Determination of the Lithosphere-Asthenosphere Boundary (LAB) beneath the Nógrád-Gömör Volcanic Field by combined geophysical (magnetotellurics) and geochemical methods

Understanding the fundamental role of LAB is substantial for the investigation of the geodynamic evolution of the Earth. The LAB depths can be estimated by different geophysical methods (seismology, magnetotellurics), however these depths are controversial. It has been emphasized in the literature that combined geophysical and geochemical approach may lead to better understanding of these depths. The magnetotellurics (MT) is very powerful method because it indicates the sudden increase in conductivity at the LAB. The mantle xenoliths (small fragments of the lithospheric mantle) provide the information to reconstruct their P-T paths. In the Carpathian-Pannon region (CPR) five, well-studied occurrences of mantle xenoliths-bearing Plio-Pleistocene alkali basalts are known, which makes the CPR a very promising area for investigating the inconsistency in the LAB estimates. As a test area Nógrád-Gömör Volcanic Field (NGVF) has been chosen. The host basalt erupted at the NGVF collected mantle xenoliths from a small volume of the upper mantle in a depth of about 40-50 km. The major element geochemistry of the studied xenoliths indicates that most of them represent common lherzolitic mantle, whereas others show strong wehrlitisation process. This metasomatism is supposed to be caused by a migrating mafic melt agent, resulting in the transformation of a large portion of lherzolite to wehrlite beneath the NGVF, possibly just below the crust mantle boundary. In aim to detect the LAB at the research area and find the correlation with petrologic and geochemical results we carried out MT deep soundings. The campaign contained 12 long period MT stations with 3-5 km average spacing along 60 km long profile SSE to NNW direction. This presentation summarizes the preliminary results of the combined geophysical and geochemical approaches to determine the LAB depths

Lateral and vertical heterogeneity in the lithospheric mantle at the northern margin of the Pannonian Basin reconstructed from peridotite xenolith microstructures

International audienceThis study analyzes the microstructures and deformational characteristics of spinel peridotite xenoliths from the Nógrád‐Gömör Volcanic Field (NGVF), located on the northern margin of a young extensional basin presently affected by compression. The xenoliths show a wide range of microstructures, bearing the imprints of heterogeneous deformation and variable degrees of subsequent annealing. Olivine crystal preferred orientations (CPOs) have dominantly [010]‐fiber and orthorhombic patterns. Orthopyroxene CPOs indicate coeval deformation with olivine. Olivine J indices correlate positively with equilibration temperatures, suggesting that the CPO strength increases with depth. In contrast, the intensity of intragranular deformation in olivine varies as a function of the sampling locality. We interpret the microstructures and CPO patterns as recording deformation by dislocation creep in a transpressional regime, which is consistent with recent tectonic evolution in the Carpathian‐Pannonian region due to the convergence between the Adria microplate and the European platform. Postkinematic annealing is probably linked to percolation of metasomatism by mafic melts through the upper mantle of the NGVF prior to the eruption of the host alkali basalt. Elevated equilibration temperatures in xenoliths from the central part of the volcanic field are interpreted to be associated with the last metasomatic event, which only shortly preceded the ascent of the host magma. Despite well‐developed olivine CPOs in the xenoliths, which imply a strong seismic anisotropy, the lithospheric mantle alone cannot account for the shear wave splitting delay times measured in the NGVF, indicating that deformation in both the lithosphere and the asthenosphere contributes to the observed shear wave splitting

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

Seismic anisotropy in the mantle of a tectonically inverted extensional basin: A shear-wave splitting and mantle xenolith study on the western Carpathian-Pannonian region

