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Article

Petrogenesis and Provenance of the Triassic Metasedimentary Succession in the Sakar Unit, Bulgaria: Constraints from Petrology, Geochemistry, and U-Pb Detrital Geochronology

by
Tzvetomila Filipova Vladinova
1,* and
Milena Georgieva Georgieva
2
1
Department of Geochemistry and Petrology, Geological Institute of the Bulgarian Academy of Sciences, Acad. Georgi Bonchev Str., Block 24, 1113 Sofia, Bulgaria
2
Department of Mineralogy, Petrology and Economic Geology, Sofia University “St. Kliment Ohridski”, 15 Tzar Osvoboditel Blvd., 1504 Sofia, Bulgaria
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(9), 343; https://doi.org/10.3390/geosciences15090343
Submission received: 1 July 2025 / Revised: 16 August 2025 / Accepted: 18 August 2025 / Published: 2 September 2025
(This article belongs to the Special Issue Editorial Board Members' Collection Series: “Sedimentology and Stratigraphy”)
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Abstract

This study investigates the metasedimentary sequences of terrigenous–carbonate Sakar-type Triassic (TCSTT) and Sakar-type Triassic (STT) in the Sakar Unit, southeastern Bulgaria. Both share lithological similarities (alternation of carbonate–silicate schists, mica schists, marbles, and impure marbles) and are affected by post-Triassic metamorphism, but with differences in metamorphic grade and partly in the variation of potential sources of the sedimentary material. STT shows a higher metamorphic grade (lower amphibolite facies) when compared to TCSTT (lower greenschist facies). Petrographic observations and geochemical analyses indicate protoliths composed of arkosic sandstones, shales, and limestones derived from a quartz-dominated source with minor contributions from intermediate magmatic sources. The U-Pb geochronology of the detrital zircons reveals a dominant Carboniferous age complemented by an Early Ordovician age, which is consistent with the presence of Carboniferous–Permian igneous rocks in the basement. The presence of Early Paleozoic and Cambrian–Neoproterozoic zircons in the detrital zircon populations suggests that older rocks of the basement of the Sakar Unit and the Srednogorie Zone are also sources of the sedimentary material. Based on the immobile trace element content and discrimination diagrams, the siliciclastic component originates from rocks formed in a continental-arc setting. REE patterns indicate a negative Eu anomaly inherited from granitic-source rocks.

1. Introduction

The bulk composition of clastic sedimentary rocks is a fundamental indicator of paleogeographic reconstruction and the clarification of tectonic settings for sediment deposition [1]. These lithological records show good sensitivity to source characteristics and physicochemical parameters of the depositional environment [2,3]. Origin-sensitive geochemical indicators, complemented by the U-Pb geochronology of refractory detrital zircon, provide reliable constraints on sediment source terrains and maximum depositional ages of the strata [4]. Inferred geochemical characteristics of metasedimentary rocks are related to the compositional characteristics of source rocks and their metamorphic overprint [5]. The conservative behavior of specific trace elements during metamorphism provides the basis for lithostratigraphic correlations and petrogenetic interpretations ([6,7,8] and the references cited therein). Redox-sensitive geochemical indicators offer critical information on paleoenvironmental redox potentials, while protolith-sensitive geochemical indicators facilitate the characterization of protoliths.
The geochemistry of carbonates and, in particular, water-soluble trace elements is sensitive to water composition, physicochemical deposition parameters, and carbonate mineralogy [9,10]. Sr, Rb, Ba, Mn, and REE contents are important geochemical indicators of carbonate origin and evolution. The Sr/Ca ratio changes during authigenesis–diagenesis processes [11,12], the Mn content reflects marine redox conditions [13], and the Mn/Sr ratio tracks post-depositional changes [14]. The 87Sr/86Sr isotope ratio can accurately determine the timing of carbonate formation [15]. REE-Y patterns, including Ce and Eu anomalies, reflect the composition and oxidation/redox conditions of seawater and are generally diagenetically stable ([13,16,17] and the references therein). Recent studies show that variations in major elements (e.g., Fe2O3/Al2O3, MnO/Al2O3) and ratios of immobile trace elements (e.g., Ce/Ce*, Eu/Eu*, LaN/CeN, LaN/YbN, NdN/YbN, SmN/YbN) in seawater are significantly influenced by the tectonic setting of the depositional basin. These geochemical indicators offer valuable information on the paleoenvironmental reconstruction and long-term changes in seawater chemistry [18,19]. However, post-depositional recrystallization processes can alter or obscure the original sedimentary textures and primary geochemical characteristics, thereby complicating their interpretation [20,21].
In this study, we present a combination of detailed petrographic observations, whole-rock geochemistry, and LA-ICP-MS U-Pb ages of detrital zircons in metasediments from the Sakar Unit in Bulgarian territory to identify the source of the sediments and their depositional age, as well as to understand the evolution of the sedimentary basin. The studied parametamorphic sequence from pure silicatic to pure carbonatic rocks is affected by metamorphisms ranging from greenschist to amphibolite facies [22,23]. Previous research efforts were concentrated primarily on the eastern Sakar-type Triassic (STT), while the western terrigenous Carboniferous–Triassic of the Sakar type (TCSTT, [24]) remains relatively understudied. Geochemical trace element datasets and detailed petrographic observations remain limited [22], and metamorphic P-T modeling has been restricted primarily to the eastern Sakar Unit [25]. A comprehensive study on the TCSTT and STT will expand our knowledge of the Triassic metasedimentary succession, which will help us to better understand the nature of the metasedimentary cover, providing a significant basis for the future interpretation of the evolution of the SSZ (Sakar–Strandzha Zone). This need is also emphasized by the lack of a universally accepted subdivision of the SSZ that considers the westernmost rocks to be part of it [26]. The rocks of the SSZ are covered by Tertiary sediments, which complicates detailed field and structural studies. In addition, the complex geological history of the region, characterized by multiple phases of deformation and metamorphism, further complicates the interpretation of the tectonic evolution of the SSZ. The apparent lack of comprehensive research within the western Sakar Unit highlights the need for new, fundamental research in the area. Furthermore, the acquisition of additional high-resolution data from the eastern analog will facilitate more robust lithostratigraphic and tectonothermal correlations between these geographically contiguous units, thereby enabling a more definitive assessment of their potential genetic affiliations or independent evolutionary trajectories through integrated, multi-proxy analytical approaches.

2. Geological Setting

Sakar–Strandzha was considered part of the Srednogorie Zone [24], the Sakar–Strandzha Zone (SSZ, [27,28]), or the Strandzha Zone [22,29]. According to the latest geological mapping data, the Sakar region is part of the Thracian Lithotectonic Unit [30]. The latter comprises the low-temperature regionally metamorphosed rocks located between the Rhodope Massif and the Srednogorie Zone, which are characterized by deformation related to the Maritsa Shear Zone and intrusion of Late Cretaceous plutons [31]. In this study, we consider the STT and TCSTT as members of the SSZ [27], as both are composed of the Sakar and Strandzha Units.
The SSZ is located in southeastern Bulgaria (Figure 1a) and northwestern Turkey. It is included in the Inner Balkanides and Variscan orogen in southeastern Europe [27]. In the Turkish literature, the southeastern part of the SSZ is categorized as the Strandzha Massif (e.g., [32,33,34,35,36]) and it is considered the westernmost part of the external Pontides with strong Cimmerian footprints. The SSZ consists of a Paleozoic metamorphic basement unconformably overlain by a thick Triassic–Jurassic metasedimentary sequence and Cenozoic (Eocene–Quaternary) sedimentary rocks [22,24,27,28,29,32,37] (Figure 1b). The Paleozoic metamorphic basement (paragneisses, amphibolites, mica-gneisses, and schists) locally preserves relicts of Neoproterozoic rocks [38,39,40]. Metagranitoids and gneisses in the SSZ basement of the Turkish territory have Late Paleozoic protoliths [32,38,41]. The basement is intruded by Permian and Late Carboniferous metagranitoids [28,32,37,42,43,44]. The Sakar granitic batholith is the largest Late Paleozoic intrusion on the Bulgarian territory (~300 Ma, [28,44,45]). However, some metagranitoid complexes to the east of it show crystallization ages between 230 and 312 Ma [28,46]. Late Paleozoic magmatism is associated with subduction and high-grade metamorphism. This Variscan high-grade metamorphic event is characterized by zircon ages of 271 Ma [32] and 317 ± 3 Ma [47], complemented by structural data spanning the period from 309 ± 24 to 257 Ma [48] in Turkey. This metamorphism is locally constrained in Bulgaria by zircon rims of 334 ± 3 Ma [40] and 327 ± 2 Ma [49], and it is also supported by structural evidence indicating that the maximum age of the metamorphism is 319 Ma [50]. These observations suggest that the metamorphism across the region was a widespread and temporally diachronous event. The interpretation of widespread magmatism in the region also varies, being characterized as either two separate events [46] or a single Late Paleozoic–Early Mesozoic tectono-magmatic cycle inferred from similar geochemical characteristics of granitoids [51]. This would indicate a change from post-collisional Permo–Triassic magmatism to subsequent rift and back-arc evolution of the basin [52]. Continental sedimentation in this basin had already begun during the Carboniferous–Permian and evolved with the subduction and continued consumption of the oceanic crust of the Paleotethys [22].
The protoliths of the Triassic metasedimentary complex in the eastern part of the Sakar Unit (assigned to STT) [22] consist of basal conglomerates and arkosic sandstones, passing upward into lithic sandstones with pelitic alternations and impure limestones, indicating shallow and deep-marine to turbiditic deposition [22,48]. The sediment deposition ends with limestones and dolostones, whose metamorphic analogs contain preserved fossils from the Early and Middle Triassic (crinoids, bivalves, conodonts; [54,55,56]). The metasediments from the westernmost deposits have not been studied in detail, but the authors of [24] assigned them to the STT as TCSTT, which could be correlated with the Ustrem Formation. Sr isotopes on carbonate rocks suggest a Late Paleozoic and/or Mesozoic time of sedimentation [57]. Detrital zircon ages in metasediment cover a range from Ordovician (433–446 Ma) to Carboniferous (305 Ma) [34,40,48,58,59,60] and are consistent with the time of crystallization of metagranitoids in the basement. Both the cover and basement were affected by a metamorphism of greenschist to amphibolite facies during the Late Jurassic–Early Cretaceous [25,26,32,48,61,62,63,64,65,66,67,68,69], followed by rapid post-Late Jurassic cooling, as inferred from fission-track dating [36].
The geological evolution of the SSZ is related to Variscan/Hercynian orogenesis, produced by a long-lived Ordovician to Triassic magmatic arc, which evolved on the northern side of Paleo-Tethys [32,39,48,70]. The SSZ represents the continuous accretion of the northern Gondwana margin to Eurasia from the mid-Paleozoic to the Cimmerian. It preserves Precambrian continental blocks, interpreted as remnants of the northern Gondwana margin (e.g., [35]), and is assigned to the southern passive continental margin of Eurasia [42].

3. Analytical Procedure

Forty-six samples of the Sakar metasedimentary cover were collected for petrographic observations, geochemical studies, and U-Pb zircon geochronology. Table 1 provides a list of the samples with their GPS coordinates. The sampling locations are shown in Figure 1b. The major elements were determined using X-ray fluorescence (XRF) at Sofia University “St. Kliment Ohridski”, in Karlsruhe, Germany, with a Bruker AXS XRF spectrometer, and at Bureau Veritas Minerals, Vancouver (Canada). The analysis was performed on powder pellets prepared using an HTP press at a constant pressure of 15 tons for 20 s. Loss on ignition was measured using a standard method. For XRF at Bureau Veritas Minerals, Vancouver (Canada), the analysis was performed on Li2B4O7/LiBO2 fusions using the STD OREAS184 and STD SY-4(D) standards. The XRF at Sofia University “St. Kliment Ohridski” was conducted using an EDXRF Epsilon 3XLE instrument (PANalytical) with the Omnian 3SW software. The quantitative analysis was performed on a melt obtained by homogenizing approximately 1 g of sample with an additional 3 g of lithium metaborate (LiBO2) and 6 g of lithium tetraborate (Li2B4O7), which were used as fluxes. Trace elements were measured using an LA-ICP-MS (New Wave Research (NWR), 193 nm excimer laser UP-193FX attached to a Perkin–Elmer ELAN DRC-e quadrupole inductively coupled plasma mass spectrometer at the Geological Institute, Bulgarian Academy of Sciences, in Sofia, Bulgaria, using SiO2 and CaO as internal standards and NIST 610 as an external standard. The trace elements were measured in the same fused glass in which the major elements were analyzed. To avoid micro-domains, three analytical measurements were performed in each fused glass, and their average values were used. Zircon separation of 8 samples was conducted by following standard techniques while using heavy liquids. The selected grains (200–60 μm) were arranged in epoxy resin and dated using LA-ICP-MS with U-Pb dating at the Geological Institute of BAS, Bulgaria, and the Magma and Volcanoes Laboratory in Clermont-Ferrand, France, using GJ1 as a primary standard and Plešovice as a secondary standard. The ages used were at a 10% level of discordance (206Pb/238UMa)/(207Pb/235U Ma) × 100), accompanied by the calculation of a non-iterative probabilistic model for determining a single concordant age and its concordance class from 1 to 7 [71]. The detrital zircons belonged to the Ustrem (TV-13, TV-17, TV-39, TV-40, TV-41, TV-45, TV-48) and Paleokastro Formations (TV-49).

