Overprinted Metamorphic Assemblages in High-Alumina Metapelitic Rocks in Contact with Varnous Pluton (NNW Greece)

Abstract

The Varnous Mt. area in the northern Pelagonian Nappe is characterized by the intrusion of an Early Permian pluton, with its tectonic setting and igneous petrology well constrained in earlier studies. The metamorphic basement rocks warrant further detailed investigation due to their complex history. These rocks are polymetamorphosed, preserving a sequence of overprinting metamorphic and deformational events. The metapelitic rocks have undergone an initial, pre-Carboniferous regional metamorphism of unknown grade before or during Hercynian Orogeny, followed by a thermal metamorphic event associated with the intrusion of the Varnous pluton at 297 Ma. The assemblage attributed to this event is And + Crd + Bt + Ms (west), while the first assemblage identified at the eastern part is Sil + Bt + Gt. Additionally, three regional tectonometamorphic events occurred during the Alpine Orogeny. For the Alpine events, the assemblages are as follows: first, the development of St + Gt + Chl + Kfs + Pl + Qtz at 150–130 Ma; second, retrograde metamorphism of these assemblages with Cld + Gt + Ser + Mrg + Chl ± Sil (Fi) at 110–90 Ma; and finally, mylonitization of all previous assemblages at 90–70 Ma with simultaneous annealing and formation of Cld + Chl + Ms.

1. Introduction

The mountainous area of Varnous is characterized by the intrusion of the pluton of the same name. The area is in the northwestern region of Greece, specifically to the west of the town of Florina and to the east of Mikri Prespa Lake, just south of the border with the Republic of North Macedonia. The Varnous pluton extends northward, crossing over the border between Greece and North Macedonia. The southern edge of this igneous body reaches the foothills of Mount Vernon (see Figure 1). The pluton itself exhibits a range of differentiated products, containing various petrological types that span from leucogranite to monzodiorite [1,2]. This pluton intruded the basement of the Pelagonian Nappe/Zone around 297 million years ago [3,4].

While numerous studies have noted the presence of metamorphic rocks in close contact with the Varnous pluton, these rocks have not been extensively examined [1,2,5]. There remains an ongoing debate within the scientific community regarding whether these metamorphic rocks have been formed under conditions of a contact aureole due to the plutonic intrusion, or if they are the result of regional metamorphism as part of larger tectonic processes [6]. The primary objective of the current study is to systematically identify and analyze the different metamorphic assemblages, as well as to reconstruct the metamorphic and deformation history of the area.

2. Geological Setting

According to the typical geotectonic classification of the Hellenides [4], Greece is divided into zones of predominantly NW-SE orientation (Figure 1). The study area lies within the Pelagonian Nappe, a continental fragment considered to have originated from Gondwana [7]. As mentioned previously, the Varnous area is part of the northern Pelagonian Nappe. The Pelagonian Nappe mainly consists of crystalline rocks (granites and orthogneisses) and overlying sedimentary rocks (Figure 2). East of the Pelagonian Nappe is the Axios/Vardar zone, the basement of which consists mainly of ophiolites. The basement of the Pelagonian Nappe dates back at 699 ± 7 Ma to 713 ± 18 Ma using U–Pb single-zircon and SHRIMP ages in shists of the area [8,9,10,11]. These ages suggest that the basement of the Pelagonian Nappe had already been formed and possibly underwent tectonometamorphic events during the Hercynian Orogeny. The area of study has undergone the Alpine Orogeny, making it difficult to identify these events with certainty, as they have been overprinted by several subsequent episodes.

