Shock melting of ordinary chondrite powders and implications for asteroidal regoliths

Abstract— A series of 59 impacts in the laboratory reduced a coherent 460 g piece of the L6 ordinary chondrite ALH 85017 to a coarse‐grained “regolith.” We then subjected the 125–250 μm fines from this sample to reverberation shock stresses of 14.5–67 GPa in order to delineate the melting behavior of porous, unconsolidated, chondritic asteroid surfaces during meteorite impact. The initial pore space (40–50%) was completely closed at 14.5 GPa and a dense aggregate of interlocking grains resulted. Grain‐boundary melting commenced at <27 GPa and ?50% of the total charge was molten at 67 GPa; this stress corresponds to typical asteroid impacts at ?5 km/sec. Melting of the entire sample most likely mandates >80 GPa, which is associated with impact velocities >8 km/sec. The Fe‐Ni and troilite clasts of the original meteorite melted with particular ease, forming immiscible melts that are finely disseminated throughout the silicate glass. These metal droplets are highly variable in size, extending to <100 nm and most likely to superparamagnetic domains; such opaques are also observed in the natural melt veins of ordinary chondrites. It follows that melting and dissemination of pre‐existing, Fe‐rich phases may substantially affect the optical properties of asteroidal surfaces. It seems unnecessary to invoke reduction of Fe²⁺ (or Fe³⁺) by sputtering or impact‐processes—in analogy to the lunar surface—to produce “space weathering” effects on S‐type asteroids. We note that HED meteorites contain ample FeO (comparable to that in lunar basalts) for reduction processes to take place, yet their probable parent object(s), Vesta and its collisional fragments, display substantially unweathered surfaces. Howardites, eucrites, and diogenites (HEDs), however, contain little native metal (typically <0.5%), in contrast to ordinary chondrites (commonly 10–15%) and their S‐type parent objects. These considerations suggest that the modal content of native metal and sulfides is more important for space weathering on asteroids than total FeO.     

The northern Ossa-Morena Cadomian batholith (Iberian Massif): magmatic arc origin and early evolution

Diorites and related rocks in the Mérida area of northern Ossa-Morena (SW Iberia) are intrusive into Precambrian metavolcanic and metasedimentary sequences. Cumulate products from the H₂O-rich magmas are amphibole-rich gabbros to hornblendites. Major and trace element compositions, including Sr and Nd isotope data, allow the definition of a calc-alkaline series likely formed in relation to an immature arc setting. Crystallization of the intrusives has been established between ca. 570 and 580 Ma by U-Pb dating of constituent zircons. Garnet growth in dioritic rocks reflects a tectono–thermal overprint dated by Sm-Nd internal isochrons at around 555 Ma. Older Sm-Nd and Lu-Hf results between ca. 593 and 637 Ma on the same rocks suggest an earlier stage of regional metamorphism within the arc environment. The northern Ossa-Morena composite batholith and related metamorphic units have been tectonized and dismembered in the course of subsequent low-grade events during final stages of the Cadomian orogeny and the Variscan cycle. The units studied represent a well preserved segment of the arc region that evolved in Neoproterozoic times along the western border of Gondwana to conform the Cadomian–Avalonian basement of the Hercynian realm.This revised version was published in October 2004 with corrections to the names and order of the authors.     

High resolution fabry-perot and multi-pupil spectral observations of the genuine blue compact dwarf galaxy IZW18

We present the observations of the BCDG IZW18 performed with a Fabry-Perot interferometer at the CFH 3.6 m telescope and with a multi-pupil spectrograph at the SAO (Russia) 6 m telescope. The morphological structure of the galaxy in emission lines and in continuum, the velocity field of the ionized gas, and [OIII]/H ratio distribution along the NW component have been investigated. Besides the NW and SE HII components, we find a population of small HII regions. Continuum maps show that the peaks of the stellar light distribution are displaced with respect to the emission lines maxima. the velocity field shows peculiar motions superposed on an approximately regular background implying solid body rotation. Emission line profiles exhibit an asymmetric structure, except for the NW compact component. The [OIII]/H ratio decreases from the center of the NW component to its edge with the gradient of 1.86 kpc^–1.Published in Astrofizika, Vol. 38, No. 4, pp. 602–615, October–December, 1995.     

