Assimilation and diffusion during xenolith-magma interaction: a case study of the Variscan Karkonosze Granite, Bohemian Massif

Magmatic enclaves from the Rudolfov quarry near Liberec (Czech Republic) are interpreted to represent remnants of lamprophyric melt that intruded the Karkonosze granite at a stage at which the granite was not fully solidified. Based on the observation that larger enclaves are generally more circular than the smaller ones, we conclude that bigger blobs of mafic magma became more spherical during flow in the gravity field (sink or float). This flow is also interpreted to be responsible for the incorporation of mineral grains into the enclaves and may have facilitated the assimilation of granitic melt. Linear mixing trends on Harker diagrams for most network-forming and mainly slow-diffusing or fluid-immobile elements indicate such an assimilation process between granite and lamprophyre. In contrast, all fast-diffusing or fluid-mobile elements display scattered element distributions, implying that chemical diffusion also played a role. Pressure and temperature for this late magmatic stage are estimated at around 1 kbar and 500°C. These results suggest that two processes modified the composition of the enclaves in the Karkonosze granite: (1) assimilation (mechanical mixing) of granitic melt during the injection of the lamprophyric melt and the subsequent flow of the forming enclaves in the gravity field (responsible for the linear mixing trends) and (2) diffusion-controlled redistribution of elements between both solidifying rock types at the magmatic stage and/or due to late-stage magmatic fluids (responsible for the scattering and deviation from the linear mixing trends).     

Krypton and Xenon Radionuclides Monitoring in the Northwest Region of Russia

Monitoring of Xe and Kr radionuclides was conducted from August 2006 to 30 July 2008 within the framework of ISTC Project #2133. Cherepovets City in Vologda Province and St. Petersburg were chosen as monitoring locations. Kr–Xe concentrate samples were obtained as a result of processing of several thousand m³ of atmospheric air. New results of ⁸⁵Kr monitoring show, that for last 15 years, the ⁸⁵Kr volumetric activity in the atmospheric air of the northwest region of Russia has increased approximately 50% and has achieved a level of 1.5 Bq/m³. This value correlates well with similar data for Western Europe and Japan. The xenon fraction (80–160 cm³ under STP) is adsorbed on charcoal in the ampoule, which is measured in the well of HPGe gamma detector. Minimum detectable concentration (MDC) of ¹³³Xe for this technique is 0.008 mBq/m³, and it is the most sensitive method used today. The ¹³³Xe concentration in the atmospheric air of Cherepovets City varied in the monitoring period ranging from 0.09 to 2.5 mBq/m³. During the period of March 2007–30 July 2008, ¹³³Xe activity concentration in the atmospheric air of St. Petersburg changed from background values (0.2–0.3 mBq/m³) to 185 mBq/m³ and for approximately 20% of the samples ¹³⁵Xe was also measured with the ¹³⁵Xe/¹³³Xe activity ratio varied within the range of 0.03–3.5.     

Identifying low-temperature hydrothermal karst and palaeowaters using stable isotopes: a case study from an alpine cave,Entrische Kirche,Austria

The area south of the prominent east–west trending Salzach Valley at the northern rim of the Central Alps of Austria has long been known to host anomalously warm springs emerging from a highly deformed calcite marble (Klammkalk). This unit also hosts cavities whose shapes suggest a hydrothermal karst origin and which are lined by calcite spar. We report here petrographic and isotopic evidence suggesting that dissolution by ascending low-temperature thermal waters also played an important role in the origin of a large cave in this region, Entrische Kirche. A paleo cave wall, preserved behind a thick flowstone in the interior of this cave, revealed a brownish bleaching zone which contrasts to the medium grey colour of the unaltered marble beneath. Across this zone the C and O isotope values gradually decrease by 3 and 11‰, respectively. These compositions are very different from those of the speleothem above but are similar to phreatic calcite spar from hydrothermal karst cavities in other outcrops in the area, where the absence of two-phase fluid inclusions suggests a low-temperature (less than ca. 50°C) hydrothermal origin. U/Th dating of the flowstone capping the alteration zone yielded a minimum age of the thermal water invasion in Entrische Kirche of ca. 240 kyr. There is no evidence in Entrische Kirche that these palaeowaters reached the point of calcite precipitation, but it is physically conceivable that higher and as yet unexplored parts of this deep (ca. 900 m) cave contain cavities lined by phreatic cave spar.     

