Glassy orthopyroxene granodiorites of the Pannonian Basin: tracers of ultra-high-temperature deep-crustal anatexis triggered by Tertiary basaltic volcanism

Glassy orthopyroxene granodiorite-tonalite (named pincinite after type locality) was described from basaltic lapilli tuffs of the Pliocene maar near Pinciná village in the Slovakian part of the Pannonian Basin. Two pincinite types exhibit a qualitatively similar mineral composition (quartz, An_20–55 plagioclase, intergranular silicic glass with orthopyroxene and ilmenite, ±K-feldspar), but strongly different redox potential and formation PT conditions. Peraluminous pincinite is reduced (6–7% of total iron as Fe³⁺ in corundum-normative intergranular dacitic glass) and contains ilmenite with 8–10 mol% Fe₂O₃ and orthopyroxene dominated by ferrosilite. High-density (up to 0.85 g/cm³) primary CO₂ inclusions with minor H₂, CH₄, H₂S, CO and N₂ (<2 mol% total) are present in Qtz and Plg. Equilibrium PT conditions inferred from the intergranular Opx–Ilm–Glass assemblage and fluid density correspond to 1,170±50°C, 5.6±0.4 kbar, respectively. Metaluminous pincinite is more oxidised (25–27% of total iron as Fe³⁺ in diopside-normative intergranular glass of rhyolite–trachyte–dacite composition) and contains Fe₂O₃-rich ilmenite (17–29 mol%) associated with enstatite. Fluid inclusions are composed of CO₂–H₂O mixtures with up to 38 mol% H₂O. Raman spectroscopy revealed H₂S along with dominant CO₂ in the carbonic phase. Equilibrium PT parameters for the intergranular Opx–Ilm–Glass assemblage correspond to 740±15°C, 2.8±0.1 kbar, respectively. Reducing gas species (<2 mol% total) in the CO₂-inclusions of the peraluminous pincinite resulted from hydrogen diffusion due to fH₂ gradient imposed during decrease of redox potential from the log fO₂ values near QFM during Qtz + Plg growth, to QFM-2 incidental to the superimposed Opx + Ilm assemblage in the intergranular melt. The decrease in oxygen fugacity was recorded also in the metaluminous pincinite, where log fO₂ values changed from ~QFM + 2.6 to QFM + 0.4, but hydrogen diffusion did not occur. Absence of OH-bearing minerals, major and trace element abundances (e.g. REE 300–320, Nb 55–57, Th 4–31, Zr 240–300 ppm, FeO_tot/MgO up to 11), and Sr–O isotope ratios in the pincinites are diagnostic of high-temperature anorogenic magmas originated by dehydration melting of biotite in quartz-feldspathoid crust (⁸⁷Sr/⁸⁶Sr>0.705–0.706, ¹⁸O>9 V-SMOW) around alkali basalt reservoir in depths between 17 and 20 km, and around late stage derivatives of the basalt fractionation, intruding the crust up to depths of 10–11 km. Low water activity in the pincinite parental melt was caused by CO₂-flux from the Tertiary basaltic reservoirs and intrusions. The anatexis leads to generation of a melt-depleted granulitic crust beneath the Pannonian Basin, and the pincinites are interpreted as equivalents of igneous charnockites and enderbites quenched at temperatures above solidus and unaffected by sub-solidus re-equilibration and metamorphic overprint.     

GGR Critical Review of Analytical Developments in 2004–2005

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.     

Localization and characterization of an active fault in an urbanized area in central Guatemala by means of geoelectrical imaging

The Polochic and Motagua faults define the active plate boundary between the North American and Caribbean plates in central Guatemala. A splay of the Polochic Fault traverses the rapidly growing city of San Miguel Uspantán that is periodically affected by destructive earthquakes. This fault splay was located using a 2D electrical resistivity tomography (ERT) survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built. ERT images show the fault as a ~50 m wide, near-vertical low-resistivity anomaly, bounded within a few meters by high resistivity anomalies. Forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location, geometry, and internal structure of the fault zone as well as the affected lithologies. Our results indicate that the city is constructed on a ~20 m thick surficial layer consisting of poorly consolidated, highly porous, water-logged pumice. This soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking. The electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might, at least in part, be fed by water rising along the fault. Therefore, the potential threat posed by this fault splay may not be limited to its seismic activity per se, but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments. The results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of San Miguel Uspantán and illustrate the potential of ERT surveying for paleoseismic studies.     

