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Volcanism of the Carpathian-Pannonian region, Europe: The role of subduction, extension and mantle plumes

Szabolcs Harangi

Department of Petrology and Geochemistry, Volcanology Group, Eötvös Loránd University, H-1117 Budapest, Pázmány sétány 1/C, Hungary, szabolcs.harangi@geology.elte.hu

 

This webpage was summarized in a lecture given as part of the 2009 Eötvös Lecture Series "Petrogenesis and geodynamic relationships of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region", 5th November 2009, Eötvös College, Budapest

 

Introduction

The Carpathian-Pannonian region (CPR) is a key natural laboratory for studying the interaction of deep lithospheric processes and tectonic events such as lateral microplate escape, subduction roll-back, basin subsidence, tectonic inversion and asthenospheric updoming (Horváth et al., 2006). This region also provides an excellent opportunity to study the interaction between tectonic processes, deep mantle processes and igneous activity. In this review, I summarise important points related to the genesis and geodynamic relationships of the Neogene to Quaternary volcanism of the CPR, particularly concerning the possible role of a mantle plume, laying out my personal view.

Geological background

The Carpathian-Pannonian region lies in the northeastern part of the Alpine-Mediterranean region and is characterized by an arcuate orogenic belt (Carpathians) with a basin area behind (the Pannonian basin; Figure 1). The Pannonian basin is surrounded by the Alpine, Carpathian and Dinarides mountain belts. It is underlain by thin lithosphere (50-80 km) and crust (22-30 km) coupled with high heat flow (> 80 mW/m2; Horváth et al., 2006). It is regarded as a special type of back-arc basin formed by heterogeneous stretching of the lithosphere. The extension of the lithosphere started in the Early Miocene and the syn-rift phase was finished by the end of Miocene. Significant thinning of the lithosphere was accompanied by asthenospheric updoming. As a consequence, the Pannonian basin is one of the hottest basins in continental Europe. This fact, as well as the results of numerical modeling (Burov et al., 2007; Burov & Cloetingh, 2009) and interpretation of the isotope geochemistry of the alkaline basaltic magmas (Embey-Isztin et al., 2001; Seghedi et al., 2004a) have led to the proposal that a mantle plume had a role in the evolution of this region.

Figure 1: Neogene to Quaternary volcanic rocks in the Carpathian-Pannonian region (only those that outcrop are shown). Localities mentioned in the text: 1. Southern foreland of the Bükk Mts. (Miocene silicic ignimbrites); 2. Northern Pannonian basin (Miocene to Quaternary calc-alkaline and alkaline volcanic rocks); 3. Ciomadul (K-dacite; location of the last volcanic eruption of the CPR); 4. Lucaret (2.5-Ma-old alkali basalt).

The nature of the upper mantle beneath the CPR is inferred from seismic tomographic models. These show a high-velocity body in the transition zone (400-670 km) interpreted as accumulated subducted slab material (Wortel & Spakman, 2000; Piromallo & Morelli, 2003; Hetényi et al., 2009), a near-vertical high-velocity slab beneath the southeastern margin of the CPR (Vrancea zone), regarded as the trace of final-stage subduction (Sperner et al., 2001; 2004) and relatively low velocity material between the transition zone and the base of lithosphere.

Classification and temporal evolution of the Neogene to Quaternary volcanic rocks

The complex geodynamic evolution of the CPR involved the formation of a wide range of magmatic rocks over the last 20 Ma (Szabó et al., 1992; Lexa & Konecný, 1998; Harangi, 2001; Seghedi et al., 2004b; 2005; Harangi & Lenkey, 2007). They can be divided into the following main groups based on their geochemistry (Harangi, 2001):

  1. Miocene (21-13 Ma) silicic pyroclastic rocks;
  2. Middle Miocene to Quaternary (16.5-2 Ma) calc-alkaline volcanic rocks;
  3. Miocene and Quaternary (15-13 Ma and 2-0.02 Ma) potassic and ultrapotassic rocks;
  4. Late Miocene to Quaternary (11-0.2 Ma) alkaline sodic volcanic rocks (Figure 1).

In the following, I give a brief summary of the genesis of these four volcanic groups.

