György Falus

Deformation in the asthenospheric mantle beneath the Carpathian-Pannonian Region

To better understand the evolution and present-day tectonics of the Carpathian-Pannonian Region (CPR), we characterize the upper mantle anisotropic structure. We present a shear wave splitting analysis from teleseismic events recorded at the Carpathian Basin Project and permanent stations located in the CPR. The results show a large-scale uniform NW-SE fast orientation under the entire CPR. Compared with the complexity of geologic structures, the anisotropy expresses a relatively simple pattern of deformation. We attribute this anisotropy to an asthenospheric origin and interpret it as flow-induced alignments within the upper mantle. We also observe a few measurements depicting NE-SW fast orientation in line with the Mid-Hungarian Shear Zone. This suggests the likely contribution of either lithosphere or northeastward flow into a slab gap under the northern Dinarides. We observe splitting delay times on average of 1 s, showing noticeable change (60%) in the middle Pannonian basin. This change correlates well with the variation in the thickness of low-velocity zones that were previously imaged between a depth of 75 and 400 km by velocity tomography. In order to evaluate the relation between anisotropy and tectonics, we compare our data with the tectonic models that have so far been suggested to explain the evolution and current-stage tectonics of the region. We present here a plausible tectonic model responsible for the NW-SE anisotropy within the asthenospheric mantle. In this model, NW-SE deformation is mainly generated in a northeastward compressional tectonic regime acting in a wide region between the Adriatic microplate and the East European platform.

Effects of Particle Size on the Attenuated Total Reflection Spectrum of Minerals

This study focuses on particle size effect on monomineralic powders recorded using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. Six particle size fractions of quartz, feldspar, calcite, and dolomite were prepared (<2, 2–4, 4–8, 8–16, 16–32, and 32–63 µm). It is found that the width, intensity, and area of bands in the ATR FT-IR spectra of minerals have explicit dependence on the particle size. As particle size increases, the intensity and area of IR bands usually decrease while the width of bands increases. The band positions usually shifted to higher wavenumbers with decreasing particle size. Infrared spectra of minerals are the most intensive in the particle size fraction of 2–4 µm. However, if the particle size is very small (<2 µm), due to the wavelength and penetration depth of the IR light, intensity decreases. Therefore, the quantity of very fine-grained minerals may be underestimated compared to the coarser phases. A nonlinear regression analysis of the data indicated that the average coefficients and indices of the power trend line equation imply a very simplistic relationship between median particle diameter and absorbance at a given wavenumber. It is concluded that when powder samples with substantially different particle size are compared, as in regression analysis for modal predictions using ATR FT-IR, it is also important to report the grain size distribution or surface area of samples. The band area of water (3000–3620 cm–1) is similar in each mineral fraction, except for the particles below 2 µm. It indicates that the finest particles could have disproportionately more water adsorbed on their larger surface area. Thus, these higher wavenumbers of the ATR FT-IR spectra may be more sensitive to this spectral interference if the number of particles below 2 µm is considerable. It is also concluded that at least a proportion of the moisture could be very adhesive to the particles due to the band shift towards lower wavenumbers in the IR range of 3000–3620 cm–1.

The relevance of dawsonite precipitation in CO2 sequestration in the Mihályi-Répcelak area, NW Hungary

Abstract A natural CO2 reservoir system with a sandstone lithology in NW Hungary has been studied due to its similarities to a large saline reservoir formation that is widespread in the the Pannonian Basin (Central Europe) and is suggested to be one of the best candidates for industrial CO2 storage. A range of analytical techniques has been used on core samples from CO2-containing sandstone layers that represent a wide range of pressures (90–155 bar), temperatures (79–95°C) and pore fluid compositions (total dissolved solids between 18 000 and 50 700 mg l−1) to identify the mineralogy and textural characteristics of the natural reservoir. The only clear CO2-related feature in the studied lithology was the occurrence of dawsonite (NaAlCO3(OH)2) in a close textural relationship with albite. This is in clear agreement with our geochemical modelling results, which also underline the presence of albite as a precondition for the crystallization of dawsonite at the given P–T–X conditions. Our results suggest that, at least in the Pannonian Basin, dawsonite may be an important mineral for the safe sequestration of industrial CO2 in the subsurface.

Origin and weathering of landslide material in a loess area: a geochemical study of the Kulcs landslide, Hungary

Geochemical characteristics of sediments are responses to physical and chemical alteration in landslides. However, consequences of in situ interactions associated with landslides are difficult to distinguish from those related to long-term weathering in young soft sediments such as loess. In this study, geochemical characteristics of the Kulcs landslide in Hungary are studied to identify the provenance of the loess–paleosol–red clay sequence and geochemical signatures that can potentially be attributed to the effects of landsliding. Results indicate that sliding is largely initiated by the lithological changes within the landslide body. Sediments above the sliding zone closely resemble the non-slipped Pleistocene old loess deposits from Hungary. It is also confirmed that the sliding zone develops in old paleosols in the loess sequence and red clays at its base which are all characterized by the enrichment of Al, K, Na, H2O and considerable depletion in Ca and Mg associated with carbonates. Altogether, these geochemical characteristics indicate that chemical weathering trend of unconsolidated landslide sediments is slightly modified by the redistribution of carbonates and decomposition of plagioclase. It is assumed that the distribution of Mn and Ba is modified by the water–sediment interaction in the landslide.

