The bombardment history of the Moon as recorded by 40Ar‐39Ar chronology

New petrography and ⁴⁰Ar‐³⁹Ar ages have been obtained for 1–3 mm sized rock fragments from Apollo 16 Station 13 soil 63503 (North Ray crater ejecta) and chips from three rocks collected by Apollo 16 and Apollo 17 missions. Selection of these samples was aimed at the old ⁴⁰Ar‐³⁹Ar ages to understand the early history of the lunar magnetic field and impact flux. Fifteen samples were studied including crustal material, polymict feldspathic fragmental breccias, and impact melts. The impact ages obtained range between approximately 3.3 and 4.3 billion years (Ga). Polymict fragmental breccia 63503,1 exhibits the lowest signs of recrystallization observed and a probable old relic age of 4.547 ± 0.027. The plateau age of 4.293 ± 0.044 Ga obtained for impact melt rock 63503,13 represents the oldest known age for such a lithology. Possibly, this age represents the minimum age for the South Pole‐Aitken (SPA) Basin. In agreement with literature data, these results show that impact ages >3.9 Ga are found in lunar rocks, especially within soil 63503. Impact exhumation of deep‐seated warm crustal material onto the lunar surface is considered to explain the common 4.2 Ga ages obtained for weakly shocked samples from soil 63503 and Apollo 17. This would directly imply that one or more basin‐forming events occurred at that time. Some rock fragments showing none to limited petrologic features indicate thermal annealing. These rocks may have lost Ar while resident within the hot‐ejecta of a large basin. Concurrent with previous studies, these results lead us to advocate for a complex impact flux in the inner solar system during the initial approximately 1.3 Ga.     

Kinematics and geochronology of Early Cretaceous thrusting in the northwestern paleozoic of Graz (Eastern Alps)

Abstract

The multiply deformed Upper Austro-Alpine nappe pile of the Graz area is built up of low-grade metamorphosed Paleozoic rocks which are discordantly overlain by sediments of Santonian (Late Cretaceous) age (“Gosau” formation). Slices of Permo-Mesozoic rocks are absent. Analyses of structures, microfabrics, strain and shear directions were used to decipher the kinematic history; geochronological investigations to date the age of thrusting. K/Ar and Rb/Sr ages of synkinematically grown mica suggest an eo-Alpine (Early Cretaceous) age for the major deformation D1. D1 is characterized by non-coaxial rock flow which caused SW- to W directed nappe imbrication. Incremental strain measurements indicate the progressive superposition of D2 over Dl. In the higher nappe (Rannach Nappe) nappe imbrication continued during D2 changing the direction of nappe transport from SW to NW. Enhanced flattening strain in the deeper nappe (Schöckel Nappe) led to recumbent folds in all scales during D2. This study emphasized two interpretations : (1) The Alpine deformation in the Upper Austro-Alpine nappe pile of the Paleozoic of Graz started in the Earliest Cretaceous (about 125 Ma.). (2) The emplacement of nappes followed a curved translation path in the studied area.     

Deciphering climatic history from lake sediments

Reconstructing climate from lake sediments can be challenging, because the response of lakes and various components of lake systems are mediated by non-climatic factors, such as geomorphic and hydrologic stetting. As a result, the magnitude of lake response to climatic forcing may be non-linear. In addition, changes in the lake system associated with the aging process or non-climatic influences may alter the response to a given climate perturbation. These non-linear and non-stationary characteristics can produce spatial heterogeneity in the pattern and timing of inferred change. One approach for generating regionally robust climatic interpretations from lakes is to increase coordinated efforts to generate and synthesize large data sets, so that localized influences can be more clearly distinguished from broad-scale regional patterns. This approach will be most successful for evaluating climate variation at multi-decadal or longer temporal scales; the climatic interpretation of higher frequency limnological variation can be more complicated, because of dating uncertainties and differential response times of individual proxies and systems. This paper is based on a plenary talk at the 10th International Paleolimnology Conference in Duluth, Minnesota in July 2006.     

An Injectable Apatite Permeable Reactive Barrier for In Situ 90Sr Immobilization

An injectable permeable reactive barrier (PRB) technology was developed to sequester ⁹⁰Sr in groundwater through the in situ formation of calcium‐phosphate mineral phases, specifically apatite that incorporates ⁹⁰Sr into the chemical structure. This injectable barrier technology extends the PRB concept to sites where groundwater contaminants are too deep or where site conditions otherwise preclude the application of more traditional trench‐emplaced barriers. An integrated, multiscale development and testing approach was used that included laboratory bench‐scale experiments, an initial pilot‐scale field test, and the emplacement and evaluation of a 300‐feet‐long treatability‐test‐scale PRB. The apatite amendment formulation uses two separate precursor solutions, one containing a Ca‐citrate complex and the other a Na‐phosphate solution, to form apatite precipitate in situ. Citrate is needed to keep calcium in solution long enough to achieve a more uniform and areally extensive distribution of precipitate formation. In the summer of 2008, the apatite PRB technology was applied as a 91‐m‐long (300 feet) PRB on the downgradient edge of a ⁹⁰Sr plume beneath the Hanford Site in Washington State. The technology was deployed to reduce ⁹⁰Sr flux discharging to the Columbia River. Performance assessment monitoring data collected to date indicate that the barrier is meeting treatment objectives (i.e., 90% reduction in ⁹⁰Sr concentration). The average reduction in ⁹⁰Sr concentrations at four downgradient compliance monitoring locations was 95% relative to the high end of the baseline range approximately 1 year after treatment, and continues to meet remedial objectives more than 4 years after treatment.     