4. Field Observation and Sampling

The main outcrops of STT and TCSTT metasediments are located to the east and west of the Sakar batholith (Figure 1b), near Topolovgrad City to the east and Klokotnitza village to the west.
In the eastern part, the metasediments belong to STT [22]. The lowermost Paleokastro Formation consists of metasandstones and metaconglomerates, formed in a continental environment with typical alluvial characteristics [72]. The terrigenous material is represented by rounded and semi-rounded quartz crystals of ~3 cm in size (Figure 2a), surrounded by a finer-grained matrix of chlorite, biotite, muscovite, and epidote. Fine- to coarse-grained metasandstones contain quartz, white mica, biotite, feldspar, rounded and semi-rounded granite, and gneiss fragments (Figure 2b). The gradually overlying metaclastic–carbonate Lower Triassic Ustrem Formation comprises a gradual transitional alternation of calcite–biotite schist (Figure 2c), quartz–muscovite schist, muscovite–quartz schist, and marbles. In sandy marbles, metasandstones and quartz amphibolites of the Ustrem Formation preserve bivalve shell negatives (e.g., Myophoria costata, Myalina spp.) and crinoids [22,72], which indicate the Upper Triassic age of the sediments. The Ustrem Formation is conformably overlain by conodont-bearing Middle Triassic calcite and dolomite marbles of the Srem Formation (Figure 2d, [22]). The metasediments of Sakar-type Triassic were deposited in a fluvial to shallow marine carbonate platform setting, and for a short period in the Early to Middle Triassic, they reached a thickness of over 2400 m [22].
In the western outcrops in the Klokotnitsa village area (Figure 1b), Triassic metasediments transgressively overlie Late Paleozoic terrigenous silicate–carbonate series [72,73]. The lithological sequence starts with metaconglomerates, metasandstones, muscovite–calcite schist, muscovite–dolomite schist, quartz–muscovite schist (Figure 2e), and phyllites (Figure 2f). The upper part of the succession is dominated by carbonate rocks (calcite, dolomite, or impure marbles and carbonate–silicate schists). More visible in marble quarries, the metasediment layers are sub-vertical and folded, often with alternation of silicate- and carbonate-dominated layers. The greenish phyllite, composed primarily of muscovite, quartz, and chlorite, exhibits two distinct foliation planes (Figure 2f), reflecting the complex deformational history of the region.

5. Petrographic Observation

According to the systematic of metacarbonate rocks by modal composition [74], the following lithologies can be distinguished: pure marbles (>95% carbonate minerals), impure marbles (50–95% carbonate minerals), carbonate–silicate rocks (5–50%), and silicate and carbonate-bearing silicate rocks (<5%).

5.1. Pure Marbles

The structure of pure calcite and dolomite marbles is granoblastic with unclear foliation. The metamorphic recrystallization leads to the amalgamation of mineral grains and the appearance of deformation lamellae in calcite. Foliation is best defined by elongate calcite grains and muscovite found in the marbles from the area of Oreshnik village (Figure 3a). Bioclasts (crinoid fragments) and fine-grained partly recrystallized fossil remains with an irregular to oval shape are common (Figure 3b). The most common silicate minerals are quartz and muscovite. Opaque minerals are abundant in various shapes and sizes, while detrital rutile is less frequently observed.

5.2. Impure Marbles

Impure marbles are dominated by elongate calcite with deformation twins and rarely by rhombohedral dolomite grains. Carbonate minerals are present in coarser sub- to euhedral crystals, and dolomite often forms uniform-grained monomineral areas. Foliation is marked by thin phyllosilicate (muscovite, ±chlorite) bands, defining lepido-granoblastic to granoblastic textures. Rhombohedral calcites suggest former dolomite crystals that underwent dedolomitization during metamorphism [75], with associated thin Fe oxide/hydroxide rims indicating compositional changes during this transformation [76].
The well-presented clasts of quartz, plagioclase, and K-feldspar are the common silicate minerals. The mica bands with elongated plagioclase grains are captured by polygonized quartz aggregates. Relict clay mineral components are inferred to be present in the fine-grained matrix of the TCSTT impure marbles (Figure 3c). The impure marbles from the eastern outcrops contain subhedrals rich in grossular garnet porphyroblasts (Figure 3d), along with minor epidote and diopside. Opaque minerals (magnetite, pyrite, and hematite) are abundant and oriented along the foliation. Syn- to postmetamorphic coarse-grained calcite veins crosscut the foliation and lead to remobilization and recrystallization of minerals from the finer-grained matrix.

5.3. Carbonate–Silicate Rocks

The foliation of carbonate–silicate rocks (e.g., muscovite–calcite schist, muscovite–dolomite schist, calcite–biotite schist) is traced using phyllosilicate bands alternating with bands of calcite or dolomite with deformation lamellae. Plagioclase grains are often included in phyllosilicate bands and are parallel to the foliation. Lenticular to recrystallized polygonal quartz aggregates are also distinguished. K-feldspar clasts are rounded with microcline twinning, enveloped by quartz–muscovite pressure shadows and dolomite lenses. The phyllites of TCSTT preserve two perpendicular foliations (S1—traced by muscovite, chlorite, calcite, ilmenite, and quartz; S2—traced mainly by muscovite) and small synkinematic porphyroblasts of calcite, chlorite, and muscovite subparallel to the S1 foliation (Figure 3e). Carbonate–silicate schists from the eastern outcrops do not contain dolomite and K-feldspar, but aggregates of syn- to postkinematic biotite and epidote porphyroblasts and opaque minerals (hematite and magnetite) form. The biotite porphyroblasts include numerous minerals from the matrix and larger epidote grains (Figure 3f). The growth of biotite porphyroblasts with abundant epidote inclusions marks increasing temperature without significant deformation. Syn- to postkinematic porphyroblast formation is a typical phenomenon for the area and is accompanied by quartz and calcite annealing. Oxidized calcite clasts are resorbed and randomly distributed in the samples.

5.4. Silicate and Carbonate-Bearing Silicate Rocks

The foliation in silicate and carbonate-bearing silicate rocks (muscovite–biotite–quartz schist, muscovite–chlorite schist, garnet–biotite–muscovite schists) is defined by the alternation of thin phyllosilicate (muscovite, ±chlorite, ±biotite) bands and quartz–feldspathic bands with intensive static recrystallization (Figure 4a). The metaterrigenous rocks (metasandstones and metaconglomerates of the STT) are characterized by a muscovite–sericite recrystallized matrix, within which large isometric polycrystalline quartz clasts dominate, along with plagioclase, K-feldspar, and occasionally calcite. Both rock types contain phyllosilicate-rich bands with prismatic, elongated plagioclase crystals and euhedral epidote (~0.05 mm), aligned with their long axes parallel to the foliation. Quartz clasts (~1 cm) exhibit undulose extinction. Sericitized K-feldspar clasts show microcline grid patterns and, more rarely, Carlsbad twinning. Plagioclase clasts are strongly sericitized and display deformation lamellae. Calcite clasts are xenomorphic and contain numerous inclusions of quartz and, less commonly, chlorite.
In our samples, garnets appear as larger, disintegrated clasts; they are resorbed and replaced by chlorite and biotite (Figure 4b), and they probably have a detrital origin. In quartz-richer schists, smaller oval-shaped grains grew during the last Mesozoic metamorphic event (Figure 4c). In phyllosilicate-rich samples, postkinematic garnet porphyroblasts are common (Figure 4d). Syn- to postkinematic porphyroblasts of biotite and epidote (~2 mm) grow in the carbonate-bearing silicate samples (Figure 4e). The postkinematic calcite veins are coarser-grained and crosscut the foliation, and there are remobilized brownish-red Fe oxides and hydroxides along cleavage planes. The association of the newly formed metamorphic minerals depends on the detrital material that built up the sediments’ protoliths and, consequently, on the components available during metamorphic transformations. The accessory minerals are randomly distributed among the samples, and many of them are of detrital origin. The high closure temperature of the zircon makes it a convenient mineral for the tracing of the provenance of the sediment material (Figure 4f). Other accessory minerals have the potential to re-equilibrate and to reset their isotope systems during metamorphism (rutile, monazite, apatite) and could be used to date the last metamorphic event. Opaque minerals (magnetite, ilmenite) trace the foliation, suggesting syn-metamorphic formation.
Petrographic observations of diverse Triassic metasedimentary rocks (carbonates, carbonate–silicates, silicates, and carbonate-bearing silicates) within the Sakar Unit revealed distinct mineral associations for each lithological type (Table 2), confirming their para-sedimentary origin. Detrital components include quartz, with subordinate plagioclase and K-feldspar, as well as accessory minerals such as zircon, monazite, and apatite, all of which are indicative of a predominantly granitic provenance. The marble protoliths are interpreted as calcitic and dolomitic limestones containing variable amounts of detrital silicate material. The metamorphic mineral assemblages reflect heterogeneous metamorphic conditions, ranging from lower to upper greenschist facies in the western part of the unit to lower amphibolite facies in the east.

6. Geochemistry

The bulk geochemistry of the metasedimentary rocks is controlled by common carbonate and silicate minerals with detrital or sedimentary origin. The trace element contents are controlled mainly by the accessory mineral associations, as well as by some major minerals.

6.1. Minerals Controlling Whole-Rock Geochemistry

The major oxides in the studied metasedimentary rocks (pure, impure marbles, carbonate–silicate rocks, carbonate-bearing silicate rocks, and silicate rocks) are presented in Table 3. The correlation coefficient (r) used is derived from the whole-rock data. The main content of CaO and MgO participates in carbonate minerals (calcite and dolomite), as confirmed by the negative correlation between CaO+MgO and SiO2 (Figure 5a). The pronounced negative relationships of r(SiO2, CaO) = −0.90 compared with r(SiO2, MgO) = −0.51 correspond to calcite dominance. Excluding dolomite-bearing rocks, the participation of MgO (<5 wt%) in silicate minerals (chlorite, biotite) is evidenced by the positive correlation with Al2O3 (Figure 5b). Both positive and negative correlations distinguished the relationship of SiO2 with Al2O3, TiO2, Fe2O3*, and K2O (Figure 5c,d). The positive relationship observed for SiO2 < 60 wt% confirms the predominance of chlorite, white mica, and feldspar over quartz. Conversely, the negative correlation of SiO2 (>60 wt%) with Al2O3, TiO2, Fe2O3, and K2O corresponds to the dominance of quartz over the other silicate minerals. The positive correlation between Al2O3 and K2O (Figure 5e) is due to the presence of muscovite, biotite, and K-feldspar in the mineral composition. The ratio of K2O/Al2O3 is most often in the characteristic interval for muscovite (0.2–0.4, [77]), which shows the leading role of this mineral in the distribution of K and Al in the studied samples. The Na2O/Al2O3 ratio (Figure 5f) ranges from values typical of muscovite (≤0.02) to plagioclase (≥0.40), the main sodium-bearing mineral in the studied rocks.

6.2. Minerals Controlling the Whole-Rock Trace Element Composition

The contents of trace elements in bulk-rock samples are provided in Table 4 and Table 5. Most of the trace elements (Sc, Ti, V, Cr, Co, Ni, Cu, Ga, Rb, Y, Zr, Nb, Sn, Sb, Cs, Ba, Hf, Ta, W, Pb, Th, U, and REE) are carried by the silicate minerals, as confirmed by the statistically significant positive correlation with the silicate major oxides and the negative correlation with CaO, i.e., r(Zr, CaO) = −0.81. The contents of alkaline and alkaline trace earth elements correlate positively with K2O (r(Rb, K2O) = 0.87, r(Cs, K2O) = 0.76, r(Ba, K2O) = 0.76)), which indicates their association with the most common potassic rock-forming minerals (white mica, biotite, K-feldspar; Figure 6a). This is supported by the low Rb content (~1 ppm) in marbles, as opposed to the samples with abundant mica (e.g., Grt-Bt-Ms schist TV-58 with Rb = 435 ppm). The gallium content reaches up to 64.6 ppm in mica- and chlorite-rich rocks, isovalently replacing Al (r(Ga, Al2O3) = 0.86, Figure 6b) in aluminosilicate minerals (micas, feldspars, epidotes, garnets). The uneven content of Fe2O3* (higher values in terrigenous rocks (0.86–6.47 wt%) and rutile–ilmenite-bearing rocks (1.15–7.59 wt%)) shows strong to moderate positive correlations with transition metals (rSc = 0.65, rV = 0.59, rCr = 0.52, rCo = 0.53, rNi = 0.62, rZn = 0.63), indicating residence in mafic (e.g., biotite, chlorite, garnet) and accessory (rutile, ilmenite) minerals.
The high-field-strength elements (HFSEs) (Zr, Hf, Ta, Nb) and actinides (Th, U) reside in accessory minerals and rarely in rock-forming minerals through isomorphic substitution of major elements (e.g., Ti). The strong positive correlation between Zr and SiO2 (at SiO2 from 0.4 to 60 wt%, Figure 6c) is related to the increased proportion of detrital zircon and other accessory minerals with increasing silicate components in rocks. The lack of correlation observed at SiO2 > 60 wt% is associated with the increasing dominance of quartz and a corresponding decrease in zircon, which is corroborated by the consistent Zr/Hf ratio of ~40.
The Th and U content and Th/U ratio increase from carbonate to silicate rocks (Figure 6d; from 0.28 to 16.47 ppm, mean: 4.42), with two trends being observed: r(Th/U, SiO2 < 60 wt%) = 0.81 and r(Th/U, SiO2 > 60%) = 0.68. This corresponds to the upper continental crust composition [78]. The Th/U variation could be related to weathering and sedimentation processes, considering the mobilization of oxidized U6+ [1,80,81,82,83]. Sr is highly abundant in carbonate rocks compared with other elements (Figure 6e). Its preference for calcite is confirmed by higher Sr contents (220–4268 ppm) in calcite marbles and lower contents (58–195 ppm) in dolomite and calcite–dolomite marbles (Figure 6f). The higher Th/U ratios (0.28–7.33) and uranium content (0.24–4.18 ppm) in metacarbonate rocks point to an oxic environment of precipitation.
The contents of rare-earth elements (REE) are presented in Table 4. The post-Archean Australian shale (PAAS) values [78] and chondrite [79] are used for the normalization of metacarbonate and metasiliciclastic rocks, respectively. Most of the HREEs in metacarbonate rocks were under the detection limit, but a few REE patterns are similar to seawater REE patterns; with LREE depletion (average (Nd/Yb) n = 0.51, n = 6), there are negative to small positive Ce/Ce* anomalies (0.39–1.07, average = 0.8, n = 12) and positive La anomalies. Ce and La anomalies are sensitive to detrital contamination, and in the studied samples, they indicate precipitation from seawater with some clastic input. The variable detrital input is visible in the lack of positive Eu/Eu* anomalies (0.95–1.61, average = 1.21, n = 4) ([83] and references therein).
The chondrite-normalized REE diagrams of carbonate–silicate to silicate rocks display LREE enrichment, a flat heavy HREE pattern, and a negative Eu anomaly (Figure 7a), equivalent to the upper continental crust. The LaN/SmN (1.10–4.70) and GdN/YbN (1.06–2.12) ratios fall into a narrow range for silicate-rich rocks. The prominent Eu depletion (Eu/Eu*= 0.49–0.86, and single Eu/Eu* = 1.01 for metasandstone TV-47) could be related to chemical fractionation within the continental crust, associated with the production of K-rich granitic rocks, which typically possess negative Eu anomalies (Figure 7a, [84]).