Information on seismic anisotropy in the Earth's mantle can be obtained from (1) shear-wave splitting analyses which allow to distinguish single or multi-layered anisotropy and delay time of the fast and slow polarized wave can indicate its thickness, and (2) studying mantle peridotites where seismic properties can be inferred from lattice preferred orientation of deformed minerals. We provide a detailed shear-wave splitting map of the western part of the Carpathian-Pannonian region (CPR), an extensional basin recently experiencing tectonic inversion, using splitting data. We then compare the results with seismic properties reported from mantle xenoliths to characterize the depth, thickness, and regional differences of the anisotropic layer in the mantle. Mantle anisotropy is different in the northern and the central/southern part of the western CPR. In the northern part, the lack of azimuthal dependence of the fast split S-wave indicates a single anisotropic layer, which agrees with xenolith data from the Nógrád-Gömör volcanic field. Systematic azimuthal variations in several stations in the central areas point to multiple anisotropic layers, which may be explained by two distinct xenolith subgroups described in the Bakony-Balaton Highland. The shallower layer probably has a ‘fossilized’ lithospheric structure, representing former asthenospheric flow, whereas the deeper one reflects structures attributed to present-day convergent tectonics, also observed in the regional NW-SE fast S-wave orientations. In the Styrian Basin at the western rim of the CPR, results are ambiguous as shear-wave splitting data hint at the presence of multiple anisotropic layers. Spatial coherency analysis of the splitting parameters places the center of the anisotropic layer at ~140–150 km depth under the Western Carpathians, which implies a total thickness of ~220–240 km. Thicknesses estimated from seismic properties of xenoliths give lower values, pointing to heterogeneously distributed anisotropy or different orientation of the mineral deformation structures

Metasomatism-induced wehrlite formation in the upper mantle beneath the Nógrád-Gömör Volcanic Field (Northern Pannonian Basin): Evidence from xenoliths

Clinopyroxene-enriched upper mantle xenoliths classified as wehrlites are common (~20% of all xenoliths) in the central part of the Nógrád-Gömör Volcanic Field (NGVF), situated in the northern margin of the Pannonian Basin in northern Hungary and southern Slovakia. In this study, we thoroughly investigated 12 wehrlite xenoliths, two from each wehrlite-bearing occurrence, to determine the conditions of their formation. Specific textural features, including clinopyroxene-rich patches in an olivine-rich lithology, orthopyroxene remnants in the cores of newly-formed clinopyroxenes and vermicular spinel forms all suggest that wehrlites were formed as a result of intensive interaction between a metasomatic agent and the peridotite wall rock. Based on the major and trace element geochemistry of the rock-forming minerals, significant enrichment in basaltic (Fe, Mn, Ti) and high field strength elements (Nb, Ta, Hf, Zr) was observed, compared to compositions of common lherzolite xenoliths. The presence of orthopyroxene remnants and geochemical trends in rock-forming minerals suggest that the metasomatic process ceased before complete wehrlitization was achieved. The composition of the metasomatic agent is interpreted to be a mafic silicate melt, which was further confirmed by numerical modelling of trace elements using the plate model. The model results also show that the melt/rock ratio played a key role in the degree of petrographic and geochemical transformation. The lack of equilibrium and the conclusions drawn by using variable lherzolitic precursors in the model both suggest that wehrlitization was the last event that occurred shortly before xenolith entrainment in the host mafic melt. We suggest that the wehrlitization and the Plio–Pleistocene basaltic volcanism are related to the same magmatic event.This research was financially facilitated by Orlando Vaselli, supported by the Bolyai Postdoctoral Fellowship Program, a Marie Curie International Reintegration Grant (Grant No. NAMS-230937) and a postdoctoral grant (Grant No. PD101683) of the Hungarian Scientific Research Found (OTKA) to I. J. K., as well as a grant of the Hungarian Scientific Research Found (Grant No. 78425) to Cs. Sz. Work done at Virginia Tech was supported by a grant from the U. S. National Science Foundation (EAR-1624589) to R. J. B. L. Patkó was supported by the GINOP-2.3.2-15-2016-00009 research program. This is the 88 publication of the Lithosphere Fluid Research Lab (LRG)

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

Influence of socioeconomic factors on pregnancy outcome in women with structural heart disease

