Neoproterozoic and Cambrian successions deposited on the East European platform and Cadomian basement area in Poland

Summary A short review of the Neoproterozoic and Cambrian sedimentary and volcanogenic successions in Poland is concerned with depositional and tectonic developments. The successions accumulated in shallow shelf and deeper slope environments. They overlie Palaeoproterozoic crystalline basement of the Baltic Craton and Gondwana-derived Neoproterozoic Cadomian basement. This discrepancy in the nature of the basement is viewed as indicating distinct terranes. During the course of Palaeozoic time, the discrete terranes were assembled along the Teisseyre-Tornquist Lineament and the Trans-European Suture Zone adjacent to the Baltica palaeocontinent.     

Palaeomagnetism and palaeogeography of Variscan formations of the Bohemian massif: A comparison with other regions in Europe

Summary Statistical evaluation of palaeomagnetic data from the Early Carboniferous to the Middle Triassic rocks in Europe, north of the Alpine tectonic belt, confirmed previously defined palaeotectonic stability of the whole European Plate since the Early Permian. The Trans-European Suture Zone represents a plate boundary, SW of which the Early Variscan and pre-Variscan formations show different degrees of palaeotectonic rotations, predominantly rotations of clockwise sense. A theoretical model simulating the translation and rotation movements was proposed showing that the West European Variscides underwent Hercynian palaeotectonic rotations comparable with the rotations derived for the Alpine tectonic belt.     

Study of a few palaeozoic ignimbrites in the armorican massif and in the central Massif,France

A detailed study of the petrographical characteristics of the acid palaeovolcanic formations in the Armorican Massif and in part of the Central Massif (France) reveals important ignimbritic provinces ranging from Precambrian to Carboniferous age. Close comparisons show that the ignimbrites, though varied in the details, form a whole which has constant characteristics. They can thus be related or opposed to ignimbrites of more recent origin. Field data, essential for the identification of recent ignimbrites, are of little practical help when dealing with old ones. But the study of macroscopic samples proves highly effective: heterogeneity, pseudo-fluidality, spindle-shaped structures, etc…, are among the relevant features. Only a microscopic study, however, can show vitroclastic structures and reveal the striking similarity between spindle-shaped structures and the « fiammae » of more recent ignimbrites.     

Spectrum of the geomagnetic field in central Europe

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History of tectono-magmatic evolution in the Western Kunlun Orogen

Based on the statistical and analytical data on more than 170 isotopic ages published since the 1980s of magmatic rocks, metamorphic rocks, tectonites and ores from the Western Kunlun Orogen, and the characteristics of sedimentation, magmatism, metamorphism and tectonic activities in the region studied in conjunction with geological field investigations and necessary supplementary isotope data, five stages of tectono-magmatic evolution, i.e. Ar³-Pt ₂ ¹ tectono-magmatic active stage (I), pt ₂ ² stable stage (II), Pt ₃ ¹ -p₂ active stage (III), T₁-T₂ stable stage (IV), and T₃-Q active stage (V) can be distinguished in the Western Kunlun Orogen. Moreover, the tectono-magmatic active style and general trend, the characteristics of tectonic settings, etc. of each stage and substage in the region studied are also discussed. Project supported by the State Key Science and Technology Program (No. 305) for the Ninth Five-Year Plan Period of China.     

Groundwater potential of the Egbe-Mopa basement area,central Nigeria

Abstract

An investigation on the groundwater potentials of the Egbe-Mopa area in central Nigeria, underlain by the Basement Complex, is presented. The investigation involved mapping of the subsurface by use of vertical electrical soundings; measurement of depth to groundwater; and evaluation of hydraulic conductivity, transmissivity and yield by means of pumping test interpretation. The results indicate subsurface units that range from three to five resistivity layers; depth to groundwater of 0–10 m; overburden thickness of 3–16 m; hydraulic conductivity of 6.2?×?10^?6 to 3.4?×?10^?4 m/s; transmissivity of 4.3?×?10^?7 to 2?×?10^?3 m²/s; and groundwater yield of 0.2–2.5 L/s. The hydraulic head assessments revealed a general northward groundwater flow direction. The study identified three aquifer potential types, of high, medium and low productivity, respectively. Based on the longitudinal conductance of the overburden units, four distinct Aquifer Protective Capacity zones were delineated, namely, poor, weak, moderate and good.

Citation Okogbue, C.O. and Omonona, O.V., 2013. Groundwater potential of Egbe-Mopa basement area, central Nigeria. Hydrological Sciences Journal, 58 (4), 826–840.     