6.3. Protoliths: Provenance, Weathering, and Hydraulic Sorting

The affinity of most major and trace elements to the siliciclastic component and the low mobility during diagenesis and metamorphism support their use as classification parameters of protoliths and provenance. The geochemical signature demonstrates differences in silicate protolith components such as arkoses, litharenites, and graywackes according to the classification diagram of [85], with low Na2O/K2O and SiO2/Al2O3 ratios for clay-rich materials, as well as high Na2O/K2O and SiO2/Al2O3 ratios for sandy material (Figure 8a). Some very low values of these ratios, log(Na2O/K2O) < −1 and log(SiO2/Al2O3) < 1, appear outside the diagram fields due to Na mobility during the weathering of the source area. The discriminant functions of major oxides indicating the sedimentary origin [3] determine the quartz-dominant province with a partial felsic igneous source (Figure 8b). The provenance is primarily characterized as having a dominant acidic to mixed arc source, as indicated by La/Th < 5 and Hf < 5 ppm, a minor contribution from an andesitic arc source, where La/Th > 5 while Hf < 5 ppm, and the presence of old sedimentary material with La/Th < 5 and Hf > 5 ppm (Figure 8c, after [86]).
The Th/Sc and Zr/Sc ratios are consistent with the upper continental crust composition, along with significant sediment recycling and the enrichment of heavy minerals, particularly zircon (Figure 8d, after [1]). The low-mobility elements (La, Sc, Ti, Zr) are unambiguously plotted in the continental island arc field [2], with a slight deviation from the continental island arc field towards the active and/or passive continental margin field (Figure 8e,f).

7. U-Pb Detrital Zircon Geochronology

The U-Pb ages vary from Precambrian to Paleozoic based on 168 zircon grains, 293 analytical points, and 280 concordant results (Table 6). The abundance of data necessitates the presentation of selected representative data that encompass all age determinations from each sample, as shown in Table 7, Table 8 and Table 9. The major age clusters include Paleozoic or Paleozoic to Neoproterozoic zircons with secondary Meso- and Paleoproterozoic to Neoarchean ages. The key range under 800 Ma features three frequency peaks at 320 Ma, 455 Ma, and 580 Ma, which are linked to variations in source provinces (see Figure 9), with the prevalence of Late Ordovician ages in the TCSTT and Carboniferous–Neoproterozoic ages in the STT.
The Late Paleozoic zircon population (quartz–muscovite schist TV-45, calcite–biotite schist TV-48, and metaconglomerate TV-49) of STT is composed of euhedral, long to short, prismatic, and minor well-rounded grains, which are colorless or yellowish to pink. The internal texture is typical for igneous zircon, with a homogeneous euhedral core and oscillatory-zoned rims (Figure 10a–k) or fully oscillatory-zoned grains (Figure 10l). Grains with completely homogeneous (Figure 10m–o), complex, and weak convolute zoning (Figure 10p,q) or with occasionally thin recrystallized rims are rare. The age variation (287–622 Ma) yielded an Early Permian–Late Carboniferous cluster (287–346 Ma) and a second group of Early Silurian–Neoproterozoic ages (439–622 Ma). The younger ages are related to concentric zoning, homogeneous cores, and completely zoned grains (Th/U = 0.13–1.49). The Th/U ratio (0.09–0.94) in the oscillatory or homogeneous zones where the older ages were measured is comparable and suggests a magmatic origin consistent with the internal zircon texture. The TV-45 sample (coarse-grained fraction) demonstrates Early Permian–Late Cambrian variety (305–501 Ma) with Carboniferous predominance (305–346 Ma, Th/U = 0.13–1.11) and a major age cluster of ~330 Ma (Figure 10r,s). The youngest zircon age is 305.1 ± 4.3 Ma (№ 3c, Table 7). The zircon ages from the TV-48 sample vary between 287 and 586 Ma with a maximum frequency at ~300 Ma (Figure 10t,u) and Th/U = 0.26–1.49. The data define the earliest time of zircon input as being during the Early Permian. The results of <300 Ma (286.5–298.2 Ma in five zircon grains (№ 9-c, 11-c, 13-c, 13-r, 15-c, 17-r; Table 7)) yield a concordant age of 297.0 ± 2.4 Ma (MSWD of 0.98, Figure 10v) and a preserved primary morphology of close source provenance. The zircon ages in the TV-49 sample scatter from Early Permian to Neoprotezoic (307–622 Ma), with a major group from 300 to 350 Ma. The coarse-grain zircons show older ages (330–622 Ma, cluster at 333 Ma) compared with the younger ages in fine grains (307–345 Ma, cluster at 320 Ma, Figure 10w). A single crystal from the fine-grained fraction (№ 36, Table 7) yielded the youngest ages in this study. The euhedral core and oscillatory-zoned rim display the youngest ages of 310.1 ± 3.8 Ma and 307.1 ± 3.7, respectively (№ 36, Table 7), with a concordant age of 308.1 ± 2.5 Ma and an MSWD of 1.3, thus indicating a Late Carboniferous maximum age deposition.
The Early Paleozoic igneous zircon population (quartz–muscovite schists TV-13 and TV-17) of TCSTT comprises colorless and pale to deep pink grains, which are dominated by subrounded grains with low proportions of euhedral prismatic and completely rounded shapes. The fine-grained zircons (60–100 μm) differ due to the predominance of long prismatic crystals. The CL images reveal three types of internal structures: (1) xenocrystic cores and oscillatory rims (Figure 11a,b); (2) concentric-zoned grains with unzoned euhedral cores and oscillatory rims (Figure 11c,d); (3) complex-textured grains of recrystallized or newly grown convolute zones (Figure 11e–j). The zircon ages in coarse-grained crystals (200–100 μm, TV-13) vary between ~400 Ma and ~1400 Ma, with a major cluster of 460 and several older grains of sub-concordant to discordant ages (580 to 707 Ma and 903 to 1430 Ma, Figure 11k,l). The euhedral cores range from 405 to 481 Ma, with an average Th/U ratio of 0.27; the age range for the oscillatory zones is 440 to 473 Ma, with an average Th/U ratio of 0.25. For grains with complex to convolute zoning, the ages range from 410 to 461 Ma, with an average Th/U ratio of 0.20. In the fine-grained zircon fraction (100–60 μm, TV-13 and TV-17), the ages range from 406 to 590 Ma, with major frequencies at ~420 Ma (TV-13) and ~480 Ma (TV-17) (Figure 11k–m) and Th/U ratios of 0.14–0.94. Patchy recrystallization and magmatic zoning disturbances are rarely related to lower Th/U ratios from 0.03 to 0.09 (473–411 Ma, TV-13). The youngest ages (405–412 Ma) were found in five grains from both size fractions (TV-13), and they define a concordant age of 404.6 ± 4.9 Ma (Figure 11n) and an Early Devonian maximum sedimentation age of the protolith.
Cambrian and Precambrian ages (Paleoproterozoic to Neoarchean) were obtained for detrital zircons from muscovite–quartz schist (TV-39) and muscovite–quartz schists (TV-40, TV-41) of STT. The zircon grains are semi-rounded, short and prismatic, or completely rounded. The dominant internal textures show homogeneous cores with oscillatory-zoned rims (Figure 12a–e), xenocryst cores with homogeneous or oscillatory rims (Figure 12f–j), and completely homogeneous grains (Figure 12k–m). Sectoral zonation (Figure 12n) and complex to convolute structures (Figure 12o) are rarely observed. The age data range from 498 to 2876 Ma, with two major clusters: Neoarchean–Paleoproterozoic and Neoproterozoic–Cambrian. Neoarchean (2545–2876 Ma) and Paleoproterozoic (1731–2385 Ma) ages were established in 14 grains (TV-39, TV-40, and TV-41). These older ages are generally related to xenocryst cores with younger Neoproterozoic and Cambrian mantles, with the Th/U ratio (0.09–1.40) indicating a magmatic origin. The TV-39 sample exhibits Neoproterozoic–Cambrian ages (Figure 12p), as expressed in two major clusters at ~620 and ~530, respectively (Figure 12q). The Neoproterozoic age variation (552–673 Ma with Th/U = 0.12–0.82, except for grain № 11c with 858 and 899 Ma, Table 9) is related to the coarse-grain fraction. The fine-grain zircons are distinguished by their younger Neoproterozoic ages (548–609 Ma, Th/U = 0.12–0.47) with the presence of Cambrian ages (498–534 Ma, Th/U = 0.11–0.29, Figure 12p,q). The younger (498.2 ± 5.3 Ma) and concordant ages (505.7 ± 7.6 Ma with MSWD 6.3, Figure 12s) can be considered as the earliest time of deposition of the detrital zircon in the sedimentary protolith. The Neoproterozoic age of TV-40 shows variation from 543 to 707 Ma (Table 8), with a major cluster between 570 and 580 Ma. The Th/U ratios (0.10–0.94) suggest a magmatic origin. The youngest Cambrian zircon (536.3 ± 6.8 Ma) indicates Proterozoic–Early Cambrian for the earliest time of zircon deposition. The major age of the coarse-grained fraction (TV-41) indicates Neoproterozoic age variation from 539 to 937 Ma, with a maximum of ~660 Ma and ~550 Ma (Figure 12r). The Th/U ratios from 0.13 to 2.17 indicate the predominantly magmatic origin of the detrital zircons, with the exception of a low Th/U ratio (Th/U = 0.04, № 15-r, Table 8). The youngest (539 ± 26 Ma, № 12-r, 36-r, Table 9) and concordant ages of 544 ± 15, MSWD = 1.12 indicate Early Cambrian deposition.