On the influence of DC railway noise on variation data from Belsk and Lviv geomagnetic observatories

Geomagnetic variation data from the observatories in Belsk (BEL, Poland) and Lviv (LVV, Ukraine) significantly suffer from disturbances caused by direct current (DC) electric railways. The aim of this study is to quantify the impact of these disturbances on quantities derived from such data, as the K index of magnetic activity and the induction arrow used in the geomagnetic deep sounding method to indicate lateral contrasts of electric conductivity in the solid earth. Therefore, undisturbed data have been reconstructed by means of a frequency-domain transfer function that relates the horizontal magnetic field components of the observatory to the ones synchronously recorded at a noise-free reference station. The comparison of the K index derived from original and reconstructed data shows an increase of quiet time segments by 29% for LVV and by 14% for BEL due to our noise removal procedure. Furthermore, the distribution of the corrected K indices agrees well with the one from the Niemegk observatory in Germany.     

Integrated magnetobiochronology of the Pliocene–Pleistocene Miyazaki succession,southern Kyushu,southwest Japan: Implications for an Early Pleistocene hiatus and defining the base of the Gelasian (P/P boundary type section) in Japan

An integrated magnetobiochronology of the Miyazaki Pliocene–Pleistocene succession in the Miyazaki area, southwest Japan, was established using planktic foraminiferal and calcareous nannofossil biostratigraphy together with paleomagnetic data. The upper Miyazaki succession in the northern Miyazaki region can be divided into the Takanabe, Hisamine (redefined), and Higoyashiki (new) Formations, in ascending order. A depositional hiatus between the Hisamine Formation and the Takanabe and/or older formations was also identified based on integrated magnetobiostratigraphy from five sections including the Nagatani River (NGT) section through the uppermost Miyazaki succession. The hiatus, herein called the Hisamine unconformity, is equivalent to the Kurotaki unconformity between the Miura and Kazusa groups of the Boso Peninsula in central Japan. The depositional hiatus recognised in the lower Pleistocene of Pacific coastal areas in southwestern and central Japan may have resulted from tectonic activity associated with a change in the subduction direction of the Philippine Sea plate, which commenced prior to ca. 2.2 Ma. The youngest unit just below the hiatus is the upper part of the Takanabe Formation in the NGT section. The NGT section represents the continuous Late Pliocene to earliest Pleistocene sequence including the Gauss/Matuyama boundary and is here proposed as the type section for the Pliocene/Pleistocene boundary in Japan, which the IUGS ratified as the base of the Gelasian in 2009.     

Particle Acceleration in Reconnecting Current Sheets in Impulsive Electron-Rich Solar Flares

Electron and proton acceleration in reconnecting current sheets in electron-rich solar flares is considered. A significant three-dimensional magnetic field is assumed in the current sheet where the particles are accelerated by the DC electric field. The tearing instability of a pre-flare current sheet leads to the formation of multiple singular lines of magnetic field where the electric and magnetic fields are coaligned. Magnetized electrons are shown to be accelerated to a few tens of MeV before they leave the vicinity of a singular line. The acceleration time is estimated to be less than 10^–3 s. By contrast, much heavier protons are unmagnetized and their energy gain is more modest. The model explains a high electron-to-proton ratio and the unusually intense gamma-ray continuum above 1 MeV observed in the electron-rich flares.     

