Constraints on the thickness and seismic properties of the lithosphere in an extensional setting (Nógrád-Gömör Volcanic Field, Northern Pannonian Basin)

TheNógrád-GömörVolcanic Field (NGVF) is one of the five mantle xenolith bearing alkaline basalt locations in the Carpathian Pannonian Region. This allows us to constrain the structure and properties (e.g. composition, current deformation state, seismic anisotropy, electrical conductivity) of the upper mantle, including the lithosphere-asthenosphere boundary (LAB) using not only geophysical, but also petrologic and geochemical methods. For this pilot study, eight upper mantle xenoliths have been chosen from Bárna-Nagyk˝o, the southernmost location of the NGVF. The aim of this study is estimating the average seismic properties of the underlying mantle. Based on these estimations, the thickness of the anisotropic layer causing the observed average SKS delay time in the area was modelled considering five lineation and foliation end-member orientations. We conclude that a 142– 333km thick layer is required to explain the observed SKS anisotropy, assuming seismic properties calculated by averaging the properties of the eight xenoliths. It is larger than the thickness of the lithospheric mantle. Therefore, the majority of the delay time accumulates in the sublithospheric mantle. However, it is still in question whether a single anisotropic layer, represented by the studied xenoliths, is responsible for the observed SKS anisotropy,as it is assumed beneath the Bakony–Balaton Highland Volcanic Field (Kovács et al. 2012), or the sublithospheric mantle has different layers. In addition, the depths of the Moho and the LAB (25 ± 5, 65 ± 10 km, respectively) were estimated based on S receiver function analyses of data from three nearby permanent seismological stations

The role of water and compression in the genesis of alkaline basalts: Inferences from the Carpathian-Pannonian region

We present a new model for the formation of Plio-Pleistocene alkaline basalts in the central part of the Carpathian-Pannonian region (CPR). Based on the structural hydroxyl content of clinopyroxene megacrysts, the ‘water’ content of their host basalts is 2.0–2.5 wt.%, typical for island arc basalts. Likewise, the source region of the host basalts is ‘water’ rich (290–660 ppm), akin to the source of ocean island basalts. This high ‘water’ content could be the result of several subduction events from the Mesozoic onwards (e.g. Penninic, Vardar and Magura oceans), which have transported significant amounts of water back to the upper mantle, or hydrous plumes originating from the subduction graveyard beneath the Pannonian Basin. The asthenosphere with such a relatively high ‘water’ content beneath the CPR may have been above the ‘pargasite dehydration’ (90 km) solidi. This means that neither decompressional melting nor the presence of voluminous pyroxenite and eclogite lithologies are required to explain partial melting. While basaltic partial melts have been present in the asthenosphere for a long time, they were not extracted during the syn-rift phase, but were only emplaced at the onset of the subsequent tectonic inversion stage at ~8–5 Ma. We propose that the extraction has been facilitated by evolving vertical foliation in the asthenosphere as a response to the compression between the Adriatic indenter and the stable European platform. The vertical foliation and the prevailing compression effectively squeezed the partial basaltic melts from the asthenosphere. The overlying lithosphere may have been affected by buckling in response to compression, which was probably accompanied by formation of deep faults and deformation zones. These zones formed conduits towards the surface for melts squeezed out of the asthenosphere. This implies that basaltic partial melts could be present in the asthenosphere in cases where the bulk ‘water’ content is relatively high (>~200 ppm) at temperatures exceeding ~1000–1100 °C. These melts could be extracted even under a compressional tectonic regime, where the combination of vertical foliation in the asthenosphere and deep fractures and deformation zones in the folded lithosphere provides pathways towards the surface. This model is also valid for deep seated transpressional or transtensional fault zones in the lithosphere

Preliminary physical and geochemical study on a sedimentary rock series of the Pannonian Basin for CCS (Hungary)

AbstractOne of the largest storage potential for CCS is in the deep saline aquifers because their pore water cannot be used for drinking and for agricultural activities. In the Pannonian Basin (Hungary) there are sedimentary sub-basins filled up by sedimentary rock sequences containing such aquifers, which have the main potential for CCS in Hungary. Our chosen study area in the Pannonian Basin was the Jászság Subbasin, well known by numerous seismics and hydrocarbon exploration wells. As Hungary is situated in the middle of the Pannonian Basin, its emissions could be significantly reduced by CCS. That is the main reason to find a suitable place for CCS.The process filling up the basin resulted in a sedimentary system from deep-water to deltaic sediments, including thick facies units of reservoir quality as well as thick facies units acting as seals above it. During the evolution of the basin, large rivers brought huge amounts of sediments from the NE and NW towards the deeper parts of Lake Pannon, forming huge deltas on the river mouths.The potential reservoir formations now form a hidrogeologically coherent regional system, indicating a large potential for storage capacity. Furthermore, the saline aquifer system is large enough to ensure its long-term industrial usage for CCS, because the injection does not cause critical increase in the pressure. However, the system is not homogenous: there are siltstone interbeddings both in the Algyő (clayey cover formation), and the Szolnok Formations (dominantly sandstone), as we could see on well-logs of HC exploration wells. The siltstone in these formations does not have porosity high enough to be the storage rock, whereas the permeability is not low enough to be a good cap rock. That is why we try to avoid sampling siltstone-rich regions in the whole Jászság Basin. On the other places, and depth intervals we have used drilling cores to get a realistic quality and representative quantity of the tested formations.Our detailed studies deal with the sandy Szolnok Formation, and the clayey Algyő Formation. The Szolnok Fm. is mainly formed by sandstone, its bottom is nearly 1000 to 3500 m deep under the surface, thus it would be used as a storage rock. Its cap rock (seal) is the Algyő Fm. with more than 1000 m thickness, and a clayey composition.These potential rock associations are examined in detail in our ongoing research. We will do ex situ tests observing the behavior of the rocks when injecting supercritical CO2 in the saline pore water on pressure and temperature representing the depth of planned injection conditions