Evidence for xenolith–host basalt interaction from chemical patterns in Fe–Ti-oxides from mafic granulite xenoliths of the Bakony–Balaton Volcanic field (W-Hungary)

We investigate the effects of xenolith–host basalt interaction on lower crustal mafic granulite xenoliths from the Central Pannonian Basin. The xenoliths are devoid of any signs of melting, nevertheless various phenomena are identified, which indicate that the original mineralogy and chemistry of the xenoliths was modified during interaction with the host basalt. The rock-forming silicates are only slightly affected by alteration, but the Fe–Ti-oxides are overprinted to a significant extent. Complex chemical zoning patterns are detected using high-resolution element mapping in ilmenites and in lamellar titanomagnetite–ilmenite intergrowths. The chemical alteration of the Fe–Ti-oxides was diffusion-controlled and, hence, time and temperature dependent. On the basis of diffusion profiles in titanomagnetite we estimate the duration of xenolith–host basalt interaction to be at least 9–20 h. This is comparable to the time necessary for the ascent of the host basalt to the surface. It is too short to reflect alteration during granulite facies metamorphism in the deep crust. The chemical alteration of the titanomagnetite thus reflects the total duration of the xenolith–host basalt interaction.     

Determination of hydrocarbon distributions in oils and sediment extracts by gas chromatography—high resolution mass spectrometry

The distributions of steroid and triterpenoid hydrocarbons in crude oils and sedimentary rock extracts can be routinely determined by the direct injection of the sample into a gas chromatograph coupled to a mass spectrometer (GC-MS). The mass spectrometer is operated at a resolution of about 2500 (10% valley), and only the ion intensities at selected accurate mass values, diagnostic of the structural types of interest, are monitored throughout the analysis. The distributions, so obtained, find application in the assessment of the source and thermal maturity of crude oil accumulations in the subsurface. This technique eliminates chromatographic separation steps and combines two analyses in one. Thus, more geological samples and reference mixtures may be analyzed in a given time.     

Resolution dependent relative dispersion statistics in a hierarchy of ocean models

In order to determine the effect of Eulerian spatial resolution on the two particle statistics of synthetic drifter trajectories, we examine a hierarchy of ocean models, starting from 2D turbulence simulations, progressing to idealized simulations of a buoyant coastal jet with ROMS, and finally to realistic HYCOM simulations of the Gulf Stream. In each case, particle dispersion at large time and space scales is found to be controlled by energetic meso-scale features of the flow that are relatively insensitive to the resolution of finer scale motions. In all cases, time-distance graphs given in terms of computed Finite Scale Lyapunov Exponents show an expected increase in the extent of exponential scaling with increasing spatial smoothing of the velocity field. The limiting value of the FSLE at small separation distances is found to scale remarkably well with the resolution of Eulerian velocity gradients as given by the average of positive Okubo–Weiss parameter values.     

A study of wind speed modification and internal boundary-layer heights in a coastal region

Wind profile data within the first two kilometres of a coast have been used to study the wind field modification downstream of this surface discontinuity. The land area is generally very flat, having an overall roughness length of 0.04 m. A wind model, suitable for practical applications and inexpensive to run, has been tested against the data and was found to give satisfactory results. Knowing the climatological statistics of wind and stratification, e.g., at the coast, the model may thus be used to estimate, on a climatological basis, how the wind field is modified with distance inland, at least in areas with only minor topography. This type of information is of great importance when locating wind turbines. It is in these cases also important to know the statistics of the internal boundary-layer (IBL) height, as the turbulence intensity may be quite different in and above the IBL, which in turn may influence load and fatigue calculations. Using the wind profile data, the IBL height was clearly discernible in the majority of cases. Having very unstable stratification over land, the IBL height could, however, not be determined from the wind profiles, as the wind in these cases did not decrease inland. This result was also obtained using the wind model. A simple model of the type z _IBL = a · x ^b, was instead tested, and was shown to give reasonable results.     

Variability of unsaturated Bromide fluxes as measured through a layered volcanic vadose zone in New Zealand

The measured drainage fluxes through a layered volcanic vadose zone exhibited high spatial variability as a consequence of heterogeneous flow conditions. The drainage flux variability was quantified using automated equilibrium tension lysimeters, installed in close‐proximity and resulted in high variability in the Br masses recovered from a conservative tracer experiment. The primary cause of the heterogeneous flow was attributed to textural changes occurring at the interface between volcanic layers, resulting in development of funnel‐flow patterns, and further enhanced by the existence of hydrophobic conditions. The Br recoveries in individual automated equilibrium tension lysimeters were used to determine the corresponding variable sizes of the surface areas contributing drainage to the lysimeters. The tracer experiment confirmed the existence of unsaturated lateral transport occurring at the sloping interface of the coarse Taupo Ignimbrite material with the silty Palaeosol layer at approximately 4.2 m depth. This study demonstrates that measurements of both flux and solute concentrations at multiple locations are essential when heterogeneous flow is suspected to be present, to be able to determine reliable estimates of contaminant leaching through the vadose zone at the plot scale. Copyright © 2013 John Wiley & Sons, Ltd.     

