous content and assuming that these elements are bound exclusively to ideally composed Ap. JAK-30. *—calculated bulk composition for metamorphic veinlets.

. Figure 26 shows that resultant P–T estimates at 520 °C at 1.55 GPa fit peak D1 metamorphic Grt–Gln–Ph assemblage with a Grt composition of Alm_0.55Grs_0.24Sps_0.21 and Si in Ph 3.53 a.p.f.u. (Table 2, Table 4 and

Table 10. P–T estimates based on combined thermodynamic modelling and the geothermobarometry of Bôrka Unit rocks.

Sample	Sample Description and Locality	Perple_X [30,102]		Grt–Ph [100]	Cal–Dol [109]	Chl [43]	Chl–Ph [43]	Ph [101]	Ch [108]	Mineral Assemblage
		T (°C)	P (GPa)	T (°C)	T (°C)	T (°C)	P (GPa)	P (GPa)	T (°C)
HAC-1	Blueschist layer in marble, Hačava	520	1.55	* 475–505						Gln–Grt–Ph–Chl–Ep–Ab
SUG-10	Blueschist layer in marble, Šugov Valley at Medzev					335–353	1.1–1.3	1.5–1.6	341	Gln–Ph–Ttn–Chl–Ep–Ab
DO-12	Blueschist lens in serpentinite, Dobšiná					281	0.4	0.45–0.85	332	Gln–Ph–Chl–Ep–Ab
DO-31	Blueschist lens in serpentinite, Dobšiná							0.85–1.1	245-257	Gln–Ph–Tlc–Chl–Ep–Ab
MEL-11/19	Marble block in flysch, Meliata				280–290			0.6		Cal–Dol–Ph–Ap

* Calculated for pressures 1.4–1.6 GPa.

).

Similar 475–505 °C temperatures were obtained by Grt–Ph thermometry for 1.4–1.6 GPa pressures [100] (Table 10). This approximately coincides with phengite geobarometer pressures for Si content 3.43–3.51 a.p.f.u. at 500 °C [101]. This also considers a ±0.2 GPa error.

Figure 27 highlights that the post-peak metamorphic P–T conditions of blueschist from Šugov Valley near Medzev village (Figure 4C,D and Figure 17A) are in accordance with Chl–Ph pairs at 353 °C and 1.1 GPa. This was accomplished with multi-equilibria Chl–Ph–Qtz–H₂O geothermobarometry [43].

The geothermometry conventional method gives a similar Chl crystallisation temperature of 340 °C at 1.5 (±0.2) GPa [108]. This was obtained by Si-in-Ph geo-barometry for 3.51 a.p.f.u. Si content. (Table 4 and Table 10).

The Chl–Ph pair in lensoidal blueschist fragments in serpentinite from Dobšiná quarry samples DO-12 and DO-31 provide 281 °C and 0.4 GPa (Figure 27). These P–T estimates were calculated from Chl replacing Gln and Ph with a lower 3.25 a.p.f.u. Si content (Table 2). However, we obtained pressures of 0.85–1.1 (±0.2) GPa by combining Chl temperatures of approximately 330 °C in the DO-12 sample and 245–257 °C in DO-31 with a higher-Si Ph at 3.40–3.51 a.p.f.u. [43] (Table 4).

Marbles

Bôrka Unit marble block sample MEL-11/19 in Meliata Unit flysch contains Cal intergrown with tiny Dol grains (Figure 24D; Table 6). These carbonates yielded equilibrium temperatures of 286 °C by Cal–Dol thermometry [109] (Table 10).

4.4.2. Jaklovce Unit

Metabasites

Perple_X pseudosection modelling determined the precise D1 stage P–T of the Jaklovce metabasalts greenschist-facies metamorphic veinlets (Figure 14A,B). This was accomplished by the calculated whole-rock composition of the studied rocks (Table 9). Figure 28 shows that the resultant P–T estimates of 390–420 °C at 1.1–1.3 GPa fit a peak D1 metamorphic Act–Chl–Ph–Ep–Ab–Ttn assemblage with a Chl composition of Fe/(Fe + Mg) = 0.36–0.38 and Si in Ph 3.45–3.62 a.p.f.u. (Table 4 and Table 5). For Ph, typical slightly lower values of Si were used, instead of maximal 3.62 a.p.f.u. to prevent pressure overestimation. These isopleths are crosscut by the Act composition of Fe/(Fe + Mg) = 0.30–0.40 characteristic of the JAK-30 sample (Table 3).