During the Alpine Orogeny, the Tethys Ocean closed, and parts of the oceanic crust were subducted under the continental margin, while a small portion was obducted over the Pelagonian Nappe, forming ophiolites [4]. Several granitic intrusions of the Pelagonian Nappe were formed primarily during the Permian to Carboniferous period, ranging in age from 320 ± 12 to 280 ± 10 Ma [10], indicating a significant magmatic episode (Figure 3). The geotectonic setting of this magmatic event, as inferred from the chemical composition of the rocks, corresponds to a magmatic arc environment, confirming the subduction of an oceanic plate beneath a continental margin [12]. The Varnous pluton, which has been dated at 297 ± 25 Ma with whole-rock Rb-Sr geochronology [3], belongs to this magmatic event. The Varnous pluton has been studied separately by different researchers at the eastern and western part, who reached different conclusions [1,2,5]. The eastern part of the Varnous pluton consists of five petrographic types resulting from differentiation through fractional crystallization: Hbl-Bt monzodiorite, Hbl-Bt-Qtz monzonite, Bt-Qtz monzonite, Bt granite, and leucogranite (see abbreviations at the end). These rocks crystallized under pressures ranging from 2 kbar (leucogranite), at a depth of 2–3 km, to 4.6 kbar (Hbl-Bt monzodiorite), corresponding to depths of up to 15.5 km [2,13,14].

Figure 2. Geological map of the study area: al = alluvial deposits, sl = marshy areas, Q.sc,cs = old and recent scree and talus cones, Pt.t = old terrestrial terraces, Ng = Neogene sands, clays, and conglomerates, Tm-Ji.k = Middle Triassic–Lower Jurassic limestone and dolomitic limestone, gneissic pluton = part of the pluton with gneissic texture from a later tectonic event, metapelites = metamorphic rocks with contact metamorphism, pluton = plutonic body of Varnous, and basement = metapelitic rocks from the basement, (modified after [15,16]). Sampling locations are marked in cyan. Blue rectangle indicates the western part of the region, yellow indicates the southern part, and red indicates the eastern part.

Figure 2. Geological map of the study area: al = alluvial deposits, sl = marshy areas, Q.sc,cs = old and recent scree and talus cones, Pt.t = old terrestrial terraces, Ng = Neogene sands, clays, and conglomerates, Tm-Ji.k = Middle Triassic–Lower Jurassic limestone and dolomitic limestone, gneissic pluton = part of the pluton with gneissic texture from a later tectonic event, metapelites = metamorphic rocks with contact metamorphism, pluton = plutonic body of Varnous, and basement = metapelitic rocks from the basement, (modified after [15,16]). Sampling locations are marked in cyan. Blue rectangle indicates the western part of the region, yellow indicates the southern part, and red indicates the eastern part.

Figure 3. Schematic geotectonic setting of the studied area during the Carboniferous (red with white crosses indicates the basement of Pelagonian Zone), showing the Hercynian intrusions (white with black crosses) [4]. The blue circle shows Varnous pluton intrusion.

Figure 3. Schematic geotectonic setting of the studied area during the Carboniferous (red with white crosses indicates the basement of Pelagonian Zone), showing the Hercynian intrusions (white with black crosses) [4]. The blue circle shows Varnous pluton intrusion.

In contrast, the western part of the pluton is believed to have been formed under two major intrusion phases with genetic affinity. Additionally, the pluton was partially metamorphosed due to the influence of alkali-rich hydrothermal fluids. Although minerals such as andalusite, garnet, and chloritoid have been identified in the surrounding rocks, no direct contact has been observed between the pluton and the basement, as no direct contact between the granite and the host rocks was found [1].

In the central and southern regions, parts of the pluton exhibit schistosity and are considered to have been affected by a later tectonometamorphic event that metamorphosed them into gneiss [1,5]. These igneous rocks intruded an already metamorphosed metapelitic basement [5,6]. There is an ongoing debate regarding the existence of a thermal aureole around the intrusion. Some researchers propose that the high-temperature/low-pressure metamorphic rocks around the pluton are part of the thermal aureole created by the intrusion [5], while others suggest that these rocks were already metamorphosed under such conditions prior to the intrusion [6].