Geopotential model testing sites in the central part of Europe

Summary Sixteen geopotential model testing sites in the central part of Europe, coinciding with the first-order leveling network points, have been established. The geopotential values for these sites were determined with an accuracy not limiting the testing procedure. Tests have been carried out for models GEM-Tl, GEM-T3, JGM-l, JGM-2, JGM-3 and OSU91A.     

Constraints on the age of basement and crustal growth in Tianshan Orogen by Nd isotopic composition

Based on study of Nd isotopic composition for 101 rocks of various types from Tianshan Orogen, the age and character of basement and continental crustal evolution of the Tianshan Orogen were proposed. It is deduced that the continental crustal basement of the Tianshan Orogen was formed 1. 8 Ga ago. The protolith of its metamorphic rocks was derived from long-term depleted mantle source in the ancient are tectonic setting probably. The Tianshan Orogen is obviously different from the North Tarim Block in age of basement and post-evolution history. It was also shown that Paleozoic continental crustal growth happened extensively in the Tianshan Orogen, which is distinguished from Yangtse Block and Cathaysia Block in eastern China. Project supported by the National Natural Science Foundation of China (Grant No. 49633250). It belongs to the National “305” Project in Xinjiang, which is one of the National Key Projects in the Ninth Five-Year Plan (96-915-07-05A).     

Peculiarities of geomagnetic variations in the central part of the Russian platform

The instrumental observations of geomagnetic variations in the middle latitudes are analyzed. The main periodicities are revealed in the background local variations of the magnetic field of the Earth. Besides the 27–29-day variations, which are associated with the rotation of the Sun around its axis, also the harmonic components with periods of ～1, 6–8, 13–14, 57–60 days, and about a year are identified. It is shown that the periodicities in the background variations are both regular and sporadic. The peculiarities in the time behavior of some spectral components of geomagnetic variations are established.     

Geochemical and Sr–Nd–Pb isotopic investigation of Triassic granitoids and basement rocks in the northern Gyeongsang Basin, Korea: Implications for the young basement in the East Asian continental margin

Abstract We present chemical and Sr–Nd–Pb isotopic compositions of three Triassic (226–241 Ma) calc‐alkaline granitoids (the Yeongdeok granite, Yeonghae diorite and Cheongsong granodiorite) and basement rocks in the northern Gyeongsang basin, south‐eastern Korea. These plutons exhibit typical geochemical characteristics of I‐type granitoids generated in a continental magmatic arc. The Yeongdeok and Yeonghae plutons have similar initial Sr, Nd and Pb isotope ratios (⁸⁷Sr/⁸⁶Sr_initial = 0.7041 ~ 0.7050, ?_Nd(t) = 2.3 ~ 4.0, ²⁰⁶Pb/²⁰⁴Pb_feldspar = 18.22 ~ 18.34), but distinct rare earth element patterns, suggesting that the two plutons formed from partial melting of a similar source material at different depths. The Cheongsong pluton has slightly more enriched Sr–Nd–Pb isotopic compositions (⁸⁷Sr/⁸⁶Sr_initial = 0.7047 ~ 0.7065, ?_Nd(t) = 3.9 ~ 2.8, ²⁰⁶Pb/²⁰⁴Pb_feldspar = 18.24 ~ 18.37) than the other two plutons. The Nd model ages of the basement rocks (1.1 ~ 1.4 Ga) are slightly older than those of the plutons (0.6 ~ 1.0 Ga). The initial Sr and Nd isotopic ratios of the plutons can be modeled by the mixing between the mid‐oceanic ridge basalt‐like depleted mantle component and the crustal component represented by basement rocks, which is also supported by Pb isotope data. The Sr and Nd isotope data from granitoids and basement rocks suggest that the Gyeongsang basin, the Hida belt and the inner zone of south‐western Japan share relatively young basement histories (middle Proterozoic), compared with those (early Proterozoic to Archean) of the Gyeonggi and Yeongnam massifs and the Okcheon belt. The Nd isotope data of basement rocks suggest that the Hida belt might be better correlated with the basement of the Gyeongsang basin than the Gyeonggi massif, the Okcheon belt or the Yeongnam massif, although it may represent an older continental margin of East Asia than the Gyeongsang basin considering its slightly older Nd model ages.     

Debates about the pre-Variscan tectonics of Poland

Summary The tectonic nature of the deformed Early Palaeozoic belt along the southwestern border of the East European Craton (EEC) has long been debated. The essence of these debates is reviewed and the recently published map of the Variscan tectonics in Poland is discussed from methodological and regional points of view. The terrane origin of the Pomeranian and ysogóry regions is questioned; they are inferred to be parts of the passive margin of the EEC (miogeocline), deformed into a marginal fold-and-thrust belt. The Maopolska Block and especially the Upper Silesian Block could be Caledonian (proximal?) terranes.     