Retrograde Chl temperatures for the blueschist MR-1 Malý Radzim/Brdárka are 306 or 278 °C [43,108] (Figure 8F and Figure 17B;

Table 11. Jaklovce Unit rock P–T estimates by combined geothermobarometry.

Sample	Sample Description and Locality	Perple_X [30,102]		Chl [43]	Chl–Ph [43]	Ph [101]	Chl [108]	Mineral Assemblage
		T (°C)	P (GPa)	T (°C)	P (GPa)	P (GPa)	T (°C)
JAK-6/19	Metaradiolarite, Jaklovce			250–266	0.55	0.8–1.05	300–327	Qtz–Ph–Chl
JAK-204B	Metaradiolarite, Jaklovce			234–245	0.4	0.65–0.75	310	Qtz–Ph–Chl
MR-1	Blueschist, Malý Radzim at Brdárka			306			278	Gln–Chl–Ep–Ab
JAK-30	Greenschist, Jaklovce	390–420	1.1–1.3	292–310		1.2–1.3	266	Act–Ph–Chl–Ep–Ab
JAK-6A	Greenschist, Jaklovce			278			294	Act–Chl–Ep–Ab
J-6	Greenschist, Jaklovce			261			275	Wnc–Chl–Ep–Ab
MEL-15	Metabasalt block in flysch, Meliata			321			352	Chl–Ab–Cal
COL-1	Metabasalt block in flysch, Meliata						256	Chl–Ab–Cal
DO-K2	Metaradiolarite, Dobšiná - Končistá			272–296		0.95–1.2	291–310	Qtz–Ph–Chl

).

In addition, greenschist rocks from Jaklovce Unit JAK-30 and JAK-6A, J-6 and 7 samples yield 261–310 °C temperature by [43] Chl thermometry and similar conditions 275–294 °C by [108] Chl thermometry (Figure 14A–F, Figure 7H and Figure 17C,D; Table 11). Greenschist sample JAK-30 contains Ph1 in D1 peak metamorphic assemblage at 1.2–1.3 GPa pressure for 3.45–3.62 a.p.f.u. Si content [101] at given Chl temperatures (Table 4 and Table 11).

Metaradiolarites

Chl–Ph–Qtz multiequilibria geothermobarometry [43] for Jaklovce Unit JAK-204B and JAK-6/19 metaradiolarite samples yields 235–270 °C at 0.4–0.55 GPa (Figure 20A,B and Figure 29; Table 11). This is based on Chl–Ph equilibrium pairs. Similar Chl temperatures of approximately 300–327 °C were obtained by Chl thermometry [108]. However, the entire 3.38–3.48 a.p.f.u. range of Si-in-Ph content indicates higher pressures of approximately 0.65–1.05 GPa at given Chl temperatures (Table 11).

The metaradiolarite DO-K2 sample from Dobšiná–Končistá area has Chl temperatures of 272–296 °C [43] and 290–310 °C [108]. The Si-in-Ph barometry gives consequential peak metamorphic pressures at 0.95–1.2 GPa [101] (Figure 20C; Table 11).

4.4.3. Meliata Unit

Flysch Metasediments

The JAK-204C siliciclastic flysch sample (Figure 20E) composition enabled P–T conditions to be calculated by Chl–Ph–Qtz geothermobarometry [43]. The Chl–Ph(Cel-Ms) pairs yielded 260 °C at 0.4 GPa (Figure 30). However, the chlorite thermometer yields slightly higher temperatures at approximately 350 °C [108]. The inferred Chl temperatures indicate geo-barometric pressures of 0.4–0.6 GPa with Si-in-Cel-Ms = 3.21–3.28 a.p.f.u. [101] (

Table 12. Meliata Unit rock P–T estimates from combined geothermobarometry.

