Synorogenic melting of mafic lower crust: constraints from geochronology, petrology and Sr, Nd, Pb and O isotope geochemistry of quartz diorites (Damara orogen, Namibia)

Quartz diorites represent the earliest (ca. 540 Ma) and most primitive plutonic rocks in the Pan African Damara belt and they pre-date the main phase of high-T regional metamorphism. Two suites of synorogenic quartz diorites are unusual among Damaran intrusive rocks in their elemental and isotopic features. Comparison of the diorite compositions with melts from amphibolite-dehydration melting experiments points to a garnet-bearing meta-tholeiite, probably enriched in K₂O, as a likely source rock. Partial melting processes generated mafic (ca. 50 wt% SiO₂) quartz diorites in the deep crust at temperatures of between 1,000 and 1,100 °C, based on comparison with experimental results and similar temperature estimates based on P₂O₅ solubility in mafic rocks. Subsequently, the quartz diorites evolved by multistage, polybaric differentiation processes including fractional crystallization of mainly hornblende and plagioclase and assimilation of felsic basement gneisses. Although their chemical characteristics (high LILE, low HFSE) resemble those of other quartz diorites with calc-alkaline affinities, they differ in their enriched Sr (initial ⁸⁷Sr/⁸⁶Sr: 0.70943-0.71285), Nd (initial ) Nd: -9.1 to -15.2 ) and O ('¹⁸O: 6.8-8.1‰) isotope compositions. Neodymium model ages (T_DM) that range from 1.7 to 2.2 Ga and large variation in ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb indicates involvement of ancient crustal material. Lead (²⁰⁶Pb/²⁰⁴Pb: 17.08-17.23, ²⁰⁷Pb/²⁰⁴Pb: 15.53-15.62, ²⁰⁸Pb/²⁰⁴Pb: 37.71-38.16) isotope compositions are strongly retarded, indicating that the source underwent a pre-Pan-African U/Pb fractionation and U depletion. It is proposed that the quartz diorites originated by synorogenic high temperature melting of mafic lower crust. This contrasts with previous suggestions favouring an origin of these rocks by melting of an enriched mantle during Pan-African times with characteristics modified by subduction of oceanic crust and sedimentary rocks.     

Investigating the Effects of Different LED Wavelengths on Aggregation and Swimming Behavior of Chub Mackerel (Scomber japonicus)

Ocean Science Journal - Efficient fish aggregation systems are essential for catching chub mackerel (Scomber japonicus), which is a major target of purse seine fisheries in South Korea. To aid the...     

Characteristics and Ecosystem Changes of Marine Algal Communities in Wangdol-cho on the East Coast of Korea

Ocean Science Journal - This study sought to examine the characteristics and patterns of marine algae community changes in Wangdol-cho in order to establish a theoretical basis for the development...     

Extending the Qualitative Capabilities of GIS: Computer-Aided Qualitative GIS

A number of approaches for integrating GIS and qualitative research have emerged in recent years, as part of a resurgence of interest in mixed methods research in geography. These efforts to integrate qualitative data and qualitative analysis techniques complement a longstanding focus in GIScience upon ways of handling qualitative forms of spatial data and reasoning in digital environments, and extend engagements with 'the qualitative' in GIScience to include discussions of research methodologies. This article contributes to these emerging qualitative GIS methodologies by describing the structures and functions of 'computer-aided qualitative GIS' (CAQ-GIS), an approach for storing and analyzing qualitative, quantitative, and geovisual data in both GIS and computer aided data analysis software. CAQ-GIS uses modified structures from conventional desktop GIS to support storage of qualitative data and analytical codes, together with a parallel coding and analysis process carried out with GIS and a computer-aided data analysis software package. The inductive mixed methods analysis potential of CAQ-GIS is demonstrated with examples from research on children's urban geographies.     

Landslide susceptibility mapping using random forest and boosted tree models in Pyeong-Chang,Korea

Landslides susceptibility maps were constructed in the Pyeong-Chang area, Korea, using the Random Forest and Boosted Tree models. Landslide locations were randomly selected in a 50/50 ratio for training and validation of the models. Seventeen landslide-related factors were extracted and constructed in a spatial database. The relationships between the observed landslide locations and these factors were identified by using the two models. The models were used to generate a landslide susceptibility map and the importance of the factors was calculated. Finally, the landslide susceptibility maps were validated. Finally, landslide susceptibility maps were generated. For the Random Forest model, the validation accuracy in regression and classification algorithms showed 79.34 and 79.18%, respectively, and for the Boosted Tree model, these were 84.87 and 85.98%, respectively. The two models showed satisfactory accuracies, and the Boosted Tree model showed better results than the Random Forest model.     