8. Discussion

The metasedimentary succession in the STT (Topolovgrad area, [22]) correlates with similar TCSTT formations (Klokotnitsa area, [24]). Despite lithological similarities and post-Triassic metamorphism, the metasediments exhibit differences in metamorphic grade with analogous alternation of carbonate–silicate schists, mica schists, and impure marbles, suggesting a comparable protolith composition and depositional setting. However, while the TCSTT is dominated by impure marbles, the STT displays a wider variety of rock types and contains distinctive biotite and garnet porphyroblasts. These mineralogical differences reflect varying degrees of metamorphism. The observed metamorphic minerals indicate low-greenschist facies conditions in the TCSTT [87], which increase to low-amphibolite facies in the STT [23,25,29,64,88,89,90].
The protolithic interpretations of the studied metasedimentary sequence are based on petrographic observations and bulk-rock geochemistry. Both suggest protolithic sedimentary rocks composed of quartz, clay minerals, and carbonate minerals, such as arkosic sandstones, shales, and limestones. This is supported by the abundant presence of white mica, clastic grains (quartz, K-feldspar, and plagioclase), and calcite. Similar protolith compositions are confirmed by the major oxide contents, which correspond to a previous mixed succession of sandy materials with high Na2O/K2O and SiO2/Al2O3 and low Na2O/K2O and SiO2/Al2O3 ratios for clay-rich materials and carbonate sediments. The major oxide contents and their correlation coefficients reflect the predominance of quartz over other silicate minerals (chlorite, white mica, and feldspar) in the TCSTT and the opposite relationship (predominance of them over quartz) in the STT. The bulk of trace elements (Rb, Ba, Cs, Pb, Zr, Hf, Nb, Ta, Th, U, Ga, Sc, Th, U, Co, Ni, REEs, etc.) are hosted in silicate minerals, with the exception of Sr, which is associated with the carbonate component.
The clastic material in the rocks can be linked to a quartz-dominated provenance with a minor contribution from intermediate magmatic sources [3]. Such a source province is typically associated with acidic magmatic bodies that are the source of quartz, K-feldspar grains, and accessory minerals such as zircon. The presence of the latter is confirmed by the high degree of sorting of the sedimentary material with Th/Sc ~ 1 and Zr/Sc > 1. The acidic composition of the source province is further supported by the contents of immobile elements (La, Th, Hf), which indicate a dominant felsic arc source for both studied areas. Discrimination diagrams [2,86] for determining the tectonic setting indicate a dominance of a continental arc setting for the source province. The association of the metasediments with the upper continental crust is also supported by chondrite-normalized REE patterns and the prevailing Th/U ≈ 4 ratio for both study areas. The REE distribution is characterized by higher contents of light REEs, a uniform distribution of heavy REEs, and a negative Eu anomaly. The europium anomaly may be controlled by the composition of the source province and is commonly associated with granitic rocks [84]. This aligns with models proposing an active continental margin where the subduction of oceanic crust beneath a continental plate leads to the generation of a magmatic arc and concomitant sedimentation in adjacent basins. The observation is directly linked to the Late Paleozoic geological setting related to the closure of the Paleotethys Ocean and the formation of an extensive continental island–arc system along the southern margin of Laurussia (e.g., [28,51,56,91]). Magmatic processes associated with subduction in this environment generated acidic igneous rocks, which were subsequently eroded and contributed to the composition of the investigated metasediments. Despite ongoing debates regarding the temporal relationship between magmatism and tectonic phases [28,39,41,44,46,52], our geochemical data support a scenario where the erosion of igneous rocks related to subduction processes significantly contributed to the composition of the studied metasediments. It is also plausible that post-orogenic magmatism and sedimentation associated with the collapse and erosion of the Variscan orogenic structure [92] played a role, particularly given the mention of acidic volcanism and supracrustal clastic sedimentation preceding marine sedimentation.
The source rocks of the marbles correspond to limestones with varying proportions of detrital silicate minerals. The trace element contents indicate the deposition of the carbonate protoliths in an oxygenated environment, as evidenced by the low U content. Similar interpretations of the protoliths for the Topolovgrad region are consistent with previous studies [22,93,94,95]. Negative Ce anomalies are more common in the TCSTT and less common in the STT, often coinciding with the predominance of the carbonate component in the rocks. This suggests their inheritance from seawater. This relationship is supported by the preservation of the primary REE composition of the metacarbonates with a pronounced negative Ce anomaly.
U-Pb geochronology of detrital zircons provides information on the age of deposition of the metasedimentary sequence, which shows some differences in the province of origin of the sedimentary material: a predominance of Early Paleozoic ages (400–500 Ma) in the TCSTT and Cambrian–Neoproterozoic ages (500–700 Ma) in the STT. The internal structures and Th/U ratios indicate a dominant contribution of magmatic zircons with a well-defined maximum in Carboniferous ages, complemented by the youngest data in the Early Permian. Detrital zircons from the STT are associated with Carboniferous–Permian magmatic rocks (346–286 Ma). Abundant information on granites and metagranites with Late Carboniferous–Triassic ages in the basement of the studied metasedimentary rocks [28,37,44,46,50] provides an explanation for the nearby sources of magmatic detrital zircons. The potential source can be linked to the established Early Paleozoic magmatic bodies in the basement of the western part of the Sakar Unit (530.4 ± 6.3 Ma, [40]) and the basement of the eastern part of the Sakar Unit (461.6 ± 2.7 Ma and 489.9–496.7 Ma, [28]). Other possible sources with similar age determinations are magmatic bodies from the Thracian lithotectonic unit (Pervents complex, 452 ± 16 Ma and ~470 Ma, [96]) and the basement of the Central Srednogorie (460–500 Ma, [97,98] and 616.9 ± 9.5, 595 ± 23 Ma [99]). Analogous Early Cambrian ages of orthometamorphic rocks are also known in the Strandzha basement (Ҫatalca, İhsaniye, Binkiliç metagranites) in Turkey (discussion in [100]). This determines the basement of the metasediments as the main source of partially recycled Early Paleozoic, Cambrian–Neoproterozoic, and older zircons.

9. Conclusions

The petrography and whole-rock geochemistry of the TCSTT and STT suggest previous sandy, clay, and calcareous sediment protoliths. The clastic material is predominantly derived from a quartzose sedimentary province with a low proportion from a felsic igneous source, which is deposited into a continental island–arc setting. The petrological observation suggests that the low-grade TCSTT metamorphism (greenschist facies) increases eastward toward low-temperature STT amphibolite facies. The U-Pb geochronology of detrital zircons reveals a dominant Carboniferous age, supplemented by early Permian ages, which is consistent with the presence of Carboniferous–Permian magmatic rocks in the basement. The source province is interpreted as a continental arc, supported by immobile element contents and tectonic setting discrimination diagrams. The REE patterns exhibit a negative Eu anomaly, which is likely inherited from the granitic source rocks. The presence of Early Paleozoic and Cambrian–Neoproterozoic zircons in the detrital zircon spectra suggests the basement of the Sakar Unit, as well as other nearby units such as the Thracian and Central Srednogorie, as potential sources of the sedimentary material.

