Strontium-Isotope Studies Of Chloride-Contaminated Groundwater,Denmark

Saline groundwater has three principal origins in Denmark: 1) Seawater infiltration into nearcoastal aquifers, 2) saline formation water in aquifers of marine sedimentary origin, and 3) intrusion of brines from deep saline formation waters and evaporitic deposits in the subsurface. Strontium-isotope studies of chloride-contaminated groundwater from a Quaternary sandy aquifer at Stautrup Waterworks, Denmark, indicate that the groundwater is heavily influenced by saline formation water from underlying Oligocene marine mica clay. Thus, strontium isotopic hydrochemical criteria were successfully used to identify the sources of saline groundwater.

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RESUMEN: La salinidad en las aguas subterráneas de Dinamarca tiene tres orígenes principales: 1) Infiltración de agua marina en acuíferos costeros, 2) agua de formación salina en acuíferos de origen sedimentario marino, y 3) intrusión de salmueras procedentes de aguas salinas de formaciones profundas y de depósitos evaporíticos subterráneos. Estudios isotópicos del estronico en las aguas subterráneas contaminadas or cloruros en un acuífero arenoso Cuaternario en Stautrup Waterworks, Dinamarca, indican que el agua está fuertement influenciada por el agua de formación salina correspondiente a una capa inferior de micas arcillosas oligocénicas. Por tanto, los criterios hidroquímicos isotópicos se pudieron utilizar satisfactoriamente para identificar las fuentes de salinidad de las aguas subterráneas.

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RéSUMé: La salinité des aux souterraines du Danemark possède trois origines principales: 1) l'intrusion d'eau de mer dans les aquifères littoraux, 2) les eaux connées des sédiments marins constituant l'aquifère, 3) la remontée dans les aquifères superficiels de saumures provenant d'eaux connées de sédiments et de formations évaporitiques profonds. L'étude des isotopes du strontium d'eaux souterraines chargées en chlorures d'un aquifère sableux du Quaternaire du champ captant de Stautrup (Danemark) montre que le chimisme des eaux souterraines est fortement marqué par les eaux connées des argiles micacées marines sous-jacentes de l'Oligocène. Des critères hydrochimiques des isotopes du strontium ont par conséquent permis d'identifier les sources de la salinité d'eaux souterraines.

     

Non-recognition of continental tholeiites using the Ti-Y-Zr diagram

Continental tholeiites cannot be identified using the Ti-Y-Zr diagram. Two-hundred and thirteen analyses from 16 localities representing 7 continental tholeiitic provinces all plot outside the within-plate basalt field of this diagram.Analyses representing about 50% of the population plot in the ocean-floor basalt field, the rest plots in the calc-alkali basalt field. Therefore problems might arise when attempts are made to classify ancient tectonomagmatic environments using the Ti-Y-Zr diagram.     

Palaeomagnetic distortion modelling and possible recovery by inversion

A robust finite-element technique is presented for computation of both the internal demagnetization effects and magnetic terrain effects in bodies with arbitrary shape and arbitrary susceptibility distribution. This method facilitates a flexible analysis of the palaeomagnetic deflection problem. Tests on geologically realistic settings of highly magnetic rocks demonstrate that deflections of several degrees may occur even for relatively simple two-dimensional models. Similarly, the magnetic intensity may well be biased by 5-15% by demagnetization effects. The present paper focuses on deflections and intensity variations inside the magnetized body, where we find a systematic shallowing of inclination for bodies with a horizontal elongation. Because the bodies sampled at a typical palaeomagnetic site will have a dominant direction of elongation, the magnetic deflection effect will tend to impose a systematic bias which doesn’t average out. An inversion-based procedure for elimination of the deflection effect is presented. It requires that the magnetic body is quite homogeneous and that its surface geometry is known, as may be the case for historical lava flows. Tests demonstrate that in order to recover both ambient palaeofield direction and the effective susceptibility at blocking temperature it is necessary to sample near strong topographic elements in the magnetic body. Since the surface geometry rarely is known it is proposed as an alternative to inversion that an effective susceptibility is assessed and a horizontal slab correction is applied for samples taken far from topographical features. When shape geometry is unknown and no correction applied, palaeomagnetic conclusions must take into account the possible bias from internal demagnetization and magnetic terrain effects.     

A New Magnetically Active Binary System Discovered in Yunnan-Hong Kong Wide Field Survey

We present a newly discovered magnetically active binary system detected by Yunnan-Hong Kong wide field survey, with an orbital period of 0.60286 days. Two color photometry for the system was performed using the 1 m Cassegrain telescope of Yunnan Observatories with its CCD (Charge-Coupled Device) camera. In the observed light curves, there are clearly different light maxima existed in the out-of-eclipse regions. We made spectroscopic observations for the binary system using the 2.4 m telescope and YFOSC (Yunnan Faint Object Spectrograph and Camera) of Lijiang station of Yunnan Observatories, China. The radial velocity curve was derived for primary star of the binary system. The primary star exhibited strong chromospheric activity, which confirms that the distortion of the light curves results from the starspot activity on the primary star. Through analyzing the light curves and RV (Radial Velocity) curve mentioned above by means of the W-D (Wilson-Devinney) code, orbital parameters and starspot configuration of the binary system are obtained. Finally, we have discussed the properties of the binary system, and given the prospects on the future work.     