The solubility of copper in high-temperature magmatic vapors: A quest for the significance of various chloride and sulfide complexes

We conducted experiments to determine the effect of various chemical components (NaCl, KCl, HCl, FeCl₂, H₂S, SO₂) on the solubility of Cu in single phase aqueous vapors at 1000 °C and 150 MPa. The experiments were conducted in Au₉₇Cu₃ alloy capsules buffering Cu activities at 0.01. The volatile phase was sampled at run conditions by the entrapment of synthetic fluid inclusions in quartz. To test if the volatile phase had reached equilibrium before the isolation of the inclusions by fracture healing, we trapped two inclusion generations, one in an initially prefractured chip and another in a quartz chip that was fractured in situ during the experiments. The synthetic fluid inclusions were subsequently analyzed by laser ablation inductively coupled plasma mass spectrometry. In pure water, the apparent solubility of Cu is below the limits of detection of 6 μg/g, showing the low stability of hydroxy Cu complexes at our experimental conditions. The presence of alkali chlorides supports modest Cu solubility likely in the form of NaCuCl₂ and KCuCl₂ complexes. In the H₂O-H₂S (+SiO₂ and Au₉₇Cu₃) system at an fH₂S of 10.4 MPa the apparent solubility of Cu is lower by a factor of ∼5 than that in a S-free 0.5 m NaCl solution, showing that copper hydrosulfide complexes are only moderately stable at these conditions. Addition of 4.7 mol% of sulfur to the H₂O-NaCl system at an fO₂ of 0.4 log units below the Ni-NiO buffer, yielding dominantly H₂S species, results in only a moderate increase in apparent Cu solubility, which diminishes in the presence of HCl. The addition of KCl results in a strong increase of apparent Cu solubility in the presence of H₂S. The solubility of Cu increases with the fugacity of oxygen in both the H₂O-NaCl and the H₂O-S-NaCl system following an approximately fourth root relationship as expected based on the stoichiometry of the involved redox reactions. Replacement of NaCl by FeCl₂ exerted only a minor effect on the Cu solubility.Results of our experiments, combined with thermochemical data obtained by ab initio quantum chemical calculations, suggest dissolution of Cu dominantly as Na(/K)CuCl₂, Na(/K)Cu(HS)_2, H₂SCuHS, and Na(/K)ClCuHS, the relative abundance of which are dictated by the H₂S/total chloride and HCl/alkali chloride ratios.     

Simulating the diurnal cycle of rainfall in global climate models: resolution versus parameterization

The effects of horizontal resolution and the treatment of convection on simulation of the diurnal cycle of precipitation during boreal summer are analyzed in several innovative weather and climate model integrations. The simulations include: season-long integrations of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit clouds and convection; year-long integrations of the operational Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts at three resolutions (125, 39 and 16 km); seasonal simulations of the same model at 10 km resolution; and seasonal simulations of the National Center for Atmospheric Research (NCAR) low-resolution climate model with and without an embedded two-dimensional cloud-resolving model in each grid box. NICAM with explicit convection simulates best the phase of the diurnal cycle, as well as many regional features such as rainfall triggered by advancing sea breezes or high topography. However, NICAM greatly overestimates mean rainfall and the magnitude of the diurnal cycle. Introduction of an embedded cloud model within the NCAR model significantly improves global statistics of the seasonal mean and diurnal cycle of rainfall, as well as many regional features. However, errors often remain larger than for the other higher-resolution models. Increasing resolution alone has little impact on the timing of daily rainfall in IFS with parameterized convection, yet the amplitude of the diurnal cycle does improve along with the representation of mean rainfall. Variations during the day in atmospheric prognostic fields appear quite similar among models, suggesting that the distinctive treatments of model physics account for the differences in representing the diurnal cycle of precipitation.     

Non-parametric simulations-based conditional stochastic predictions of geologic heterogeneities and leakage potentials for hypothetical CO2 sequestration sites

The present study focuses on understanding the leakage potentials of the stored supercritical CO₂ plume through caprocks generated in geostatistically created heterogeneous media. For this purpose, two hypothetical cases with different geostatistical features were developed, and two conditional geostatistical simulation models (i.e., sequential indicator simulation or SISIM and generalized coupled Markov chain or GCMC) were applied for the stochastic characterizations of the heterogeneities. Then, predictive CO₂ plume migration simulations based on stochastic realizations were performed and summarized. In the geostatistical simulations, the results from the GCMC model showed better performance than those of the SISIM model for the strongly non-stationary case, while SISIM models showed reasonable performance for the weakly non-stationary case in terms of low-permeability lenses characterization. In the subsequent predictive simulations of CO₂ plume migration, the observations in the geostatistical simulations were confirmed and the GCMC-based predictions showed underestimations in CO₂ leakage in the stationary case, while the SISIM-based predictions showed considerable overestimations in the non-stationary case. The overall results suggest that: (1) proper characterization of low-permeability layering is significantly important in the prediction of CO₂ plume behavior, especially for the leakage potential of CO₂ and (2) appropriate geostatistical techniques must be selectively employed considering the degree of stationarity of the targeting fields to minimize the uncertainties in the predictions.     

Effects of Resonances in Corrugated Horn Antennas for a 22-GHz Balancing Radiometer

The Stratospheric WAter vapor RAdiometer (SWARA) is a microwave radiometer designed for ground-based measurements of water vapor (H₂O) in the middle atmosphere (20 to 80 km), including the stratosphere and mesosphere. The instrument is operating in a noncryogenic balancing calibration mode. Since its deployment, features have been observed in the spectrum which can be attributed to resonant variations of the antenna pattern of the corrugated horn. This paper presents copolar and crosspolar antenna pattern measurements of two sister antennas of the SWARA horn, as well as water vapor measurements from both antennas on the ground-based microwave radiometer MI ddle Atmospheric WAter vapor RA diometer. We show that small irregularities in the frequency spectrum at the -20-dB level are visible in the copolar pattern, which, due to the balancing operation scheme used for the radiometer, lead to features in the spectrum that have the same or even higher brightness temperature as the line of interest.