Author Contributions

Conceptualization, visualization, investigation, validation, writing—original draft preparation; funding acquisition, formal analysis, visualization, data curation, T.F.V. and M.G.G.; formalanalysis, visualization, T.F.V.; writing, T.F.V.; review and editing, M.G.G.; investigation, visualization T.F.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Tectonic subdivision of Bulgaria [27]; (b) simplified geological map of Sakar unit compiled after [22,28,53].
Figure 1. (a) Tectonic subdivision of Bulgaria [27]; (b) simplified geological map of Sakar unit compiled after [22,28,53].
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Figure 2. Field photographs of the Triassic metasedimentary sequence: (a) large quartz clasts (~3 cm) in metaconglomerate (STT, TV-49); (b) metasandstone containing various fragments of gneisses and granites (STT, TV-60; (c) alternation of metasandstone (TV-47) and calcite–biotite schist (TV-48) (STT); (d) thick-layered to massive porcelain-like marbles (STT, TV-52); (e) quartz–muscovite schist composed of alternating quartz and mica bands (TCSTT, TV-13a); (f) fine-grained phyllites with two perpendicular foliation planes (TCSTT, TV-24a). The scale bar (coin) diameter is 2.54 cm.
Figure 2. Field photographs of the Triassic metasedimentary sequence: (a) large quartz clasts (~3 cm) in metaconglomerate (STT, TV-49); (b) metasandstone containing various fragments of gneisses and granites (STT, TV-60; (c) alternation of metasandstone (TV-47) and calcite–biotite schist (TV-48) (STT); (d) thick-layered to massive porcelain-like marbles (STT, TV-52); (e) quartz–muscovite schist composed of alternating quartz and mica bands (TCSTT, TV-13a); (f) fine-grained phyllites with two perpendicular foliation planes (TCSTT, TV-24a). The scale bar (coin) diameter is 2.54 cm.
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Figure 3. Photomicrographs of selected Triassic carbonate and carbonate–silicate rocks: (a) elongate calcite grains and muscovite flakes defining foliation in pure calcite marble; single quartz grain and opaque minerals are also present (XN, TV-70, STT); (b) bioclasts (crinoid fragments) or well-defined areas of oval or arcuate shape in pure dolomite marble (XN, TV-46, STT); (c) quartz clasts in fine-grained sericite–carbonate matrix with relict clay minerals, impure marble (XN, TV-26, TCSTT); (d) subhedral grossular-rich garnet in calcite matrix, impure calcite marble (XN, TV-51, STT); (e) calcite porphyroblasts in chlorite–muscovite matrix that preserves S1 and S2 foliations (BSE, TV-24, TCSTT); (f) biotite porphyroblasts with inclusions of quartz and epidote in a fine-grained muscovite–quartz–calcite matrix with larger hematite–magnetite (Opq) clusters, calcite–biotite schist (IIN, TV-48, STT). Mineral abreviations: Ms—muscovite, Ser—sericite, Bt—biotite, Chl—chlorite, Grt—garnet, Pl—plagioclase, Ep—epidote, Cc—calcite, Dol—dolomite, Ilm—ilmenite, Qtz—quartz, Opq—opaque minerals.
Figure 3. Photomicrographs of selected Triassic carbonate and carbonate–silicate rocks: (a) elongate calcite grains and muscovite flakes defining foliation in pure calcite marble; single quartz grain and opaque minerals are also present (XN, TV-70, STT); (b) bioclasts (crinoid fragments) or well-defined areas of oval or arcuate shape in pure dolomite marble (XN, TV-46, STT); (c) quartz clasts in fine-grained sericite–carbonate matrix with relict clay minerals, impure marble (XN, TV-26, TCSTT); (d) subhedral grossular-rich garnet in calcite matrix, impure calcite marble (XN, TV-51, STT); (e) calcite porphyroblasts in chlorite–muscovite matrix that preserves S1 and S2 foliations (BSE, TV-24, TCSTT); (f) biotite porphyroblasts with inclusions of quartz and epidote in a fine-grained muscovite–quartz–calcite matrix with larger hematite–magnetite (Opq) clusters, calcite–biotite schist (IIN, TV-48, STT). Mineral abreviations: Ms—muscovite, Ser—sericite, Bt—biotite, Chl—chlorite, Grt—garnet, Pl—plagioclase, Ep—epidote, Cc—calcite, Dol—dolomite, Ilm—ilmenite, Qtz—quartz, Opq—opaque minerals.
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Figure 4. Photomicrographs of selected Triassic silicate and carbonate-bearing silicate rocks: (a) biotite–muscovite bands in quartz-dominated matrix, quartz–muscovite schist (IIN, TV-43, STT); (b) resorbed and cracked garnet fragments, partially enveloped by chlorite and biotite in muscovite–biotite–quartz schist (BSE, TV-39, STT); (c) smaller, oval garnets that grew during the last metamorphic event, muscovite–biotite–quartz schist (BSE, TV-40, STT); (d) postkinematic garnet porphyroblast in a fine-grained matrix dominated by phyllosilicates, garnet–biotite–muscovite schist (IIN, TV-58, STT); (e) biotite porphyroblast with epidote inclusions, in chlorite–sericite–quartz matrix, metasandstone (IIN, TV-68, STT); (f) zircon and opaque minerals in phyllosilicate bands, metasandstone (IIN, TV-60, STT). Mineral abbreviations: Ms—muscovite, Ser—sericite, Bt—biotite, Chl—chlorite, Grt—garnet, Pl—plagioclase, Ep—epidote, Cc—calcite, Dol—dolomite, Mgt—magnetite, Qtz—quartz, Zrn—zircon, Opq—opaque minerals.
Figure 4. Photomicrographs of selected Triassic silicate and carbonate-bearing silicate rocks: (a) biotite–muscovite bands in quartz-dominated matrix, quartz–muscovite schist (IIN, TV-43, STT); (b) resorbed and cracked garnet fragments, partially enveloped by chlorite and biotite in muscovite–biotite–quartz schist (BSE, TV-39, STT); (c) smaller, oval garnets that grew during the last metamorphic event, muscovite–biotite–quartz schist (BSE, TV-40, STT); (d) postkinematic garnet porphyroblast in a fine-grained matrix dominated by phyllosilicates, garnet–biotite–muscovite schist (IIN, TV-58, STT); (e) biotite porphyroblast with epidote inclusions, in chlorite–sericite–quartz matrix, metasandstone (IIN, TV-68, STT); (f) zircon and opaque minerals in phyllosilicate bands, metasandstone (IIN, TV-60, STT). Mineral abbreviations: Ms—muscovite, Ser—sericite, Bt—biotite, Chl—chlorite, Grt—garnet, Pl—plagioclase, Ep—epidote, Cc—calcite, Dol—dolomite, Mgt—magnetite, Qtz—quartz, Zrn—zircon, Opq—opaque minerals.
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Figure 5. Correlation diagrams of major oxides (wt %): (a) SiO2 vs. CaO + MgO negative correlation (r = −0.99); (b) MgO vs. Al2O3; (c) SiO2 vs. Al2O3 and SiO2/Al2O3 isolines; (d) SiO2 vs. K2O and SiO2/K2O isolines; (e) positive correlation between Al2O3 vs. K2O and K2O/Al2O3 isolines; (f) Al2O3 vs. Na2O diagram and Na2O/Al2O3 isolines.
Figure 5. Correlation diagrams of major oxides (wt %): (a) SiO2 vs. CaO + MgO negative correlation (r = −0.99); (b) MgO vs. Al2O3; (c) SiO2 vs. Al2O3 and SiO2/Al2O3 isolines; (d) SiO2 vs. K2O and SiO2/K2O isolines; (e) positive correlation between Al2O3 vs. K2O and K2O/Al2O3 isolines; (f) Al2O3 vs. Na2O diagram and Na2O/Al2O3 isolines.
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Figure 6. Geochemistry of selected trace elements: (a) positive correlation K2O wt% vs. Rb, Cs, Ba, and Pb ppm; (b) positive correlation Al2O3 wt% vs. Ga ppm; (c) SiO2 wt% vs. Zr and Hf ppm; (d) correlation SiO2 vs. Th and U ppm; (e) PAAS-normalized spider diagram for trace elements (values of [79]; (f) correlation between CaO wt% and Sr ppm.
Figure 6. Geochemistry of selected trace elements: (a) positive correlation K2O wt% vs. Rb, Cs, Ba, and Pb ppm; (b) positive correlation Al2O3 wt% vs. Ga ppm; (c) SiO2 wt% vs. Zr and Hf ppm; (d) correlation SiO2 vs. Th and U ppm; (e) PAAS-normalized spider diagram for trace elements (values of [79]; (f) correlation between CaO wt% and Sr ppm.
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Figure 7. REE patterns: (a) chondrite-normalized REE plot of carbonate–silicate to silicate samples, chondrite values from [82]; (b) PASS-normalized REE diagram of metacarbonates, PAAS values from [78].
Figure 7. REE patterns: (a) chondrite-normalized REE plot of carbonate–silicate to silicate samples, chondrite values from [82]; (b) PASS-normalized REE diagram of metacarbonates, PAAS values from [78].
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Figure 8. Classification and discrimination geochemical plots: (a) diagram of [86]; (b) discriminant diagram for province [3], DF1 = (−1.773 TiO2 + 0.607 Al2O3 + 0.76 Fe2O3t − 1.5 MgO + 0.616 CaO 0.509 Na2O − 1.224 K2O) − 9.09; DF2 = (0.445 TiO2 + 0.07 Al2O3 − 0.25 Fe2O3t − 1.142 MgO + 0.438 CaO + 1.475 Na2O + 1.426 K2O) − 6.861; (c) La/Th and Hf diagram to determine a sedimentary source [87]; (d) Zr/Sc versus Th/Sc plot to determine the degree of sediment sorting [1]; (e) Ti/Zr-La/Sc diagram to determine geodynamic setting [2]; (f) La-Th-Sc discriminant triangle diagram for determining sedimentary tectonic setting [2].
Figure 8. Classification and discrimination geochemical plots: (a) diagram of [86]; (b) discriminant diagram for province [3], DF1 = (−1.773 TiO2 + 0.607 Al2O3 + 0.76 Fe2O3t − 1.5 MgO + 0.616 CaO 0.509 Na2O − 1.224 K2O) − 9.09; DF2 = (0.445 TiO2 + 0.07 Al2O3 − 0.25 Fe2O3t − 1.142 MgO + 0.438 CaO + 1.475 Na2O + 1.426 K2O) − 6.861; (c) La/Th and Hf diagram to determine a sedimentary source [87]; (d) Zr/Sc versus Th/Sc plot to determine the degree of sediment sorting [1]; (e) Ti/Zr-La/Sc diagram to determine geodynamic setting [2]; (f) La-Th-Sc discriminant triangle diagram for determining sedimentary tectonic setting [2].
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Figure 9. Probability density plot for the most common U-Pb ages of the studied detrital zircon.
Figure 9. Probability density plot for the most common U-Pb ages of the studied detrital zircon.
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Figure 10. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from quartz–muscovite schist (TV-45), metaconglomerate (TV-49), and calcite–biotite schist (TV-48) of STT. White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 7). (a–k) concentrically zoned zircons with homogeneous cores and oscillatory rims; (l) entirely oscillatory zonation; (m–o) homogeneously zoned; (p,q) complex-zoned; (r,s) concordia diagram with major age group and probability density plot (TV-45); (t,u) concordia diagram with major age group inset (TV-48); (v) concordia diagram with major age group inset (TV-49); (w) concordia diagram of youngest group age 297.0 ± 2.4 Ma, MSWD 0.98 (TV-48).
Figure 10. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from quartz–muscovite schist (TV-45), metaconglomerate (TV-49), and calcite–biotite schist (TV-48) of STT. White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 7). (a–k) concentrically zoned zircons with homogeneous cores and oscillatory rims; (l) entirely oscillatory zonation; (m–o) homogeneously zoned; (p,q) complex-zoned; (r,s) concordia diagram with major age group and probability density plot (TV-45); (t,u) concordia diagram with major age group inset (TV-48); (v) concordia diagram with major age group inset (TV-49); (w) concordia diagram of youngest group age 297.0 ± 2.4 Ma, MSWD 0.98 (TV-48).
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Figure 11. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from quartz–muscovite schists (TV-13 and TV-17). White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 8). (a–f) Concentrically zoned zircons with homogeneous cores and oscillatory rims; (g–i) complex textured grains of recrystallized or newly grown convolute zones; (j) homogeneous zircon; (k) concordia diagram with major age group inset (TV-13); (l) probability density plot of both size fractions (TV-13); (m) concordia diagram of all ages (TV-17) (n) concordia diagram for youngest zircon 404.6 ± 4.9 Ma (TV-13).
Figure 11. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from quartz–muscovite schists (TV-13 and TV-17). White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 8). (a–f) Concentrically zoned zircons with homogeneous cores and oscillatory rims; (g–i) complex textured grains of recrystallized or newly grown convolute zones; (j) homogeneous zircon; (k) concordia diagram with major age group inset (TV-13); (l) probability density plot of both size fractions (TV-13); (m) concordia diagram of all ages (TV-17) (n) concordia diagram for youngest zircon 404.6 ± 4.9 Ma (TV-13).