Upper mantle xenoliths as sources of geophysical information: the Perşani Mts. area as a case study

The aim is to give an overview on how geochemical and petrological data, obtained from upper mantle xenoliths, could be utilized to provide information on the geophysical properties of the upper mantle at their origin. First we demonstrate how a tentative lithospheric column may be constructed based on the equilibrium temperature of upper mantle xenoliths and the area specific depth-temperature curves. Then it is described how the speed of seismic waves at the given pressure and temperature conditions could be calculated from the modal composition and geochemistry of major rock forming minerals of upper mantle xenoliths (e.g. olivine and orthopyroxene). It is also discussed how the lattice preferred orientation of minerals in upper mantle xenoliths provides information on the seismic anisotropy of the upper mantle, and how this information could be used to calculate the orientation and thickness of the anisotropic layer in the upper mantle if one anisotropic layer is assumed. Structural hydroxyl (or most commonly referred to as ‘water’) incorporated in nominally anhydrous minerals plays a critical role in determining the electrical conductivity and rheology of the upper mantle. Finally, it is presented how electrical conductivity and effective viscosity of the upper mantle could be approximated based on the structural hydroxyl content in olivine, the most abundant mineral constituent of the upper mantle. Our study area, the Perşani Mountains is situated in the Carpathian Bend area (Romania) which is geologically one of the most active areas in Europe. Abundant upper mantle xenoliths from the Perşani Mountains (Eastern Carpathians) will serve as examples how meaningful geophysical information can be obtained for the upper mantle. Furthermore, it is shown how these pieces of information may be utilized in interpreting geophysical and geodynamic challenges of this area.

Geochemical modeling possibilities of CO 2 and brine inflow to freshwater aquifers

In worst-case leakage scenarios of CO2 geological storage, CO2 or brine may contaminate shallower drinking water aquifers. This work applies an advanced geochemical modeling methodology to predict ...

Accessing effects and signals of leakage from a CO2 reservoir to a shallow freshwater aquifer by reactive transport modelling

CO2 geological storage is a transitional technology for the mitigation of climate change. In the vicinity of potential CO2 reservoirs in Hungary, protected freshwater aquifers used for drinking water supplies exist. Effects of disaster events of CO2 escape and brine displacement to one of these aquifers have been studied by kinetic 1D reactive transport modelling in PHREEQC. Besides verifying that ion concentrations in the freshwater may increase up to drinking water limit values in both scenarios (CO2 or brine leakage), total porosity of the rock is estimated. Pore volume is expected to increase at the entry point of CO2 and to decrease at further distances, whereas it shows minor increase along the flow path for the effect of brine inflow. Additionally, electrical conductivity of water is estimated and suggested to be the best parameter to measure for cost-effective monitoring of both worst-case leakage scenarios.

Evidence for post-depositional diffusional loss of hydrogen in quartz phenocryst fragments within ignimbrites

Abstract Ignimbrite-hosted quartz phenocryst fragments contain much lower hydroxyl defect concentration than quartz in igneous rocks. Pre-eruptive and post-depositional loss of hydrogen were hypothesized as the main processes for lowering the initial magmatic concentrations of hydroxyl defects. The aim of this study was to examine the hydroxyl defect concentration of quartz phenocryst fragments from various vertical positions above the base of pyroclastic density current (PDC) deposits. It aims to record the vertical variations of hydroxyl defect concentrations to have an insight into potential post-depositional hydrogen loss of PDC deposits. Ignimbrite-hosted quartz phenocryst fragments were examined from two different ignimbrites in the Bükk Foreland Volcanic Area (North Hungary). Unpolarized micro-FTIR measurements on 23–35 unoriented crystal fragments from each sample were performed representing four different vertical positions of each site. Present results imply that hydroxyl defect concentrations show a pronounced decrease upward from the base of the deposits. The initial ~12 ppm hydroxyl defect concentration decreases to <3 ppm within <10 m from the base. Ignimbrites with contrasting degree of welding are characterized by different hydroxyl defect concentrations of quartz phenocryst fragments at the same height above the base. Thus, post-depositional dehydration is supposed to be the main factor causing the observed vertical decreasing trend. The modeling of post-depositional dehydration by considering typical ignimbrite emplacement temperatures (300–700 °C) and thicknesses (20–50 m) revealed that neither different cooling rates or different crystal diameters could cause the observed decrease in hydroxyl defect concentrations in ignimbrites. Other factors, such as contrasting pre-depositional thermal history, presence of melt- and fluid inclusion, and crack density of crystals could also play an important role in affecting the final hydroxyl defect concentrations.