It is important to note that the basement of the Pelagonian Nappe is considered a continental fragment of Gondwana [4]. Having been formed before the Alpine Orogeny, all the aforementioned rocks were subsequently affected by it, with multiple tectonometamorphic events, each of which overprinted the previous ones. These tectonometamorphic events have been documented in several studies, have been dated by K/Ar, Ar/Ar, and Rb/Sr geochronology [4,17,18,19,20], and can be summarized into six main episodes (D1 to D6), with the first three in ductile or semi-ductile conditions and the latter three in brittle conditions:

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D1—A compressional event with folding and foliation in a general NNW-SSE trend, occurring at 150 ± 6–130 ± 5 Ma [19,20], accompanied by metamorphism. This event is linked with an intraoceanic thrusting event, which resulted in the obduction of ophiolites above the continental margin and a metamorphic episode of amphibolite facies;

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D2—Another compressional event with folding and foliation in a general NW-SE trend, occurring at 110 ± 5–95 ± 4 Ma [19,20], accompanied by metamorphism. This event is linked with nappe stacking and retrograde greenschist metamorphism;

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D3—An extensional event, which creates shear zones and mylonitic zones in a general NE trend, occurring at 90 ± 4–70 ± 3 Ma [19,20];

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D4—A compressional event in brittle conditions characterized by kink folds and reverse faults in a NW-SE trend, juxtaposing the basement above the pluton;

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D5 and D6—Later deformation events characterized by normal faulting.

3. Materials and Methods

Seventy-eight polished thin sections were prepared by the authors at the School of Geology, Aristotle University of Thessaloniki. The samples were collected between November 2020 and October 2023, both from the pluton and the surrounding rocks, and were studied using optical and scanning electron microscopy for the determination of their mineralogical composition and their textures (see Figure 1 and Figure 2 for sampling locations). The optical microscope used was a Zeiss Axioskop 40 (Zeiss, Oberkochen, Germany) dual reflected-transmitted light polarizing microscope (SEM) coupled with a Canon Powershot A640 (EDS, Canon Inc., Tokyo, Japan) at the School of Geology, Aristotle University of Thessaloniki. The scanning electron microscope was a JEOL JSM-6390LV type equipped (JEOL Ltd., Tokyo, Japan)with an energy dispersive spectrometer INCA 300 (Oxford Instruments, Oxfordshire, UK), at the Laboratory of Scanning Electron Microscopy at Aristotle University of Thessaloniki. Analytical conditions were 20 kV operating voltage, 0.4 mA beam current, 80 s analysis time, and ≈1 μm beam diameter.

4. Results and Discussion

To facilitate better data management and analysis, the study area has been divided into three distinct regions. The first region is located in the eastern part of the study area, running parallel to the Florina-Agia Paraskevi Road, hereafter referred to as the eastern part. The second region lies parallel to the Andartiko-Mileonas Road, referred to as the western part, and the third region runs parallel to the Florina-Vigla-Andartiko Road, referred to as the southern part (Figure 2). It has been observed that the southern and eastern regions exhibit significant mineralogical similarities, whereas the western region is distinctly different in terms of its geological and mineralogical characteristics.

The eastern part contains the most complex assemblages within the study area. Within a single thin section, a diverse range of minerals formed under varying temperature–pressure conditions can be identified. As an example, some samples contain sillimanite, staurolite, and chloritoid in the same thin section. The samples from this region can be grouped into three main categories: the first one being those containing sillimanite, the second one being those containing staurolite, and the third being those containing chloritoid. Chemical analyses of minerals are presented in

Table A1. Representative compositions of minerals from the samples of the area. The structural formulae were calculated on the basis of fixed oxygen. FeOt = total iron; for more analysis see Supplementary Material.