FRAGMENTAL BRECCIAS AND THE COLLISIONAL EVOLUTION OF ORDINARY CHONDRITE PARENT BODIES

Our survey of type 4–6 ordinary chondrites indicates that gas-poor, melt-rock and/or exotic clast-bearing fragmental breccias constitute 5%, 22% and 23%, respectively, of H, L and LL chondrites. These abundances contrast with the percentages of solar-gas-rich regolith breccias among ordinary chondrites: H (14%), L (3%) and LL (8%) (Crabb and Schultz, 1981). Petrologic study of several melt-rock-clast-bearing fragmental breccias indicates that some acquired their clasts prior to breccia metamorphism and others acquired them after metamorphism of host material. In general, the melt-rock clasts in gas-poor H chondrite fragmental breccias were acquired after breccia metamorphism and were probably formed by impacts into boulders or exposed outcrops of H4-6 material in the H chondrite parent body regolith. In contrast, most of the melt-rock clasts in gas-poor L and LL fragmental breccias were acquired prior to breccia metamorphism. The low abundance of regolith breccias among L chondrites and evidence that at least two-thirds of the L chondrites suffered a major shock event 0.5 Gyr ago, suggest that the L parent body may have been disrupted by a major collision at that time and that the remaining parent body fragments were too small to develop substantial regoliths (e.g., Heymann, 1967; Crabb and Schultz, 1981). Such a disruption would have exposed a large amount of L chondrite bedrock, some of which would consist of fragmental breccias that acquired melt-rock clasts very early in solar system history, prior to metamorphism. The exposed bedrock would serve as a potential target for sporadic meteoroid impacts to produce a few fragmental breccias with unmetamorphosed melt-rock clasts. The high proportion of genomict brecciated LL chondrites reflects a complex collisional history, probably including several episodes of parent body disruption and gravitational reassembly. Differences in the abundances of different kinds of breccias among the ordinary chondrite groups are probably due to the stochastic nature of major asteroidal collisions.     

The origin of chondrules: experimental investigation of metastable liquids in the system Mg2SiO4-SiO2

Laser-melted magnesium silicate droplets, supercooled 400–750°C below their equilibrium liquidus temperatures before crystallization, were examined to provide a comparison with meteoritic and lunar chondrules and to examine physicochemical parameters that may indicate the conditions of their formation. Internal textures of the spherules strikingly resemble textures observed in some chondrules. Definite trends in crystal morphology, crystal width and texture were established with respect to nucleation temperature and bulk composition. Such trends provide a framework for determining the nucleation temperature of chondrules. The only phase to nucleate from the supercooled forsterite-enstatite normative melts was forsterite, which was present in more-than-normative amounts. Highly siliceous glass (~65wt. % SiO₂) was identified interstitially to the forsterite crystals in seven of the spherules and is thought to be present in all. The presence of enstatite and the large proportion of crystals in some meteoritic chondrules implies that they were maintained at temperatures considerably in excess of 600°C at some point in their history.     

Solar and stellar chromospheric contrast

Positions of active regions estimated from observations of the whole solar disk in Caii K _iv during the period 1977–1989 at the Coimbra Astronomical Observatory are compared with the time-dependent latitudinal distribution of background solar magnetic fields and with the latitudinal shifts of boundaries of their polarities. We confirm that the sunspot groups are located near the zonal boundaries between the opposite polarities of the solar background magnetic field during different phases of the two recent consecutive cycles of activity. We demonstrate a probable connection between the increased number of groups and the commencement of poleward migration of zonal boundaries in both hemispheres. But the influence of the dominant convective rolls seems to he still unclear. A new problem of interrelation between the zonal and sector boundaries has also appeared.     

Comparison of an Electrochemical and Luminescence‐Based Oxygen Measuring System for Use in the Biodegradability Testing According to Closed Bottle Test (OECD 301D)

The effects of persistent organic pollutants on the aquatic environment still can hardly be assessed. Therefore, ready biodegradability is a desired key characteristic of chemicals. Accordingly, biodegradation testing is of utmost importance and is a vital part within the risk assessment for organic chemicals. In the closed bottle test (CBT; OECD 301D) the degree of biological degradation of a chemical is assessed by monitoring the oxygen consumption so far with a Clark electrode as standard method. However, this method is time‐consuming, laborious and led to frequent fluctuations of the test results, which limited their validity. Due to these shortcomings, an optical system that enables contact‐free measuring of the oxygen concentration in a closed bottle, based on dynamic luminescence quenching, was examined. The test results were compared to those obtained with the “classical” electrochemical technique (Clark electrode). At first, a basic standard for the handling of the new instrument in the laboratory was developed. Then possible influencing factors, reliability, comparability, and reproducibility of the test results were investigated by running the CBTs in parallel with the electrode and optode method. The findings proved the new optode method to be unambiguously superior to the electrode technique. The frequency of fluctuations of the test results and time and effort necessary for the test run could considerably be reduced. The degradation kinetics of the test substances could be followed easily in the CBT by increasing the measuring points without much additional effort.     

Rockfall Hazard Analysis From Discrete Fracture Network Modelling with Finite Persistence Discontinuities

Developing an accurate representation of the rock mass fabric is a key element in rock fall hazard analysis. The orientation, persistence and density of fractures control the volume and shape of unstable blocks or compartments. In this study, the discrete fracture modelling technique and digital photogrammetry were used to accurately depict the fabric. A volume distribution of unstable blocks was derived combining polyhedral modelling and kinematic analyses. For each block size, probabilities of failure and probabilities of propagation were calculated. A complete energy distribution was obtained by considering, for each block size, its occurrence in the rock mass, its probability of falling, its probability to reach a given location, and the resulting distribution of energies at each location. This distribution was then used with an energy–frequency diagram to assess the hazard.