The optical properties of the finest fraction of lunar soil: Implications for space weathering     

Sarah K. NOBLE  Carl M. PIETERS  Lawrence A. TAYLOR  Richard V. MORRIS  Carlton C. ALLEN  David S. McKAY  Lindsay P. KELLER 《Meteoritics & planetary science》2001,36(1):31-42

Abstract— The fine fraction of lunar soils (<45 μm) dominates the optical properties of the bulk soil. Definite trends can be seen in optical properties of size separates with decreasing particle size: diminished spectral contrast and a steeper continuum slope. These trends are related to space weathering processes and their affects on different size fractions. The finest fraction (defined here as the <10 μm fraction) appears to be enriched in weathering products relative to the larger size fractions, as would be expected for surface correlated processes. This <10 μm fraction tends to exhibit very little spectral contrast, often with no distinguishable ferrous iron absorption bands. Additionally, the finest fractions of highland soils are observed to have very different spectral properties than the equivalent fraction of mare soils when compared with larger size fractions. The spectra of the finest fraction of feldspathic soils flatten at longer wavelengths, whereas those of the finest fraction of basaltic soils continue to increase in a steep, almost linear fashion. This compositional distinction is due to differences in the total amount of nanophase iron that accumulates in space weathering products. Such ground‐truth information derived from the <10 μm fraction of lunar soils provides valuable insight into optical properties to be expected in other space weathering environments such as the asteroids and Mercury.  相似文献   

西藏冈底斯矿带南缘矽卡岩型铜矿床含矿岩体锆石U-Pb年龄及意义   总被引：11，自引：4，他引：7  

梁华英  魏启荣  许继峰  胡光黔  Charllote Allen 《岩石学报》2010,26(6):1692-1698

西藏冈底斯矿带发育大量斑岩铜钼矿床及铜铅锌多金属矿床,形成斑岩铜矿带及多金属矿带。过去的工作表明,冈底斯带南部矿床同位素年龄多小于30Ma,形成于碰撞期后伸展环境。本文测定了冈底斯矿带南缘克鲁-冲木达矽卡岩型铜(金、钼)矿集区桑布加拉矽卡岩型铜(金)矿化岩体锆石LA-ICP-MSU-Pb年龄及锆石Ce4+/Ce3+比值。矿化岩体锆石U-Pb年龄:92.1±0.6Ma,MSWD=1.0,锆石Ce4+/Ce3+比值在90～562之间,平均值为287。锆石Ce4+/Ce3+比值和玉龙矿带含矿岩体锆石的比值基本一致,显示矽卡岩矿化岩体岩浆氧逸度较高。印度板块与欧亚板块碰撞时间在65～45Ma之间,桑布加拉矽卡岩型铜矿化岩体锆石U-Pb年龄表明冈底斯带不但发育碰撞期后大规模成矿作用,也发育与洋壳俯冲构造岩浆事件有关的成矿作用。这为冈底斯矿带洋壳俯冲有关矿床的寻找提供了依据。  相似文献   

STUDIES IN FLUVIATILE SEDIMENTATION: SIX CYCLOTHEMS FROM THE LOWER OLD RED SANDSTONE, ANGLOWELSH BASIN   总被引：2，自引：0，他引：2  

J. R. L. ALLEN 《Sedimentology》1964,3(3):163-198

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Counterpoint     

P.A. ALLEN  ROBERT CAMPBELL 《Geology Today》1985,1(3):74-74

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PUERTO PEÑASCO: FISHING VILLAGE TO TOURIST MECCA     

JOHN FINN  ARIANNA FERNANDEZ  LINDSEY SUTTON  DANIEL D. ARREOLA  CASEY D. ALLEN  CLAIRE SMITH 《Geographical review》2009,99(4):575-597

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ETHNIC RESIDENTIAL CONCENTRATIONS IN UNITED STATES METROPOLITAN AREAS     

JAMES P. ALLEN  EUGENE TURNER 《Geographical review》2005,95(2):267-285

ABSTRACT. Although residential concentrations of immigrant ethnic groups in cities were common a century ago, it is not clear to what extent members of more recently arrived groups live near each other. We attempt to determine how common such clustered settlement is today, using 2000 census data to measure concentrations of Asians, Hispanics, and their larger ethnic subgroups in fifteen large metropolitan areas. The percentage of an ethnic group that is residentially concentrated correlated significantly with the group's proportion in an area. With metropolitan areas weighted equally, 38 percent of Hispanics and 13 percent of Asians were concentrated. However, when we analyzed eight specific nationality groups, the residentially concentrated proportion ranged from 14 to 59 percent. Level of cultural assimilation appears to explain group differences in level of concentration. Although ethnic concentrations were more pronounced in the largest metropolitan areas, important concentrations were also found in many of the smaller areas in our study.  相似文献   

In-Situ SHRIMP U-Pb Dating of Xenotime Outgrowth on Detrital Zircon Grains from the Changzhougou Formation of the Ming Tomb District, Beijing     