Sample	Sample Description and Locality	Cal–Dol [109]	Chl [43]	Chl–Ph [43]	Ph [101]	Chl [108]	Mineral Assemblage
		T (°C)	T (°C)	P (GPa)	P (GPa)	T (°C)
JAK-202B	Calciclastic flysch Jaklovce	284–323					Cal–Dol–Ab–Kfs–Qtz
JAK-204C	Siliciclastic flysch, Jaklovce		260	0.4	0.4–0.6	348	clast(Ms)–Qtz–Chl–Cel–Ms–Ab
MEL-14/19	Black-gray radiolarite layer in siliciclastic flysch, Meliata		296			340	Qtz–Chl
MEL-17B/19	Contact of dark red radiolarite layer with flysch, Meliata		305–323			341–355	clasts(Chl–Ms–Rt)–Qtz–Chl

).

Calciclastic flysch from Jaklovce Unit samples JAK-202 A and B contain Cal–Dol intergrowths which yield 335–350 °C equilibrium temperature from Cal–Dol solvus thermometry [109] (Figure 24A–C).

Metaradiolarites

Sample MEL-17B/19 from Meliata Unit flysch metaradiolarite layer contains a newly formed Chl which yielded temperatures of 296–323 °C [43] and 340–355 °C [108] (Figure 20F; Table 12).

PXRD Results in P–T Estimates

The Chl and Cal–Dol geothermobarometry results are supported by Ms and Chl PXRD patterns. The full width at half maximum (FWHM) for selected diffraction maxima (002) of Ms, (001) and (002) of Chl show decreasing values in Ms (Kübler index—KI [116,117,118]) and Chl (Árkai index [119]) indicates diagenetic zone (KI > 0.42 Δ°2θ CuKα, <200 °C), anchizone (0.42 > KI > 0.25 Δ°2θ CuKα, <300 °C) and epizone (KI < 0.25 Δ°2θ CuKα, >300 °C). The PXRD measurement and following peak-shape fitting (

Table 13. Meliata Unit flysch metasediments. Full width at half maximum of selected Chl and Ms diffraction maxima at Δ°2θ CuKα.

Phase	Diffraction maxima	DO-F1	DO-F2	DO-K11	JAK-202A	JAK-202B	MEL-2/19	MEL-3/19	MEL-10/19	MEL-13/19	MEL-18/19
Chlorite	(001)	0.077	0.075	0.070	0.069	0.081	0.136	0.073	0.089	0.171	0.079
Muscovite	(002)	0.076	0.082	0.077	0.076	0.095	0.095	0.125	0.090	0.152	0.120
Chlorite	(002)	0.064	0.061	0.057	0.104	0.101	0.110	0.067	0.075	0.109	0.069

) were not calibrated for the studied samples, and the data were used only as the additional support for the determination of P–T conditions. However, the comparison of calibrated and uncalibrated illite measurement shows that variations and differences are smaller in the epizone samples than in anchizone and diagenetic illite [120]. Both values for Ms and Chl from the studied samples indicate their crystallisation at the epizone greenschist facies conditions, with a good correlation between these minerals (Figure 31 and Figure 32). The estimation of metamorphic conditions for both minerals is safely within the epizone, and this reduces the possibility of data misinterpretation. Consequently, the studied samples most likely experienced at least 300 °C which supports Chl and Cal–Dol geothermobarometry results.

4.4.4. Silica Nappe Hanging Wall Mélange

Figure 18 and Figure 19 depict the relic magmatic Mhs and Mh in the Silica Unit amphibole metagabbro sample SA-6. These provided temperatures of magmatic crystallisation at 880–803 ± 22 °C and 1.88 ± 0.21–0.79 ± 0.09 GPa by [110].

5. Discussion

This study provides a comprehensive analysis of metamorphic conditions determined in the IWC Meliatic Superunit, which is also called Meliaticum. Three basic paleotectonic units of Meliaticum [48] were subjected to variable P–T conditions (Figure 33 and Figure 34;

Table 14. Review of P–T estimates from the Meliatic units used in reconstructing the P–T paths (Figure 34).