Miocene (21-13 Ma) silicic volcanism

This volcanism resulted mostly in extensive ignimbrite sheets. Effusive rocks have not been found. At the southern foot of the Bükk Mts. (Northern Hungary), fresh Miocene silicic ignimbrites are preserved and therefore provide an excellent opportunity for detailed investigations (Harangi et al., 2005; Lukács, 2009). All the pumices have silicic (> 65 wt% SiO2) composition, whereas the scoriae and the cognate lithic clasts are mostly andesites (Figure 2). Thus, this volcanism seems to reflect a bimodal (andesitic-rhyolitic) composition with a significant gap between the compositions. A detailed mineral-scale investigation (Lukács, 2009) has revealed, however, that the bulk composition of the lithic clasts does not necessarily represent an andesitic magma having a role in magma evolution. These fragments, which could derive from different parts of the crystal mush zone of the silicic magma reservoir, contain disequilibrium mineral assemblages (plagioclases with 40-90 mol% An-content and orthopyroxenes with 50-85 mol% En-content) sitting in a rhyolitic glassy matrix, which resembles the composition of the glass shards in the ignimbrite. The most striking observation is the finding of magnesian orthopyroxenes in these rocks (Lukács, 2009). They clearly suggest the role of mafic magmas with fairly primitive (Mg# > 0.6) composition. These mantle-derived mafic magmas contributed significantly to the evolution of the shallow-level silicic magma reservoirs. Therefore, the Miocene silicic volcanism of the CPR might be intracontinental bimodal basalt-rhyolite style, even though no basaltic magmas erupted along with the rhyolitic ignimbrites.

Figure 2: Major-element data of the pumices (open circles) and the scoriae and cognate lithic clasts (filled circles; after Lukács, 2009). Composition of the glass shards representing the fragmented melt is also shown. The andesitic chemistry of the lithic clasts and scoriae does not mean that andesitic magma participated in the magma evolution. Instead, it reflects mixing of various mineral phases, including those crystallized from mantle-derived mafic magmas, and silicic residual melt.

The early-stage pumices have a strong crustal component (87Sr/86Sr= 0.7010-0.7012; Harangi, 2001; Seghedi et al., 2004b). However, the isotopic composition of their cognate “andesitic” lithic clasts (87Sr/86Sr = 0.7068-0.7090) indicates also the role of mantle-derived magmas. Thus, mixing of magmas from the mantle and from the lower crust is inferred in their genesis. Silicic volcanism lasted for 8 Ma with repetitive explosive eruptions. The initial 87Sr/86Sr isotope ratio of the pumices decreases, while the 143Nd/144Nd isotope ratio increases with time (Figure 3), implying a decreasing crustal component in their evolution. This is consistent with a gradually thinning continental plate and a geodynamic relationship between lithospheric extension and silicic volcanism.

Figure 3: A temporal decrease in the initial 87Sr/86Sr isotope ratios of the rhyolitic pumices implies decreasing crustal involvement, which could be consistent with a gradually thinning lithosphere. The wide isotopic composition in the initial rhyolitic volcanic products can be explained as volcanism triggered by mafic mantle-derived magmas.

Middle Miocene to Quaternary (16.5-2 Ma) calc-alkaline volcanism

One of the most striking features of the Neogene to Quaternary volcanism in the CPR is the development of andesite-dacite volcanic complexes roughly parallel to the Carpathian mountain chain (Figure 1). This spatial distribution, as well as the calc-alkaline character and the subduction-related trace-element signature of the volcanic products (Mason et al., 1996; Seghedi et al., 2004b; Harangi et al., 2007) could be simply explained by a relationship with coeval subduction process (Szabó et al., 1992; Downes et al., 1995). Indeed, it is supported by many geological and geophysical models (e.g., Royden et al., 1982; Tomek & Hall, 1993; Tasarová et al., 2009). However, alternative explanations are proliferating (Knapp et al., 2005; Grad et al., 2006; Houseman & Gemmer, 2007), which argue against the traditional view of a significant role of subduction.

