MERRE TOVÁBB, VULKANOLÓGIA? A 21. SZÁZAD KIHÍVÁSAI

A vulkanológia, azaz a vulkáni működés sokrétű kutatása az egyik legrégebbi (hiszen már Anaxagorász és Arisztotelész is behatóan foglalkozott vele mintegy 2500 évvel ezelőtt), és az egyik legújabb (hiszen az elmúlt néhány évtizedben hatalmas változáson ment keresztül) tudományterület. Jelentősége nem lebecsülendő, hiszen olyan természeti folyamatot kutat, amely a Föld kialakulása óta, azaz mintegy 4,6 milliárd éve formálja bolygónkat. A vulkáni kitörések közvetlen és szoros kölcsönhatásban vannak a környezettel, befolyásolják az élővilágot, átalakítják a felszíni formákat, módosítják a klímát, kihatnak társadalmi folyamatokra. Nincs kétség afelől, hogy ez a jövőben is így lesz

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

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 ‘subduction-related’ magmas irrespective of their geodynamic relationships. Intraplate alkali basalts are also found in the region generally postdated the ‘subduction-related’ 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 “subduction-related” 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 (‘source contamination’) 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 ‘subduction-related’ 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 “statistical sampling” of the strongly inhomogeneous mantle followed by variable degrees of crustal contamination

On the age of the Harsány ignimbrite, Bükkalja volcanic field, Northern Hungary — a discussion

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 Bükkalja volcanic field. The interpretation of these papers shows an apparent contradiction in the age of the ignimbrite, which crops out at Tibolddaróc and Harsány. This paper attempts to resolve this contradiction. We show that the Harsány ignimbrite defined by Lukács et al. (2007) was indeed formed at 13.5 Ma and is not the same as was described by Márton et al. (2007). We redefine the possible locations of the Harsány and Tibolddaróc samples of Márton et al. (2007). The Tibolddaróc sample could represent the ash flow unit in the middle part of the Tibolddaróc volcanic section, whereas the Harsány sample could be derived from the ‘Harsány-bend’ outcrop. Both rocks have different geochemical character compared to the Harsány ignimbrite. This work emphasizes the usefulness of geochemical correlation of scattered rhyolitic ignimbrites, combined with detailed volcanological field observations