Sample	Sample Description and Locality	Perple_X [30,102]		Grt–Ph [100]	Cal–Dol [109]	Chl [43]	Chl–Ph [43]	Ph [101]	Chl [108]	Mineral Assemblage
		T (°C)	P (GPa)	T (°C)	T (°C)	T (°C)	P (GPa)	P (GPa)	T (°C)
		Bôrka Unit
HAC-1	Blueschist layer in marble, Hačava	520	1.55	* 475–505						Gln–Grt–Ph–Chl–Ep–Ab
SUG-10	Blueschist layer in marble, Šugov Valley at Medzev					335–353	1.1–1.3	1.5–1.6	341	Gln–Ph–Ttn–Chl–Ep–Ab
DO-12	Blueschist lens in serpentinite, Dobšiná					281	0.4	0.45–0.85	332	Gln–Ph–Chl–Ep–Ab
DO-31	Blueschist lens in serpentinite, Dobšiná							0.85–1.1	245–257	Gln–Ph–Tlc–Chl–Ep–Ab
MEL-11/19	Marble block in flysch, Meliata				280–290			0.6		Cal–Dol–Ph–Ap
		Jaklovce Unit
JAK-6/19	Metaradiolarite, Jaklovce					200-266	0.55	0.8-1.05	300-327	Qtz-Ph-Chl
JAK-204B	Metaradiolarite, Jaklovce					234-245	0.4	0.65-0.75	310	Qtz-Ph-Chl
MR-1	Blueschist, Malý Radzim at Brdárka					306			278	Gln-Chl-Ep-Ab
JAK-30	Greenschist, Jaklovce	390-420	1.1-1.3			292-310		1.2-1.3	266	Act-Ph-Chl-Ep-Ab
DO-K2	Metaradiolarite, Dobšiná–Končistá					272-296		0.95-1.2	291-310	Qtz-Ph-Chl
		Meliata Unit
JAK-204C	Siliciclastic flysch, Jaklovce					260	0.4	0.4-0.6	348	clast(Ms)-Qtz -Chl-Ph-Ab

* Calculated for pressures 1.4–1.6 GPa.

).

5.1. The Bôrka Unit

Blueschist samples do not contain any preserved magmatic assemblages nor do they show any differences in the texture, pointing out that the bulk composition re-equilibrated well during the metamorphic overprint [124]. The modelled pseudosection (Figure 26; sample HAC-1) then matches quite well the observed mineral assemblage of Gln, Ph, Grt, Chl, ±Bt, Ep, Ab in the studied rocks (Figure 6A and Figure 15A,B).

Garnet grains regardless of their size in the studied samples show increasing values of Alm and Grs while exhibiting decreasing Sps indicating garnet growth during the prograde metamorphic conditions [125,126] (Figure 16A–D). Based on these observations, the garnets rim composition with the highest Alm and Grs values coupled with the lowest Sps will reflect the peak D1 stage P–T conditions (Table 2, Figure 26). The growth histories are generally lost in garnets that have attained a temperature in excess of 600–700 °C [126,127] which indicates lower temperatures during the growth of the garnet in the investigated blueschists.

The growth of an additional thin outer zone around the garnets most likely reflects a P–T decrease during the D2 exhumation stage (Figure 16C–E).

Widening the miscibility gap between muscovite and celadonite with either rising pressure or decreasing temperature was initially reported by [128,129], thus confirming the pressure dependency of Si⁴⁺ in Ph (inverse Tschermak´s substitution of Mg²⁺ + Si⁴⁺ for 2Al³⁺) used in the geothermobarometry of phengite bearing metamorphic rocks [101,130,131]. Analyses with the highest Si substitution in Cel-Ms (Table 4) were therefore used with the garnet isopleths to model the peak D1 stage P–T estimates.

White micas from metabasites exhibit variable Si⁴⁺ substitution (Figure 33, Table 4), where Si decreases with pressure during exhumation processes [101,130,131]. This provides us with a wider pressure interval of 0.4–1.6 GPa based on Ph barometers indicating different burial/exhumation depths. Moreover, the content of ^VIAl in all the studied samples from the Bôrka Unit is typical for low-crystallisation temperatures [108], giving an interval of approximately 250–350 °C (Figure 33; Table 10 and Table 14). These data mostly constrain the post-peak D2 stage exhumation conditions. This is also true for Chl–Ph–Qtz geothermobarometry with a similar range of estimates, showing a microscale equilibration of Chl–Ph pairs at different P–T conditions during exhumation (Figure 27; Table 10 and Table 14).