Correlation between gravity anomalies and the crust-mantle boundary in central Europe

Summary Methods of simple and multiple linear correlation have been used in investigating the mutual statistical dependence of Bouguer anomalies, terrain elevations and the depths of the crust-mantle boundary determined by the method of Deep Seismic Sounding. Numerical results show a considerable degree of correlation among the quantities mentioned in Central Europe.Dedicated to Academician Alois Zátopek on His 65th Birthday     

Regional fabric of the deep lithosphere in central Europe from seismic anisotropy

Summary The large scale anisotropic structures with plunging symmetry axes in the subcrustal lithosphere of central Europe were derived from independent observations of teleseismic P-residual spheres and polarizations of the split SKS waves. The dipping structures are interpreted as remnants of palaeo-subduction systems which retain olivine orientations from ancient oceanic lithosphere. Values of k_P and k_S estimated from observed teleseismic P and SKS data are within the range of anisotropies found for the upper mantle rocks. The Variscides of central Europe may thus be characterized by two palaeo-subduction systems, with symmetry axes divergent relative to the suture between the Moldanubicum and Saxothuringicum.     

华北克拉通中东部基底构造单元的重磁特征

系统收集并重新处理了华北克拉通中东部的重磁资料,利用处理结果,结合近年来华北克拉通前寒武纪结晶基底构造研究的进展,重新将华北克拉通中东部划分为2个一级重磁异常单元和7个二级重磁异常单元;重点描述了7条分划性断裂的重磁特征,特别指出中国东部重力梯度带正是华北克拉通中部带的集中表现,而郯庐断裂带和兰考～聊城～盐山～台安-大洼断裂带是燕山期陆内不同刚性块体调整的重要边界,所以也是重磁特征的变异带．据此,对华北克拉通断裂与构造单元的重磁异常特征赋予了新的地质意义．研究表明,华北克拉通现今的地球物理特征能够反映结晶基底构造,其原因是华北克拉通现今构造格局是中新生代构造继承结晶基底构造的结果．     

Analysis of laminated structure in ozone vertical profiles in central Europe

Using statistical techniques, we study the relationship between the long-term changes in the laminar structure of the ozone vertical profile at two central-European stations - Hohenpeissenberg and Lindenberg - and other quantities potentially affecting the state of the lower stratosphere, and total-ozone content. We consider only positive laminae greater than 30 nbar. Laminae contribute non-negligibly to total ozone, and this contribution varies strongly with season. The maximum laminae-occurrence frequency in late winter/early spring is five-times higher than the minimum in early autumn. The main result of the paper is the discovery of a strong negative trend in the frequency of laminae occurrence, about -15% per decade, and even a slightly stronger negative trend in ozone content in laminae. Strong negative trends in laminae occurrence imply negative changes in total ozone as well. No pronounced effect of the quasi-biennial oscillation and solar cycle on laminae was found, whereas the 100-hPa temperature had a clear effect, and there was an indication of substantial effects of volcanic eruptions and El Niño southern oscillation events. Long-term changes in individual time series of meteorological parameters measured over Hohenpeissenberg do not indicate their significant role in the observed trend in laminae occurrence. On the other hand, there is some increase in the occurrence of very zonal circulation patterns, as well as slight decrease in very meridional circulation patterns. Together with other indications this allows us to say that dynamical effects are expected to be a principal contributor. Thus changes in laminae occurrence will probably be able to serve as an indicator/tracer of long-term changes in lower-stratospheric dynamics.     

On the comparison of tidal gravity parameters with tidal models in central Europe

Two accurately calibrated superconducting gravimeters (SGs) provide high quality tidal gravity records in three central European stations: C025 in Vienna and at Conrad observatory (A) and OSG050 in Pecný (CZ). To correct the tidal gravity factors from ocean loading effects we compared the load vectors from different ocean tides models (OTMs) computed with different software: OLFG/OLMP by the Free Ocean Tides Loading Provider (FLP), ICET and NLOADF. Even with the recent OTMs the mass conservation is critical but the methods used to correct the mass imbalance agree within 0.1 nm/s². Although the different software agrees, FLP probably provides more accurate computations as this software has been optimised. For our final computation we used the mean load vector computed by FLP for 8 OTMs (CSR4, NAO99, GOT00, TPX07, FES04, DTU10, EOT11a and HAMTIDE). The corrected tidal factors of the 3 stations agree better than 0.04% in amplitude and 0.02° in phase. Considering the weighted mean of the three stations we get for O1 δ_c = 1.1535 ± 0.0001, for K1 δ_c = 1.1352 ± 0.0003 and for M2 δ_c = 1.1621 ± 0.0003. These values confirm previous ones obtained with 16 European stations. The theoretical body tides model DDW99/NH provides the best agreement for M2 (1.1620) and MATH01/NH for O1 (1.1540) and K1 (1.1350). The largest discrepancy is for O1 (0.05%). The corrected phase α_c does not differ significantly from zero except for K1 and S2. The calibrations of the two SG's are consistent within 0.025% and agree with Strasbourg results within 0.05%.     