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Figure 12. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from muscovite–quartz schist (TV-39) and muscovite–quartz schists (TV-40, TV-41). White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 9). (a–e) Concentrically zoned zircons with homogeneous cores and oscillatory rims; (f–j) xecocrystalline cores with homogeneous or oscillatory rims; (k–m) homogeneously zoned; (n,o) sectoral- to convolute-zoned; (p) concordia diagram with major age group inset (TV-39); (q) probability density plot of both size fractions (TV-39); (r) youngest zircons—concordia diagram for 505.7 ± 7.6 Ma included youngest age of 498.2 ± 5.3 Ma (dashed ellipse, TV-39); (s) concordia diagram with major age group inset from 539 to 692 Ma and probability density plot inset for most common ages (TV-41).
Figure 12. CL images of zircons (60–200 μm) and U-Pb detrital zircon geochronological data from muscovite–quartz schist (TV-39) and muscovite–quartz schists (TV-40, TV-41). White circles correspond to 206Pb/238U ages. The grains are assigned to a sample and a zircon number (Table 9). (a–e) Concentrically zoned zircons with homogeneous cores and oscillatory rims; (f–j) xecocrystalline cores with homogeneous or oscillatory rims; (k–m) homogeneously zoned; (n,o) sectoral- to convolute-zoned; (p) concordia diagram with major age group inset (TV-39); (q) probability density plot of both size fractions (TV-39); (r) youngest zircons—concordia diagram for 505.7 ± 7.6 Ma included youngest age of 498.2 ± 5.3 Ma (dashed ellipse, TV-39); (s) concordia diagram with major age group inset from 539 to 692 Ma and probability density plot inset for most common ages (TV-41).
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Table 1. Samples, lithology, and locations with GPS coordinates. Qtz—Quartz, Ms—Muscovite, Chl—Chlorite, Bt—Biotite, Grt—Garnet, Cc—Calcite, Dol—Dolomite.
Table 1. Samples, lithology, and locations with GPS coordinates. Qtz—Quartz, Ms—Muscovite, Chl—Chlorite, Bt—Biotite, Grt—Garnet, Cc—Calcite, Dol—Dolomite.
Sample № LithologyLocationLatitude, NLongitude, E
TV-13Qtz-Ms schistS of Klokotnitza41°58′28.6125°29′05.11
TV-14impure Cc marbleS of Klokotnitza41°58′20.5625°29′02.19
TV-15impure Cc marbleBanska River valley41°58′16.9825°29′07.95
TV-16impure Cc marbleBanska River valley41°58′23.8025°29′10.47
TV-17Qtz-Ms schistBanska River valley41°58′30.0025°29′14.27
TV-18impure Cc marbleBanska River valley41°58′31.3325°29′29.19
TV-19impure Cc marbleS of Klokotnitza41°58′31.3325°29′29.19
TV-20Ms-Cc schistSE of Klokotnitza41°59′35.4325°30′42.08
TV-21Cc-Dol marbleSE of Klokotnitza41°59′29.7525°30′27.59
TV-22impure Cc marbleSE of Klokotnitza41°59′38.8625°34′21.12
TV-23impure Cc marbleSE of Klokotnitza41°59′38.8625°34′21.12
TV-24phylliteSE of Klokotnitza41°59′38.8625°34′21.12
TV-25pure Dol marbleSE of Klokotnitza41°59′38.8625°34′21.12
TV-26impure Cc marbleSE of Klokotnitza41°59′38.8625°34′21.12
TV-31impure Dol marbleSW of Krepost41°59′38.8625°34′21.12
TV-32impure Dol marbleSW of Krepost41°59′38.8625°34′21.12
TV-33Ms-Cc schistSW of Krepost42°00′07.0225°31′35.40
TV-34Ms-Dol schistSW of Krepost42°00′07.0225°31′35.40
TV-35impure Cc marbleSW of Krepost42°00′07.0225°31′35.40
TV-39Ms-Bt-Qtz schistE of Hlyabovo42°04′21.5626°18′7.86
TV-40Ms-Bt-Qtz schistE of Hlyabovo42°04′21.5626°18′7.86
TV-41Ms-Chl schistE of Hlyabovo42°04′21.5626°18′7.86
TV-43Qtz-Ms schistE of Hlyabovo42°03′42.5226°16′36.10
TV-44metasandstoneNE of Topolovgrad42°04′56.0326°17′36.21
TV-45Qtz-Ms schistNE of Topolovgrad42°04′44.76″26°18′11.99
TV-46Cc-Dol marbleS of Srem42°02′43.0626°29′07.23
TV-47metasandstoneS of Srem42°01′43.3026°29′37.60
TV-48Cc-Bt schistS of Srem42°01′43.3026°29′37.60
TV-49metaconglomerateS of Srem42°01′43.3026°29′37.60
TV-50impure Cc marbleS of Srem42°02′07.5926°29′25.93
TV-51impure Cc marbleS of Srem42°02′07.5926°29′25.93
TV-52pure Dol marbleS of Ustrem42°00′56.9426°27′41.44
TV-53pure Cc marbleS of Oreshnik42°04′07.6226°21′52.49
TV-56pure Cc marbleSW of Melnitza42°02′6.0626°32′36.48
TV-57pure Cc marbleSW of Melnitza42°02′6.0626°32′36.48
TV-58Grt-Bt-Ms schistSW of Melnitza42°01′50.4126°32′54.87
TV-59pure Cc marbleSW of Melnitza42°01′50.4126°32′54.87
TV-60metasandstoneSW of Melnitza42°01′35.2526°33′7.57
TV-67metaconglomerateSW of Melnitza42°01′20.4026°32′32.27
TV-68metasandstoneSW of Melnitza42°01′27.4926°32′36.71
TV-69Cc-Bt schistSW of Oreshnik42°03′55.1326°21′52.37
TV-70pure Cc marbleSW of Oreshnik42°03′53.6826°21′51.10
TV-71pure Cc marbleSW of Oreshnik42°03′35.9226°21′25.49
TV-72Cc-Bt schistSW of Oreshnik42°03′38.5326°21′28.97
Table 2. Mineral assemblages by lithology for all study areas.
Table 2. Mineral assemblages by lithology for all study areas.
SampleTCSTTSTT
Pure marblesCc and/or Dol Qtz Ms OpqCc and/or Dol Qtz Ms Opq
Impure marblesCc and/or Dol Qtz ± Fs ± Chl ± Ms ± Rut ± Ap ± Zrn ± OpqCc Qtz Fs Ep Titn Opq ± Zo ± Grt
Carbonate–silicate rocksCc and/or Dol Qtz ± Fs Ms ± Chl ± Bt ± Rut ± Ilm ± Ap ± Zrn ± Mnz OpqCc Qtz Fs Ms Tour Opq ± Ep ± Zo ± Grt ± Zrn ± Mlh
Silicate and carbonate-bearing silicate rocksMs Fs Qtz Rut Opq ± Cc ± Chl ± Titn ± Ap ± Zrn ± MnzBt Fs Ms Opq ± Cc Qtz ± Chl ± Ep Grt ± Rut ± Titn ± Ilm ± Ap ± Zrn ± Mnz
Table 3. The major oxides (wt%) of metasediments of the Sakar Unit. Results of XRF.
Table 3. The major oxides (wt%) of metasediments of the Sakar Unit. Results of XRF.
Sample №SiO2TiO2Al2O3Fe2O3*MnOMgOCaONa2OK2OP2O5L.O.I.TotalSiO2/Al2O3Na2O/K2O
Pure marbles
TV-21 10.570.010.220.380.0924.2227.770.040.020.1046.59100.002.592.00
TV-25 10.790.010.180.140.0123.2329.520.070.020.0945.9499.994.393.50
TV-46 10.370.010.080.050.0124.8328.230.040.000.1546.2299.994.63
TV-52 10.480.010.130.090.0123.9029.020.050.010.2846.0299.993.695.00
TV-53 11.980.010.420.490.011.8952.000.060.040.1842.8299.904.711.50
TV-56 14.230.051.061.540.111.3049.830.180.100.2641.1399.793.991.80
TV-57 18.100.010.440.340.011.5748.850.010.060.0740.3599.8018.410.17
TV-70 16.440.061.580.580.010.7849.420.260.190.1140.1899.614.081.37
TV-71 16.300.102.450.890.041.1748.290.150.500.2439.6699.792.570.30
Impure marbles
TV-14 121.410.102.400.570.040.5440.850.030.430.0933.5299.978.920.07
TV-15 17.140.092.190.660.045.0043.770.010.550.1140.4199.983.260.02
TV-16 14.590.041.420.580.0320.9228.460.180.290.2343.2599.983.230.62
TV-18a 138.290.133.351.280.051.4129.590.080.700.0725.0499.9811.430.11
TV-19 122.130.256.072.230.061.9535.250.261.680.1529.9599.973.650.15
TV-22 14.110.041.070.680.031.0051.150.080.180.1141.4899.933.840.44
TV-23 18.820.071.921.070.040.6347.920.450.260.0838.5799.964.591.73
TV-31 118.130.133.721.810.0511.3029.300.031.000.0934.3299.994.870.03
TV-32 117.770.205.061.430.2416.0422.910.041.560.0634.6799.973.510.03
Carbonate–silicate rocks
TV-17 142.900.7721.017.420.084.686.911.174.820.0810.0999.962.040.24
TV-20 131.940.429.742.510.051.5026.970.142.820.0923.4799.973.280.05
TV-24 157.600.8719.857.590.053.610.800.674.480.074.2399.972.900.15
TV-24a 155.390.6920.837.060.023.691.460.794.520.045.4999.982.660.17
TV-33 139.510.439.642.750.051.6421.880.612.940.1019.6499.944.100.21
TV-34 138.400.3910.572.190.0710.7011.620.105.260.0520.0799.963.630.02
TV-48 252.600.8515.005.710.072.6310.001.564.010.177.1099.703.510.39
TV-69 330.300.4511.103.820.062.0127.300.612.100.0921.1098.962.730.29
TV-72 331.300.3810.903.710.051.8826.700.631.940.0821.2098.782.870.32
Silicate and carbonate-bearing silicate rocks
TV-13a 179.370.3810.762.080.010.930.231.972.800.071.43100.027.380.70
TV-13b 176.490.4312.132.470.021.070.282.033.260.121.6799.976.310.62
TV-39 276.900.5510.503.590.051.561.162.681.640.071.1099.807.321.63
TV-40 270.700.9113.005.110.091.761.593.061.900.121.3099.545.441.61
TV-41 270.200.8214.104.790.071.771.072.302.620.101.9099.744.980.88
TV-43 277.800.3511.001.800.041.160.872.862.300.081.0099.267.071.24
TV-44 266.400.159.400.860.070.3412.603.991.020.065.0099.897.063.91
TV-45 268.300.5515.903.470.021.530.190.376.130.113.0099.574.300.06
TV-47 270.200.249.001.150.070.408.382.560.920.086.1099.107.802.78
TV-49 275.100.4012.202.390.031.760.432.812.460.111.8099.496.161.14
TV-58 355.900.8721.807.240.072.760.480.594.710.144.8099.392.560.13
TV-60 384.400.148.411.760.020.490.060.142.880.041.3099.6510.040.05
TV-67 373.500.9911.006.470.062.030.200.232.740.172.3099.716.680.08
TV-68 378.800.2510.201.740.080.732.173.161.120.081.4099.747.732.82
The samples denoted with superscript were analyzed as follows: 1 by XRF in the Chemical Laboratory at Sofia University “St. Kliment Ohridski”; 2 by XRF at the Natural History Museum in Berlin, Germany; 3 by XRF in Canada. Fe2O3* represents total Fe as Fe2O3.
Table 4. The trace elements (ppm) of the metasediments. Results from LA-ICP-MS. Values with < are below the detection limit.
Table 4. The trace elements (ppm) of the metasediments. Results from LA-ICP-MS. Values with < are below the detection limit.
Sample №ScTiVCrMnCoNiCuZnGaRbSrYZrNbSnSbCsBaHfTaWPbThUTh/U
Pure marbles
TV-21<1.3849.337.6742.46670.9514.815.214.4<1.951.3580.9<4.940.581.29<1.01<0.2913.6<0.120.092.22.10.230.240.96
TV-25<1.3046.6112.248.582.9<0.64<3.726.5<10.80<1.731.371041.92<3.650.51<0.14<0.530.299.79<0.11<0.051.172.190.320.460.70
TV-46<1.2720.931.9<28.8763.8<0.58<17.2721.6<6.77<1.83<0.751244.5<3.260.28<1.07<0.61<0.195.54<0.14<0.07<0.221.07<0.144.18 non
TV-52<1.1227.039.294492.5<0.73<15.319.09<8.60<1.70<0.7687.41.77<2.400.351.46<0.90<0.297.29<0.11<0.270.381.19<0.030.39 non
TV-53<1.9788.969.8554.7991.71<22.335.92<11.71<2.162.1510862.775.290.73<1.67<0.73<0.2829.20.360.150.791.350.280.660.42
TV-562.229612.441.68841.4<14.2812.155.81.715.1721986.679.321.131.52<0.920.328.70.38<0.190.8613.80.730.491.49
TV-572.1675.237.5140.875.8<0.91<4.3010.7<10.81<2.513.9621882.76<4.700.68<1.51<0.610.545<0.14<0.051.011.730.30.560.54
TV-702.235213.3<31.321011.4812.39.27<11.763.29.2842682.9915.61.79<1.37<0.890.6246.3<0.64<0.201.133.681.080.861.26
TV-712.5254819.542.23652.24<27.90<5.0715.54.1519.623246.9118.82.471.42<1.340.7571.5<0.13<0.210.566.162.071.111.86
Impure marbles
TV-14 5.9364322.735.33331.2117.75318.43.6919.922622.825.52.341.71.070.97640.720.210.614.671.860.682.74
TV-152.849919.6<39.303512.12<21.109.8929.24.1718.722015.320.61.67220.91730.64<0.261.155.281.70.35.67
TV-163.0519413.1<30.222712.53<6.699.1523.7<2.479.1216415.58.1711.24<0.640.8342.4<0.64<0.18<0.224.810.43<0.16 non
TV-18a6.8684427.335.24033.4417.320.830.34.683022620.337.35.231.6801.86750.860.260.535.332.980.496,08
TV-198.1515173742.85425.8615.715.635.48.8263.321514.659.45.342.211.344.461301.680.410.811.24.180.577.33
TV-22<2.0124112.8<34.44264<1.04<25.80<6.32<12.21<2.217.237784.1610.51.47<1.71<0.970.5434.3<0.67<0.061.762.410.582.080.28
TV-233.2242512.226.83001.5711.24.318.712.39.023697.925.91.531.370.710.56460.440.130.495.231.331.071.24
TV-315.6677823.128.53793.4210.83519.55.7334.745.912.929.12.571.660.512.641370.880.190.54.642.710.446.16
TV-324.1811133037.118113.5916.71441.86.0851.51951253.44.151.7<0.592.771841.640.421.2246.83.30.734.52
Carbonate–silicate rocks
TV-17 21.3478112111361415.452.529.991.330.518112721.816216.94.060.5310.24464.241.232.158.912.73.14.10
TV-2011.127206768.24547.4123.910.452.315.811110521.41009.332.820.8510.33062.780.651.7822.46.763.571.89
TV-2420.752431251274261650.734.19330.117250.129.5166193.711.068.854254.341.241.4123.313.22.754.80
TV-24a20.5423211712317313.741.735.18031.617335.920.914914.63.760.668.774613.890.911.273.3211.21.686.67
TV-338.74279865.610440911.339.621.842.312.611374522.61419.982.69<0.7010.13463.380.852.2611.57.191.564.61
TV-3412.3229957.166.56026.23233012324.118410119.41099.843.671.177.527543.50.792.4758.59.552.443.91
TV-4814.7459397.886.644011.334.68.2989.220.615748918.316216.84.11<0.3310.54493.371.153.0815.911.22.294.89
TV-6911294674.277.54089.2430.916.542.413.9103211613.679.69.232.251.598.482812.20.590.826.597.851.854.24
TV-7211.3245776.576.13559.7429.418.751.512.787.6209414.389.810.12.62.018.462362.190.660.765.766.971.434.87
Silicate and carbonate-bearing silicate rocks
TV-13a7.04213939.942.6946.9735.313610210.313929.123.222710.21.242.039.246606.810.893.416.3310.21.158.87
TV-13b11.6234142.347.81444.1817.420.337.221.314626.6242139.633.610.94106405.320.912.934.78100.7613.16
TV 3910.9323476.574.13788.6930.619117111.182.510814.11686.87<1.152.444.73223.70.463.4636.14.321.054.11
TV 4015.7524912211575713.631.862166.816.375.412522.932511.51.42.583.574808.470.843.4311.56.922.52.77
