Independent ages of magmatic and hydrothermal activity in alkaline igneous rocks: The Motzfeldt Centre,Gardar Province,South Greenland     

J.?A.?McCreath  A.?A.?FinchEmail author  S.?L.?Simonsen  C.?H.?Donaldson  A.?Armour-Brown 《Contributions to Mineralogy and Petrology》2012,163(6):967-982

The Motzfeldt Centre is one of four major alkaline centres belonging to the Igaliko complex, part of the Mid-Proterozoic Gardar province of South Greenland. Motzfeldt comprises syenites and nepheline syenites displaying complex magmatic and subsolidus histories. Ta, Nb and REE-rich zones are associated with a pervasive hydrothermal alteration process in the North and East of the complex, part of a subdivision of the Centre called the Motzfeldt Sø Formation (MSF). The zircons from the MSF show textures that are both magmatic and altered, whereas the textures of pyrochlore have a predominantly subsolidus chemistry. We compare and contrast the radiogenic isotope geochemistry of the zircon and pyrochlore to obtain independent age estimates of the magmatic and hydrothermal episodes. Selected analyses of magmatic zircons are concordant with an age of 1,273 ± 6 Ma. Altered zircons are normally discordant with one intercept at 1,261 ± 28 Ma and the other at 349 ± 49 Ma. This younger age would appear on face value to date the hydrothermal event at Motzfeldt to ~900 Ma after the magmatism. However, the Pb–Pb isotope systematics from altered pyrochlore define an isochron age of 1,267 ± 6 Ma for isotopic closure of the pyrochlore following alteration during the subsolidus. There is no known magmatic event in Southern Greenland at ~350 Ma and discordant points have high common lead. We therefore infer that the younger intercept age is spurious. The overlap between the magmatic U–Pb zircon and the Pb–Pb pyrochlore age suggests that alteration of the Motzfeldt centre occurred shortly after magmatism.  相似文献   

A strain-induced freshwater pump in the Liverpool Bay ROFI     

Matthew?Robert?PalmerEmail author  Jeff?A.?Polton 《Ocean Dynamics》2011,61(11):1905-1915

Liverpool Bay is a region of freshwater influence which receives significant freshwater loading from a number of major English and Welsh rivers. Strong tidal current flow interacts with a persistent freshwater-induced horizontal density gradient to produce strain-induced periodic stratification (SIPS). Recent work (Palmer in Ocean Dyn 60:219–226, 2010; Verspecht et al. in Geophys Res Lett 37:L18602, 2010) has identified significant modification to tidal ellipses in Liverpool Bay during stratification due to an associated reduction in pycnocline eddy viscosity. Palmer (Ocean Dyn 60:219–226, 2010) identified that this modification results in asymmetry in flow in the upper and lower layers capable of permanently transporting freshwater away from the Welsh coastline via a SIPS pumping mechanism. Observational data from a new set of observations from the Irish Sea Observatory site B confirm these results; the measured residual flow is 4.0 cm s⁻¹ to the north in the surface mixed layer and 2.4 cm s⁻¹ to the south in the bottom mixed layer. A realistically forced 3D hydrodynamic ocean model POLCOMS succeeds in reproducing many of the characteristics of flow and vertical density structure at site B and is used to estimate the transport of water through a transect WT that runs parallel with the Welsh coast. Model results show that SIPS is the dominant steady state, occurring for 78.2% of the time whilst enduring stratification exists only 21.0% of the year and enduring mixed periods, <1%. SIPS produces a persistent offshore flow of freshened surface water throughout the year. The estimated net flux of water in the surface mixed layer is 327 km³ year ⁻¹, of which 281 km³ year⁻¹ is attributable to SIPS periods. Whilst the freshwater component of this flux is small, the net flux of freshwater through WT during SIPS is significant, the model estimates 1.69 km³ year⁻¹ of freshwater to be transported away from the coast attributable to SIPS periods equivalent to 23% of annual average river flow from the four catchment areas feeding Liverpool Bay. The results show SIPS pumping to be an important process in determining the fate of freshwater and associated loads entering Liverpool Bay.  相似文献   

Effects of basin activities and land use on water quality trends in Tahtali Basin, Turkey   总被引：1，自引：1，他引：0  