Mapping ecosystem services at the regional scale: the validity of an upscaling approach

Mapping ecosystem services (ES) over large scales is important for environmental monitoring but is often prohibitively expensive and difficult. We test a hybrid, low-cost method of mapping ES indicators over large scales in Pará State, Brazil. Four ES indicators (vegetation carbon stocks, biodiversity index, soil chemical quality index and rates of water infiltration into soil) were measured in the field and then summarized spatially for regional land-cover classes derived from satellite imagery. The regionally mapped ES values correlated strongly with independent and local measures of ES. For example, regional estimates of the vegetation carbon stocks are strongly correlated with actual measures derived from field samples and validation data (significant anova test – p-value = 4.51^e?9) and differed on average by only 20 Mg/ha from the field data. Our spatially-nested approach provides reliable and accurate maps of ES at both local and regional scales. Local maps account for the specificities of an area while regional maps provide an accurate generalization of an ES’ state. Such up-scaling methods infuse large-scale ES maps with localized data and enable the estimation of uncertainty of at regional scales. Our approach is first step towards the spatial characterization of ES at large and potentially global scales.     

Geological evolution of the tethys belt from the atlantic to the pamirs since the LIAS

We discuss nine palinspastic geological maps (Plates 1–9), at scale, which depict the evolution of the Tethys belt from the Pliensbachian (190 Ma) to the Tortonian (10 Ma). A Present structural map (Plate 10) is shown for comparison at the same scale with the same conventions. Our reconstructions are based on a kinematic synthesis (Savostin et al., 1986), a paleomagnetic synthesis (Westphal et al., 1986) and geological compilations and analyses concerning in particular the western domain (Ricou et al., 1986), the eastern passive margins (Kazmin et al., 1986a), the eastern active margins (Kazmin et al., 1986b), the Black Sea-Caspian Sea basins (Zonenshain and Le Pichon, 1986) and the ophiolites (Knipper et al., 1986).     

A NUMERICAL STUDY OF THE WINTERTIME CIRCULATION IN THE BOHAI AND HUANGHAI SEAS

The paper presents a numerical two-dimensional model (with a realistic sea basin and wind fields as exter nal forcing) to simulate the basic features of the wintertime circulation in the Bohai and Huanghai (Yellow) Seas (BHS) and to show how the circulation can be driven by wind. The main results can be summarized as follows (1) The basic features of the BHS wintertime circulation can be depicted by the wind-driven barotropi'c motion. (2) The traditionally named Huanghai Sea Warm Current (HSWC) is actually generated by the north wind field, at least in winter. (3) The southward coastal current off the Korean west coast plays a more significant role in the southern Huanghai Sea wintertime circulation than traditionally believed. (4) Though the coastal landform and bottom topography play important roles in the wintertime BHS circulation pattern, the wind is a primary forcing.     

中国城市休闲商业街区研究进展

随着人们闲暇时间和收入的增长,休闲旅游不断发展,而城市休闲商业街区(RBD)作为城市旅游的重要游憩空间,受到普遍关注.城市RBD是传统商业与旅游业的融合,对于城市旅游业的发展、经济转型、城市形象的提升具有重要意义.本文以知网检索到的与RBD相关的246 篇文献为基础,以论文年发表数量和增长率作为主要的评价依据,首先分析国内RBD研究进程,将其分为起步发展、快速发展、巩固发展3 个阶段,从研究主题、使用方法、研究层次等角度对每个阶段特征进行分析.其次,分析文献内容,对RBD的相关研究方向进行划分,共分为12 大类,并从RBD的相关概念与定义、RBD的特征功能与分类、形成机制与过程、空间结构与布局、RBD发展对城市的影响、RBD的旅游形象与游客体验感知、RBD的开发与规划7 个方面对国内RBD研究现状进行了综述.最后对RBD的研究中存在的问题进行总结,其中,概念定义的统一、深化案例研究、细化研究方向、提炼理论层次、应用定量化研究方法、建立评价指标体系等都是今后的研究中应加强的环节,并对今后的研究方向和重点进行展望.     

GIS支持的土壤贫瘠化区域分异研究——以福建为例

区域分异研究是区域开发及生态环境保护的重要基础工作 ,GIS在土壤贫瘠化区域分异研究中的应用是GIS技术在土壤地理学中应用的重要方面。以福建为例 ,在GIS技术支撑下 ,利用多元数理统计方法 ,提出了一个反映土壤养分贫瘠化状况的综合性指标 ,计算并输出福建土壤贫瘠化等级图 ,据此分析了土壤贫瘠化的区域分异特征 ,表明 ,GIS技术在这一领域的应用具有先进性、区域分异研究工作的高效性和成果的实用可靠性。     

岔巴沟、大理河与无定河水土保持减水减沙作用的尺度效应

运用经验公式法、双累积曲线法和不同系列对比法计算出岔巴沟、大理河与无定河流域在20世纪70年代水土保持综合措施的平均减水效益分别为14.47%、20.22%和20.78%,平均减沙效益为64.97%、43.62%和47.26%.对计算结果进行分析发现,用3种方法对岔巴沟、大理河与无定河流域水土保持综合措施减水减沙效益的...