Tracing the source of metals in Geogas from metal deposits in a loess-covered region北大核心CSCD

In order to test the distribution characteristics of metallogenic elements and the application effectiveness of the traee elements and REE for tracing the source of Geogas anomaly, the distribution characteristics of metallogenetic elements .trace elements and REE in different media of the Jiaolongzhang Pb-Zn deposit underneath the loess have been studied in this paper. Results indicate that the distribution characteristics of Geogas anomalous elements over the concealed orebodies are coincided with those of the enriched elements of ores, while the distribution characteristics of trace elements and REE in background Geogas samples are distinctly different from those of other media, indicating that the source of background Geogas materials is influenced by various factors( geological bodies, lab environment and blank reagent). The similar distribution characteristics of the trace elements in the Geogas samples of anomalous areas and in the ores suggested that Geogas anomaly is affected by concealed orebodies in depth. The difference between REE patterns of the Geogas samples of the anomalous area and those of other solid media might be caused by inadequate analytical precision and low collecting efficiency of the instrument. It is believed that the REE tracing method can provide the information on the source of Geogas anomaly if the analytical precision and collecting efficiency of REE could be constantly increased.     

Rock associations and their spatial-Temporal variations of the early mesozoic igneous rocks in the NE Asia: Constraints on the initial subduction timing of the paleo-pacific plate北大核心CSCD

This paper summarizes rook associations and spatial-Temporal variations of the early Mesozoic igneous rocks in the NE Asia, with the aim of revealing the initial subduction timing of the Paleo-Pacific Plate beneath the Eurasia, and the relationships between the early Mesozoic magmatisms and the Paleo-Asian tectonic system, Mongol-Okhotsk tectonic system, and amalgamation of the Yangtze and North China cratons. Dating results indicate that the early Mesozoic magmatisms in the NE Asia can be subdivided into three stages, i.e., Early-Middle Triassic, Late Triassic, and Early Jurassic. The early Mesozoic calc-Alkaline magmatisms within the Erguna Massif reveal southward subduction of the Mongol-Okhotsk oceanic plate. The Triassic alkaline and bimodal magmatisms within the northern margin of the North China Craton indicate an extensional environment related to the final closure of the Paleo-Asian Ocean. The Late Triassic A-Type rhyo- lites and bimodal magmatisms, together with the Late Triassic stable sedimentary rocks, in eastern Heilongjiang-Jilin provinces, reveal an extensional environment and passive continental margin setting, whereas the Early Jurassic calc-Alkaline magmatisms and its compositional variations, together with the coeval accretionary complex, reveal the onset of the Paleo- Pacific plate beneath the Euirasian continent.     

Effects of nonlinear model response on allocation of streamflow depletion: exemplified by the case of Beaver Creek,USA

Anomalies found when apportioning responsibility for streamflow depletion are examined. The anomalies arise when responsibility is assigned to the two states that contribute to depletion of Beaver Creek in the Republican River Basin in the United States. The apportioning procedure for this basin presumes that the sum of streamflow depletions, computed by comparing simulation model runs with and without groundwater pumping from individual states, approximates the streamflow depletion when both states are pumping. In the case study presented here, this presumed superposition fails dramatically. The stream drying and aquifer-storage depletion, as represented in the simulation model used for allocation, are examined in detail to understand the hydrologic and numerical basis for the severe nonlinear response. Users of apportioning procedures that rely on superposition should be aware of the presence and likely magnitude of nonlinear responses in modeling tools.     

Heat tracing to examine seasonal groundwater flow beneath a low-gradient stream in rural central Illinois,USA

The thermal profile of a streambed is affected by a number of factors including: temperatures of stream water and groundwater, hydraulic conductivity, thermal conductivity, heat capacity of the streambed, and the geometry of hyporheic flow paths. Changes in these parameters over time cause changes in thermal profiles. In this study, temperature data were collected at depths of 30, 60, 90 and 150 cm at six streambed wells 5 m apart along the thalweg of Little Kickapoo Creek, in rural central Illinois, USA. This is a third-order low-gradient baseflow-fed stream. A positive temperature gradient with inflection at 90-cm depth was observed during the summer period. A negative temperature gradient with inflection at 30 cm was observed during the winter period, which suggests greater influence of stream-water temperatures in the substrate during the summer. Thermal models of the streambed were built using VS2DHI to simulate the thermal profiles observed in the field. Comparison of the parameters along with analysis of temperature envelopes and Peclet numbers suggested greater upwelling and stability in temperatures during the winter than during the summer. Upwelling was more pronounced in the downstream reach of the pool in the riffle and pool sequence.     

Long-term cooling history of the Albertine Rift: new evidence from the western rift shoulder,D.R. Congo

To determine the long-term landscape evolution of the Albertine Rift in East Africa, low-temperature thermochronology was applied and the cooling history constrained using thermal history modelling. Acquired results reveal (1) “old” cooling ages, with predominantly Devonian to Carboniferous apatite fission-track ages, Ordovician to Silurian zircon (U–Th)/He ages and Jurassic to Cretaceous apatite (U–Th–Sm)/He ages; (2) protracted cooling histories of the western rift shoulder with major phases of exhumation in mid-Palaeozoic and Palaeogene to Neogene times; (3) low Palaeozoic and Neogene erosion rates. This indicates a long residence time of the analysed samples in the uppermost crust, with the current landscape surface at a near-surface position for hundreds of million years. Apatite He cooling ages and thermal history models indicate moderate reheating in Jurassic to Cretaceous times. Together with the cooling age distribution, a possible Albertine high with a distinct relief can be inferred that might have been a source area for the Congo Basin.