The origin of selected lunar geochemical anomalies: Implications for early volcanism and the formation of light plains     

Bernard Ray Hawke  Paul D. Spudis  P. E. Clark 《Earth, Moon, and Planets》1985,32(3):257-273

The Apollo orbital geochemistry, photogeologic, and other remote sensing data sets were used to identify and characterize geochemical anomalies on the eastern limb and farside of the Moon and to investigate the processes responsible for their formation. The anomalies are located in the following regions: (1) Balmer basin, (2) terrain northeast of Mare Smythii, (3) near Langemak crater, (4) Pasteur crater, (5) terrain northwest of Milne basin, (6) northeast of Mendeleev basin, (7) north and northeast of Korolev basin, (8) terrain north of Taruntius crater, and (9) terrain north of Orientale basin. The anomalies are commonly associated with Imbrian- or Nectarian-aged light plains units which exhibit dark-haloed impact craters. The results of recent spectral reflectance studies of dark-haloed impact craters plus consideration of the surface chemistry of the anomalies strongly indicate that those geochemical anomalies associated with light plains deposits which display dark-haloed impact craters result from the presence of basaltic units that are either covered by varying thickness of highland debris or have a surface contaminated with significant amounts of highlands material. The burial or contamination of ancient volcanic surfaces by varying amounts of highland material appears to have been an important (though not the dominant) process in the formation of lunar light plains. Basaltic volcanism on the eastern limb and farside of the Moon was more extensive in both space and time than has been accepted.  相似文献   

Viscosity in spherically symmetric accretion     

Arnab K. Ray 《Monthly notices of the Royal Astronomical Society》2003,344(4):1085-1090

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Screening of polymers on selected Hawaii soils for erosion reduction and particle settling     

James A. Teo  Chittaranjan Ray  Samir A. El‐Swaify 《水文研究》2006,20(1):109-125

In recent years, high‐molecular‐weight anionic polyacrylamides (PAMs) have been tested on a variety of soils, primarily in temperate climates. However, little information is available regarding the effectiveness of PAM for preventing soil loss through runoff in tropical settings. Screening tests were performed using three negatively charged PAMs and one positively charged PAM on five Hawaii soils (two Oxisols, one Vertisol, and two Aridisols) to determine erosion loss, sediment settling, and aggregate stability. A laboratory‐scale rainfall simulator was used to apply erosive rainfall at intensities from 5 to 8·5 cm h^?1 at various PAM doses applied in both dry and solution forms. Soil detachment due to splash and runoff, as well as the runoff and percolate water volumes, were measured for initial and successive storms. The impact of PAM on particle settling and aggregate stability was also evaluated for selected soil‐treatment combinations. Among the PAMs, Superfloc A‐836 was most effective, and significantly reduced runoff and splash sediment loss for the Wahiawa Oxisol and Pakini Andisol at rates varying between 10 and 50 kg ha^?1. Reduced runoff and splash sediment loss were also noted for PAM Aerotil‐D when applied in solution form to the Wahiawa Oxisol. Significant reductions in soil loss were not noted for either the Lualualei Vertisol or the Holomua Oxisol. It is believed that the high montmorillonite content of the Lualualei Vertisol and the low cation‐exchange capacity of the Holomua Oxisol diminished the effectiveness of the various PAMs tested. The polymers were also found to enhance sediment settling of all soils and helped improve their aggregate stability. This screening study shows the potential use of PAM for tropical soils for applications such as infiltration enhancement, runoff reduction, and enhanced sedimentation of detention ponds. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Subaqueous pyroclastic flows and ignimbrites: an assessment   总被引：2，自引：0，他引：2  

Ray AF Cas  John V Wright 《Bulletin of Volcanology》1991,53(5):357-380

An assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary, hot gas-rich pyroclastic flows, mass-flows which resulted from the transformation of gassupported flows into water-supported ones, and secondary mass-flows carrying redeposited pyroclastic debris. Based on subaerial pyroclastic flows, the term pyroclastic flow should be restricted to demonstrably hot, gas-rich mass-flows of pyroclastic debris. Using this definition, very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described. In the majority of these cases, the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate. The only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the Ordovician nearshore, shallow marine ignimbrites of Ireland and Wales, and Miocene ignimbrites of southwest Japan, resulting from the passage of subaerially erupted pyroclastic flows into shallow water. Other possible examples are near-vent dense clast deposits in the Donzurobo Formation of Japan, possible submarine intra-caldera ponded ignimbrite successions in California and Wales, and near-vent pumiceous deposits of Ramsay Island, Wales. All other purported cases are either clearly the result of water-supported mass-flow transportation and deposition (debris avalanches, debris flows, turbidity currents), or lack adequate supporting evidence regarding the heat state or the palaeoenvironment. Only the shallow marine ignimbrites of Ireland and Wales show adequate evidence of welding, but even these could have been nearly wholly exposed above sea-level when welding occurred. We conclude that when pyroclastic flows enter water they are generally disrupted explosively and/or ingest water and transform into water-supported mass-flows, and we suggest the various scenarios in which this occurs. There is no evidence to suggest that welding in wholly subaqueous environments is common.  相似文献   

Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications     

Kusala Rajendran  C.P. Rajendran  Anil Earnest  G.V. Ravi Prasad  K. Dutta  D.K. Ray  R. Anu 《Tectonophysics》2008,455(1-4):53-60

The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr^− 1 in the Little Andaman to 2.80 mm yr^− 1 in South Andaman and 2.45 mm yr^− 1 in the North Andaman. Our radiocarbon dates converge on  600 yr and  1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.  相似文献   

Mineralogical sources of the buffer capacity in a granite catchment determined by strontium isotopes     

Christina Weyer  Gunnar Lischeid  Luc Aquilina  Anne-Catherine Pierson-Wickmann  Charlotte Martin 《Applied Geochemistry》2008

The role of different minerals in base cation release and thus the increase of buffering capacity of groundwater against acid deposition is controversially discussed in the literature. The ⁸⁷Sr/⁸⁶Sr ratios and base cation concentration were investigated in whole rock leachates, mineral separates, precipitation, soil solution, groundwater and stream water samples in the Lehstenbach catchment (Germany) to identify the weathering sequence of the granite bedrock. Three different approaches were followed in parallel. It was assumed that the contribution of different minerals to base cation supply of the groundwater with increasing weathering intensity would be observed by investigating (1) unweathered rock leachates, deep groundwater and shallow groundwater, (2) groundwater samples from new groundwater wells, reflecting the initial weathering of the drilled bedrock, and groundwater from wells that were drilled in 1988, (3) stream water during baseflow, dominated by deep groundwater, and stream water during high flow, being predominantly shallow groundwater. Whereas the first approach yielded consistent patterns, there was some evidence that groundwater from the new wells initially reflected contamination by the filter gravel rather than cation release in an initial stage of weathering. Time series samples of stream water and groundwater solute concentrations and isotope ratios turned out to reflect varying fractions of soil water and precipitation water at baseflow and high flow conditions rather than varying contributions of different minerals that prevail at different stages of granite weathering.  相似文献   

Aspects of conservation in the excavation site of the Athribis temple in Egypt     

Hans Leisen  Esther von Plehwe-Leisen  Christina Verbeek  Christine Jürgens  Sabine Krause 《Environmental Geology》2008,56(3-4):689-697

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Mineral assemblages occurring around hydrocarbon vents in the northern Gulf of Mexico     

Ray E. Ferrell Jr.  Paul Aharon 《Geo-Marine Letters》1994,14(2-3):74-80

Magnesian calcites are the most abundant authigenic minerals associated with hydrocarbon vents at 25 sites, in water depths ranging from 100 to 600 m in the Green Canyon area and about 2200 m in the Alaminos Canyon area on the Continental Slope of the northern Gulf of Mexico. The most frequently encountered magnesian calcites have 10–15 mol% MgCO₃ and the apparent structural disorder revealed by XRD peak widths increases with Mg substitution. There are no systematic variations in Mg content with respect to water depth or geographic location. The calcite saturation state of the precipitating fluid is primarily determined by the nature of the fluids escaping from the vents, not the ambient seawater.  相似文献   

The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s     

Manfred Mensch  Reinhold Bayer  John L. Bullister  Peter Schlosser  Ray F. Weiss 《Progress in Oceanography》1996,38(4):377-388

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).  相似文献   

On the geologic structure of the Explora Escarpment (Weddell Sea,Antarctica) revealed by satellite and Shipboard data evaluation     

Ute Christina Herzfeld  Arnold L. Brodscholl 《Marine Geophysical Researches》1994,16(5):325-345

Bathymetric, gravity, and magnetic data from Antarctic expeditions with RV POLARSTERN and satellite altimeter data from the Geosat Geodetic Mission are analysed using methods from geostatistics and geophysical inverse theory.The Explora Escarpment represents the edge between the Antarctic Continental Shelf and the Weddell Abyssal Plain. It is an important link in the reconstruction of Gondwana breakup, but a feature as large as the 2000 m deep Wegener Canyon was only discovered in 1984, when extensive bathymetric, gravimetric, and magnetic surveys with RV POLARSTERN began.Geostatistics, the theory of regionalized variables, is applied to integrate dense surveys of Wegener Canyon and sparse observations in adjacent areas into maps with full coverage of the 230 km by 330 km area at 10°–20° W/70°–72° S. The resultant highresolution bathymetric and gravity maps reveal detailed structures of the Explora Escarpment. Using geophysical inversion, the gravity terrain effect is calculated. Satellite data are used for their better coverage, but have much lower resolution. Nevertheless, the structures of Wegener Canyon and other more prominent features appear with surprisingly good correlation also in the Geosat altimeter data. While it was initially supposed that Wegener Canyon is purely an erosional structure, the magnetic map now provides evidence of the canyon's tectonic origin.  相似文献