Some observations imply no direct relationship between the calc-alkaline volcanism and active subduction. The volcanic complexes along the northern part of the Pannonian basin are underlain by thin (< 100 km) lithosphere and crust, suggesting that these areas underwent significant stretching during the Middle Miocene, coeval with the 16.5-9 Ma volcanism. Syn-extensional timing for volcanism is supported also by structural and paleomagnetic studies (Nemcok & Lexa, 1990; Karátson et al., 2000; 2007). In the eastern parts of the CPR, the volcanoes are parallel to the Carpathians, extending only 50-100 km from the assumed suture zone, and at the southeasternmost segment they developed even on flysch sediments considered to represent the accretionary wedge. The volcanic activity lasted from about 14 Ma until 2 Ma with a gradual southward migration of the eruptions (Pécskay et al., 1995). However, the volcanism postdated the supposed active subduction, which is inferred to have finished by about 12 Ma. Thus, the calc-alkaline volcanism can be classified as post-collisional. While the origin of these rocks were discussed by Mason et al. (1996; 1998) and Seghedi et al. (2004b; 2005), I present here a couple of significant observations regarding the calc-alkaline volcanic rocks of the northern part of the Pannonian basin (Figure 1). These have implications about their origin and geodynamic relationships. This region is a peculiar one, since it is characterized by long (since 16.5 Ma) and varied volcanic activity. The calc-alkaline volcanism (16.5-9 Ma) was followed by eruptions of alkaline mafic magmas (6.5-0.13 Ma).

A unique feature of the early stage (15-16.5 Ma) calc-alkaline volcanic products in this segment is the relatively frequent occurrence of garnet (almandine) in the andesites and dacites (Harangi et al., 2001). The presence of primary Ca-bearing almandine in these volcanic rocks suggests relatively rapid ascent of andesitic to rhyodacitic host magmas from the lower crust. This could have been promoted by a tensional stress field (regional extension). Indeed, formation of the garnet-bearing calc-alkaline volcanic rocks at the northern Pannonian basin was coeval with the peak extension of the area and thus these rocks may be a sign of a change of the stress field from compression to extension.

A detailed description of the geochemical features of the calc-alkaline volcanic rocks in the northern Pannonian basin is provided by Harangi et al. (2007). A gradual change of magma composition can be observed, e.g., La/Nb, Th/Nb and 87Sr/86Sr ratios decrease, whereas 143Nd/144Nd and 206Pb/204Pb increase with time (Figure 4). In contrast, the Ba/La and 207Pb/204Pb and 208Pb/204Pb isotope ratios do not show any clear temporal change. This compositional variation can be explained by a decreasing crustal component in magmagenesis and/or an increasing role of enriched asthenospheric mantle. In addition, a change in the mantle source, i.e. from metasomatized, slightly enriched MORB source mantle to a more enriched, OIB-source mantle can be also inferred at about 13-14 Ma (Figure 5). The appearance of the OIB-like, enriched mantle component in the late-stage calc-alkaline volcanism can be explained by various models as discussed by Harangi et al. (2007). The most plausible one is the progressive thinning of the continental lithosphere with a change in the mantle source region from metasomatized lithospheric mantle to passively upwelling asthenosphere. In this scenario the early-stage (14-16 Ma) magmatism is a sign of the initiation of lithospheric thinning when partial melting took place in the lower part of the lithosphere metasomatized by earlier subduction. The mafic magmas may have ponded beneath the thick continental crust resulting in melting of the lower crust. As lithospheric extension progressed, the crustal component decreased and the mantle source changed to a sublithospheric one.

Figure 4: Temporal variation of the La/Nb trace-element ratio and initial 87Sr/86Sr isotopes in the calc-alkaline (filled squares) and alkaline (open circles) volcanic rocks of the Northern Pannonian Basin. Note the gradual temporal change in geochemical composition.

Figure 5: A two-stage model for the genesis of the calc-alkaline rocks of the northern Pannonian basin (Harangi et al., 2007) based on the variation of 143Nd/144Nd (sensitive to involvement of a crustal component) and 206Pb/204Pb (sensitive to the type of mantle component) isotope ratios. Model parameters are given in Harangi et al. (2007). The preferred model involves an E-MORB-source mantle, which was contaminated by 2-3% subducted sediment (mixing line ’A’). The mafic melt formed from this metasomatized mantle source (metasomatized mantle2) subsequently mixed with the lower crustal material (mixing line ’B’). This scenario could be applicable to the older (>15 Ma) magmatism, but does not explain the genesis of the <15 Ma magmas. For this, a sharp change in composition of the mantle source is needed, i.e. from an E-MORB-type to a FOZO-type mantle. The isotopic variation of the post-15 Ma magmas can be explained by modification of a FOZO-like, enriched mantle by 1-2% subducted sedimentary component (trend C; resulting in metasomatized mantle1) followed by mixing of mafic melt derived from this metasomatized mantle with silicic melt from the metasedimentary lower crust (trend D).