SHI Yuruo  Kennedy ALLEN  Aleinikoff JOHN  SONG Tianrui  LI Linlin  SUN Huiyi 《《地质学报》英文版》2015,89(1):304-305

<正>SHRIMP U-Pb dating of diagenetic xenotime from sedimentary rocks has provided age constraints for sedimentary diagenesis(Mc Naughton et al.,1999;Fletcher et al.,2000;England et al.,2001;Rasmussen et al.,2004;Vallini et al.,2007).Xenotime(YPO4)may grow during early diagenesis,typically being present as a trace constituent in siliciclastic sedimentary rocks(Rasmussen,2005),in the form of syntaxial outgrowths on detrital zircon grains.Diagenetic xenotime occurs in a  相似文献   

Architecture and formation of transgressive–regressive cycles in marginal marine strata of the John Henry Member,Straight Cliffs Formation,Upper Cretaceous of Southern Utah,USA     

JESSICA L. ALLEN  CARI L. JOHNSON 《Sedimentology》2011,58(6):1486-1513

Marginal marine deposits of the John Henry Member, Upper Cretaceous Straight Cliffs Formation, were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits. Complete transgressive–regressive cycles, comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies, are distinguished based on their internal facies architecture and bounding surfaces. Two main types of boundaries occur between the transgressive and regressive portions of each cycle: (i) surfaces that record the maximum regression and onset of transgression (bounding surface A); and (ii) surfaces that place deeper facies on top of shallower facies (bounding surface B). The base of a transgressive facies (bounding surface A) is defined by a process change from wave‐dominated to tide‐dominated facies, or a coaly/shelly interval indicating a shift from a regressive to a transgressive regime. The surface recording such a process change can be erosional or non‐erosive and conformable. A shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces (bounding surface B). These two main bounding surfaces and their subtypes generate three distinct transgressive – regressive cycle architectures: (i) tabular, shoaling‐upward marine parasequences that are bounded by flooding surfaces; (ii) transgressive and regressive unit wedges that thin basinward and landward, respectively; and (iii) tabular, transgressive lagoonal shales with intervening regressive coaly intervals. The preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive–regressive cycles. Acknowledging variation in transgressive–regressive cycles, and recognizing transgressive successions that correlate to flooding surfaces basinward, are both critical to achieving an accurate sequence stratigraphic interpretation of high‐frequency cycles.  相似文献   

赣南大吉山五里亭岩体的锆石ELA-ICP-MS定年及其与钨成矿关系的新认识   总被引：39，自引：3，他引：36  

邱检生  McInnes BIA  徐夕生  Allen C M 《地质论评》2004,50(2):125-133

大吉山是南岭地区一个著名的大型钨多金属矿床,五里亭岩体是矿区出露规模最大的火成岩体,岩性为中粗粒似斑状黑云母二长花岗岩。锆石 ELA-ICP-MS 定年结果表明其形成年龄为 237.5±4.8 Ma,属印支期岩浆活动的产物。与南岭地区典型钨多金属矿床成矿岩体相比,五里亭岩体贫硅,富钙、镁、铁,Rb/Sr、Rb/Ba 和 U/Th 比值低,K/Rb 比值高,铕负异常不显著,分异指数低,尚未达到矿化岩体的分异演化程度,不具备矿化岩体的地球化学特征。元素—同位素综合示踪显示区内白云母碱长花岗岩为五里亭岩体经高度分异演化的产物,它与钨多金属矿成矿直接有关。矿区范围内出露的闪长岩起源于地幔,这一岩浆侵位所引起的高热场环境有利于花岗质岩石的形成与演化,对成矿具有重要的意义。  相似文献   

Sensitivity analysis of the climate of a chaotic system     

DANIEL J. LEA  MYLES R. ALLEN  THOMAS W. N. HAINE 《地球，A辑:动力气象学与海洋学》2000,52(5):523-532

This paper addresses some fundamental methodological issues concerning the sensitivity analysis of chaotic geophysical systems. We show, using the Lorenz system as an example, that a naïve approach to variational ("adjoint") sensitivity analysis is of limited utility. Applied to trajectories which are long relative to the predictability time scales of the system, cumulative error growth means that adjoint results diverge exponentially from the "macroscopic climate sensitivity"(that is, the sensitivity of time‐averaged properties of the system to finite‐amplitude perturbations). This problem occurs even for time‐averaged quantities and given infinite computing resources. Alternatively, applied to very short trajectories, the adjoint provides an incorrect estimate of the sensitivity, even if averaged over large numbers of initial conditions, because a finite time scale is required for the model climate to respond fully to certain perturbations. In the Lorenz (1963) system, an intermediate time scale is found on which an ensemble of adjoint gradients can give a reasonably accurate (O(10%)) estimate of the macroscopic climate sensitivity. While this ensemble‐adjoint approach is unlikely to be reliable for more complex systems, it may provide useful guidance in identifying important parameter‐combinations to be explored further through direct finite‐amplitude perturbations.  相似文献