Mineral	Ms-Ph	Mrg	Pg	Bt	Chl	And	Sil	Crd	Cld	Gt	Pl	Kfs
Sample	Le-1a	Ka-2	Le-2	Le-2	Le-4a	Le-17	Le-10	Le-14	Ka-2	Ka-4a	Le-11	Le-13
SiO2	45.57	32.04	46.87	39.40	29.66	37.00	37.06	46.90	23.83	38.67	63.16	64.22
TiO2	0.31	-	0.25	3.28	0.18	0.09	0.04	-	-	0.25	-	18.78
Al2O3	34.67	49.77	39.02	20.11	21.20	62.55	61.51	32.67	40.94	20.36	23.01	-
FeOt	1.75	0.30	0.29	18.23	24.29	0.03	0.14	11.25	24.23	30.9	0.1	0.12
MnO	0.08	0.25	-	0.88	1.01	-	0.4	0.11	2.12	6.74	-	-
MgO	0.48	0.03	0.10	6.00	8.44	-	-	5.62	1.48	2.77	-	-
CaO	0.12	11.27	0.53	0.17	-	0.16	0.49	0.43	0.16	1.23	4.02	0.22
Na2O	0.29	1.35	6.19	-	0.75	-	-	0.38	0.22	-	9.09	0.91
K2O	9.84	0.06	1.75	8.58	0.26	-	0.23	0.64	0.30	-	0.46	15.43
Total	95.1	95.06	95.03	96.66	85.72	99.84	99.65	98.01	93.29	100.92	99.83	99.68
No. of O	22	22	22	22	28	20	20	18	14	12	8	8
Si	6.31	4.25	6.02	5.78	6.17	4.00	4.027	4.95	1.97	3.00	2.80	2.97
Al IV	1.69	3.75	1.98	2.22	-	-	-	1.05	3.00	-	1.20	1.02
Al VI	3.73	4.02	3.93	1.26	5.20	7.97	7.88	3.01	1.00	1.92	-	-
Ti	0.03	-	0.02	0.36	0.03	0.01	-	-	-	0.02	-	-
Fe2+	0.19	0.03	0.03	2.24	3.45	-	0.01	0.99	1.68	2.07	-	-
Mn	0.01	0.03	-	0.11	0.18	-	0.04	0.01	0.18	0.46	-	-
Mg	0.09	0.01	0.02	1.31	2.62	-	-	0.88	0.15	0.33	-	-
Ca	0.02	1.60	0.07	0.03	-	0.02	0.06	0.05	0.01	0.11	0.19	0.01
Na	0.07	0.35	1.54	-	0.60	-	-	0.08	0.04	-	0.78	0.08
K	1.67	0.01	0.29	1.61	0.14	-	0.03	0.09	0.03	-	0.03	0.91

All minerals that form solid-solution series with Fe-Mg are iron rich. Chl is classified as brunsvigite, a type of chamosite, with Fe/Fe + Mg ratio of 0.62, while in Bt, the same ratio is 0.63. In Ctd, the ratio Fe/Fe + Mg ratio is 0.8, whereas in Crd, the ratio is 0.53. As shown by the representative analyses, micas exhibit a wide range of compositions. The different micas are formed during different tectonometamorphic events. Phengitic mica was likely formed during a higher-pressure tectonic event, while paragonite and margarite seem to have formed during retrograde metamorphic conditions of minerals such as cordierite and andalusite. Garnet, where present, is almost always represented by the following composition: Alm66Sps14Py9Grs4Adr2. Plagioclase is classified as albite in some samples, while in others it is identified as oligoclase.

, and representative microphotographs are shown in Figure 4, Figure 5 and Figure 6. The main assemblages are as follows (abbreviations after [21]):

• Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Kfs ± Ap;
• Qtz + Mica (Ms-Ph) + St + Gt + Chl + Sil (Fi) ± Pg;
• Qtz + Gt + Cld + Ser;
• Qtz + Mica (Ms) + Cld + Chl ± Ilm.

The first assemblage is characterized by the presence of large euhedral crystals of sillimanite and garnet accompanied by biotite. Both sillimanite and biotite in these samples are unaltered. In Figure 4a,b, the brownish spots correspond to staurolite, which likely begins to form via the reaction of Gt + Bt + Als ⇌ St. The formation of staurolite attests to the overprinting of the first assemblage from a later metamorphic event, along with mica of muscovitic and phengitic compositions and the appearance of a lepidoblastic texture.

In the samples containing sillimanite, garnet crystals are enlarged, and fibrolite is formed around the large sillimanite crystals. In other samples, this stage is marked by pseudomorphs of chloritoid replacing garnet (Figure 4c,d). Chlorite is also present in this metamorphic stage, along with chloritoid and sericite, which are formed while the texture of the rocks remains lepidoblastic, showing more obvious foliation and schistosity.

