A unique Valanginian paleoenvironment at an iron ore deposit near Zengővárkony (Mecsek Mts, South Hungary), and a possible genetic model

Abstract The spatially restricted Early Valanginian iron ore (limonite) and manganese deposit at Zengõvárkony (Mecsek Mts, southern Hungary) contains a rich, strongly limonitized, remarkably large-sized (specimens are 30–70% larger than those at their type localities) brachiopod-dominated (mainly Lacunosella and Nucleata) megafauna and a diverse crustacean microfauna, which indicates a shallow, nutrient-rich environment possibly linked to an uplifted block, and/or a hydrothermal vent

Noble gas and carbon isotope systematics at the seemingly inactive Ciomadul volcano (Eastern‐Central Europe, Romania): evidence for volcanic degassing

Ciomadul is the youngest volcano in the Carpathian-Pannonian Region, Eastern-Central Europe, which last erupted 30 ka. This volcano is considered to be inactive, however, combined evidence from petrologic and magnetotelluric data, as well as seismic tomography studies suggest the existence of a subvolcanic crystal mush with variable melt content. The volcanic area is characterized by high CO2 gas output rate, with a minimum of 8.7 × 103 t yr-1. We investigated 31 gas emissions at Ciomadul to constrain the origin of the volatiles. The δ13C-CO2 and 3He/4He compositions suggest the outgassing of a significant component of mantle-derived fluids. The He isotope signature in the outgassing fluids (up to 3.10 Ra) is lower than the values in the peridotite xenoliths of the nearby alkaline basalt volcanic field (R/Ra 5.95Ra±0.01) which are representative of a continental lithospheric mantle and significantly lower than MORB values. Considering the chemical characteristics of the Ciomadul dacite, including trace element and Sr- Nd and O isotope compositions, an upper crustal contamination is less probable, whereas the primary magmas could have been derived from an enriched mantle source. The low He isotopic ratios could indicate a strongly metasomatized mantle lithosphere. This could be due to infiltration of subduction-related fluids and postmetasomatic ingrowth of radiogenic He. The metasomatic fluids are inferred to have contained subducted carbonate material resulting in a heavier carbon isotope composition (13C is in the range of -1.4 to -4.6 ‰) and an increase of CO2/3He ratio. Our study shows the magmatic contribution to the emitted gases

Early Miocene pyroclastic rocks of the Bükkalja lgnimbrite Field (North Hungary) - A preliminary stratigraphic report

This preliminary report provides a detailed description of several stratigraphie sequenees of the Early Miocene Bükkalja Ignimbrite Field, summarizing the main volcanosedimentological eharacters. Many volcanological features suggest that most of the deposits can be classified as high volume pyroclastie flows (ignimbrite). Two major ignimbritie units have been distinguished, which may belong to two different stages of the vo1canism and form a SW-NE orientated belt. The first (lower) unit is eharaeterized predominantly by non-welded ignimbrites, whereas the second (upper) unit, usually found south of the first unit, shows variable degrees of welding. Hydrovolcanic deposits also occur in different stratigraphie horizons. The final phases of volcanism could have been contemporancous with lacustrine sedimentation

Radiocarbon Dating of the Last Volcanic Eruptions of Ciomadul Volcano, Southeast Carpathians, Eastern-Central Europe

From the 20th International Radiocarbon Conference held in Kona, Hawaii, USA, May 31-June 3, 2009.This paper provides new accelerator mass spectrometry (AMS) radiocarbon age data for the last volcanic events in the Carpathian-Pannonian region of eastern-central Europe. The eruption ages were determined on charcoal fragments collected from pumiceous pyroclastic flow deposits at 2 localities of the Ciomadul Volcano. Two charcoal samples from the southeastern margin of the volcano (Bixad locality) set the date of the last volcanic eruption to 27,200 +/- 260 yr BP (29,500 +/- 260 cal BC). On the other hand, our data show that the Tusnad pyroclastic flow deposit, previously considered as representing the youngest volcanic rock of the region, erupted at ~39,000 yr BP (~41,300 cal BC). Thus, a period of dormancy more than 10,000 yr long might have elapsed between the 2 volcanic events. The different ages of the Tusnad and Bixad pyroclastic flow deposits are confirmed also by the geochemical data. The bulk pumices, groundmass glass, and the composition of the main mineral phases (plagioclase and amphibole) suggest eruption of slightly different magmas. Considering also the assumed long volcanic history (~600 ka) of the Ciomadul, these data suggest that further detailed studies are necessary on this seemingly inactive volcano in order to evaluate the possible renewal of volcanic activity in the future.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Amphiboles as indicators of mantle source contamination: Combined evaluation of stable H and O isotope compositions and trace element ratios

Stable isotope and trace element compositions of igneous amphiboles from different tectonic settings (ocean island basalts, intraplate alkaline basalts, subduction-related andesitic complexes) were compiled to help understand the role of fluids and melts in subduction-related mantle metasomatism and to evaluate the use of selected trace element ratios (Pb/Pb*(N) = Pb/(?(Ce·Pr)) and Ba/Nb(N), normalized to primitive mantle) to help detect possible metasomatism. Comparisons of stable H and O isotope compositions and trace element ratios of amphiboles from ocean island basalts (Canary Islands), intraplate basalts, and subduction-related calc-alkaline andesitic series (Carpathian–Pannonian Region, CPR) indicate systematic distributions in ?D–?18O–Pb/Pb*(N)–Ba/Nb(N) diagrams that are related to metasomatic processes in the mantle and the migration of fluids and melts derived from subducted crustal slabs. In order to interpret these data for the amphiboles from the CPR, ophiolites of the Penninic and the Meliata–Vardar complexes as potential sources of subducted crustal melts and fluids in the mantle of the Carpathian–Pannonian Region were also analyzed. On the basis of published fluid/rock partition coefficients the compositions of fluids emanating from subducted ophiolites were calculated. The calculated fluid compositions—especially for blueschists of the Meliata complex—fit the amphibole trends, indicating that such fluids could have been responsible for the mantle metasomatism beneath the CPR