香港花岗岩地貌地质旅游的开发

地质旅游利用现有的地质资源，以一种崭新的角度去发展可持续性的旅游景点。香港地少人多，发展旅游吸引点是极度困难的。香港陆地约有30％为花岗岩覆盖，其中的一半已在城市之下，其余的则拥有相当吸引人的地质景象，有极大潜力发展地质旅游。除吸引地质生态有关游客外，在花岗岩地区开发地质旅游，更容易普及地球科学，同时增强公众对地质地貌之欣赏能力，提高环保及地质保护意识。不过，于香港花岗岩区发展地质旅游所遇到的困难亦不少，主要来自规划、行政及安全的问题，当中需要政府、地区民众及地质旅游工作者并肩合作，寻求最佳解决方法。     

Radioactive disequilibria and apparent ages of secondary uranium minerals from Sweden

Thorium and uranium nuclides have been measured using high-resolution alpha spectrometry in order to examine the potential of secondary uranium minerals for disequilibrium dating purposes. Mineral ages are proportional to the distance below the bedrock surface. Minerals coated on the bedrock surface are usually postglacial with apparent ages below 10 000 years. Minerals collected from cracks and fissures 3–100 mm below the bedrock surface give apparent ages from 14 000 years to equilibrium ages of more than 300 000 years. Samples from drill-cores collected more than one metre below the surface approach equilibrium. Some mineral samples have lost uranium, indicating open system conditions. The examined material does not allow the establishment of a definite relationship between glaciation and mineral ages.     

兰州-西宁-银川城市带与西部开发

通过对有关城市、区域的统计分析,在评述兰州-西宁-银川城市带基本特征的基础上,重点讨论其在西部大开发中四个方面的地位作用：我国内陆腹地的战略要地和开发据点,沟通我国东西部间、我国与中亚、欧洲国家间的桥梁和纽带,保障国家资源安全的能源重化工基地和重要进口通道,保障国家生态安全的重点生态建设区。并针对其在内部结构、市场化、开放度方面的主要问题,指出其发展趋势和战略选择：加快城市带交通通道建设,将潜在资源优势转化为现实经济优势,创造局部优势投资环境和开放社会,重视教育、科技和生态建设。     

Changing compositions in the Iceland plume; Isotopic and elemental constraints from the Paleogene Faroe flood basalts

Elemental and Sr, Nd, Hf and high precision Pb isotopic data are presented from 59 low-Ti and high-Ti lavas from the syn-break up part of the Faroe Flood Basalt Province. The depleted MORB-like low-Ti lavas erupted in the rift zone between the Faroe Islands and central East Greenland around the time of break up of the North Atlantic have isotopic end-member compositions different from the depleted Iceland lavas. We suggest that the main low-Ti mantle component is NAEM (North Atlantic End-Member (Ellam and Stuart, 2000, J. Petrol. 41, 919) and that the ²⁰⁷Pb/²⁰⁴Pb value of the component should be 15.35 and ε_Hf = + 16.5. NAEM is the main depleted component in the early Iceland plume. This is supported by high mantle potential temperatures (up to 1550 °C) calculated for the source of the low-Ti basalts. The unique mantle isotopic composition of NAEM with low ²⁰⁶Pb/²⁰⁴Pb (17.5) and Δ7/4Pb (? 3.8) precludes a derivation from recycled MORB lithosphere. Instead we suggest that NAEM represents a plume component of recycled depleted Archean lithospheric mantle that was further depleted ~ 500 Ma ago, possibly in connection with the recycling process. Two other isotopic end-members are required to explain the variation of the Faroe low-Ti basalts: (1) The Faroe depleted component (FDC), with ⁸⁷Sr/⁸⁶Sr = 0.7025, ε_Nd = + 11, ε_Hf = + 19.5, ²⁰⁶Pb/²⁰⁴Pb = 18.2, ²⁰⁷Pb/²⁰⁴Pb = 15.454 and ²⁰⁸Pb/²⁰⁴Pb = 37.75, which is similar in composition to some Atlantic MORB and is regarded as a local upper mantle source. (2) An enriched EM-type component similar in geochemistry to the Icelandic Öræfajökull lavas. This component is believed to be recycled pelagic sediments in the plume but it can alternatively be a local crustal or lithospheric mantle component. The enriched Faroe high-Ti lavas erupted inland from the rift have isotopic compositions very similar to the enriched Icelandic neo-volcanics and these lava suites apparently share the two enriched plume end-members IE1 and IE2 (Geochim. Cosmochim. Acta 68, 2, 2004). The lack of mixing between high and low-Ti melts at the time of break up, is explained by a zoned plume where only low-Ti sources were present beneath the rift zone surrounded by high-Ti sources on both sides of the rift. The enriched plume components in the high-Ti lava sequences on the Faroe Islands and central East Greenland changed rapidly on a ka-scale which implies, from geophysical modelling, that this area was positioned above the center of the plume, and that the Iceland plume was centered under the Atlantic ridge already from the Paleocene.     

Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C

Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine.The results show low temperature CH4 production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH4 source trapped in the crystal structure of the olivine showed no signs of incorporated CH4. Also, the available sources of organic carbon were not enough to support the total amount of CH4 detected in our experiments. There was also a linear relationship between silica release into solution and the net CH4 accumulation into the incubation bottle headspaces suggesting that CH4 formation under these conditions could be a qualitative indicator of olivine dissolution.It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH4, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH4 formation both on Earth and on other terrestrial bodies.