The role of the wind-transported dust in slope streaks activity: Evidence from the HRSC data

Slope streaks are gravity-driven albedo features observed on martian slopes since the Viking missions. The debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting. A systematic mapping of slope streaks from the High Resolution Stereo Camera is presented in this paper. Two regions known for their slope streaks activity have been studied, the first one is located close to Cerberus lava flow, and the second one is inside the Olympus Mons Aureole. The statistics of slope streaks shapes measured from orthorectified images confirm previous results from Mars Orbiter Camera surveys. Preferential orientations of slope streaks are reported. Slope streaks occur preferentially on west facing slopes at latitudes lower than 30° N for Olympus and on south-west facing slopes for Cerberus. Wind directions derived from a General Circulation Model during the dusty season correlate with these orientations. Furthermore, west facing slopes at Olympus have a thicker dust cover. These observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow. The paucity of slope streaks at high latitudes and their preferential orientation on south-facing slopes have been presented as an evidence for a potential role of H₂O phase transition in triggering or flow. The potential role of H₂O cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations. The role of H₂O might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes (30° N-33° N) and on all slopes further north.     

88小时:美国地质调查局国家地震信息中心对2011年3月11日Mw9.0日本地震的响应

引言 2011年3月11日日本本州岛东海岸附近海域发生的M9．0地震（Tohoku earthquake,以下称“东日本大地震”——译者注）及其引发的海啸造成数以万计的人员死亡,造成的财产损失可能超过1万亿美元,这是有历史记录以来最严重的自然灾害之一。     

内蒙古柳坝沟一哈达门沟金矿田稳定同位素地球化学研究

内蒙古柳坝沟一哈达门沟金矿田是华北地台北缘成矿带上的一处以广泛发育钾长石化为特色的超大型金矿田。本文在成矿地质条件分析的基础上,系统研究了柳坝沟、哈达门沟金矿床的氢、氧、碳和硫同位素组成特征,探讨了成矿热液类型和成矿物质来源。研究表明,成矿热液早期以岩浆水或初始岩浆水为主,后期有部分大气降水的加入,且柳坝沟金矿床中大气降水的参与程度更高。热液中碳主要为深源岩浆来源。矿石中硫化物的硫同位素组成特征反映了硫具有地层和岩浆的混合硫特征。柳坝沟金矿床的δ34S值低于哈达门沟金矿床;哈达门沟金矿床东段的δ34S值低于西段,可能反映了柳坝沟金矿床较哈达门沟金矿床剥蚀程度小,哈达门沟会矿床东段较西段剥蚀程度小。     

差分GPS在乌拉特后旗1:25万区域重力调查中的应用

测地工作精度的高低直接影响着重力测量的精度,研究并采取行之有效的测地方法来配合重力测量工作是十分必要的。乌拉特后旗1:25万区域重力调查GPS测地工作采用1954年北京坐标系,重力测点平面位置、正常高采用差分GPS测量方法。结果表明,采用此方法既能满足技术要求,又达到了省时省力,且达到了重力测量的精度要求。     

青南高原西部砂金成矿条件分析

青南高原西部,处于柴达木准地台与松潘—甘孜印支褶皱系衔接部位。属于青藏高原北部的可可西里地区,平均海拔4800—5000m,属高寒荒漠干旱气候区。由昆仑山大起伏高山区及江河源高海拔波状平原区组成二级地貌区。通过对该区近代砂金矿形成的物质来源、新构造运动、地貌、气候、水动力条件及供源条件进行分析,认为该区砂金矿床的规模以及砂金找矿的前景并非如人们估计的那样乐观。     

Scaling relations of field spirals at intermediate redshift

In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical simulations based on the hierarchical merging scenario. This revised version was published online in August 2006 with corrections to the Cover Date.     

柴北缘铅石山榴辉岩地质特征

根据对铅石山榴辉岩岩石学、岩石化学、地球化学元素、变质岩相及变质作用等特征,该类岩石形成时代可能为中元古代后期,并经历了四堡期、晋宁期、加里东期三次快速折返及相应的退变质作用叠加,进一步证实了柴北缘地区高压变质带的存在。     

秦、祁、昆三大造山带的结合特征

秦、祁、昆三大造山带结合地区的物质组成及结构特征显示,其间存在不同时期发育起来的陆缘、陆内转换断层,受其制约,造山带内曾发生大规模侧向运动和由此引起的岩心活动及复杂的构造变形。据此,结合演化可分三阶段,并且秦、祁、昆三大造山带间并不存在东西向贯通的单一结合带,而是在转换断层作用下,分阶段逐步完成了转换结合的结合方式。     

Composition of Titan''s surface from Cassini VIMS

Titan's bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite's dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan's solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan's history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission's visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 μm were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan T_a encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79 μm in the poorly understood 2.8-μm methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-μm methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8 μm that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface.     

青海省大柴旦镇红柳沟金矿床地质特征及其成因

通过对红柳沟金矿床地质特征及围岩蚀变的研究,总结了金矿控矿因素及其富集规律,认为该矿床的成因为动力变质热液型。