Perple_X pseudosection modelling shows that the Bôrka Unit of the Meliatic continental margin underwent HP blueschist facies metamorphism at approximately 520 °C and 1.55 GPa (Figure 26). This is compatible with the peak Grt–Gln–Ph assemblage from the D1 stage subductional burial to maximum ca. 50 km depth following the closure of the Neotethys Meliata Basin.

Former estimates reported slightly lower P–T conditions in greenschist to epidote-blueschists facies at 380–460 °C and 1.2–1.3 GPa peak pressure. In addition, estimates at 400–460 °C and 1.05–1.2 GPa and 360–400 °C at 0.8 GPa were provided for glaucophane, pyroxene and chloritoid-bearing metapelitic to metapsammitic rocks [63,64]. However, the [71] estimated 520–620 °C and 1.1–1.4 GPa peak metamorphic conditions for metapelites from basal parts of the Bôrka Nappe have slightly lower pressures and overestimated temperatures.

5.2. The Jaklovce Unit

The Jaklovce metabasalts differ from the investigated Bôrka Unit blueschist samples by having clear textural differences in some parts of the rocks. The metamorphic overprinting in the Jaklovce Unit metabasalts, metadolerites, metaradiolarites and siliceous metacarbonates, in the form of metamorphic veinlet networks crosscutting homogeneous parts of these rocks, suggests a significant amount of metamorphic fluids.

These metabasalts have partly preserved magmatic textures crosscut by meso- and microscopically visible metamorphic veinlets (Figure 12A and Figure 14A). We, therefore, calculated the ‘bulk’ whole-rock composition for Perple_X modelling from representative metamorphic veins. The resultant bulk has a higher CaO and MgO content linked to Cal, Ep and Chl in the veinlets compared to the homogeneous part of metabasalt bulk. There is also a small increase in K₂O linked to newly formed Ph in veinlets. The remaining SiO₂, Al₂O₃ and Na₂O oxides related to Pl–Aug relic magmatic texture have on the other hand higher contents than an estimated bulk composition of metamorphic veinlets (Table 9).

Perple_X pseudosection modelling of Jaklovce metabasalt sample JAK-30 metamorphic veinlet mineral assemblage provided P–T conditions of approximately 390–420 °C at 1.1–1.3 GPa (Figure 28). This is consistent with an observed assemblage of Act–Chl–Ph–Ep–Ab–Ttn in veinlets. These inferred the D1 stage peak metamorphic conditions indicate maximum burial of this Jaklovce Unit oceanic crust fragment to a maximum 35–40 km depth in a subduction channel.

Chlorite ^IVAl values are typical for low-temperature crystallisation [108] resulting in an approximately 200–330 °C interval, with the highest ^IVAl reflecting conditions close to the peak D1 stage (Figure 33, Table 5 and Table 14), likewise in the Bôrka Unit. Furthermore, Act amphibole exhibits a low content of ^IVAl common for low crystallisation metamorphic condition in low-greenschist facies (Table 3, Figure 18D,E). Typical zonality of Act amphibole (Figure 17C,D) with Wnc/Fwn rims and rare Mrbk implies several metamorphic phases. A prograde D1 stage increase in pressure is corroborated by Na-rich Amp rims, and a lower-pressure Act in outermost rims may occur due to D2–stage exhumation in greenschist facies. Finally, the single MR-1 (N-MORB type) metabasalt sample of this unit contains Gln and documents oceanic HP subduction. The different pressure conditions are also further confirmed by variable Si⁴⁺ content in Cel-Ms from metasilicites to impure metaradiolarites provide broad pressure estimates between 1.3 and 0.4 GPa (Figure 29 and Figure 33; Table 11 and Table 14) consequently reflecting different D1 burial/D2 exhumation depths. These conditions are consistent with the determined Mrbk, Fwn, Act, Chl, Ab, Ep and Ph mineral assemblages.