Şebnem Elçi  Pelin Selçuk 《Environmental Earth Sciences》2013,68(6):1591-1598

Bi-weekly water quality data from seven monitoring stations located within Tahtali Watershed, ?zmir, Turkey and digital land use/land cover data of the same watershed are analyzed in this study. To examine the changes in land use associated with urbanization, the satellite images of the main pool of the Tahtali reservoir prior to filling and subsequent to filling, respectively, are analyzed. Aerial photos of the basin taken in 1995 (October) are compared with images taken in 2005 (November) from the IKONOS satellite through use of several GIS techniques. New residential buildings, greenhouses, and industrial buildings are presented in separate layers, and changes in basin activities are quantified. The effects of urbanization on the water quality are investigated through statistical analysis. The seasonal Kendall test is applied to the water quality parameters monitored bi-weekly at seven stations within the basin for the duration 1997–2005. There was no trend in phosphorus, but there was a negative trend in boron and nitrate and a positive trend in the parameters of biological oxygen demand (BOD) and chemical oxygen demand (COD). The improvement in nitrate concentrations is attributed to the new regulations on the use of fertilizers in greenhouses. However, increase of BOD and COD concentrations is related to the growing settlement areas and industrial zones, which point to the insufficient wastewater treatment within the basin. Soil erosion within the basin is also quantified by the universal soil loss equation using available maps. Estimated total soil loss rate increased about 2.5 times that of 1995 when the changed land use composition in 2005 is considered in the calculations.  相似文献   

Depositional environment in and around Tamiraparani estuary,and off Tuticorin,Tamil Nadu,India: clues from grain size studies     

A.?Solai  M.?Suresh?GandhiEmail author  K.?Chandrasekaran  V.?Ram?Mohan 《Arabian Journal of Geosciences》2013,6(7):2419-2446

The sediments of the estuaries and offshore Tuticorin along the southern coast of Tamil Nadu were studied for their textural variation. Ninety sediment samples were collected from three sectors (river, estuary, offshore) on the basis of prevailing energy conditions and oceanographic parameters. Frequency curves show unimodal to bimodal in nature. Offshore samples also fall in bimodal with medium and fine sand where sediment is additionally deposited by the Tamiraparani River. The mean values ranging from 1.69 to 2.01 φ with medium to fine sand. The fine sand in the riverine region indicates the depositional nature of the sediments. In pre-monsoon, the standard deviation ranges from 0.29 to 0.81 φ, which falls in the very well sorted to moderately well sorted. Estuary ranges from 0.63 to 1.30 φ, with moderately sorted, whereas in the marine sediments ranges from 0.4 to 1.01 φ, with moderately to moderately well- sorted and some patches of poorly sorted is observed. In both monsoons, the grain size variations are mostly influenced in river and offshore samples compared to the estuaries. The CM pattern indicates the deposition of sediments in graded suspension. In estuary, the sediments are medium sand with moderately to poorly sorted, fine skewed which are indicative of denudation processes taking place there. In marine, the sediments are medium-to-fine, moderately-to-well sorted, and fine skewed to very fine skewed sediments, probably as a result of the influence of palaeo-sediments deposited by rivers from inland as well as by waves and currents from offshore. Further, the marine samples also highlight depositional processes.  相似文献   

Approximate retrieval of the point source in anisotropic media: numerical modelling by indirect parametrization of the source   总被引：1，自引：0，他引：1  

Jan &#;&#;´lený  Václav Vavry&#;uk 《Geophysical Journal International》2000,143(3):700-708

  相似文献   

Fluid flow and pore pressure development throughout the evolution of a trough mouth fan,western Barents Sea     

Jaume Llopart  Roger Urgeles  Carl Fredrik Forsberg  Angelo Camerlenghi  Maarten Vanneste  Michele Rebesco  Renata Giulia Lucchi  Denise Christina Rüther  Hendrik Lantzsch 《Basin Research》2019,31(3):487-513

Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure.  相似文献   

Determination of surfactant activity and anionic detergents in seawater and sea surface microlayer in the Mediterranean     

B Ćosović  V Ẑutić  V Vojvodić  T Pleše 《Marine Chemistry》1985,17(2):127-139

The study of the physico-chemical properties and the determination of different classes of organic substances in the sea are of substantial interest and importance for understanding biogeochemical processes in the sea. The preferable method should be sensitive enough for direct measurement without pretreatment procedures in order to avoid changes in the composition of organic substances initially present in the sample.Surfactant activity data are presented here as measured by electrochemical methods during 1979, 1980 and 1981 in samples from open waters of the Western Mediterranean, and in a few characteristic coastal areas of the Adriatic Sea with different biological activity and different influence of man's activities. Data on sea surface microlayer samples collected during 1977, 1978 and 1981 at different locations and seasons in the Rijeka Bay, which is an integral part of the Adriatic Sea, are presented and discussed in more detail.It was found that the type and concentration of natural surface active material vary within different Mediterranean regions and along the depth profile of the water column.Petroleum hydrocarbons and detergents were found to be prevalent pollutants responsible for high surfactant activity values. Pollution effects are most pronounced in the sea surface microlayer.Electrochemical methods are proposed for research and monitoring of surface-active substances in the sea.  相似文献   