The supposed OIB-type mantle source has an isotopic character similar to FOZO as defined by Stracke et al. (2005) or to the common European Asthenospheric Reservoir (EAR; Cebriá & Wilson, 1995; Hoernle et al., 1995; Lustrino & Wilson, 2007). A plume origin of this mantle component is unlikely in the Pannonian Basin (Harangi & Lenkey, 2007). Instead, it could reside in the shallow asthenosphere and possibly also in the lower lithosphere causing small-scale heterogeneity (Rosenbaum et al., 1997). Transition from calc-alkaline to alkaline magmatism is observed in many parts of the Mediterranean region (Wilson & Bianchini, 1999). In the northern Pannonian basin, this transition does not necessarily indicate a change in the geodynamic setting, i.e. from subduction to extension. Instead, both types of magmatism were somehow related to lithospheric extension. Calc-alkaline magmas were generated during the period of peak extension, by melting of metasomatized lithospheric mantle, and were contaminated by various crustal materials, whereas the alkaline mafic magmas formed during the post-extensional stage by low-degree melting of the shallow heterogeneous asthenosphere.

Miocene and Quaternary (15-13 Ma and 2-0.02 Ma) potassic and ultrapotassic rocks

Potassic and ultrapotassic rocks occur sporadically in the CPR (Harangi et al., 1995). Some of them were formed during the Middle Miocene (13-15 Ma; Harangi et al., 1995) and therefore their origin could be explained by thinning of the lithosphere and, as a consequence, decompression melting of their strongly metasomatized lower parts. Later, there was a second pulse of potassic-ultrapotassic volcanism in the Quaternary (< 2 Ma). Remarkably, these volcanic eruptions occurred along a west-east trending zone at the south-southeast margin of the Pannonian basin (Figure 1). The last volcanic eruption of the CPR involved the formation of K-rich dacites at 30 ka (Ciomadul; SE-Carpathians).

The origin of this kind of volcanism is still enigmatic. Since further lithospheric extension is excluded during this period, a hot mantle upwelling could be invoked as a possible mechanism to remobilize the metasomatized mantle region (Ed: see also Anatolia). The intermittent volcanic eruptions along as belt ~ 600 km long, and the close relationship with major tectonic lines, suggest, however, plate tectonic control. For the last 5 Ma, the hot, thin and therefore weak lithosphere has undergone tectonic reactivation related to basin inversion (Cloetingh et al., 2005; Horváth & Cloetingh, 2006; Bada et al., 2007). This implies changes in the regional stress field from tension to compression resulting in different, and in some cases kilometer-scale, vertical movements. The consequence of the short- and long-wavelength differential vertical movements for the mostly elastic lower lithosphere and the underlying asthenosphere is unclear, but it might have intermittently reactivated mantle domains with low solidus.

Mafic magmas from the asthenosphere could also contribute to this volcanism as revealed by detailed mineral-scale investigation on the youngest volcanic rocks of the CPR. The Mg-rich olivine (Fo-content is up to 90 mol%) and/or orthopyroxene (Mg# ~ 0.9) and oscillatory zoned clinopyroxenes (Mg# up to 0.92) suggest the role of mafic magma with fairly primitive composition in the genesis of the dacitic volcanism! Subcrustal seismic attenuation has been detected beneath this region at 50-60 km depths that may indicate the presence of shallow, hot asthenosphere, possibly with partially melted zones (Popa et al., 2005; Russo et al., 2005). Horizontal delamination of the lower lithosphere (Gîrbacea & Frisch, 1998; Chalot-Prat & Gîrbacea, 2000) or toroidal flow at the narrow, downgoing plate edge could initiate asthenospheric upwelling and decompression melting. Some mafic magmas could pond beneath the thick (40-45 km) crust and cause crustal melting.

