the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Mar 2026
Mid-Triassic rhyolitic lavas and ignimbrites as markers of Eoalpine high-pressure metamorphism and large-scale lateral extrusion of Adria derived units at the edge of the European Alps
Abstract. Middle Triassic felsic volcanic rocks exposed at Margečan and in the Kjumberk area, located along the Periadriatic Fault System and the Mid-Hungarian Shear Zone, have long been assigned to the Southern Alpine domain and interpreted mainly in terms of their magmatic affinity. This study demonstrates that ignimbritic rhyolites from the Margečan area record a previously unrecognized high-pressure, low-temperature metamorphic overprint reaching blueschist-facies conditions. Phengitic muscovite compositions indicate peak pressures of ~1.1–1.2 GPa at temperatures around 300 °C, providing the first evidence that these felsic volcanic rocks were involved in Eoalpine subduction-related metamorphism and represent a part of the Austroalpine units. In contrast, felsic volcanic rocks from the nearby Kjumberk area, although compositionally and temporally similar, show no evidence of overprint and retain their Southern Alpine affinity, thus outlining a first order tectonic boundary between the two areas. U–Pb zircon ages constrain felsic volcanism to the late Anisian–early Ladinian (~244–242 Ma). Whole-rock geochemistry and Nd isotopic compositions indicate derivation from a subduction-modified mantle source with substantial crustal contribution, consistent with Triassic calc-alkaline magmatism along the Adriatic margin. These petrogenetic characteristics provide a framework for regional correlations but do not explain the contrasting metamorphic overprint. The recognition of Cretaceous Eoalpine blueschist-facies metamorphism in the Margečan ignimbrites therefore revises the tectonic interpretation of this sector of the Adriatic margin and implies large-scale eastward extrusion of the Austroalpine units into the Carpathian embayment, accommodated by high-offset right-lateral strike-slip faults.
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Status: open (until 14 May 2026)
- RC1: 'Comment on egusphere-2026-1092', Franz Neubauer, 15 Apr 2026 reply
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RC2: 'Comment on egusphere-2026-1092', Emilio Saccani, 17 Apr 2026
reply
General overview
The paper entitled: “Mid-Triassic rhyolitic lavas and ignimbrites as markers of Eoalpine high-pressure metamorphism and large-scale lateral extrusion of Adria derived units at the edge of the European Alps” presents new data on Middle Triassic rhyolitic rocks exposed in two areas located along the Periadriatic Fault System and the Mid-Hungarian Shear Zone, both marking the boundary between the Austroalpine units and the Southern Alpine units.
This study benefits from high-quality analytical data obtained from several different methods, including electron microprobe analyses for mineral chemistry, X-ray fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS) for whole rock chemistry, mass spectrometry for Nd isotopic compositions, and laser ablation (LA) ICP-MS for zircon U-Pb geochronology. In addition, metamorphic re-equilibration pressures have been estimated using phengitic mica geobarometers.
A key finding of this study is that it demonstrates that ignimbritic rhyolites from the Margečan area record a high-pressure, low-temperature (HP-LT) metamorphic overprint reaching blueschist-facies conditions and are thus re-interpreted as belonging to the Austroalpine units, in contrast to previous interpretations that have ascribed them to the Southern Alpine domain. In contrast, rhyolitic lavas from the Kjumberk area show no evidence of HP-LT overprint and their Southern Alpine affinity is therefore confirmed in this study.
These two distinct rhyolitic suites are compositionally and temporally similar, suggesting a common tectonic setting of formation. Whole-rock geochemistry and Nd isotopic compositions indicate derivation from a subduction-modified mantle source with substantial upper crustal contribution, consistent with Triassic calc-alkaline magmatism developed along the Adriatic margin during continental rift heralding the opening of the Neo-Tethys. The authors explain the contrasting metamorphic evolution of these two rock-series invoking large-scale eastward extrusion of the Austroalpine units into the Carpathian embayment, accommodated by high-offset right-lateral strike-slip faults.
General Comments
The manuscript is generally well written (with some exceptions), well organized, and concise. The references are appropriate, and the data are of high quality and fully support the discussion and conclusions. The topic is of broad scientific interest.
Overall, this represents a significant contribution, as it provides new insights into the tectono-magmatic evolution of the Neo-Tethys and the subsequent geodynamic history of the Alpine–Carpathian–Dinaridic orogenic system.
Specific comments and suggestions
I suggest some revisions to improve the quality and readability of the manuscript, as detailed below.
1- Title: “Mid-Triassic rhyolitic lavas and ignimbrites as markers of Eoalpine high-pressure metamorphism and large-scale lateral extrusion of Adria derived units at the edge of the European Alps”
This title can be definitely improved.
- “Mid-Triassic“ (descriptive) is used only here, while “Middle Triassic” (formal) is used throughout the text. While the descriptive form is fine in titles, I suggest using the formal term for consistency with the manuscript.