Chlorite thermometry and Chl–Ph–Qtz and Ph barometry determined that both N-MORB metabasalts to metadolerites and the associated metaradiolarites were mostly subducted to medium-pressure depths. In addition, 600 MPa pressure was estimated for the Jaklovce metabasalt Fwn [73] by the empiric [74] Al^IV geobarometer compared to the Na^B result. This could be a Mrbk minimum pressure.

However, Bretka Mhb epidote amphibolites may indicate the base of the obducted and thrust oceanic crust slices onto the exhuming continental margin wedge. Finally, the Bretka amphibolites may suggest the P–T conditions achieved due to the ridge subduction of the lower oceanic plate.

Sample SA-6 metagabbro in the Silica Nappe hanging wall at Gemerská Hôrka is considered a detached exhumed Meliatic oceanic fragment included in the Permian salinar mélange during the Cretaceous Silica Nappe overthrusting. Estimated Amp magmatic crystallisation temperatures of 880–803 ± 22 °C and 1.88 ± 0.21–0.79 ± 0.09 GPa in pressures imply a crystallisation depth of 3–5 km. These higher temperatures and low pressures are obviously related to amphibole gabbro magmatic emplacement and crystallisation in the inferred oceanic crust. In addition, the newly formed Mrbk, Act, Ep, Ab, Chl, ±Cal and ±Qtz assemblage most likely indicate metamorphic overprinting in medium pressure greenschist facies. This is comparable to Jaklovce Unit metabasites.

5.3. The Meliata Unit

Continental and oceanic margin flysch metasediments contain newly formed Ab, Kfs and Chl associated with Qtz and/or Cal and Dol in both siliciclastic and calciclastic lithotypes. Chlorite thermometry and Chl–Ph thermobarometry (Figure 30) provided variable temperatures which may record different re-equilibration conditions of the individual Chl along the P–T path. Similarly, Cal–Dol solvus thermometry yielded 286 °C and 0.6 GPa from Ph barometry (Figure 33) in a marble olistolith in flysch. Former estimates on the Meliata Unit metamorphic overprinting at approximately 250–350 °C and 350–540 MPa [54] overlap our reported values.

PXRD study revealed rejuvenated clastogenic and newly formed white mica phases. The values of full width at half maximum (FWHM) for selected diffraction maxima (002) of Ms, (001) and (002) of Chl depend on the P–T conditions in the diagenetic zone to greenschists facies [116,117,118,121,122,123,132]. The decreasing value of FWHM in Ms (Kübler´s index—KI [116,117,118]) and Chl (Árkai´s index [119]) indicates a diagenetic zone (KI > 0.42 Δ°2θ CuKα, < 200 °C), anchizone (0.42 > KI > 0.25 Δ°2θ CuKα, 300 °C) and epizone (KI < 0.25 Δ°2θ CuKα, > 300 °C), which correspond to greenschist facies [122,123].

Crystallographic characteristics in the studied flysch samples which indicate epizonal metamorphic conditions around or slightly above 300 °C (Figure 31 and Figure 32; Table 4 and Table 13), may explain the formation of low-T Kfs, most likely at the expense of K released from rejuvenated clastogenic Ms which has a compositional trend to illite (Figure 22A,B). Many samples, especially those from the Jaklovce Unit, have white mica of transitional illite–phengite composition with decreased (Na + K) and K₂O contents typical of anchimetamorphic conditions (Figure 10 and Figure 20; Table 4) [133,134]. The correlation between illite crystallinity and mica K₂O content was described from the diagenetic grade to the epizone by [135]. The occupancy of the interlayer position of the micas gradually increases, and the (K + Na) content of the illite–muscovite increases from 0.65 to 0.9–1.0 a.p.f.u. Moreover, analyses of the phengitic white mica exhibit a small but significant deficit in the interchange layer [114]. The total interlayer charge (t.i.c.) calculated for 22 oxygens is approximately 1.7 a.p.f.u, and this is characteristic for Phengitic anchizonal white mica [114,135,136,137]. These Meliata Unit data confirm the previous results of [54].

