78 research outputs found

    Egy vulkán, amely megrengette a világot 200 éve tört ki a Tambora

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    MERRE TOV√ĀBB, VULKANOL√ďGIA? A 21. SZ√ĀZAD KIH√ćV√ĀSAI

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    A vulkanol√≥gia, azaz a vulk√°ni mŇĪk√∂d√©s sokr√©tŇĪ kutat√°sa az egyik legr√©gebbi (hiszen m√°r Anaxagor√°sz √©s Arisztotel√©sz is behat√≥an foglalkozott vele mintegy 2500 √©vvel ezelŇĎtt), √©s az egyik leg√ļjabb (hiszen az elm√ļlt n√©h√°ny √©vtizedben hatalmas v√°ltoz√°son ment kereszt√ľl) tudom√°nyter√ľlet. JelentŇĎs√©ge nem lebecs√ľlendŇĎ, hiszen olyan term√©szeti folyamatot kutat, amely a F√∂ld kialakul√°sa √≥ta, azaz mintegy 4,6 milli√°rd √©ve form√°lja bolyg√≥nkat. A vulk√°ni kit√∂r√©sek k√∂zvetlen √©s szoros k√∂lcs√∂nhat√°sban vannak a k√∂rnyezettel, befoly√°solj√°k az √©lŇĎvil√°got, √°talak√≠tj√°k a felsz√≠ni form√°kat, m√≥dos√≠tj√°k a kl√≠m√°t, kihatnak t√°rsadalmi folyamatokra. Nincs k√©ts√©g afelŇĎl, hogy ez a j√∂vŇĎben is √≠gy lesz

    Tertiary-Quaternary subduction processes and related magmatism in the Alpine-Mediterranean region

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    During Tertiary to Quaternary times, convergence between Eurasia and Africa resulted in a variety of collisional orogens and different styles of subduction in the Alpine-Mediterranean region. Characteristic features of this area include arcuate orogenic belts and extensional basins, both of which can be explained by roll-back of subducted slabs and retreating subduction zones. After cessation of active subduction, slab detachment and post-collisional gravitational collapse of the overthickened lithosphere took place. This complex tectonic history was accompanied by the generation of a wide variety of magmas. Most of these magmas (e.g. low-K tholeiitic, calc-alkaline, shoshonitic and ultrapotassic types) have trace element and isotopic fingerprints that are commonly interpreted to reflect enrichment of their source regions by subduction-related fluids. Thus, they can be considered as ‚Äėsubduction-related‚Äô magmas irrespective of their geodynamic relationships. Intraplate alkali basalts are also found in the region generally postdated the ‚Äėsubduction-related‚Äô volcanism. These mantle-derived magmas have not been, or only slightly, influenced by subduction-related enrichment. This paper summarises the geodynamic setting of the Tertiary-Quaternary ‚Äúsubduction-related‚ÄĚ magmatism in the different segments of the Alpine-Mediterranean region (Betic-Alboran-Rif province, Central Mediterranean, the Alps, Carpathian-Pannonian region, Dinarides and Hellenides, Aegean and Western Anatolia), and discusses the main characteristics and compositional variation of the magmatic rocks. Radiogenic and stable isotope data indicate the importance of continental crustal material in the genesis of these magmas. Interaction with crustal material probably occurred both in the upper mantle during subduction (‚Äėsource contamination‚Äô) and in the continental crust during ascent of mantle-derived magmas (either by mixing with crustal melts or by crustal contamination). The 87Sr/86Sr and 206Pb/204Pb isotope ratios indicate that an enriched mantle component, akin to the source of intraplate alkali mafic magmas along the Alpine foreland, played a key role in the petrogenesis of the ‚Äėsubduction-related‚Äô magmas of the Alpine-Mediterranean region. This enriched mantle component could be related to mantle plumes or to long-term pollution (deflection of the central Atlantic plume and recycling of crustal material during subduction) of the shallow mantle beneath Europe since the late Mesozoic. In the first case, subduction processes could have had an influence in generating asthenospheric flow by deflecting nearby mantle plumes due to slab roll-back or slab break-off. In the second case, the variation in the chemical composition of the volcanic rocks in the Mediterranean region can be explained by ‚Äústatistical sampling‚ÄĚ of the strongly inhomogeneous mantle followed by variable degrees of crustal contamination

    On the age of the Hars√°ny ignimbrite, B√ľkkalja volcanic field, Northern Hungary ‚ÄĒ a discussion

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    Abstract Correlation of scattered ignimbrite occurrences is crucial in the context of stratigraphy and the volcanic history of an area. In 2007, two papers were published concerning the classification of the volcanic rocks of the B√ľkkalja volcanic field. The interpretation of these papers shows an apparent contradiction in the age of the ignimbrite, which crops out at Tibolddar√≥c and Hars√°ny. This paper attempts to resolve this contradiction. We show that the Hars√°ny ignimbrite defined by Luk√°cs et al. (2007) was indeed formed at 13.5 Ma and is not the same as was described by M√°rton et al. (2007). We redefine the possible locations of the Hars√°ny and Tibolddar√≥c samples of M√°rton et al. (2007). The Tibolddar√≥c sample could represent the ash flow unit in the middle part of the Tibolddar√≥c volcanic section, whereas the Hars√°ny sample could be derived from the ‚ÄėHars√°ny-bend‚Äô outcrop. Both rocks have different geochemical character compared to the Hars√°ny ignimbrite. This work emphasizes the usefulness of geochemical correlation of scattered rhyolitic ignimbrites, combined with detailed volcanological field observations
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