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Acta Geologica Hungarica
Authors: Réka Lukács, György Czuppon, Szabolcs Harangi, Csaba Szabó, Theodor Ntaflos, and Friedrich Koller

Silicate melt inclusions are frequent in the phenocryst phases (quartz, plagioclase, orthopyroxene, ilmenite and accessory minerals) of the Miocene silicic pyroclastic rocks of the Bükkalja Volcanic Field, Northern Hungary. These melt inclusions were trapped at different stages of magma evolution; therefore, they provide important information on the petrogenetic processes. The melt inclusions in the Bükkalja pyroclastic rocks show various textures such as (1) wholly enclosed type; (2) hourglass inclusions and (3) reentrant or embayment glass. Among the wholly enclosed type melt inclusions further textural subgroups can be distinguished based on their shape: negative crystal, rounded, elongated and irregular shaped. These various textures reflect differences in the time of entrapment prior to eruption and in the post-entrapment condition in the magma chamber. The largest textural variation was found in the quartz-hosted melt inclusions. However, the major element compositions of these melt inclusions do not differ from one another in the same unit. In general, compositions of the melt inclusions are similar to the chemistry of the glass shards. Comparing the composition of the quartz-hosted melt inclusions from three main ignimbrite units (Lower, Middle and Harsány Ignimbrite Units), slight differences have been recognized, suggesting distinct erupted host magmas. Melt inclusions from the andesitic lithic clast of the Lower Ignimbrite Unit could represent heterogeneous interstitial melt in the crystal mush zone at the magma chamber wall. The largest geochemical variation was found in the melt inclusion of the Middle Ignimbrite Unit, even in single samples. This compositional variation overlaps that of the rhyolitic juvenile clasts, but does not match that of the glasses of scoria clasts. We suggest that syn-eruptive magma mixing (mingling) occurred in a compositionally heterogeneous magma chamber of the Middle Ignimbrite Unit.

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Central European Geology
Authors: Attila Demény, Alexandra Németh, Zoltán Kern, György Czuppon, Mihály Molnár, Szabolcs Leél-Őssy, Mihály Óvári, and József Stieber

Determination of the long-term behavior of cave systems and their response to changing environmental conditions is essential for further paleoclimate analyses of cave-hosted carbonate deposits. For this purpose, four actively forming stalagmites were collected in the Baradla Cave where a three-year monitoring campaign was also conducted. Based on textural characteristics and radiocarbon analyses, the stalagmites are composed of annual laminae, whose counting was used to establish age–depth relationships. Fast and slowly growing stalagmites have different stable carbon and oxygen isotope compositions as well as trace element contents that could be attributed to differences in drip water migration pathways. The stable isotope compositions were compared with meteorological data of the last ∼100 years indicating that carbon isotope compositions of the stalagmites may reflect changes in precipitation amount, while oxygen isotope compositions are more related to temperature variations. The combined textural–geochemical–meteorological interpretation lead us to select the isotope record that can best reflect variations in environmental conditions and can be used for further evaluation of the climate–proxy relationships.

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