安徽巢湖地区下三叠统综合层序

印度阶一奥伦尼克阶界线的全球层型候选剖面之一位于安徽巢湖地区;巢湖地区的下三叠统也是国际上同期地层中生物地层序列最有代表性、多重地层学手段应用齐备、研究效果最好的地层序列之一。根据巢湖地区3条代表性下三叠统剖面的岩石地层、生物地层和碳同位素地层的最新研究成果归纳出本区早三叠世综合地层序列,作为区域地层对比研究的标准．巢湖的下三叠统明确包含8个牙形石带和6个菊石带。它们具有区域甚至全球对比意义;巢湖地区早三叠世碳同位素δ^13Ccarb的演变呈现2个显著的漂移周期,这种有特色的碳同位素漂移,不仅具有地层学价值,而且可能对于三叠纪初的生物复苏和生态系演变具有指导意义．在综合地层序列基础上,将3条剖面的古地磁学研究成果链接,形成了巢湖地区完整的早三叠世磁性地层序列,包括5个主要的正向极性带和5个反向极性带,这也是目前在本区乃至华南获得的最完整的早三叠世磁极性序列之一．这些为该区域乃至全球相关地层研究树立了一个基本格架。     

Strain and competence contrast estimation from fold shape

A new method to estimate strain and competence contrast from natural fold shapes is developed and verified by analogue and numerical experiments. Strain is estimated relative to the nucleation amplitude, A_N, which is the fold amplitude when the amplification velocities caused by kinematic layer thickening and dynamic folding are identical. A_N is defined as the initial amplitude corresponding to zero strain because folding at amplitudes smaller than A_N is dominantly by kinematic layer thickening. For amplitudes larger than A_N, estimates of strain and competence contrast are contoured in thickness-to-wavelength (H/λ) and amplitude-to-wavelength (A/λ) space. These quantities can be measured for any observed fold shape. Contour maps are constructed using existing linear theories of folding, a new nonlinear theory of folding and numerical simulations, all for single-layer folding. The method represents a significant improvement to the arc length method. The strain estimation method is applied to folds in viscous (Newtonian), power-law (non-Newtonian) and viscoelastic layers. Also, strain partitioning in fold trains is investigated. Strain partitioning refers to the difference in strain accommodated by individual folds in the fold train and by the whole fold train. Fold trains within layers exhibiting viscous and viscoelastic rheology show different characteristic strain partitioning patterns. Strain partitioning patterns of natural fold trains can be used to assess the rheological behaviour during fold initiation.     

Surface structure effects on direct reduction of iron oxides by Shewanella oneidensis

The atomic and electronic structure of mineral surfaces affects many environmentally important processes such as adsorption phenomena. They are however rarely considered relevant to dissimilatory bacterial reduction of iron and manganese minerals. In this regard, surface area and thermodynamics are more commonly considered. Here we take a first step towards understanding the nature of the influence of mineral surface structure upon the rate of electron transfer from Shewanella oneidensis strain MR-1 outer membrane proteins to the mineral surface and the subsequent effect upon cell “activity.” Cell accumulation has been used as a proxy for cell activity at three iron oxide single crystal faces; hematite (001), magnetite (111) and magnetite (100). Clear differences in cell accumulation at, and release from the surfaces are observed, with significantly more cells accumulating at hematite (001) compared to either magnetite face whilst relatively more cells are released into the overlying aqueous phase from the two magnetite faces than hematite. Modeling of the electron transfer process to the different mineral surfaces from a decaheme (protoporphyrin rings containing a central hexacoordinate iron atom), outer membrane-bound cytochrome of S. oneidensis has been accomplished by employing both Marcus and ab initio density functional theories. The resultant model of electron transfer to the three oxide faces predicts that over the entire range of expected electron transfer distances the highest electron transfer rates occur at the hematite (001) surface, mirroring the observed cell accumulation data. Electron transfer rates to either of the two magnetite surfaces are slower, with magnetite (111) slower than hematite (001) by approximately two orders of magnitude. A lack of knowledge regarding the structural details of the heme-mineral interface, especially in regards to atomic distances and relative orientations of hemes and surface iron atoms and the conformation of the protein envelope, precludes a more thorough analysis. However, the results of the modeling concur with the empirical observation that mineral surface structure has a clear influence on mineral surface-associated cell activity. Thus surface structure effects must be accounted for in future studies of cell-mineral interactions.