He,Pb, Sr and Nd isotope constraints on magma genesis and mantle heterogeneity beneath young Pacific seamounts     

David W. Graham  Alan Zindler  Mark D. Kurz  William J. Jenkins  Rodey Batiza  Hubert Staudigel 《Contributions to Mineralogy and Petrology》1988,99(4):446-463

Pb, Sr and Nd isotope variations are correlated in diverse lavas erupted at small seamounts near the East Pacific Rise. Tholeiites are isotopically indistinguishable from MORB (²⁰⁶Pb/²⁰⁴Pb=18.1–18.5; ⁸⁷Sr/⁸⁶Sr=0.7023–0.7028; ¹⁴³Nd/¹⁴⁴Nd=0.51326-0.51308); associated alkali basalts always show more radiogenic Pb and Sr signatures (²⁰⁶Pb/²⁰⁴Pb=18.8–19.2; ⁸⁷Sr/⁸⁶Sr=0.7029–0.7031) and less radiogenic Nd (¹⁴³Nd/¹⁴⁴Nd=0.51289–0.51301). The isotopic variability covers 80% of the variability for Pacific MORB, due to the presence of small-scale heterogeneity in the underlying mantle. Isotope compositions also correlate with trace element ratios such as La/Sm. Tholeiites at these seamounts have ³He/⁴He between 7.8–8.7 R _A(R _A= atmospheric ratio), also indistinguishable from MORB. He trapped in vesicles of alkali basalts, released by crushing in vacuo, has low ³He/⁴He (1.2–2.6 R)_Ain conjunction with low helium concentrations ([He]<5×10^–8 ccSTP/g). In many cases post-eruptive radiogenic ingrowth has produced He isotope disequilibrium between vesicles and glass in the alkali basalts; subatmospheric ³He/⁴He ratios characterize the He dissolved in the glass which is released by melting the crushed powders. The narrow range of ³He/⁴He in the vesicles of the alkali basalts suggests that low ³He/⁴He is a source characteristic, but given their low [He] and high (U + Th), pre-eruptive radiogenic ingrowth cannot be excluded as a cause for low inherited ³He/⁴He ratios. Pb, Sr and Nd isotope compositions in lavas erupted at Shimada Seamount, an isolated volcano on 20 m.y. old seafloor at 17°N, are distinctly different from other seamounts in the East Pacific (²⁰⁶Pb/²⁰⁴Pb=18.8–19.0, ⁸⁷Sr/ ⁸⁶Sr0.7048 and ¹⁴³Nd/¹⁴⁴Nd0.51266). Relatively high ²⁰⁷Pb/²⁰⁴Pb (15.6–15.7) indicates ancient (>2 Ga) isolation of the source from the depleted upper mantle, similar to Dupal components which are more prevalent in the southern hemisphere mantle. ³He/⁴He at Shimada Seamount is between 3.9–4.8 R _A. Because the helium concentrations range up to 1.5×10^–6, the low ³He/⁴He can not be due to radiogenic accumulation of ⁴He in the magma for reasonable volcanic evolution times. The low ³He/⁴He may be due to the presence of enriched domains within the lithosphere with high (U + Th)/He ratios, possibly formed during its accretion near the ridge. Alternatively, the low ³He/⁴He may be an inherent characteristic of an enriched component in the mantle beneath the East Pacific. Collectively, the He-Pb-Sr-Nd isotope systematics at East Pacific seamounts suggest that the range of isotope compositions present in the mantle is more readily sampled by seamount and island volcanism than by axial volcanism. Beneath thicker lithosphere away from the ridge axis, smaller degrees of melting in the source regions are less efficient in averaging the chemical characteristics of small-scale heterogeneities.  相似文献   

Week-end field meeting in the Cardiff District: Saturday and Sunday,June 20th and 21st, 1936     

Professor A. Hubert CoxA. Heard  M.Sc.  Ph.D.  F.G.S. 《Proceedings of the Geologists' Association. Geologists' Association》1937,48(1):52-60

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The geology of the Dolgelley District,Merionethshire: With Map, 4 Plates and 7 Text Figures     

Arthur Hubert Cox  Alfred Kingsley Wells 《Proceedings of the Geologists' Association. Geologists' Association》1927,38(3):265-IN6

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Summer field meeting, 1944: August 24th–September 2nd     

A. Hubert Cox  H.P. Lewis 《Proceedings of the Geologists' Association. Geologists' Association》1945,56(2):59-IN2

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Analytical Solutions Using Integral Formulations and Their Coupling with Numerical Approaches          下载免费PDF全文

Hubert J. Morel‐Seytoux 《Ground water》2015,53(5):810-818

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Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment     

Schratzberger M  Daniel F  Wall CM  Kilbride R  Macnaughton SJ  Boyd SE  Rees HL  Lee K  Swannell RP 《Marine pollution bulletin》2003,46(4):430-443

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.  相似文献   

Equifinality,a blessing in disguise?     