TV 4116.2481611611255611.934.556961.215.883.410122.821010.61.762.743.476265.440.826.669.826.392.033.15
TV-434.84199434.9<19.833216.35<17.0058.752.810.912610112.51018.651.321.8410.34122.631.051.5413.39.451.426.65
TV-442.6176321.644.74162.05<34.5619517.19.2126.516610.339.44.952.382.741.24120<1.310.57<1.755.293.260.655.02
TV 459.03333284.238.51638.272286.158.318.425511130.916613.92.482.0512.28514.41.387.0817.218.13.355.40
TV 4748.411,4173463272937448727714726.528.133942.71715.84.36.270.44874.390.5324.526.21.771.251.42
TV 499.89239476.684.72869.1320.7187261.912.710217215.31085.62.163.076.539082.970.495.0812.87.611.614.73
TV-585013,747347378127115.57865.123264.643536753.135142.712.38.3118.416919.332.769.148.833.57.074.74
TV-6013.4259898.596.42689.7641.18.4344.422.331773.333.821813.76.1211.322.213455.771.317.6323.149.93.0316.47
TV-6719.5635112275.643913.71825.461.114.61014727.61628.242.552.863.93934.30.645.6712.44.661.682.77
TV-686.21164643.937.46133.2211.99.5920.58.7845.88118.91576.312.312.692.652284.170.662.3913.212.21.67.63
Table 5. The rare-earth elements (ppm) of the metasediments. PAAS values in [78] are used for matacarbonates; chondrite values from [79] are used for carbonate–silicate, silicate, and carbonate-bearing silicate rocks. Eu/Eu* = EuN/√(SmN*GdN) Ce/Ce* = CeN/√(LaN*PrN). Values with < are below the detection limit.
Table 5. The rare-earth elements (ppm) of the metasediments. PAAS values in [78] are used for matacarbonates; chondrite values from [79] are used for carbonate–silicate, silicate, and carbonate-bearing silicate rocks. Eu/Eu* = EuN/√(SmN*GdN) Ce/Ce* = CeN/√(LaN*PrN). Values with < are below the detection limit.
Sample №LaCePrNdSmEuGdTbDyHoErTmYbLuY/HoLaNPAAS/
LuNPAAS		LaNPAAS/
SmNPAAS		GdNPAAS/
YbNPAAS		NdNPAAS/
YbNPAAS		Eu/Eu*
PAAS		Ce/Ce*
PAAS
Pure marbles
TV-211.021.730.141.11<0.77<0.06<0.35<0.10<0.34<0.10<0.15<0.080.27<0.03nonnonnonnon0.34non1.07
TV-251.212.60.331.34<0.74<0.14<0.70<0.100.31<0.08<0.15<0.07<0.48<0.06nonnonnonnonnonnon0.95
TV-520.520.670.11<0.42<0.50<0.10<0.50<0.07<0.31<0.08<0.19<0.04<0.20<0.11nonnonnonnonnonnon0.63
TV-533.075.280.672.4<1.110.21<0.750.130.56<0.070.4<0.04<0.710.1non0.35nonnonnonnon0.85
TV-564.029.351.144.151.54<0.161.060.171.220.180.73<0.080.930.1336.400.360.380.690.37non1.01
TV-571.662.740.32.05<0.68<0.17<0.64<0.070.47<0.12<0.42<0.05<0.34<0.07nonnonnonnonnonnon0.90
TV-703.687.510.913.35<0.800.280.63<0.100.49<0.100.5<0.10<0.50<0.04nonnonnonnonnonnon0.95
TV-717.8216.051.847.731.830.361.470.211.230.210.81<0.110.80.1433.360.620.621.110.801.030.98
TV-462.061.590.441.920.680.17<0.680.07<0.42<0.10<0.46<0.100.51<0.04 non0.44non0.31non0.39
Impure marbles
TV-14 12.7913.852.9413.023.060.73.480.472.480.561.540.161.280.1940.570.780.611.650.851.020.52
TV-159.6110.532.058.61.890.582.540.451.960.431.19<0.150.990.235.440.540.741.550.721.260.55
TV-168.267.642.299.1720.422.130.352.320.320.780.121.49<0.1149.13non0.600.860.510.950.41
TV-18a18.2721.564.1418.393.470.83.590.472.790.591.570.181.340.1634.201.290.761.621.141.070.57
TV-1915.6325.773.4913.642.680.592.40.382.60.451.340.181.310.1732.411.060.851.110.871.100.81
TV-224.888.4613.931.280.380.960.170.8<0.14<0.51<0.13<0.84<0.11nonnon0.55nonnon1.610.89
TV-236.4412.711.526.241.620.421.650.221.360.250.690.110.690.1131.900.660.581.440.751.210.94
TV-3111.3117.142.611.132.350.572.230.382.280.461.280.21.010.1728.120.760.701.340.921.180.73
TV-3211.0422.522.469.572.150.422.050.281.960.411.130.1810.2128.980.590.751.240.800.931.00
Carbonate–silicate rocksLaNCh/
LuNCh		LaNCh/
SmNCh		GdNCh/
YbNCh		NdNCh/
YbNCh		Eu/Eu*
Ch		Ce/Ce*
Ch
TV-17 38.8377.628.5933.876.351.275.170.814.070.82.320.342.590.3127.2612.943.851.614.550.681.00
TV-2022.1644.675.1919.083.821.043.830.543.770.632.080.271.750.2233.7310.483.651.783.810.830.98
TV-2442.0185.799.6638.867.131.436.220.895.3513.040.422.550.4529.649.753.711.975.310.651.00
TV-24a30.6659.587.4728.415.250.984.010.623.930.682.150.292.170.3230.5310.103.681.504.570.660.92
TV-3319.8841.184.8818.383.970.834.40.524.060.812.340.32.290.3327.756.343.151.562.800.600.98
TV-3424.251.395.7422.015.220.7440.613.690.711.920.272.110.2927.428.792.921.543.640.491.02
TV-4833.567.917.4229.275.361.014.690.543.650.691.920.282.170.2926.4311.793.931.754.710.621.01
TV-6926.253.766.2922.4640.763.430.482.760.551.430.231.760.224.9213.824.131.584.450.620.98
TV-7222.3845.285.4620.433.990.82.970.462.70.481.610.191.390.1929.9712.353.531.745.140.710.96
Silicate and carbonate-bearing silicate rocks
TV-13a14.6729.433.3911.682.060.443.280.573.680.952.680.42.020.3524.434.404.491.322.020.520.98
TV-13b12.3537.154.6316.784.20.683.610.63.90.842.450.32.590.2928.614.401.851.132.260.541.15
TV 3912.1323.213.0312.012.670.62.380.42.360.491.560.171.50.2228.614.402.861.292.790.720.90
TV 4027.4456.636.3325.275.361.375.370.723.890.852.260.382.410.4127.075.723.221.813.660.781.01
TV-4120.9747.914.9420.094.491.014.040.63.760.932.380.432.880.3124.516.992.941.142.430.721.10
TV-4313.7528.163.0911.882.630.462.060.32.20.41.260.191.580.1831.256.963.291.062.630.601.01
TV-449.5321.672.3910.172.57<0.302.020.271.540.321.2<0.14<1.290.2132.567.902.34nonnonnon1.06
TV-4536.171.297.5631.285.81.194.360.774.830.842.870.463.120.3436.904.643.921.133.500.721.01
TV-4710.7926.313.6419.666.162.086.41.327.521.584.340.614.520.627.0511.131.101.151.521.010.98
TV-4917.3737.53.9114.292.910.792.750.482.930.61.60.21.780.2825.621.883.761.252.800.861.07
TV-5810084.321.3181.3715.963.2111.881.6210.421.955.620.895.991.0627.246.553.961.614.740.710.43
TV-6010321020.9771.813.792.077.9116.621.284.210.53.020.5326.489.804.702.128.290.601.06
TV-6716.7838.554.5619.24.281.054.720.734.960.952.980.42.980.4328.9720.182.471.282.250.711.03
TV-6824.8848.495.3120.364.290.693.820.573.10.622.010.262.320.3130.434.103.651.343.060.520.99
Table 6. Summarized U-Pb geochronological data for the studied detrital zircons.
Table 6. Summarized U-Pb geochronological data for the studied detrital zircons.
SampleNumber ofThe Youngest Zircon Age (Ma)Age Groups (Ma)
Grains
Selected		Analyses
Performed		Concordant
Results		Single Grains
206Pb/238U		Concordia
Diagrams		MajorSecondary
from–toMost Oftenfrom–to
TV-13387669404.9 ± 11.86404.6 ± 4.9405–492~420581–1123
~460
TV-1791212447.9 ± 5.8447.0 ± 14.0447–490~480548–578
TV-39346461498.2 ± 5.3505.7 ± 7.6498–676~530858–899
~6201896–2016
2522–2710
TV-40284444536.3 ± 6.8548.0 ± 16.0536–707~5702100–2943
TV-41193030539.1 ± 26.0544.0 ± 15.0505–591~550786–932
629–677~6602060–2666
TV-4591414305.1 ± 4.3311.0 ± 10.0305–346~330441–501
TV-48132321286.5 ± 3.2297.0 ± 2.4286–317~300443–593
TV-49183030307.1 ± 3.7308.1 ± 2.5307–345~320481–622
~333
Table 7. U-Pb LA-ICP-MS isotope data for late Paleozoic detrital zircons (TV-45, TV-48, and TV-49 samples).
Table 7. U-Pb LA-ICP-MS isotope data for late Paleozoic detrital zircons (TV-45, TV-48, and TV-49 samples).
ZirconIsotopic RatiosAge MaTh/UC% 1Recalculated 2 [71]
207Pb/206Pb2σ207Pb/235U2σ206Pb/238U2σRho207Pb/206Pb1σ206Pb/238U1σ207Pb/235U1σAge Ma2σClass
TV-45.100–200 μm grain size
3-c0.05560.00390.37180.02900.04850.00240.64437.6070.98305.104.28321.009.020.9495309.0739.335
5-c0.05470.00310.53400.03530.07090.00350.74398.2054.76441.305.81434.509.040.26102438.7256.103
5-r0.05450.00240.60760.03430.08090.00390.86390.7038.98501.406.26482.007.250.29104492.6759.955
7-c0.05650.00230.62400.03390.08010.00390.89471.0034.84496.806.14492.406.710.09101494.6958.982
7-r0.05700.00220.60360.03190.07670.00370.91492.7031.89476.605.86479.506.130.1299477.8555.632
12-c0.05200.00290.39550.02560.05520.00270.76284.2053.91346.304.53338.407.090.59102344.1341.074
12-r0.05290.00220.37760.02070.05180.00250.88324.1036.31325.404.07325.204.890.48100325.3436.141
16-c0.05190.00300.38940.02590.05440.00270.74281.6056.58341.404.51333.907.320.45102339.4440.854
270.05120.00230.37220.02130.05270.00260.85250.0041.48331.204.18321.305.340.51103328.7337.084
29-c0.05320.00220.36730.02000.05010.00240.89337.7035.51314.903.93317.704.710.7499315.5634.882
29-r0.05390.00220.38280.02060.05150.00250.90367.5034.63323.704.03329.104.740.6298325.0635.933
TV-48. 600–100 μm grain size
9-r0.09910.00160.68950.01150.05050.00060.621606.7030.33317.403.65532.506.940.5060448.2713.597
9-c0.05270.00090.34430.00580.04730.00050.60317.4036.82298.203.35300.404.390.3999298.678.602
10-c0.05900.00100.57270.00990.07040.00080.60566.0036.34438.704.91459.806.390.4695447.5714.865
10-r0.05660.00080.55200.00840.07080.00080.65474.1032.40440.704.86446.305.500.0799442.9513.723
11-r0.13490.00250.99890.01810.05370.00070.612163.1031.40337.104.01703.309.220.3948722.4021.267
11-l0.05640.00090.35520.00570.04570.00050.62465.7034.60288.103.22308.604.290.5493293.038.355
13-c0.05710.00120.36860.00760.04690.00060.53492.9044.51295.103.41318.605.641.4992301.059.525
13-r0.05440.00110.34970.00710.04660.00060.54387.3044.20293.703.37304.505.320.3796296.209.234
15-c0.05200.00130.33620.00840.04690.00060.46286.8056.27295.103.49294.306.390.65100294.949.911
15-r0.05430.00120.36920.00790.04930.00060.51384.8046.73310.003.57319.005.830.5197312.269.984
16-c0.06110.00110.80100.01450.09510.00110.58641.3037.95585.706.47597.408.170.4498593.3822.804
16-r0.05960.00100.77780.01290.09460.00110.61590.2034.81582.506.36584.207.360.48100583.4921.081
17-r0.05490.00090.34380.00590.04540.00050.60406.8036.84286.503.19300.104.440.6095289.618.384
TV-49.100–200 μm grain size
2-c0.05510.00210.58850.03100.07740.00370.91417.2031.47480.705.88469.905.970.94102476.0555.334
2-r0.05330.00260.39390.02360.05360.00260.81341.3045.81336.604.30337.206.140.28100336.7438.891
3-d0.05660.00480.72100.06510.09240.00470.57475.5087.24569.508.35551.3017.010.67103559.1694.755
4-c0.05330.00340.70520.05090.09610.00480.69339.3064.59591.207.87541.9012.340.80109564.5182.896
4-r0.05890.00330.82250.05380.10140.00500.75561.6052.64622.308.06609.4011.490.45102613.5188.624
29-c0.05760.00230.71450.03830.09000.00430.90512.4033.52555.706.77547.407.030.16101551.0167.093
33-c0.05330.00250.39130.02290.05330.00260.83340.2043.18334.504.23335.305.790.49100334.7038.241
33-r0.05310.00250.38980.02290.05320.00260.82332.9044.02334.304.24334.205.870.24100334.2838.311
TV-49. 60–200 μm grain size
9-c0.05200.00110.36410.01790.05080.00070.56284.8046.36319.304.05315.305.820.47101318.3010.803
9-r0.05310.00110.37060.01830.05060.00070.56331.2046.12318.504.04320.105.910.3899318.8310.891
15-c0.05330.00190.37940.02800.05160.00070.39340.9076.64324.404.39326.609.730.6299324.9813.832
15-r0.05360.00090.37480.01650.05070.00060.62352.4038.90319.103.94323.205.100.4099320.1010.222
18-r0.05420.00130.41080.02240.05490.00070.51379.6052.76344.804.40349.507.210.2699346.0612.723
30-r0.05320.00140.38810.02250.05290.00070.47338.4058.04332.104.22333.007.480.2299332.3312.321
36-c0.05310.00110.36070.01730.04930.00060.56331.6045.06310.103.80312.705.560.3699310.7210.212
36-r0.05350.00090.36000.01550.04880.00060.62350.0038.33307.103.69312.204.790.3298308.379.573
1 C%—concordance: C% = (206Pb − 238U age/207Pb − 235U age) × 100 for ages <1 Ga; C% = (206Pb − 238U age/207Pb − 206Pb age) × 100 for ages > 1 Ga. 2 Recalculated according to [71] using a non-iterative probabilistic model for determining a single concordant age and its concordance class (1 to 7). Zircon analyses were performed at the Laboratoire Magma & Volcans in Clermont-Ferrand, France. c—center; r—rim; d—dark part; and l—light part on CL images.
Table 8. U-Pb LA-ICP-MS isotope data for early Paleozoic detrital zircons (TV-13 and TV-17 samples).
Table 8. U-Pb LA-ICP-MS isotope data for early Paleozoic detrital zircons (TV-13 and TV-17 samples).
ZirconIsotopic RatiosAge MaTh/UC% 1Recalculated 2 [71]
207Pb/206Pb2σ207Pb/235U2σ206Pb/238U2σRho207Pb/206Pb2σ206Pb/238U2σ207Pb/235U2σAge Ma2σClass
TV-13. 100–200 μm grain size
20.08360.00501.33560.07680.11590.00300.591282.26114.25707.1417.55861.3632.760.1382912.2357.457
6-r0.05840.00400.59090.03920.07340.00180.58542.78146.87456.9511.28471.4724.710.2197463.2822.384
6-c0.05700.00340.57130.03260.07280.00180.59489.15127.87452.8710.81458.8920.910.1299455.3219.703
13-c0.05770.00340.57490.03260.07230.00180.59516.21126.48450.2210.70461.1920.810.1398454.7719.624
13-r0.05550.00300.54660.02840.07150.00180.59430.10117.39445.2310.34442.7918.450.10101444.1917.752
14-c0.05830.00440.80120.06020.09960.00280.57541.53167.24612.4015.93597.5433.400.16102602.6238.764
