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41.
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We thank van Emmerik et al. for their discussion of our opinion paper. We do not fully agree that publication of negative results will be very effective in promoting experimental hydrology. Instead, we think that experimental hydrology is considered to be more risky than modelling studies because of difficulties in publishing inconclusive results and the potential for failure. 相似文献
43.
Robert Temdjim Merlin Patrick Njombie Wagsong Arnold Julien Nzakou Tsepeng Stephen Foley 《地学前缘(英文版)》2020,(2):665-677
Mantle peridotites entrained as xenoliths in the lavas of Ngao Bilta in the eastern branch of the continental Cameroon Line were examined to constrain mantle processes and the origin and nature of melts that have modified the upper mantle beneath the Cameroon Line.The xenoliths consist mainly of lherzolite with subordinate harzburgite and dunite.They commonly contain olivine,orthopyroxene,clinopyroxene and spinel although the dunite is spinel-free.Amphibole is an essential constituent in the lherzolites.Mineral chemistry differs between the three types of peridotite:olivines have usual mantle-like Mg#of around 90 in lherzolites,but follow a trend of decreasing Mg#(to 82)and NiO(to 0.06 wt.%)that is continuous in the dunites.Lherzolites also contain orthopyroxenes and/or clinopyroxenes with low-Mg#,indicating a reaction that removes Opx and introduces Cpx,olivine,amphibole and spinel.This is attributed to reaction with a silica-undersaturated silicate melt such as nephelinite or basanite,which originated as a low-degree melt from a depleted source as indicated by low Al2O3 and Na2O in Cpx and high Na2O/K2O in amphibole.Thermobarometric estimates place the xenoliths at pressures of 11–15 kbar(35–50 km)and temperatures of 863–957C,along a dynamic rift geotherm and shallower than the region where carbonate melts may occur.The melt/rock reactions exhibited by the Ngao Bilta xenoliths are consistent with their peripheral position in the eastern branch of the Cameroon Volcanic Line in an area of thinned crust and lithosphere beneath the Adamawa Uplift. 相似文献
44.
M. T. Rushton T. R. Geballe A. V. Filippenko R. Chornock W. Li D. C. Leonard † R. J. Foley A. Evans B. Smalley J. Th. van Loon S. P. S. Eyres 《Monthly notices of the Royal Astronomical Society》2005,360(4):1281-1289
We report optical and near-infrared spectroscopy, and optical spectropolarimetry, of the peculiar variable V838 Mon during the multiple outburst phase in early 2002. The spectral evolution is exceptional. Our earliest spectra (2002 January) are noteworthy for their strong absorption lines of barium and strontium in the optical, and bands of CO and circumstellar H2 O in the near-infrared. All but the CO weaken or are absent in later spectra. The behaviour of the CO band during this phase is extraordinary: initially in absorption, it was observed two months later in optically thick emission. The excitation of the CO is probably the result of the propagation of a shock wave at the third maximum. The two spectropolarimetric epochs were taken 6 and 27 d after the second outburst on 2002 February 8. The polarization at both times was measured to be pV ≈ 2.7 per cent. Nearly all of the measured polarization is believed to be due to interstellar dust, a conclusion that is consistent with previous studies. At both epochs, however, a weak and variable intrinsic component is thought to be present. Between January and March of 2002 the luminosity of V838 Mon increased by a factor of 15 and the apparent diameter increased fourfold. 相似文献
45.
A. Pastorello P. A. Mazzali G. Pignata S. Benetti E. Cappellaro A. V. Filippenko W. Li W. P. S. Meikle A. A. Arkharov G. Blanc F. Bufano A. Derekas M. Dolci N. Elias-Rosa R. J. Foley M. Ganeshalingam A. Harutyunyan L. L. Kiss R. Kotak V. M. Larionov J. R. Lucey N. Napoleone H. Navasardyan F. Patat J. Rich S. D. Ryder M. Salvo B. P. Schmidt V. Stanishev P. Székely S. Taubenberger S. Temporin M. Turatto W. Hillebrandt 《Monthly notices of the Royal Astronomical Society》2007,377(4):1531-1552
46.
E. G. Drozhko Y. U. Glagolenko Y. G. Mokrov G. A. Postovalova L. M. Samsonova A. V. Glagolev S. A. Ter-Saakian M. L. Glinsky N. A. Vasil'kova A. V. Skokov H. A. Wollenberg C.-F. Tsang W. Frangos R. D. Solbau K. A. Stevenson W. M. Lowder M. G. Foley 《Environmental Geology》1997,29(3-4):216-227
In September 1994, a Russian-American team conducted hydrogeological, geochemical, geophysical, and radiometric measurements
in the territory of the Mayak Production Association, Russia. The primary purpose of these operations was to examine the frontal
area of a radioelement- and nitrate-laden groundwater plume moving from the disposal site, Lake Karachai, toward the Mishelyak
River. Activities encompassed (1) isolation of hydrologic intervals in two wells and production of water from these intervals,
to compare isolated versus open-well sampling methods and to determine hydraulic transmissivities of the aquifer(s); (2) surface
and soil-water sampling, accompanying radiometric measurements and subsequent chemical analyses; and (3) electrical resistivity
profiling in areas of expected contrasting resistivity.