- “rhyolitic lavas and ignimbrites as markers of Eoalpine high-pressure metamorphism…” strictly speaking, only the ignimbrites record HP–LT metamorphism. Therefore, this wording may be misleading and should be revised.
- “…at the edge of the European Alps”. The whole alpine belt is “European”. I think the authors mean to say “at the edge between Adria-derived and Europe-derived units (or domains?)
2- Introduction and Geological framework.
While the other sections are generally well written, these two sections read somewhat heavily. These sections would benefit from improved readability. I have suggested several changes in the attached annotated version. In general, I recommend splitting long sentences.
Finally, the first three lines of the “Geological Framework” section form a single-sentence paragraph. Single-sentence paragraphs are generally discouraged in academic English.
3- In several parts of the manuscript (lines 246, 333, 409, and 483), the authors, based on Figure 5b, describe their rocks as showing a “calc-alkaline to shoshonitic affinity.” However, in this figure, only one sample plots across the boundary between the calc-alkaline and shoshonitic compositional fields. In my opinion, a single sample, which does not even clearly plot in the shoshonite field is insufficient to support the conclusion that these rocks exhibit a “calc-alkaline to shoshonitic affinity.” I suggest cautiously using the clear evidence for a calc-alkaline affinity only.
4- Lines 313-314 and 355 versus lines 485-489
In lines 313–314: “Rhyolitic eruptions are characteristic of continental settings and are commonly associated with partial melting of the continental crust, accompanied by magma differentiation, fractional crystallization, and crustal assimilation (Wilson, 1989; Halder et al., 2021).” A similar statement is made in line 355.
As currently phrased, this suggests that rhyolites are generated primarily (or exclusively) by anatectic processes (i.e., melting of continental crust), which is not entirely correct. In fact, a more appropriate interpretation is provided later in the manuscript (lines 485–489): “The formation of these felsic volcanic rocks involved partial melting of a compositionally heterogeneous subcontinental lithospheric mantle, accompanied by subordinate melting of the continental crust and concurrent fractional crystallization of feldspar. The emplacement of rhyolitic lavas and ignimbrites occurred during passive continental rifting along the northern margin of Adria…”
It is clear that partial melting of the continental crust may occur in addition to mantle melting. Therefore, I suggest revising the earlier statements accordingly. For example:
“Rhyolitic eruptions are characteristic of continental settings and are commonly associated with partial melting of subduction-influenced mantle sources, potentially accompanied by partial melting of the continental crust, as well as magma differentiation and crustal assimilation.”
Please note that I deleted “fractional crystallization”, as it is one of the main processes of magma differentiation and should not be listed separately.
5- Lines 141-145. This section should be improved. Please specify if XRF measures were made on pressed powder pellets or on fused beads. Describe how powders were digested before ICP-MS analyses. The last sentence is unclear. Give details about detection limits.
Describe in Table which elements were analysed by XRF and ICP-MS.
Line 203 (and 224). “Diagenesis” is not the most appropriate term, as it refers to post-depositional, low-temperature processes in sedimentary rocks. It may be applied to pyroclastic rocks only when describing processes occurring at very low temperatures (< ~200 °C). Are you sure is this the case? Welding, devitrification, and vapour-phase processes are not considered diagenetic. I suggest using more appropriate terms, such as “post-depositional alteration” or “low-temperature alteration.”
Lines 227-230. “These values exceed the pressure conditions inferred from the b₀ lattice parameter of white mica (Appendix B), which yields moderate pressure estimates (b₀ = 9.04–9.08 Å).”. Give the values of those moderate pressures inferred from the b0 parameters.
Figs 1 and 12. Figure 12 differ from Fig. 1 for having been updated by incorporating the results from this study. However, it is difficult to promptly see the novelties from this paper in Fig. 12 because of graphical issues and because these two figures also differ for other aspects. It seems that Fig.12 is a simplified version of Fig.1 as it does not show anticlines and synclines and other things. Finding the core differences in two figures that are already graphically different is challenging. I suggest to uniform these two figures for their common features and highlight in Fig 12 the novelties from this paper.
Figure 11 is not very clear. I suggest to made a little effort to make it clearly readable.
Editorial comments/suggestions
- A careful cross-check between the in-text citations and the reference list is necessary. I have identified several missing and uncited.
- In the file I downloaded, all superscripts and subscripts appear to be missing. This may be an issue on my end; however, I kindly ask the authors to verify the text for this problem.
- I suggest to add a key for symbols within the graphs instead of giving it in caption. This suggestion applies to figs. 4-7 and 9-10, as well as to Fig. G1.
Many other editorial or language issues are in the annotated pdf file attached to this comment.