Double-layer structure in the boundary layer over the baltic sea

Double-layered structures found over the Baltic Sea are investigated using radiosoundings and lidar measurements. Situations with double-layer structures are also simulated with the regional model REMO in a realistic manner. The double layer consists of two adjacent well-mixed layers, with a sharp inversion in between.Results from radiosoundings show that the double-layer structure over the Baltic Sea mainly occurs during the autumn with thermally unstable stratification near the surface. The structure is present in about 50 % of the radiosoundings performed during autumn. The presence of the double-layer structure cannot be related to any specific wind direction, wind speed or sea surface temperature.The lidar measurements give a more continuous picture of the time evolution of the double-layer structure, and show that the top of the lower layer is not a rigid lid for vertical transport. Two possible explanations of the double-layer structure are given, (i) the structure is caused by `advection' of land boundary-layer air over the convective marine boundary layer or, (ii) by development of Sc clouds in weak frontal zones connected to low pressure systems. Also the forming of Cu clouds is found to be important for the development of a double-layer structure.     

Cleavage mechanism and surface chemical characterization of phengitic Muscovite and Muscovite as constrained by X-Ray Photoelectron Spectroscopy

Freshly cleaved (001) natural muscovite was chemically characterized by X-ray Photoelectron Spectroscopy (XPS). The investigated muscovite crystals have composition ranging from pure end member to phengitic muscovite. XPS provides experimental evidence that the chemical composition of the near-surface region differs from the bulk. This difference is not due to analytical problems, but to extreme surface sensitivity of XPS. Depth profiling was also carried out after tilting of 60° or 70° of the sample along an axis perpendicular to [001]. After tilting of phengitic muscovite, the concentration of Al increases and of K decreases, and therefore Al is the topmost monolayer. Repulsion between the octahedral and tetrahedral sheets, stacking faults or more probably interlayered phases (gibbsite-like) are responsible for the cleavage. Possible perturbations of surface chemistry due to X-ray radiation and Ar⁺ ion sputtering have also been investigated. X-ray radiation is negligeable, but Ar⁺ ion sputtering introduces important structural modifications, perturbation of the chemical environment of elements and minor chemical variations. Received: 13 November 1996 / Revised, accepted: 21 March 1997     

Single zircon ages and whole-rock Nd isotopic systematics of early Palaeozoic granitoid gneisses from the Czech and Polish Sudetes (Jizerské hory, Krkonoše Mountains and Orlice-Sněžník Complex)

Granitoid orthogneisses make up the predominant rock type in the West Sudetes from Jizerské hory in the NW to the Orlické hory and Sn3—ník Mountains in the SE. These generally strongly foliated gneisses are calc-alkaline in composition and display trace element characteristics suggesting generation in a volcanic arc setting. Single zircon ages reflecting the time of emplacement of the gneiss protoliths define a relatively narrow Cambro-Ordovician range between 502 and 515 Ma. This is similar to previously reported zircon ages from the Czech and Polish West Sudetes and documents an important and regionally extensive post-Cadomian magmatic event that we relate to continental arc magmatism on the margin of Avalonia that developed during closure of the Tornquist Ocean. An age of 492 Ma for a microgranite dyke cutting deformed and metamorphosed orthogneisses in the Orlické hory shows the main deformation to be early Paleozoic. Zircon xenocryst minimum ages range between 546 and 2070 Ma and show maxima in the Cadomian/Pan-African (550-850 Ma) and Grenvillian (1000-1300 Ma) time brackets. The Grenvillian event is also evident from Nd mean crustal residence ages that vary between 1.34 and 1.87 Ga. From these data we suggest that the pre-Variscan granitoid gneisses of the Czech West Sudetes were largely generated by melting of a predominantly Grenville-age basement that was part of the northern margin of Gondwana and may have been related to Grenville-age basement now identified in northern South America.     

Evidence from zircon dating for existence of approximately 2.1 Ga old crystalline basement in southern Bohemia,Czech Republic

Zircon ages are reported for three Moldanubian amphibolite grade orthogneisses from the southern Bohemian Massif obtained by conventional U/Pb analyses. For two of these orthogneisses, conventional U/Pb data are supported by ion microprobe single zircon ages or single grain evaporation data. The amphibolite grade orthogneisses, occurring in three small tectonic lenses within the Varied Group close to the South Bohemian Main Thrust, are of tonalitic, granodioritic or quartz dioritic composition.Conventional bulk size fraction and ion microprobe analyses of nearly euhedral zircons from a metatonalite, erroneously interpreted as a metagreywacke in a previous study, yielded an upper Concordia intercept age of 2048 ± 12 Ma. The well preserved euhedral grain shapes of the zircons suggest crystallization from a magmatic phase, and the upper Concordia intercept age is now interpreted as reflecting a magmatic event at that time. The age of this rock is compatible with the conventional zircon data and the (²⁰⁷Pb/²⁰⁶Pb)^* single grain evaporation result from two further orthogneisses providing intrusion ages of 2 060 ± 12, 2 104 ± 1 and 2 061 ± 6 Ma, respectively. For one sample a concordant U/Pb age for sphene of 355 ± 2 Ma defines the age of amphibolite facies metamorphism. The upper Concordia intercept ages of three orthogneisses constitute the first direct evidence for the presence of early Proterozoic crust under the supracrustal cover in the southern part of the Bohemian Massif. Correspondence to: J. I. Wendt