**Acknowledgements**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

peperites and resulting in their distinct alteration.

overlying deposits irrespectively of their lithofacies.

factor were geochemical gradients in reacting fluids.

period of time and had ephemeral character.

Carpathian-Pannonian region [9, 15–17] where the Smrekovec Volcanic Complex belongs to [29], the studies related to their alteration have been relatively scarce [15–20]. The present study gives evidence of the existence of localised and ephemeral hydrothermal conditions related to and persisting during the formation of

The Smrekovec Volcanic Complex is a remnant of an Oligocene submarine stratovolcano characterised by a complex development of an over 2500 m thick succession of volcanic rocks. Submarine environment, the style of eruptions, morphology and the abundance of pyroclastic and syn-eruptively resedimented volcaniclastic deposits were favourable for the formation of peperites that are particularly abundant in medial-zone lithofacies associations. In a succession of volcanic deposits studied in detail in two sections Krnes and Smrekovec G34 attaining 400 m and 470 m, respectively, the alteration of peperites indicates that authigenic minerals have higher temperature stability ranges than those in the adjacent underlying and

The alteration of peperites indicates close relationship to the rock composition and texture, and therefore, the style of peperite formation. Dispersed blocky peperite involving siliciclastic host sediment is commonly poorly altered. Volcanic glass in juvenile clasts is usually devitrified or hydrated, and only some clasts with perlitic texture can be altered to laumontite. In the textural types with fine-grained pyroclastic host sediment laumontite, or the assemblages of laumontite, albite, quartz, pumpellyite, incipient epidote and chlorite, or laumontite, prehnite, quartz, chlorite and incipient epidote, or laumontite, analcime and interlayered chloritesmectite may occur. The alteration minerals indicate that thermal gradients were prerequisite but not sufficient for alteration to occur and that the main controlling

Microglobular peperite developed by interaction between magma and fluidised sediment [5], and the temperatures of alteration must have been higher than in blocky peperite. Smaller microglobules are often completely altered to authigenic mineral assemblages with higher temperature stability ranges (e.g. pumpellyite, epidote) while the larger microglobules remained incompletely altered or altered to authigenic minerals with lower temperature stability ranges (e.g. laumontite). The relationship indicates that high-temperature conditions could not persist for a long

Authigenic mineral assemblages developed in peperites indicate that their formation is specific and related to the formation of parent rock itself. Thermal stability ranges of actinolite and pumpellyite indicate the highest temperatures possibly exceeded 280°C and decreased when the parent lava flow and the associated peperite underwent cooling. Hydrothermal fluids mainly originated from heated pore fluids although deuteric fluids could have been locally admixed. The evolution of fluids circulating in peperite was essential for extensive alteration to occur and that was possibly attained by interaction with unstable and highly reactive host sediment. Many peperites have been developed as low-porosity and low-permeability layers, and therefore contemporaneous and later hydrothermal activity related to the stratovolcano-hosted hydrothermal system with convective-advective flow could not have exerted any critical thermal or geochemi-

The alteration of peperites in the Smrekovec Volcanic Complex can be regarded as syn-formational, hydrothermal, ephemeral, localised and depending on many factors such as the extent and time span of thermal regime, the process of formation of parent rock and thermal and geochemical evolution of circulating hydrothermal fluids. And although peperite deposits are not rare in similar volcanic-sedimentary settings worldwide, the alteration as recognised in the present study has not been

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cal impact.

Slovenian Research Agency (ARRS) is acknowledged for granting the research (Programme Mineral Resources P-0025). The editorial work of Academic Editor Dr. Károly Németh and helpful comments of anonymous reviewers are greatly appreciated. Many thanks to Mrs. Mia Vulovic, Author Service Manager for her kind assistance. I thank Ms. Staška Čertalič and Mr. Mladen Štumergar from Geological Survey of Slovenia for technical support.