Late Miocene to Quaternary (11-0.2 Ma) alkaline sodic volcanic rocks

The origin of the alkaline basaltic volcanism is still enigmatic since it occurred during the post-rift thermal subsidence and the tectonic inversion phases of the Pannonian basin (Ed: see also Orign of OIB). Its chemical compositions resemble Neogene alkaline mafic rocks in Europe. Some of the basalts share the EAR isotopic signature and thus one popular model for their origin is a mantle plume (Embey-Isztin et al., 2001; Seghedi et al., 2004a). In the mid-1990s, integrated geochemical and seismic studies led to the proposal that localized mantle upwellings (‘mantle plume fingers’ or ‘baby-plumes’) deriving from a common mantle reservoir (EAR; Cebria & Wilson, 1995) could be responsible for the volcanism in the Massif Central, the Rhenish area, the Eger graben, Bohemia and also in the Pannonian basin (Hoernle et al., 1995; Granet et al., 1995). The EAR component of these postulated plume fingers is characterized by a HIMU- or FOZO-like isotopic composition. Upwelling of a localized mantle plume beneath the Pannonian Basin can explain the melt generation and volcanism after the peak extension (Seghedi et al., 2004a), and supporting geological, geochemical and geophysical models have also been presented (Goes et al., 1999; Buikin et al., 2005; Burov and Cloetingh, 2009). In contrast, Harangi & Lenkey (2007) argue against a mantle plume beneath the Pannonian basin. Here, I report further important observations, which must be considered in this context.

The first observation is related to the spatial distribution of the alkaline mafic volcanic fields (Figure 6). They are located mostly at the west-northwestern periphery of the Pannonian basin and not in the region which underwent significant thinning and is characterized by thin lithosphere (< 60 km in the central part of the Pannonian basin). This peripheral area is underlain by a lithosphere/asthenosphere boundary with a steep gradient (from 110 to 70 km depths). Thus, most of the basaltic volcanic fields are in transitional zones between the orogenic Alps and cratonic North European Platform areas with thick (> 160 km) lithospheric roots and the stretched Pannonian basin with thin (< 70 km) lithosphere. The Pannonian basin could act as a thin-spot providing suction in the sublithospheric mantle and generating mantle flow from below the thick lithospheric roots (Ed: see also Hydration weakening). This mantle flow will have a near-vertical component along the steep lithosphere/asthenosphere boundary that could lead to decompression melting (Figure 7). Lebedev et al. (2006) explained the hotspot-like basaltic volcanism in the Baikal rift area by asthenospheric mantle flow from the cratonic areas, which appears to be a very similar situation. However, considering the lithospheric thickness variation beneath the CPR, another scenario is possible. At the northwestern margin of the CPR a subcontinental lithospheric corridor may exist (Figure 6) that might channel asthenospheric mantle towards the thin-spot beneath the Pannonian basin. Preliminary seismic anisotropy data appear to support this, since they show dominant NW-SE directions (Stuart et al., 2007). However, the consequence of this scenario is similar to the former one, i.e. a subvertical component of a mantle flow along the steep lithosphere/asthenosphere boundary that leads to decompression melting. Nevertheless, for this mechanism to work, the mantle must be able to melt.

Figure 6: Distribution of the alkaline basalt volcanic fields and contours of lithospheric thickness (Horváth et al., 2006). Most of the volcanic fields (and the most productive) lie at the northwestern margins of the Pannonian basin, and are underlain by a sharp change in the lithosphere/asthenosphere boundary. The white line denotes the section shown in Figure 7.

Figure 7: Suggested model for the origin of the alkali basalt volcanism in the CPR. Melt generation occurred as a result of mantle flow from the Alpine regime which has a thick lithospheric root. This flow has a subvertical component at the western-northwestern margin of the Pannonian basin; resulting in melting of the heterogeneous, variously fertile sublithospheric mantle.

The chemical composition of the mafic magmas indicates that melt generation could have occurred mostly in the asthenosphere, in the garnet-peridotite stability zone, i.e. > 80 km depth by 1-4% of melting. Based on the trace-element signatures, Harangi & Lenkey (2007) distinguished two groups of basalts in the CPR. One of the main differences between the two groups is the occurrence of a negative K-anomaly in the primitive-mantle-normalized multi-element diagram. The petrogenetic model calculations suggest a K-bearing phase (either phlogopite or amphibole) in the residue and variable degrees of melting of a garnet-peridotite source (Harangi & Lenkey, 2007). However, investigating the basaltic volcanic fields separately, a weak correlation can be observed between the Sr-Nd isotopic ratios and the degree of negative K-anomaly (K/K*; Figure 8). This can be explained by mixing between an isotopically more depleted mantle domain with K-bearing phase or one with an inherited K-depletion and an isotopically less depleted mantle domain with no K-bearing phase or no K-depletion.

Figure 8: Correlation between the 143Nd/144Nd isotope ratio and the degree of negative K-anomaly (K/K*) in individual basalt volcanic field could indicate heterogeneous mantle source regions.