14-r0.06410.00420.83330.05280.09430.00240.58745.17136.51580.8414.37615.5028.890.2294605.2434.746
15-c0.05620.00540.50190.04740.06480.00200.56458.63214.05404.9111.62413.0331.720.2598407.7023.403
15-r0.05670.00440.59080.04520.07560.00200.57478.21172.44470.0212.34471.4228.580.29100470.5525.331
22-c0.05860.00380.58980.03820.07300.00180.58550.75143.90454.5511.29470.7924.200.2097461.5722.105
22-r0.06100.00400.58140.03820.06910.00180.58638.84143.90431.0110.73465.4024.320.2693445.9021.396
38-c0.07710.00401.80640.09440.17000.00420.591122.64105.571012.3023.451047.8233.380.67901073.6276.635
38-r0.07420.00541.53980.11060.15050.00440.581047.12147.82903.8024.07946.4843.000.5595967.6987.606
13b-r0.05790.00420.59700.04160.07480.00200.58524.79155.36465.2311.99475.4026.230.3198469.6723.954
13b-c0.05970.00440.58800.04340.07140.00200.57593.47162.59444.6811.79469.6227.490.4595455.5424.065
22b-c0.12480.00624.27380.21200.24840.00640.62025.4788.301430.4732.691688.3738.780.29712007.5696.367
22b-r0.06100.00520.60450.05020.07190.00220.57637.45182.15447.8212.74480.1131.400.1093462.4427.336
31-r0.05610.00560.59030.05820.07630.00240.56455.79223.13474.2414.25471.0936.671.18101472.8331.032
31-r0.05600.00360.50830.03220.06580.00180.58453.66142.62410.7810.40417.3321.480.2398413.0718.353
TV-13. 60–100 μm grain size
30-r0.05620.00520.50960.04640.06580.00320.53458.8042.36410.804.75418.206.720.0898413.4830.363
8-r0.05440.00500.50320.04600.06710.00320.53386.6042.84418.704.85413.806.700.14101416.9430.563
2-c0.05440.00600.50390.05520.06710.00340.46388.3054.46418.905.03414.308.460.20101417.2533.713
30-c0.05410.00640.50150.05920.06720.00340.43374.9059.95419.505.09412.709.190.21102417.0734.893
2-r0.05850.00640.54370.05860.06740.00340.47548.4052.27420.505.08440.908.720.1795428.5235.625
8-c0.05520.00560.51630.05180.06790.00340.49418.8048.08423.305.00422.707.700.14100423.0733.011
TV-17. 60–100 μm grain size
1-r0.05560.00180.55140.02020.07200.02020.8784435.2036.71447.905.81445.906.630.26100447.1016.212
50.05940.00220.75550.02980.09220.02980.8516583.2039.70568.507.30571.408.600.4599570.2723.632
7-c0.05720.00180.75570.02640.09580.02640.8919498.6035.07589.907.39571.507.620.21103578.8422.455
7-r0.05710.00180.70770.02440.08990.02440.8927495.9034.93554.606.94543.407.270.19102548.4220.564
150.05520.00180.57540.02020.07560.02020.882420.8036.94469.705.79461.506.530.20102466.3116.563
17-r0.05540.00180.55230.01880.07240.01880.8914426.1035.34450.405.53446.506.150.94101448.8615.462
9-c0.05450.00240.56800.02500.07560.02500.7987390.1048.07470.105.91456.708.100.21103464.5618.304
9-r0.05610.00240.59090.02540.07640.02540.8078454.7046.40474.805.93471.408.080.39101473.3118.582
1 C%—concordance: C% = (206Pb − 238U age/207Pb − 235U age) × 100 for ages < 1 Ga; C% = (206Pb − 238U age/207Pb − 206Pb age) × 100 for ages > 1 Ga. 2 Recalculated according to [71] using a non-iterative probabilistic model for determining a single concordant age and its concordance class (1 to 7). Zircon analyses (100–200 μm) were performed at the Laboratory of the Bulgarian Academy of Sciences, Bulgaria. Zircon analyses (60–100 μm) were performed at the Magma & Volcans Laboratory in Clermont-Ferrand, France. r—rim; c—center.
Table 9. U-Pb LA-ICP-MS isotope data for Precambrian detrital zircons (TV-39, TV-40, and TV-41 samples).
Table 9. U-Pb LA-ICP-MS isotope data for Precambrian detrital zircons (TV-39, TV-40, and TV-41 samples).
ZirconIsotopic RatiosAge MaTh/UC % 1Recalculated 2 [71]
207Pb/206Pb2σ207Pb/235U2σ206Pb/238U2σRho207Pb/206Pb1σ206Pb/238U1σ207Pb/235U1σAge Ma2σClass
TV-39. 100–200 μm grain size
5-c0.06160.00310.93370.05690.11000.00540.80658.6044.73672.708.60669.608.610.49100670.0594.902
5-r0.05980.00240.89430.04800.10850.00530.90595.2032.82663.908.18648.706.800.82102652.2583.454
11-c0.06900.00311.35400.07810.14230.00700.85899.2037.82857.5010.70869.307.310.2199872.59126.664
11-r0.06750.00381.39170.09220.14960.00740.75852.5051.11898.5011.73885.4011.530.20101880.99151.794
18-r0.12410.00456.88330.35170.40230.01950.952015.8021.992179.4023.902096.5012.820.801082016.04143.706
18-c0.16640.006111.50620.59020.50140.02430.952521.8021.182619.8028.042565.1014.020.551042521.81133.255
15-c0.05770.00250.82820.04590.10410.00510.88517.6036.25638.407.97612.607.720.27104620.7880.485
15-r0.05890.00250.82860.04600.10210.00500.88561.5035.89626.707.84612.808.000.21102617.1479.484
15-r0.05880.00240.80820.04410.09970.00480.89559.1034.48612.607.64601.408.470.18102605.1476.484
17-r0.12030.00445.110.18590.30810.00710.631960.323.891731.317.111837.811.920.16881957.76144.386
20-r0.16940.00611.31060.57230.48420.02340.962551.519.832545.727.082549.112.90.021002551.5128.891
22-c0.18630.006714.40770.73210.56090.02710.952709.619.852870.229.842776.913.630.611062709.52126.615
23-c0.05820.00300.71670.04490.08940.00440.78535.5048.65551.707.19548.709.150.58100549.9873.592
27-c0.05710.00280.77140.04620.09800.00480.82493.5044.04602.807.72580.608.220.16104588.9778.955
27-l0.05890.00270.83980.04850.10330.00500.85564.5039.86633.908.03619.008.340.12102623.4582.824
29-c0.06020.00270.77300.04440.09320.00460.85609.4038.99574.307.30581.509.840.2599578.7974.403
29-r0.05790.00240.77280.04250.09690.00470.89524.0035.30596.007.46581.409.620.21102586.7974.074
26-d0.05770.00290.75640.04600.09510.00470.81518.2045.65585.407.54572.0010.430.13102577.2177.274
21-l0.05660.00310.73180.04700.09370.00460.77475.8051.61577.607.55557.608.610.16103566.0277.895
32-d0.05970.00260.87460.04880.10620.00520.87593.9036.33650.508.13638.108.510.55102641.2783.804
TV-39. 60–200 μm grain size
6-c0.05890.00220.73400.02780.09040.00210.61563.0031.22557.806.00558.906.440.17100558.4442.621
6-r0.05910.00210.70420.02500.08640.00200.64571.4027.74534.105.70541.305.640.0699538.0638.703
7-r0.05830.00200.69120.02390.08600.00190.65539.2027.02532.005.65533.505.320.15100532.7737.481
7-r0.06030.00200.66780.02270.08030.00180.66613.3025.11498.205.29519.405.050.1696509.1134.985
8-c0.12410.00426.34970.21720.37120.00840.662015.4021.002034.8019.352025.3011.050.051012015.45135.042
8-r0.12120.00425.85210.20250.35030.00790.651973.2021.611936.0018.621954.2011.160.08981973.03137.423
12-r0.06040.00250.78870.03180.09470.00220.57618.0034.57583.206.34590.507.400.4699587.8348.123
12-r0.06070.00250.78170.03180.09340.00220.57629.4034.95575.306.27586.407.450.4798582.3847.564
15-c0.06330.00250.85480.03420.09790.00230.58719.4033.52601.906.53627.307.630.2096620.1951.875
15-r0.06140.00280.78200.03500.09240.00220.53652.6040.26569.606.32586.608.540.3497580.4450.364
15-r0.06350.00290.86760.03930.09900.00230.52726.0040.41608.706.77634.309.170.2496627.5357.585
28-c0.05860.00230.67900.02600.08410.00190.60550.6032.07520.505.63526.206.280.1399523.4538.783
28-d0.05940.00220.66300.02430.08090.00180.62581.6029.39501.705.39516.405.750.2997509.2136.214
27-r0.06130.00260.81900.03400.09690.00230.56648.6035.92596.506.51607.507.870.1398603.9551.174
27-c0.17570.006310.85000.39040.44780.01020.632612.9021.792385.3022.252510.4012.810.20912612.77129.206
TV-40. 100–200 μm grain size
2-r0.05870.00260.75720.04320.09360.00460.85554.0039.19577.007.29572.408.470.12101574.1673.622
3-c0.05980.00290.78700.04770.09550.00470.81594.4044.55588.107.57589.509.750.42100588.9579.021
3-r0.05850.00250.74440.04180.09230.00450.87546.9037.12569.407.17565.008.070.45101566.7271.312
5-c0.06140.00270.82110.04630.09690.00470.86654.2036.92596.407.51608.708.610.1898604.7477.534
5-r0.05980.00240.82650.04490.10020.00490.90597.3033.29615.507.66611.707.890.10101612.8377.242
15-c0.13190.00457.13220.35610.39210.01890.972123.419.292132.623.212128.112.030.21002123.41133.882
17-c0.06210.00350.99160.06630.11590.00570.74676.4053.23706.709.32699.5013.140.53101700.39108.773
17-r0.06060.00260.88470.04960.10590.00520.87624.9036.65648.708.12643.508.870.23101644.7084.543
19-r0.05830.00240.70690.03860.08800.00430.89539.4034.96543.506.80542.907.340.31100543.0866.401
19-c0.05880.00240.74940.04040.09250.00450.90557.8032.75570.307.10567.907.330.45100568.8169.762
22-l0.05690.00330.73340.04910.09350.00460.74486.0055.09576.207.63558.5011.200.10103565.8979.955
22-d0.05830.00250.75500.04210.09390.00460.87540.6037.06578.507.26571.107.990.18101573.9972.273
27-r0.05590.00290.69830.04330.09060.00440.79446.7047.55559.307.23537.809.510.14104547.6172.725
27-c0.05930.00270.77090.04500.09440.00460.84576.3041.03581.207.40580.308.970.20100580.5975.731
30-c0.21490.007516.16100.81140.54520.02630.962943.1018.362805.3029.082886.4013.150.59952943.09118.845
30-r0.17300.006110.47770.52750.43930.02120.962586.6019.242347.3025.202477.9012.860.11912586.47126.706
31-r0.05870.00220.72160.03780.08910.00430.92556.5029.70550.306.81551.606.650.10100550.9965.871
31-c0.05830.00230.79350.04220.09870.00480.91539.7032.19607.007.51593.107.330.21102598.0174.054
32-l0.06120.00280.73240.04220.08670.00420.85647.239.14536.36.825588.450.1996548.9469.265
23-d0.06210.00270.95990.05410.11220.00550.87675.7036.78685.408.58683.209.330.94100683.5291.492
23-r0.06190.00280.96630.05540.11320.00550.85671.6038.58691.008.69686.509.740.67100687.1893.672
36-c0.05740.00240.78180.04300.09880.00480.88506.9035.92607.107.57586.507.930.28103594.0375.445
36-r0.05990.00230.79800.04180.09670.00470.93598.8029.48594.807.33595.707.030.27100595.3572.391
TV-41. 100–200 μm grain size
10.12720.00446.69850.33540.38180.01840.96206019.752084.622.822072.412.040.091012059.94136.143
12-c0.06050.00250.79450.04370.09530.00460.89619.7034.58586.807.34593.707.970.5499591.2474.183
12-r0.05940.00240.71440.03820.08720.00420.91581.1031.96539.206.70547.407.010.4198543.7665.503
18-r0.06160.00250.91640.04910.10790.00520.90659.9031.79660.508.14660.508.080.72100660.4383.971
18-c0.06140.00270.93340.05270.11030.00540.86653.0037.16674.208.42669.409.240.54101670.2989.592
15-r0.06190.00240.88890.04730.10410.00500.91671.3031.10638.407.86645.807.830.0499643.9480.683
16-r0.06030.00280.94150.05470.11330.00550.84612.9040.39691.908.70673.709.900.38103676.9893.415
16-l0.06200.00240.95100.05020.11120.00540.92674.3030.15679.808.32678.607.921.54100678.7885.841
22-c0.07000.00281.50840.08010.15640.00760.91926.8029.64936.6011.28933.809.920.48100932.42126.432
22-r0.06020.00220.91080.04680.10980.00530.94609.8027.49671.408.15657.507.170.41102660.4981.764
20-v0.18140.006214.06460.69980.56230.02710.972665.7018.142876.0029.462754.1012.641.051082665.62122.326
20-r0.17860.006112.65690.62980.51390.02480.972640.0018.202673.2027.772654.5012.551.401012640.00122.853
400.06100.00280.74860.04370.08910.00430.84637.4040.69550.106.97567.408.800.2297560.5171.945
1 C%—concordance: C% = (206Pb − 238U age/207Pb − 235U age) × 100 for ages < 1 Ga; C% = (206Pb − 238U age/207Pb − 206Pb age) × 100 for ages > 1 Ga. 2 Recalculated according to [71] using a non-iterative probabilistic model for determining a single concordant age and its concordance class (1 to 7). Zircon analyses (100–200 μm) were performed at the Laboratory of the Bulgarian Academy of Sciences, Bulgaria. Zircon analyses (60–100 μm) were performed at the Magma & Volcans Laboratory in Clermont-Ferrand, France. r—rim; c—center; l—light part; and d—dark part on CL images.
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Vladinova, T.F.; Georgieva, M.G. Petrogenesis and Provenance of the Triassic Metasedimentary Succession in the Sakar Unit, Bulgaria: Constraints from Petrology, Geochemistry, and U-Pb Detrital Geochronology. Geosciences 2025, 15, 343. https://doi.org/10.3390/geosciences15090343

AMA Style

Vladinova TF, Georgieva MG. Petrogenesis and Provenance of the Triassic Metasedimentary Succession in the Sakar Unit, Bulgaria: Constraints from Petrology, Geochemistry, and U-Pb Detrital Geochronology. Geosciences. 2025; 15(9):343. https://doi.org/10.3390/geosciences15090343

Chicago/Turabian Style

Vladinova, Tzvetomila Filipova, and Milena Georgieva Georgieva. 2025. "Petrogenesis and Provenance of the Triassic Metasedimentary Succession in the Sakar Unit, Bulgaria: Constraints from Petrology, Geochemistry, and U-Pb Detrital Geochronology" Geosciences 15, no. 9: 343. https://doi.org/10.3390/geosciences15090343

APA Style

Vladinova, T. F., & Georgieva, M. G. (2025). Petrogenesis and Provenance of the Triassic Metasedimentary Succession in the Sakar Unit, Bulgaria: Constraints from Petrology, Geochemistry, and U-Pb Detrital Geochronology. Geosciences, 15(9), 343. https://doi.org/10.3390/geosciences15090343

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