Numerical study of the cloud seeding effects     

Prof. Dr. M. Ćurić M.Sc.  M.Sc. D. Janc 《Meteorology and Atmospheric Physics》1990,42(2):145-164

The microphysical model with the bulk water parameterization is applied to simulated both contact and deposition nucleation as well as the imersion freezing for unseeded cases and the cases immediately after seeding performed for the cold continental Cb clouds with small cloud droplets. The injection of agent AgI is performed in temperature region between –8°C and –12°C. The four groups of sensitivity experiments are executed.

a.	The Brownian coagulation of rain drops is the most important contact nucleation mechanism for seeded cases with great amount of rain drops. When cloud droplets mainly contribute to the liquid water content for seeded cases, the Brownian coagulation of cloud droplets is the primary nucleation mechanism while the inertial impact is the less effective contact nucleation mechanism;
b.	the mutual interdependence of contact and deposition nucleation mechanisms shows that the contact nucleation is more effective for graupel production than the deposition one for the temperature region considered in this model;
c.	the imersion freezing is the most important mechanism for all cases with significant amount of rain drops. It is more effective than the contact nucleation mechanism in unseeded cases with insufficient number of rain drops;
d.	the nucleation mechanisms are more sensitive to temperature changes than to pressure changes.

With 14 Figures  相似文献   

Biogeographical drivers of ragweed pollen concentrations in Europe     

Matyasovszky  István  Makra  László  Tusnády  Gábor  Csépe  Zoltán  Nyúl  László G.  Chapman  Daniel S.  Sümeghy  Zoltán  Szűcs  Gábor  Páldy  Anna  Magyar  Donát  Mányoki  Gergely  Erostyák  János  Bodnár  Károly  Bergmann  Karl-Christian  Deák  Áron József  Thibaudon  Michel  Albertini  Roberto  Bonini  Maira  Šikoparija  Branko  Radišić  Predrag  Gehrig  Regula  Rybníček  Ondřej  Severova  Elena  Rodinkova  Victoria  Prikhodko  Alexander  Maleeva  Anna  Stjepanović  Barbara  Ianovici  Nicoleta  Berger  Uwe  Seliger  Andreja Kofol  Weryszko-Chmielewska  Elżbieta  Šaulienė  Ingrida  Shalaboda  Valentina  Yankova  Raina  Peternel  Renata  Ščevková  Jana  Bullock  James M. 《Theoretical and Applied Climatology》2018,133(1-2):277-295

Theoretical and Applied Climatology - The drivers of spatial variation in ragweed pollen concentrations, contributing to severe allergic rhinitis and asthma, are poorly quantified. We analysed the...  相似文献   

Non-double-couple mechanisms of microearthquakes induced during the 2000 injection experiment at the KTB site, Germany: A result of tensile faulting or anisotropy of a rock?     

Vclav Vavry uk  Marco Bohnhoff  Zuzana Jechumtlov  Petr Kol&#x;  Jan &#x;ílený 《Tectonophysics》2008,456(1-2):74

Moment tensors of microearthquakes induced during the 2000 injection experiment at the KTB deep drilling borehole at a depth level of 5.4 km are studied. A family of 37 most reliable moment tensors contains significant non-double-couple (non-DC) components. The DC is on average 60% and the non-DC is 40%. Fault plane solutions computed from the DC part show preferred strike-slip mechanisms with small normal or reverse components. A predominant azimuth of P and T axes is in the range of N320°–340°E and of N230°–250°E, respectively. The non-DC components contain both the isotropic (ISO) and compensated linear vector dipole (CLVD) components. The mean value of ISO is 1.5%, the mean value of CLVD is − 5.7%. The predominantly negative CLVD components are inconsistent with the concept of the non-DC mechanisms as a result of tensile faulting due to fluid injection into the rock. The main origin of the non-DC components is probably anisotropy in the focal area. The other origins are errors produced by mismodelling of the medium when calculating the Green functions, and numerical errors produced by noise and limitations of input data. Adopting four alternative models of anisotropy obtained by other seismic measurements at the KTB, we have employed the non-DC components for estimating an optimum orientation of anisotropy in the focal area. The optimum orientation of the symmetry plane of anisotropy is nearly vertical with a strike of N335°–340°E. This strike coincides well with the strike of 330° typical for many major lithological units and faults and with the orientation of the transversely isotropic model inferred by other authors. After removing the anisotropy effects from the moment tensors by calculating the source tensors, the distribution of ISO is significantly narrowed. This indicates predominantly shear, but not tensile faulting.  相似文献