Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex,Czech Republic: Implications for Variscan orogenesis

The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated _Nd values and initial ⁸⁷Sr/⁸⁶Sr ratios. Five of the eight eclogite samples have high _Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower _Nd values (+ 5.4 to –0.8) and widely variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7096). Such low _Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.     

Comparison between a radiative wind model for be stars and high angular resolution data from the GI2T interferometer

I present theoretical line profiles and intensity maps from an axi-symmetric radiative wind model from a rapidly rotating Be star. The introduction of a viscosity parameter in the latitude-dependent hydrodynamic code enables us to consider the effects of the viscous force in the azimuthal component of momentum equations (Araújo et al. 1994). Both velocity field and density law derived from the hydrodynamic equations have been used for solving the statistical equilibrium equations. By adopting the Sobolev approximation, we could easily obtain a good estimate of both electronic density and hydrogen level populations throughout the envelope. The numerical calculation was performed for parameters characterisic of the Be star Cassiopeiae.     

A new approach for the development and management of brackish karst springs

A new approach to the method of artificial upraising of the water outlet point, for management and development of brackish karst springs, uses the MODKARST model. Brackish karst springs simulation can be used to estimate the necessary upraising of the spring elevation, so that sea-water intrusion is blocked. The consequent freshwater loss to the sea, due to this upraising, can also be estimated. The method has been applied to the periodically brackish karst Almiros spring at Heraklion of Crete, Greece. The spring simulation showed that the sea-water intrusion could be prevented through an artificial upraising of the water-outlet point, realized by the construction of a dam. The exact upraising has been estimated. Freshwater loss to the sea because of this upraising has also been estimated. The model could also be used as a tool for the management of the spring. For example, it was used to assess management options for the spring during the depletion period of the year 1994. The best scenario for the development of the spring during this period has been estimated.     

Occurrence of salt water above fresh water in dynamic equilibrium in a coastal groundwater flow system near De Panne, Belgium

A salt water lens is found above fresh water under the shore between Dunkerque (France) and Nieuwpoort (Belgium). This inverse density distribution is in a dynamic equilibrium. It develops due to the infiltration of salt water on the back shore during high tide. Under this salt water lens, water infiltrated in the adjacent dune area flows towards the sea and discharges at the seabed. This water quality distribution differs from the classic salt water wedge under fresh water described in the literature. Here, the evolution to this water quality distribution is simulated with a density dependent numerical model. A large tidal range, shore morphology and a permeable groundwater reservoir are the main conditions for the observed water quality distribution. By altering these conditions, intermediate water quality distributions between the classic salt water wedge and the one discussed here develop. Based on these simulations, it is expected that similar kinds of inverse density distribution could be present in a number of coastal areas, which have tides, a gently sloping shore and a permeable substratum.     

安徽凤阳和张八岭地区含金石英脉的40Ar/39Ar年龄及其地质意义

用快中子活化法测定了安徽凤阳和张八岭地区朱顶、毛山和上成3个金矿床第一阶段晚期和第二阶段的含金石英脉,石英的阶段加热40Ar/39Ar坪年龄值域为(116.1±0.6～118.3±0.5)Ma,分别与其最小视年龄和等时线年龄接近.坪年龄、最小视年龄和等时线年龄3种年龄值域为(113.4±0.4～118.3±0.5)Ma,可以作为石英的形成年龄域. 根据含金石英脉和围岩的空间关系,该年龄值域作为石英脉金矿的形成年龄是合理可靠的.金矿床形成于早白垩世阿普特期,与此时郯庐断裂带略带右行走滑正断层活动一致.     

δO of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater

Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ¹⁸O values of the diagenetic water within the range of meteoric waters, the δ¹⁸O(SiO₂) yield temperatures in agreement with the apparent secondary origin of this phase. The δ¹⁸O(CO₃²⁻) range, with a certain continuity, between −10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ¹⁸O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ¹⁸O(PO₄³⁻) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ¹⁸O(PO₄³⁻) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ¹⁸O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.     

地震前兆仪器嵌入TCP/IP协议的初步试验

根据“十五”总体设计方案的要求，对TCP／IP协议在地震前兆仪器上的实现进行了试验，在有关设备上进行了程序开发，取得了预期的效果。     

Study of crustal structure with S—wave data from Maqen—Jingbian profile

2-D crustal velocity structure and vp/vs are obtained by processing and interpretation of S-wave data from Maqen-Jingbian deep seismic sounding(DSS)profile.The result shows that there exist obvious differences in 2-D S-wave velocity structure and vp/vs ratio structure along the profile.The S-wave velocities are low and vp/vs ration is high for the westem section of the profile and Haiyuan region,while they are normal for the middle and eastern sections.The changes in lithologic characters of two major anomalous zones are discussed according to lateral variation of S-wave velocity structure and vp/vs ratio structure.It is concluded that the development and occurrence of the Haiyuan strong earthquake is not only related to tectonic activities,but also to lithologic characters of the region.     

巴楚-伽师Ms6.8地震地磁异常特点分析

通过分析、比较1996--2003年喀什地震台站记录到的新疆伽师及附近地区发生的多次6级地震的地磁前兆异常特征，发现在这几组地震活动过程中喀什地震台的地磁表现出不同的异常特征，说明与地震破裂特征有更深层次的相关性，且地磁响应比异常和总强度差值异常在一定程度上反映了台站周围小范围的震源区介质电性结构的变化。巴楚-伽师6．8级地震前地磁异常特征并不十分突出，有别于1996—1998年伽师强震群震前地磁异常量较丰富的特点。     

GEOLOGICAL MARKS OF A POSSIBLE EXTRATERRESTRIAL IMPACT EVENT ON THE BOUNDARY BETWEEN SINIAN/CAMBRIAN IN TIANMENSHAN IN WESTERN HUNAN

Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary.