营口—宽甸地区重力场特征及地质解释

营口—宽甸地区重力场自北而南有逐渐增高的总趋势。中部区重力低与重力高呈带状相间出现。结合该区已知的地质构造特征综合分析,重力负值带是早元古宙拗拉槽边界深断裂和构造—岩浆岩带的反映。隐伏、半隐伏花岗岩体的解释和推断,为逃一步寻找金、硼、铅锌等矿产提供了信息。     

Remote sensing of mesospheric winds with the high-resolution doppler imager

Observations of the winds in the upper atmosphere obtained with the High-Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) are discussed. This instrument is a very stable high-resolution triple-etalon Fabry-Perot interferometer, which is used to observe the slight Doppler shifts of absorption and emission lines in the O₂ Atmospheric bands induced by atmospheric motions. Preliminary observations indicate that the winds in the mesosphere and lower thermosphere are a mixture of migrating and non-migrating tides, and planetary-scale waves. The mean meridional winds are dominated by the 1,1 diurnal tide which is easily extracted from the daily zonal means of the satellite observations. The daily mean zonal winds are a mixture of the diurnal tide and a zonal flow which is consistent with theoretical expectations.     

青海德尔尼硫化物矿床成因的新认识

通过对青海德尔尼硫化物矿床的产出部位、成矿环境、矿石矿物的组合、主要化学元素的成份及同位素测试数据等分析研究,认为该矿床具有裂谷成矿机制的特征,成因类型应属裂谷型层控矿床。     

滩间山金矿矿床成因初步探讨

本文通过对滩间山矿区地层、构造及岩浆岩与成矿关系的研究,认为中元古界万洞沟群是金的矿源层;成矿构造具有多期次、多阶段活动的特点,矿体受单一及复合型式的构造控制;华力西期侵入体对成矿作用仅体现于为矿床的形成与再造提供热源。矿质在弱酸—中偏碱性溶液中,主要呈硫络合物的形式搬运、并在还原条件下成矿。特别指出,含磷质物地层是区内重要的岩金找矿标志之一。     

东秦岭金堆城花岗斑岩体的锆石U-Pb年龄、物质来源及成矿机制

通过LA-ICP-MS方法测得金堆城和老牛山花岗岩体中锆石U-Pb年龄分别为143.7±3 Ma和144.5±4.4 Ma,与金堆城钼矿床中辉钼矿的Re-Os年龄139±3.0 Ma在误差范围内一致,界定了金堆城成岩成矿时代为侏罗纪末-白垩纪初,2个岩体为同期岩浆事件的产物,与燕山运动有关.金堆城岩体较老牛山岩体富SiO₂、K₂O,岩石地球化学数据显示2个岩体都具有一致的高硅、富碱、过铝质系列和钙碱性岩石系列特征;高的ε_Sr(t)、低的ε_Nd(t)及Pb同位素图解证明2个岩体主要来自下地壳物质部分熔融,可能有少量地幔物质加入.年代学与岩石地球化学数据证实老牛山岩体和金堆城岩体的岩浆源区与岩石成因相同,推测老牛山岩体在深部发生分异演化,为金堆城小岩体提供了大量的热液和矿物质,从而出现了金堆城小岩体成大矿现象.      

Interaction between wild camelids and livestock in an Andean semi-desert

Isoleg theory predicts that coexistence between two competing species can occur when the subordinate, generalist species uses alternative patches of resources as the density of the dominant specialist species increases. These models provide a framework to determine if a native species is subordinate to an introduced one, thus requires conservation considerations. We investigated habitat interactions between a wild neotropical camelid and domestic exotic ungulates in the Andean Puna semi-desert of South America. The Puna or Altiplano is an arid environment located in high altitudes, with cold and dry weather, and two main types of habitats, steppes and swamp areas. There was a high overlap of diets between species. Vicuñas were generalists in the use of habitat, but invested foraging effort in swamp habitats, while livestock were taken to swamp habitats by local people. Vicuñas and livestock were spatially segregated. Vicuñas used the preferred habitat less than expected from their foraging preference. We concluded that vicuñas and livestock coexist because vicuñas occupy sub-optimal habitats whilst livestock concentrate in the richest ones. Vicuñas can deal with poor habitats because they have several adaptations to live in deserts.     

Emplacement of the youngest flood lava on Mars: A short, turbulent story

Recently acquired data from the High Resolution Imaging Science Experiment (HiRISE), Context (CTX) imager, and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) spacecraft were used to investigate the emplacement of the youngest flood-lava flow on Mars. Careful mapping finds that the Athabasca Valles flood lava is the product of a single eruption, and it covers 250,000 km² of western Elysium Planitia with an estimated 5000-7500 km³ of mafic or ultramafic lava. Calculations utilizing topographic data enhanced with MRO observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks. This is the first well-documented example of a turbulently emplaced flood lava anywhere in the Solar System. However, MRO data suggest that this same process may have operated in a number of martian channel systems. The magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels, raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision.     

Radar-bright channels on Titan

During Cassini’s T44 flyby of Titan (May 28, 2008), the Cassini SAR (synthetic aperture radar) revealed sinuous channels in the Southwest of Xanadu. These channels feature very large radar cross-sections, up to 5 dB, whereas the angle of incidence was relatively high, ∼20°. This backscatter is larger than allowed by the coherent backscatter model considered to explain the unusual reflective and polarization properties of the icy satellites and only a few radar scattering mechanisms can be responsible for such high radar returns. The presence of rounded (icy) pebbles with size larger than the radar wavelength (2.18 cm) is proposed to explain the large radar cross-sections measured in these units. The radar-bright channels are thus interpreted as riverbeds, where debris, likely shaped and transported by fluvial activity, have been deposited. Similar debris were observed in the landing site of the Huygens probe. This work may point the way to an explanation for the enhanced brightness of other fluvial regions of Titan.     

Dust aerosols above the south polar cap of Mars as seen by OMEGA

The time evolution of atmospheric dust at high southern latitudes on Mars has been determined using observations of the south seasonal cap acquired in the near infrared (1-2.65 μm) by OMEGA/Mars Express in 2005. Observations at different solar zenith angles and one EPF sequence demonstrate that the reflectance in the 2.64 μm saturated absorption band of the surface CO₂ ice is mainly due to the light scattered by aerosols above most places of the seasonal cap. We have mapped the total optical depth of dust aerosols in the near-IR above the south seasonal cap of Mars from mid-spring to early summer with a time resolution ranging from one day to one week and a spatial resolution of a few kilometers. The optical depth above the south perennial cap is determined on a longer time range covering southern spring and summer. A constant set of optical properties of dust aerosols is consistent with OMEGA observations during the analyzed period. Strong variations of the optical depth are observed over small horizontal and temporal scales, corresponding in part to moving dust clouds. The late summer peak in dust opacity observed by Opportunity in 2005 propagated to the south pole contrarily to that observed in mid spring. This may be linked to evidence for dust scavenging by water ice-rich clouds circulating at high southern latitudes at this season.     

Gusev photometric variability as seen from orbit by HRSC/Mars-express

Minnaert and two-term phase function Hapke models are used to describe the photometric properties of the martian surface using HRSC (High Resolution Stereo Camera) multi-angular observations acquired along the ongoing Mars-Express mission. These observations can be pieced together to derive integrated phase functions over a wide range of phase angles. The photometric diversity at 675 nm, as seen from orbit, of the martian surface properties across Gusev is depicted with seven units. Three photometric units widespread across the flanks of Apollinaris Patera flank and the floor of Gusev Crater are identified as having high single scattering albedo with rather forward scattering properties, low to intermediate macroscopic roughness and porous or not compacted powdered surface state as indicated by the opposition parameters. Another unit has the highest single scattering albedo, the smoothest surface in terms of macroscopic roughness, associated with an extremely forward scattering behavior. The opposition parameters are consistent with the presence of transparent particles in the surface powder layer. The distribution of this unit appears quite intermittent across the crater and does not seem to indicate any relationship with a given morphological structure. It may correspond to sparse areas where the structure of the surface dust layer is the most preserved. The most pronounced photometric changes are observed in three units associated with the low-albedo features corresponding to dark wind streaks. These units have a low single scattering albedo, are the most backscattering surfaces across Gusev, have a high surface roughness and present variable surface states as shown by the opposition parameters estimates, consistent with the occurrence of large grains organized in more or less packed layers. Clear differences are seen among these units in terms of opposition effect. While one exhibits typical characteristics for the opposition effect, another appears more unusual in terms of lobe width and the third suggests the occurrence of a packed/compressed/narrow size distribution powder surface. The opposition effect thus appears to play a significant role suggesting that the surface state optical properties across Gusev are strongly influenced by the porosity and packing characteristics or grain size distribution of the upper layer of the martian soil. The mapping aspect of the investigation is quite useful to get a better sense of the meaning of the observed photometric variations. Indeed, the Hapke modeling suggests that surface organization (surface roughness, packing state) is more important than the simple physical characterization of the intrinsic optical properties of the constitutive particles. Given the overall spatial patterns derived from the photometric analysis, the variations, at least for the western and central part of Gusev Crater, are likely partly driven by the prevailing wind regimes, considered to be oriented north-northwest/south-southeast and disturbing the very upper surface layer. The present photometric results agree with independent investigations based on thermal inertia, reflectance spectroscopy, in situ photometric and microscopic imaging and support the idea of a thin layer of fine-grained dust, being stripped off in the low albedo units to reveal a dark basaltic substrate comprising coarse-grained materials.