Preliminary results indicate that (1) 60Co, 137Cs, and 90Sr are present in small concentrations (∼0.1% of permissible levels) in water of the Mishelyak River; (2) analyses of water
samples collected by a downhole sampler and of water produced from packed-off intervals agree within limits of laboratory
accuracy, attesting to the efficacy of the sampling methods presently used by the Russian workers; (3) considerable differences
in contaminant concentrations exist between nearby wells, supporting the concept that the plume from Lake Karachai toward
the Mishelyak River is controlled by steeply dipping fractures and shear zones; and (4) strong contrasts occur between the
electrical resistivities of soil and bedrock.
Further collaborative work is strongly recommended and should include more detailed isolation of intervals in wells by multi-packer
installations, to better determine the geochemical and hydrological characteristics of the Karachai-Mishelyak system; deployment
of a broader soil water and soil sampling array; a more detailed examination of the distribution and concentration of radionuclides
by high-resolution field gamma spectrometry; and a detailing of the area's electrical resistivity setting, using a mobile
electromagnetic measurement system.
Received: 22 January 1996 · Accepted: 1 April 1996 相似文献
47.
C.B. Woodson D.I. Eerkes-Medrano A. Flores-Morales M.M. Foley S.K. Henkel M. Hessing-Lewis D. Jacinto L. Needles M.T. Nishizaki J. O’Leary C.E. Ostrander M. Pespeni K.B. Schwager J.A. Tyburczy K.A. Weersing A.R. Kirincich J.A. Barth M.A. McManus L. Washburn 《Continental Shelf Research》2007
Sea breezes often have significant impacts on nearshore physical and biological processes. We document the effects of a diurnal sea breeze on the nearshore thermal structure and circulation of northern Monterey Bay, California, using an array of moorings during the summer upwelling season in 2006. Moorings were equipped with thermistors and Acoustic Doppler Current Profilers (ADCPs) to measure temperature and currents along the inner shelf in the bay. Temperature and current data were characteristic of traditional regional scale upwelling conditions along the central California coast during the study period. However, large diurnal fluctuations in temperature (up to 5 °C) were observed at all moorings inshore of the 60-m isobath. Examination of tidal, current, temperature, and wind records revealed that the observed temperature fluctuations were the result of local diurnal upwelling, and not a result of nearshore mixing events. Westerly diurnal sea breezes led to offshore Ekman transport of surface waters. Resulting currents in the upper mixed layer were up to 0.10 m s−1 directed offshore during the afternoon upwelling period. Surface water temperatures rapidly decreased in response to offshore advection of surface waters and upwelling of cold, subsurface water, despite occurring in the mid-afternoon during the period of highest solar heat flux. Surface waters then warmed again during the night and early morning as winds relaxed and the upwelling shadow moved back to shore due to an unbalanced onshore pressure gradient. Examination of season-long, moored time series showed that local diurnal upwelling is a common, persistent feature in this location. Local diurnal upwelling may supply nutrients to nearshore kelp beds, and transport larvae to nearshore habitats. 相似文献
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Evidence from Antarctic mantle peridotite xenoliths for changes in mineralogy, geochemistry and geothermal gradients beneath a developing rift 总被引:1,自引:0,他引:1
Garnet and spinel peridotite xenoliths associated with the Phanerozoic Lambert-Amery Rift in eastern Antarctica contain evidence for several stages in the development of the mantle beneath the rift. Despite the fact that equilibria were only partly attained, a combination of petrography, whole-rock geochemistry, mineral chemistry and thermobarometry can be used to decipher four stages prior to entrainment of the xenoliths in the host magma during the initial stages of the breakup of Antarctica, India and Madagascar. The first chronological stage is represented by harzburgitic protoliths represented by rare occurrences of low-Ca olivines and orthopyroxenes in spinel lherzolites: these yield the lowest temperatures of 830-850 °C, and are also characterized by distinct trace element contents; lower Ti, Cr, V and Zn in olivine and orthopyroxene, and additionally lower Cu, Ni, Ga and Li in orthopyroxene. Some garnets are subcalcic, indicating that the spinel-garnet lherzolites also formed from harzburgitic protoliths. The second stage is the formation of garnet due to a pressure increase probably related to collision at 1.1 Ga. The third stage is marked by the growth of clinopyroxene, demonstrably in cpx-poor spinel lherzolites but probably in all xenolith groups: equilibrium of clinopyroxene with olivine and orthopyroxene was not attained in all samples, so that the non-judicious use of thermobarometers can produce bewildering results. The fourth stage is an enrichment episode that affected all spinel-garnet peridotites and about half of the spinel peridotites. During this stage, reaction rims were produced on the clinopyroxenes that formed during stage 3, the modal content of olivine and Mg/(Mg + Fe) in the rocks was reduced, CaO, Al2O3 and trace elements were enriched, and garnets were almost completely transformed to kelyphites. A later stage is documented by interstitial glasses and films around spinels related to infiltration of melt from the host magma. These post-date, and are more enriched in alkalies than, partially melted rims on clinopyroxenes, demonstrating that all the three earlier episodes were pre-entrainment events. Pressures indicated by the spinel + garnet lherzolites are restricted to 20-24 kbar at 1040-1180 °C. Early harzburgitic assemblages are interpreted to represent an earlier, cooler geotherm, whereas the kelyphite assemblages indicate temperatures 180-200 °C hotter than the main xenolith geotherm. This event also caused recrystallization of the clinopyroxene rims and is attributed to heating during rifting, but not due to the host magma itself. The preservation of evidence for three progressively hotter geotherms can be related to the upward movement of isotherms during the development of the sub-rift mantle. 相似文献