The relatively wide compositional variation of the alkaline mafic rocks in the CPR both regionally and locally and the presence of the HIMU/FOZO-like isotope and trace-element ratios in some of them are consistent with a heterogeneous mantle model such as marble-cake or a streaky mantle model (Allégre & Turcotte, 1986; Smith, 2005). The shallow asthenospheric mantle could be heterogeneous on a relatively small-scale, preserving fragments of subducted crust for a long time (Meibom & Anderson, 2003; Kogiso et al., 2004). Niu & O’Hara (2003) suggested that metasomatized oceanic lithosphere portions were important geochemical reservoirs, hosting volatiles and with trace-element and isotopic characteristics that resulted from earlier metasomatism. The long history of orogenic events (Hercynian and Alpine) in Europe could have supplied a vast amount of crustal material into the upper mantle producing geochemical heterogeneity on various scales. Partial melting of different parts of the shallow asthenospheric mantle (metasomatized, phlogopite-bearing sections with HIMU-like composition and variously depleted mantle around them) and mixing of these melts could explain the compositional variation in the alkaline mafic magmas of the Pannonian Basin.

Additional implications for a small-scale heterogeneous mantle source come from a recent comprehensive study of the spinel chemistry of the basalts. Spinels are among the first phases to crystallize from basaltic magma and their compositions strongly depend on the magma- and source compositions (Arai, 1992; Barnes & Roeder, 2001; Kamenetsky et al., 2001; Roeder et al., 2003). They are commonly found in olivine phenocrysts. Their compositions show a remarkably wide variation in the Cr-Fe3+-Al plot (Figure 9). They can be divided into four separate groups, presumably suggesting that four main mantle domains are involved in the genesis of the mafic magmas. Two groups fall into the field of MORB spinels and the other two resemble spinels from OIB. The most striking feature, however, is that spinels with distinct compositions can be found even in single samples (Figure 9)! Here, only the most extreme example is shown. The 2.5 Ma old alkali basalt from Lucaret (Figure 1) contains spinels with a dominant population akin to OIB spinels, whereas a subordinate group of spinels has high Al-content and indicates a MORB-type mantle source. This bimodal composition is exactly the same that found by Paul et al. (2007) in the basaltic suite of Mauritius, but with a special feature that here it is found even in a single sample. Thus, it is supposed that basaltic magmas could represent a mixture of mafic melts occasionally coming from very different mantle source domains (e.g., pyroxenitic/eclogitic and peridotitic sources). This could have a strong implication for the small-scale (possibly in a scale of 102-103 m) heterogeneity of the shallow asthenosphere.

Figure 9: Composition of spinels in the Cr-Fe3+-Al ternary diagram. OIB and MORB spinels are after Roeder (1994). The spinel composition from the CPR basalts forms four separate groups. The Lucaret basalt contains bimodal spinel population (triangle) suggesting involvement of magma batches derived from different source region and small-scale heterogeneity in the shallow asthenosphere.

Concluding remarks

Harangi & Lenkey (2007) pointed out that the lack of broad topographic updoming, the high velocity body in the mantle transitional zone, the sporadic distribution of the mafic volcanic fields and the fairly low magma production rate are all inconsistent with the plume theory in the CPR. The observations presented here also suggest that a mantle plume beneath the Pannonian basin is highly unlikely, and instead I propose a possible mechanism for the origin of the alkaline mafic volcanism. Extension of the lithosphere played a major role in melt generation both directly and indirectly. The sublithospheric shallow mantle may be still close to its solidus as a consequence of an earlier lithospheric extension event. This, along with its heterogeneous, variously fertile nature implies that the mantle may be still capable of producing melt. Thus, further volcanic eruptions cannot be ruled out, even in this seemingly quiescent part of Europe!

Acknowledgements

I would like to thank Gillian Foulger for inviting and encouraging me to write this overview. Her constructive remarks helped me to focus on the main points and keep the text as concise as possible. The results presented here come from many beneficial discussions with Theo Ntaflos, Nino Seghedi, Hilary Downes, Réka Lukács, Balázs Kiss, Éva Jankovics, Tomi Sági, Paul Mason, Laci Lenkey, Gábor Bada, Laci Fodor, Frank Horváth and Endre Dombrádi. The enthusiastic research work of my students in the Volcanology Group on different areas of the Neogene volcanism of the CPR has provided me with continuous inspiration to search for what lies behind the observations and how to describe and understand the beauty of Nature.

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