This suggests the relatively shallow burial of the Meliata Unit olistostromatic formation (at Meliata village) in an accretionary wedge to approximately 12–14 km at 290–350 °C and 0.4–0.5 GPa (Figure 30; Table 12 and Table 14).

The contrasting metamorphic conditions in Meliata and Jaklovce units do not support the interpretation of [55] that Meliata and Jaklovce sections of the Meliaticum form one paleotectonic unit with negligible metamorphic overprinting. The determined metamorphic conditions are specific for all three partial units of the Meliaticum and therefore match the subduction/obduction-related accretionary wedge model suggested by [48].

Two, or more often all three Meliaticum paleotectonic units were incorporated in kilometre-size mélange blocks, and this indicates the transformation of the D1–D2 stage subduction-related accretionary wedge into a late D2–D3 stage mélange. Present day nappe outliers of the Meliaticum incorporate different mélange blocks overlying the Gemeric, and less the Veporic superunits of the IWC [95].

6. Conclusions

The application of thermodynamic modelling combined with the chosen geothermobarometers revealed the following metamorphic conditions in the Meliatic paleotectonic units after the closure of the Neotethyan oceanic Meliata Basin.

The Bôrka Unit of the Neotethyan northern continental margin achieved subductional burial to a maximum depth of 50 km. This is constrained by the Perple_X modelling of the D1 stage metamorphic peak P–T conditions of the HP blueschist facies at approximately 520 °C and 1.55 GPa. Confirmation is further supported by Grt–Gln–Ph D1 mineral paragenesis in the blueschists. Chl–Ph–Qtz geothermobarometry revealed a wider pressure interval of 0.4–1.6 GPa during D2 stage exhumation indicating different burial/exhumation depts. Chlorite thermometry provided temperatures of approximately 250–350 °C.

The Jaklovce Unit oceanic sliver slices were subjected to MP to HP subduction. The metamorphic conditions of 390–420 °C at 1.1–1.3 GPa (~35–40 km subductional burial) of inferred D1 stage were provided by Perple_X modelling. Interlayered metacherts to metaradiolarites underwent consistent P/T conditions. The metamorphic P–T conditions of ca. 200–330 °C and 0.4–1.3 GPa from the metamorphic vein mineral assemblages of Mrbk, Wnc, Act, Ab, Ep, Chl, Ph, Cal in metabasalts and metadolerites were constrained by the combination of Ph barometry and Ph–Chl and Chl thermometry. A single N-MORB type metabasalt with Gln suggests blueschist facies conditions in this subducted oceanic crust fragment. Exceptionally, epidote-amphibolite facies conditions were recorded in Bretka N-MORB type amphibolites which constrain the cooled base of an obducted oceanic crust sliver onto a continental margin wedge.

The Meliata Unit (former Meliata Unit s.s.) flysch metasediments yielded the shallowest subduction, or just a burial within the accretionary wedge to ca. 12–14 km at ca. 290–350 °C and 0.4–0.5 GPa that is consistent with the newly formed Ill–Ph to Ph, Qtz, Chl, Ab, Kfs, Cal and Dol.

The metamorphism of Meliaticum documents the metamorphic conditions from the D1 stage subductional burial of the Bôrka and Jaklovce units and serpentinites to the D2 stage exhumation from a subduction channel of those elements into an accretionary wedge with Meliata Unit flysch in the Late Jurassic to Early Cretaceous.

The analysis of the Meliaticum metamorphic conditions, structural observations and the published litho-geochemical and geochronological dataset [48] revealed the three principal paleotectonic Bôrka, Jaklovce and Meliata units which were transformed into three major tectonic units. Although these units have different reconstructed metamorphic P–T paths, they fit to the Meliaticum D1 and D2 stage subduction/obduction-related accretionary wedge evolution. The character of the Meliatic nappe outliers as mélange blocks incorporating different paleotectonic units with different metamorphic overprinting grade implies the late D2 and D3 stage break-up of this wedge into fragments which overloaded the passive Gemeric type continental margin being thrust further northwestward in the AD1 stage of the IWC orogenic wedge.