The last assemblage identified in these samples is characterized by chloritoid and chlorite crystals with a diablastic texture (Figure 5a–d). The chemical reaction that took place was probably 4 St + Bt + 3 H₂O ⇌ 7 Cld + Ms + Qtz. Furthermore, larger muscovite crystals are formed in contact with quartz, with random orientation. The large garnet crystals are broken by the chlorite being formed in the cracks (Figure 5a,b). Lastly, small, undeformed garnet crystals grow (Figure 5e,f). Quartz is present in all the assemblages. Chlorite from all stages has a similar chemical composition. The main differences lie in the texture and microscopic observations of the samples, indicating different origins. Specifically, chlorite can be found replacing garnet, or, as mentioned above, with a diablastic texture, as seen in Figure 5c,d. Similar assemblages are found in the southern part of the region, with the only exception being the absence of staurolite.

As mentioned above, two types of garnet crystals are found in samples. The first type consists of large broken crystals (Figure 5a,b) accompanied by sillimanite and staurolite, and the second type consists of small euhedral crystals (Figure 5e,f) with garnet accompanied by chloritoid, chlorite, and mica. The chemical profile of the first type of garnet is shown in Figure 7a, while the chemical profile of the second type of garnet is shown in Figure 7b. The outermost zone of both garnets is similar, indicating that the final event affected all of them and was universal.

The metapelitic rocks of the western part of the area bear significantly different assemblages. The largest difference observed is the presence of cordierite and andalusite. Furthermore, sillimanite, biotite, and garnet appear to a lesser extent and are altered, while the rocks appear less deformed.

Specifically, the main assemblages identified in the western part are as follows:

• Qtz + And + Crd + Bt + Ms ± Kfs ± Ab ± Ilm ± Tur;
• Qtz + Ms + Cld + Chl + Pg + Mrg ± Ph;
• Qtz + Chl + Cld + Ms.

In the first assemblage, cordierite and andalusite form poikiloblasts, but are affected by the overprinting of the second retrograde assemblage. Thus, cordierite and andalusite are found to be greatly altered by pinite and margarite—paragonite, respectively (Figure 6a,b). Only a small number of samples contain cordierite, which appears altered only in the rim by pinite (Figure 6a,b). In most of the samples, muscovite, quartz, and chlorite completely replace cordierite-forming pseudomorphs (Figure 6c,d). Sillimanite, where found, is either in the form of fibrolite or found only in a few preserved relics remaining after the reaction: Kfs + Sil + H₂O ⇌ Ms + Qtz (Figure 6e,f). A later assemblage with larger crystals of muscovite, chlorite, and chloritoid, and a diablastic texture, is also identified in some of these samples (Figure 6g,h).

The minerals found in each assemblage indicate formation under different metamorphic conditions. Geothermometric and geobarometric methods were utilized to determine these conditions. The results of the geothermometers and geobarometers used are summarized in

Table 1. Assemblages in each part of the study area. Pluton conditions are also added for comparison.

East	South	Conditions
Pluton		3 kbar
Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Kfs ± Ap	Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Kfs ± Ap	3–4 kbar, 600–700 °C
Qtz + Mica(Ms-Ph) + St + Gt + Chl + Sil(Fi) ± Pg	Qtz + Mica(Ms-Ph) + Gt + Chl + Sil(Fi) ± Pg	6–8 kbar, 400–550 °C
Chl + Cld + Ser + Gt	Chl + Cld + Ser + Gt	400–500 °C
Chl + Cld + Ms	Chl + Cld + Ms	300–400 °C
West
Pluton		1.4 kbar
Crd + And + Bt + Gt + Qtz + Ms ± Pl ± Kfs		0–2 kbar, 600–700 °C
-		-
Ms + Cld + Chl + Qtz + Pg + Mrg ± Ph		5–6 kbar, 400–500 °C
Chl + Cld + Ms		300–400 °C