Hubert H. G. Savenije 《水文研究》2001,15(14):2835-2838

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Auroral ion velocity distribution function: Generalized polynomial solution of Boltzmann's equation     

D. Hubert 《Planetary and Space Science》1983,31(1):119-127

The ion distribution function is calculated for the E and the F regions of the auroral latitudes. In these regions the plasma is weakly ionized and there exist convective electric fields which may attain very significant intensities. Boltzmann's equation is solved in the limit where the ion-neutral collision frequency is much lower than the ion gyrofrequency. This solution is obtained in the form of a generalized polynomial series expansion starting from a good zeroth-order approximation. With this weight function, and considering a development to the order of the 32 moments, good approximations are obtained for high electric fields. The resonant charge exchange model and the polarization model are successively considered. The Post-Rosenbluth instability threshold is discussed for the above two models.  相似文献   

Greenland surface mass balance simulated by a regional climate model and comparison with satellite-derived data in 1990–1991     

Xavier Fettweis  Hubert Gallée  Filip Lefebre  Jean-Pascal van Ypersele 《Climate Dynamics》2005,24(6):623-640

The 1990 and 1991 ablation seasons over Greenland are simulated with a coupled atmosphere-snow regional climate model with a 25-km horizontal resolution. The simulated snow water content allows a direct comparison with the satellite-derived melt signal. The model is forced with 6-hourly ERA-40 reanalysis at its boundaries. An evaluation of the simulated precipitation and a comparison of the modelled melt zone and the surface albedo with remote sensing observations are presented. Both the distribution and quantity of the simulated precipitation agree with observations from coastal weather stations, estimates from other models and the ERA-40 reanalysis. There are overestimations along the steep eastern coast, which are most likely due to the “topographic barrier effect”. The simulated extent and time evolution of the wet snow zone compare generally well with satellite-derived data, except during rainfall events on the ice sheet and because of a bias in the passive microwave retrieved melt signal. Although satellite-based surface albedo retrieval is only valid in the case of clear sky, the interpolation and the correction of these data enable us to validate the simulated albedo on the scale of the whole Greenland. These two comparisons highlight a large sensitivity of the remote sensing observations to weather conditions. Our high-resolution climate model was used to improve the retrieval algorithms by taking more fully into account the atmosphere variability. Finally, the good agreement of the simulated melting surface with the improved satellite signal allows a detailed estimation of the melting volume from the simulation.  相似文献   

Seismicity wedge beneath the Upper Rhine Graben due to backwards Alpine push?   总被引：1，自引：0，他引：1  

Jean-Bernard Edel  Hubert Whitechurch  Marc Diraison 《Tectonophysics》2006,428(1-4):49-64

The distribution of hypocentres in the Upper Rhine Graben area is re-examined, and discussed with respect to the present day tectonic framework. Most earthquakes occur within a N60° striking wedge, located on top of a Moho dome. This wedge is limited by the surface and at depth, by a plane which, in the south of the dome, coincides with the SE dipping Conrad discontinuity. In depth, the seismicity shows a normal distribution the maximums of which are located on a surface dipping 6° towards SE, parallel to the south-eastward dipping Conrad and Moho. This surface outcrops along the north-western edge of the uplifted crystalline Vosges and Black-Forest. The main shocks in earthquake swarms in the region often occur in the vicinity of this surface and along pre-existing N–S to NE–SW Variscan or Tertiary faults and show focal mechanisms of strike-slip. In contrast, part of the aftershocks show focal mechanisms of reverse faulting associated with SE–NW striking compression. The seismic wedge and the north-westward rising seismic surface suggest initiation of crustal ramp, which starts at the south-eastern rim of the Conrad dome and which may become a thrust plane if SE–NW compression continues. In the south-eastern edge of the graben and above the south-eastern ridge of the Moho dome, where evidences for extension have been found, we identify clustering of hypocentres along a surface that strikes N150°, parallel to the main compression and dipping towards NE. Dominant normal faulting mechanisms along this surface suggests initiation of a normal, probably listric fault. At depth, the onset of the future fault plane is located on top of the NW–SE striking ridge of the lower crust and Moho, which act as a an indenter. In addition to thrusting of the whole wedge towards NW, increasing of NW–SE compression would lead to the formation of a half graben at the place of the present Sierentz depression.  相似文献