OBJECTIVE: Cardiac disease is the leading cause of indirect maternal mortality. The aim of this study was to analyse to what extent socioeconomic factors influence the outcome of pregnancy in women with heart disease.  METHODS: The Registry of Pregnancy and Cardiac disease is a global prospective registry. For this analysis, countries that enrolled ≥10 patients were included. A combined cardiac endpoint included maternal cardiac death, arrhythmia requiring treatment, heart failure, thromboembolic event, aortic dissection, endocarditis, acute coronary syndrome, hospitalisation for cardiac reason or intervention. Associations between patient characteristics, country characteristics (income inequality expressed as Gini coefficient, health expenditure, schooling, gross domestic product, birth rate and hospital beds) and cardiac endpoints were checked in a three-level model (patient-centre-country).  RESULTS: A total of 30 countries enrolled 2924 patients from 89 centres. At least one endpoint occurred in 645 women (22.1%). Maternal age, New York Heart Association classification and modified WHO risk classification were associated with the combined endpoint and explained 37% of variance in outcome. Gini coefficient and country-specific birth rate explained an additional 4%. There were large differences between the individual countries, but the need for multilevel modelling to account for these differences disappeared after adjustment for patient characteristics, Gini and country-specific birth rate.  CONCLUSION: While there are definite interregional differences in pregnancy outcome in women with cardiac disease, these differences seem to be mainly driven by individual patient characteristics. Adjustment for country characteristics refined the results to a limited extent, but maternal condition seems to be the main determinant of outcome

Lateral and Vertical Heterogeneity in the Lithospheric Mantle at the Northern Margin of the Pannonian Basin Reconstructed From Peridotite Xenolith Microstructures

This study analyzes the microstructures and deformational characteristics of spinel peridotite xenoliths from the Nógrád-Gömör Volcanic Field (NGVF), located on the northern margin of a young extensional basin presently affected by compression. The xenoliths show a wide range of microstructures, bearing the imprints of heterogeneous deformation and variable degrees of subsequent annealing. Olivine crystal preferred orientations (CPOs) have dominantly [010]-fiber and orthorhombic patterns. Orthopyroxene CPOs indicate coeval deformation with olivine. Olivine J indices correlate positively with equilibration temperatures, suggesting that the CPO strength increases with depth. In contrast, the intensity of intragranular deformation in olivine varies as a function of the sampling locality. We interpret the microstructures and CPO patterns as recording deformation by dislocation creep in a transpressional regime, which is consistent with recent tectonic evolution in the Carpathian-Pannonian region due to the convergence between the Adria microplate and the European platform. Postkinematic annealing is probably linked to percolation of metasomatism by mafic melts through the upper mantle of the NGVF prior to the eruption of the host alkali basalt. Elevated equilibration temperatures in xenoliths from the central part of the volcanic field are interpreted to be associated with the last metasomatic event, which only shortly preceded the ascent of the host magma. Despite well-developed olivine CPOs in the xenoliths, which imply a strong seismic anisotropy, the lithospheric mantle alone cannot account for the shear wave splitting delay times measured in the NGVF, indicating that deformation in both the lithosphere and the asthenosphere contributes to the observed shear wave splitting.The authors would like to thank the people who contributed to this work. We owe thanks to Fabrice Barou and David Adams for their help with EBSD-SEM analyses at Geosciences Montpellier and at CCFS Macquarie University, respectively. L?szl? Aradi is acknowledged for his help with field work, petrography and MTEX application. We are grateful for the constructive criticism of Sandra Piazolo and Jacques Pr?cigout and two anonymous reviewers, as well as for the editorial handling of Stephen Parman. Our research received financial support from a Marie Curie International Reintegration Grant (grant NAMS-230937), a postdoctoral grant (grant PD101683) of the Hungarian Scientific Research Fund (OTKA), and a Bolyai J?nos Postdoctoral Research Fellowship of the Hungarian Academy of Sciences to I. J. K., as well as from the Lend?let Pannon LitH2Oscope Research Group (Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences). N. L. received support from Macquarie University international PhD scholarship and project and travel funding from ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS). K. H. acknowledges funding from Ministry of Economy, Industry and Competitiveness (MINECO, Spain) and the State Research Agency (AEI, Spain; grants FPDI-2013-16253 and CGL2016-81085-R). Instruments used at Macquarie University are funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS/AuScope, industry partners, and Macquarie University. The data used in this paper are listed in the references, tables, and supporting information. The raw EBSD data are available from the corresponding author upon request. This is the 92nd publication of the Lithosphere Fluid Research Lab (LRG), contribution 1361 from the ARC Centre of Excellence for Core to Crust Fluid Systems (www.ccfs.mq.edu.au) and 1320 from the GEMOC Key Centre (www.gemoc.mq.edu.au)