for each assemblage. These results were compared with the pressures estimated at the western and eastern margins of the pluton using Hbl geothermometers [22,23,24,25] from previous research [1,2]. The pressure of the pluton in the eastern and western part differs, as shown in Table 1, with the eastern part having higher pressure. For the assemblage Sil + Bt + Gt + Qtz + Ms ± Pl ± Kfs in the east and south, the Bt geothermometer [26,27] was utilized. The same geothermometer, as well as the Crd geothermometer [28,29,30], was used for the assemblage Crd + And + Bt + Qtz + Ms ± Pl ± Kfs in the west. For the pressure of the same assemblages, the geobarometer of Gt-Pl-Sil-Qtz and Gt-Pl-And-Qtz [31,32] was utilized. The temperatures estimated for these two assemblages are similar, while the pressure is significantly different. For the second assemblage, the temperature was determined by the geothermometers of Gt-Bt [33,34], Gt-Chl [35,36], and Gt-Cld [36], while the pressure was determined based on white mica compositions obtained using the thermodynamic model of Massone and Szpurka [37], which is suitable for intermediate- to high-pressure conditions in metapelites. Although empirical phengite-based barometers [38] have been widely applied in high-pressure subduction environments, they require Si > 3.2 (per 11 O), which is not reached in samples of the study area. This assemblage is observed only in the eastern part, and no assemblage corresponding to these conditions was found in the western part. For the third assemblage observed in the western and eastern part, the temperature was determined by the geothermometers of Chl-Cld [36,39], while the pressure was determined only for the former using the Ph geobarometer. For the final assemblages, only the geothermometers of Chl-Cld were applied.

Since the pluton intruded into the basement, the surrounding rocks must predate the intrusive rock, with some studies estimating their age at approximately 700 Ma [10,11,12]. Consequently, the tectonic history of the area supports the evidence of polymetamorphism observed in the samples.

The first significant tectonometamorphic event of the area is linked to the intrusion at 297 Ma. The first assemblage identified at the western part with Crd + And + Bt + Qtz + Ms ± Pl ± Kfs yields conditions of 0–2 kbar, 600–700 °C. Rocks of the western part exhibit diablastic and granoblastic textures, which, combined with the conditions necessary for the formation of cordierite–andalusite, provide evidence of a high-temperature and low-pressure event. The estimated pressure for the margin of the pluton coincides with the pressure determined for the metapelitic samples in the same area. Given the proximity of these samples to the pluton, it is most likely that these assemblages belong to the thermal aureole caused by the intrusion of the granitic body.

The assemblage Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Kfs ± Ap at the eastern part was formed at 3–4 kbar, 600–700 °C (Table 1), indicating high temperature, but medium pressure. The typical upper limit for the pressure of contact metamorphism is 3.5 kbar [40]. The pressure of these samples meets the threshold, but because of the proximity to the pluton and the similar pressure of the pluton in this area, it could be assumed that it has been formed by the intrusion of the granitic body, although further research needs to be conducted to validate this hypothesis.

As mentioned previously, the area of study underwent the tectonometamorphic events of Alpine Orogeny. The Alpine metamorphism in the study area has been well-documented [17,18]. The assemblage Ms + Ph + Gt + St/Cld + Chl + Qtz ± Pg with Ph points towards higher pressures, 6–8 kbars (Table 1). This assemblage at the eastern (southern) part exhibits relatively higher pressures, indicating a regional rather than a thermal metamorphic event. When compared to the conditions of the tectonic events of the Alpine Orogeny that affected the Pelagonian Nappe, the D1 tectonic event [17,18] dated to 150–130 Ma is probably responsible for this metamorphism. This assemblage is observed in the eastern part only, and an assemblage of similar conditions is not observed in the western part.

Another metamorphic event, dated to 110–90 Ma during the D2 tectonic event, overprinted the previous assemblage, as evidenced by the alteration of mica to sericite and garnet to chlorite, along with quartz and plagioclase [17,18]. Similar assemblages are found in the eastern and western parts. Since the assemblages and their temperatures are similar in the whole area, it can be assumed that they formed under the same tectonic event. In some samples, sillimanite occurs as small fibrolite crystals forming an ino-lepidoblastic texture together with chlorite, chloritoid, garnet, and mica. In these samples, the texture indicates an increase in tectonic strain, while the minerals suggest a decrease in temperature. This assemblage is likely the result of a retrograde syntectonic event. In this later event, fibrolite appears at the rim of the older sillimanite crystals. The later assemblage corresponds to the one described in relation to the D2 tectonometamorphic event that occurred between 110 and 90 Ma [17]. In the western part during this event, andalusite and cordierite, as mentioned earlier, appear altered to margarite and pinite, respectively.