The oldest basement rock in the Yangtze Craton revealed by zircon U-Pb age and Hf isotope composition

Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of them have thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of 3218±13 Ma, indicating the gneiss is the oldest basement rock in the Yangtze Craton found to date. They have εHf(t) value of -2.33±0.51,and two-stage Hf model age of 3679±49 Ma,indicating that the gneiss was der...     

Mantle heat flow and geotherms for major tectonic units in central Europe

The results of seismic measurements along the deep seismic sounding profile VII and terrestrial heat flow measurements used for construction of heat generation models for the crust in the Paleozoic Platform region, the Sudetic Mountains (Variscan Internides) and the European Precambrian Platform show considerable differences in mantle heat flow and temperatures. At the base of the crust variations from 440–510°C in the models of Precambrian Platform to 700–820°C for the Paleozoic Platform and the Variscan Internides (Sudets) are found. These differences are associated with considerable mantle heat flow variations.The calculated models show mantle heat flow of about 8.4–12.6 mW m^–2 for the Precambrian Platform and 31 mW m^–2 to 40.2 mW m^–2 for Paleozoic orogenic areas. The heat flow contribution originating from crustal radioactivity is almost the same for the different tectonic units (from 33.5 mW m^–2 to 37.6 mW m^–2). Considerable physical differences in the lower crust and upper mantle between the Precambrian Platform and the adjacent areas, produced by lateral temperature variations, could be expected. On the basis of carbon ratio data it can be concluded that the Carboniferous paleogeothermal gradient was much lower in the Precambrian Platform area than in the Paleozoic Platform region.     

The discovery of the Neoarchean mafic dyke swarm in Hengshan and reinterpretation of the previous "Wutai greenstone belt"

The structural mapping and section study indicate that the "greenstone belts" in the southern to central parts of Hengshan were intensively sheared and transposed mafic dyke swarm,which originally intruded into the Neoarchean grey gneiss and high-pressure granulite terrain(HPGT).The HPGT is characterized by flat-dipping structures,to the south it became steep and was cut by the Dianmen mafic dyke swarm.After high-pressure granulite-facies metamorphic event,the mafic dyke swarm occurred,and was associated with the extensional setting and reworked by the late strike-slip shearing.The zircon age dating proves that the Dianmen mafic dyke swarm was emplaced during the period between 2499±4 Ma and 2512±3 Ma,followed by late tectonothermal reworking.The Dianmen mafic dyke swarm further documents the extensional episode in the central to northern parts of North China Craton(NCC),providing the important constraint for the limit between Archean and Proterozoic and correlation between NCC and other cratonic blocks of the world.     

Analysis of central western Europe deformation using GPS and seismic data

The kinematic field of central western Europe is characterized by relatively small movements (around 1–2 mm/year) and diffuse seismicity with earthquakes occurring mostly in the shallow crust (within 15 km), prevalently concentrated along the Alps and the European Cenozoic Rift System (ECRIS). In order to study and constrain the current crustal kinematic field we reconstructed the velocity and the strain field using permanent GPS stations, belonging to different networks (AGNES, EUREF, REGAL, RGP). The 2D strain rate tensor has been calculated using the method of least-squares collocation. Our results show that the area of maximum compression is located along the Alpine chain, where maximum values of 7 ± 2 nstrain/year are found, while maximum extension is measured between the Armorican Massif and the Massif Central, where values of 4 ± 2 nstrain/year are reached.The earthquakes with M > 3.0, have been used to estimate the seismic strain rates, while the style of the seismic deformation was reconstructed from the fault plane solutions (FPS) available from the literature. Relatively high values of seismic strain rates (around 10 nstrain/year) are measured along the Alpine Chain and the ECRIS. Results obtained by geodetic and seismic data are quite in agreement and reflect the different tectonic evolution of the geological features characterizing the area of study. The orientation of the compressional geodetic and seismic strain axes are NW-SE in most of the area of study, on account of the action of plate boundary forces. A rotation of the same axes to N-S direction along the eastern Alps, possibly related to the Adria convergence, is found.