Best Regards
Emilio
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General comments
The manuscript describes petrographic features, microstructures, U-Pb zircon dating and Sm-Nd isotope composition and majar and trace element geochemistry of two Middle Triassic felsic volcanic rocks from two distinct areas of the Southalpine unit of Eastern Alps. Electron microprobe data from fine-grained, metamorphically grown sericite show a phengite composition. Together with the assumed temperature estimate of 300 °C, high-pressure conditions are assumed, within blueschist facies conditions for felsic ignimbrites of the Margečan locality. This locality is located on the tectonic boundary of the Southalpine unit to Dinarides. The authors interpret the high-pressure conditions as related to the Cretaceous Koralpe-Wölz high-pressure unit.
The felsic late Anisian–early Ladinian (~244–242 Ma) volcanism is calc-alkaline in nature and is interpreted to represent an aborted rift within Greater Adria behind a back-arc rift related to the westward subducting Balkan Paleo-Tethys Ocean.
Basically, the story is interesting, and I recommend following revisions to convince the interested audience:
Specific comments and editorial remarks
Figure 1: Write Margečan and Krumbjerk areas into the map. Explain abbreviations PFS, MHZ in captions. What is the nature of the boundary between Dinarides and Soutalpine unit in the eastern part of the map?
Figure 2: In legend to Fig 2: correct to brackish. siltites = siltstones; low-grade schist: say rather phyllite or whatever; schist is more coarse-grained. Instead of complicated numbering 1 - 9, write sample names directly into the map. In legend, correct “riolites” to “rhyolites”.
Lines 91-92: For offset along the Periadriatic fault system, mention also Haas et al., 1994, Tectonophysics who convincingly postulated ca. 450 km displacement because facies offset.
Line 93: Correct author name to “Reinecker”
Line 128: Abbreviation LOD not needed, used only once in the further text.
Line 183: “The rhyolitic lavas exhibit a porphyritic texture and a homogeneous structure”: Mention the locality to be clear. At present not clear which locality you mean.
Line 187: “fine-sized quartz and white mica crystals”: Give numerical values for grain size.
Line 191: “Wmca”: Wm would be sufficient.
Line 204: “schistosity cleavage”: Term is somehow contractory. Be careful with these terms and their combination. It is not schistosity, use better simply foliation instead schistosity.
Line 227: Mention, on which data the temperature estimate of 300 °C is based.
Line 259: “multielement spider patterns”: use better “multielement variation patterns”
Line 260: Explain abbreviation PMN
Line 264: Explain abbreviation CN
Line 289: “Langmior”: Correct author name to “Langmuir”
Line 294-295: “while five were rejected as discordant, likely due to Pb loss or crystal alteration”: It is unclear whether these five spots are included in Fig. 8b. Mention this also in the text.
Figure 8: In Fig. 8b: There are potentially two age populations. Calculate average 206Pb/238U ages for these separate groups. Add rock type and sample no. directly to the figure.
Line 308: “exceptionally rare”: “rare” is sufficient.
Line 395: Use better Variscan instead Hercynian. Hercynian means, in short, the strike if some basement massifs. There was a long discussion on these terms two decades ago.
Figure 11: Fig. 11a: Figure needs much more explanation. E.g., what represents the greenish color N and E of the Balkan Paleotethys Ocean?nLegend to 11b: Explain 1 - 4 directly in the figure.
Figure 12: The North Karawanken unit (= thrust sheet) did not reach very low-grade conditions. See papers of Rantitsch, Rainer, Heberer et al. (2017; International Journal of Earth Sciences).
References cited:
De Min A, Velicogna M, Ziberna L, Chiaradia M, Alberti A, Marzoli A (2020) Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up. Geological Magazine, 157:1800–1822
Haas, J., Kovács, S., Krystyn, L., Lein, R., 1995. Significance of Late Permian-Triassic facies zones in terrane reconstructions in the Alpine-North Pannonian domain. Tectonophysics 242, 19–40.
Kövér, S., Fodor, L., Kovács, Z., Klötzli, U., Haas, J., Zajzon, N., Szabó, C., 2018. Late Triassic acidic volcanic clasts in different Neotethyan sedimentary mélanges: paleogeographic and geodynamic implications. International Journal of Earth Sciences (2018) 107:2975–2998. https://doi.org/10.1007/s00531-018-1638-2
Putiš, M., Soták, J., Li, Q.L., Ondrejka, M., Li, X.-H., Hu, Z.-C., Ling, X.-X., Nemec, O., Németh, Z., Ružička, P., 2019. Origin and Age Determination of the Neotethys Meliata Basin Ophiolite Fragments in the Late Jurassic–Early Cretaceous Accretionary Wedge Mélange (Inner Western Carpathians, Slovakia). Minerals, 9, 652, doi:10.3390/min9110652.
Putiš et al., 2025. Neotethyan Jurassic supra-subduction ophiolitic complex with Triassic subducted sole: Mineral chemistry, sole P–T estimates, and U/Pb geochronology of an intra-oceanic domain (Central Dinarides, Bosnia and Herzegovina). Geochemistry 85, 126263, https://doi.org/10.1016/j.chemer.2025.126263.