The D3 mylonitic event of 90–70 Ma formed mylonites in both granitic and metamorphic rocks, which can be observed in zones throughout the study area [17,18]. This event caused the formation of new minerals Qtz + Mica(Ms) + Ctd + Chl ± Ilm, with large muscovite crystals and a diablastic texture. Small euhedral garnet crystals found at the eastern part are associated with chlorite and mica, suggesting a metamorphic event under lower pressure than the previous one, which coincides with the D3 tectonometamorphic event. Furthermore, this metamorphic event is responsible for the annealing of minerals and can be attributed to decompression.

The later tectonic events happened in brittle conditions and were not accompanied by metamorphism. These later events are responsible for the final placement of the rocks in the study area, further complicating the identification of the assemblages and the definition of the metamorphic conditions. Specifically, the D4 event juxtaposes the basement above the igneous rocks [17,18], bringing rocks from deeper levels with an east–west orientation, possibly justifying the difference in pressures along the eastern and western parts.

The sequence of metamorphic events in the area can be summarized as follows:

• Formation of Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Ap (east) and And + Crd + Bt + Ms (west) at approximately 297 Ma due to the plutonic intrusion;
• Development of Qtz + Mica (Ms-Ph) + St + Gt + Chl (east) during the D1 Alpine event at 150–130 Ma;
• Retrograde alteration of the previous assemblages to Qtz + Mica (Ms-Ph + Pg) + Ctd + Chl + Gt (small euhedral) + Sil (Fi) ± Bt ± Ilm (east) and And + Crd + Chl + Mrg +Pg + Ms (west), at 110–90 Ma;
• Mylonitization of all previous assemblages and annealing and formation of Cld, Chl, and Ms at 90–70 Ma;
• Brittle compressional tectonic event juxtaposing the basement above the igneous rocks.

5. Conclusions

The metapelitic assemblages of the Varnous area record a polymetamorphic evolution reflecting a complex tectonometamorphic history. Εach metamorphic assemblage reflects distinct pressure–temperature conditions linked to specific tectonic events through petrographic, microstructural, and geothermobarometric data. The earliest metamorphic event (~297 Ma) is attributed to the intrusion of the Varnous pluton, which is responsible for the high-temperature, low-pressure assemblages with And + Crd + Bt + Ms in the western part and possibly Qtz + Bt + Gt + Sil ± Ilm ± Pl ± Ap in the eastern part. The first identified regional metamorphic overprint (150–130 Ma) associated with the D1 tectonic event generated medium- to high-pressure assemblages Qtz + Mica (Ms-Ph) + St + Gt + Chl. These assemblages are preserved in the eastern and southern parts of the area and are consistent with metamorphism during early Alpine convergence. A retrograde phase during the D2 tectonometamorphic event (110–90 Ma) led to the development of lower-temperature assemblages with Qtz + Mica (Ms-Ph + Pg) + Ctd + Chl + Gt (small euhedral) + Sil (Fi) ± Bt ± Ilm and And + Crd + Chl + Mrg +Pg + Ms in the eastern and western parts, respectively, suggesting a decompression. The D3 tectonic event (90–70 Ma) resulted in mylonitization, mineral annealing, and further metamorphic overprinting under low to medium temperature conditions. Finally, the D4 tectonic event affected the placement of the different petrographic types. This brittle tectonic event caused structural juxtaposition, elevating the basement above the pluton in the eastern part, and is likely responsible for the observed differences between the eastern and western parts of the study area.

Further research is ongoing to determine the exact pressure–temperature conditions of each assemblage and the factors responsible for the formation of different assemblages in the eastern and western parts of the contact aureole.