大气CO2富集对根际NaCl盐渍的人参果植株干物质生产和水分利用的影响

对单株砂培盆栽的半木质化枝条扦插生根的一月龄人生果(Solanum muricatum Ait.)栽培品种"Xotus",每周浇两次200mL NaCl质量浓度分别为0mg·L^-1和25mg·L^-1的Hoagland营养液处理2个月,第二个月在控制空气CO₂体积分数为(350±10)×10^-6、(700±10)×10^-6和(1050±10)×10^-6的植物生长箱内试验。结果表明,人参果植株干物质生产量和耗水量受根际NaCl盐渍而下降,又随大气CO₂升高而增加。根际NaCl盐渍能增大植株叶片蒸腾系数、根/冠比和干物质向枝干和根部分配的比例及积累量,降低根系吸收水分的效率和耗水量。升高大气CO₂能促进叶片发育及干物质向地上部其他器官和地下部组织分配,增加总叶面积、比叶干重和各种器官中干物质增长量,提高干物质生产率和水分利用率。根际经25mg·L^-1NaCl盐渍处理的植株,总干物质增长量和水分利用率相应下降50%～54%和24%～37%;与350×10^-6CO₂的处理的植株相比,700×10^-6及1050×10^-6CO₂的处理分别使这两项指标提高到79%～106%和61%～88%以及133%～189%和99%～142%。大气CO₂富集能改善受NaCl盐渍的植株干物质生产力、提高水分利用率。根际NaCl盐渍和大气CO₂富集对人参果植株干物质生产和水分利用有生物互作效应。它们的共同作用会促进植株干物质的增长及叶片中合成的干物质向其他器官分配,提高干物质生产率和水分利用率,同时减少总叶面积、枝条和根系干重、根系吸水效率、植株耗水量和叶片蒸腾系数。因此,全球大气CO₂富集将有利于该作物的干物质生产和水分利用。     

Hot granulite nappes — Tectonic styles and thermal evolution of the Proterozoic granulite belts in East Africa

A section through the Neoproterozoic Mozambique Belt of Tanzania exposes western foreland (Archaean Tanzania Craton and Palaeoproterozoic Usagaran Belt), marginal (Western Granulites) and eastern, internal (Eastern Granulites) portions of the orogen. The assembly of granulite nappes at ca. 620 Ma displays westward emplacement along an eastward deepening basal decollement and forward propagation of thrusts, climbing from the deep crust to the surface. This goes along with eastward increase of syntectonic temperatures, derived from prevalent deformation mechanisms, and eastward decrease of the kinematic vorticity number. Distinctly different pressure - temperature paths with a branch of isothermal decompression (ITD) in Western Granulites and isobaric cooling (IBC) in Eastern Granulites reflect residence times of rocks within lower crustal levels. Western Granulites, exhumed rapidly at the orogen margin, display ITD and non-coaxial fabrics. Eastern Granulites in the internal orogen portions escaped from rapid exhumation and show IBC and co-axial flow fabrics. The vertical variation of structural elements, i.e. basement — cover relations within the Eastern Granulites, shows decoupling between lower and middle crust with horizontal west — east stretching in the basement and horizontal west — east shortening in the cover.A model of hot fold nappes [Beaumont, C., Nguyen, M.H., Jamieson, R.A., Ellis, S., 2006. Crustal flow modes in large hot orogens. In: Law, R.D., Searle, M.P., Godin, L., (eds). Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications. vol. 268, 91–145] is adopted to explain flow diversity in the deep crust. The lower crust represented by Eastern Granulite basement flowed coaxially outwards (westward) in response to thickened crust and elevated gravitational forces, supported by a melt-weakened, viscous channel at the crustal base. Horizontal flow with rates faster than thermal equilibration gave rise to isobaric cooling. Simultaneously the mid crust (Eastern Granulite cover) was shortened when hot fold nappes moved along upward climbing thrust planes. Western Granulites preserved isothermal decompression through exhumation by thrusting and coeval erosion at the orogen front.Two different styles define the Neoproterozoic East African Orogen between northern Egypt and southern Mozambique. The Arabian Nubian Shield in the north is classified as small and cold orogen in which thin — skinned thrusting was associated with lateral extrusion. The Central Mozambique Belt in Tanzania/Southern Kenya is classified as large and hot orogen characterized by thick-skinned thrusting and assembly of large granulite nappes.     

A review of terrestrial radar interferometry for measuring surface change in the geosciences

This paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement. Different hardware‐types and acquisition concepts are described, which use either real or synthetic aperture for radar image formation. We present approaches for data processing procedures, paying special attention to the separation of high resolution displacement information from atmospheric phase variations. Recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection. Applications range from detection and quantification of very slow moving (millimeters to centimeters per year) displacements in rock walls from repeat monitoring, to rapid processes resulting in fast displacements (~50 m/yr) acquired during single measurement campaigns with durations of only a few hours. Fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes. A concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique, as well as in areas characterized by rapid decorrelation. Empirical data from a Ku‐band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock‐surfaces and after a few seconds to minutes in vegetated areas during windy conditions. The examples show that the displacement field can be measured for landslides in dense grassland, ice surfaces on flowing glaciers and snowpack creep. Copyright © 2014 John Wiley & Sons, Ltd.     

2001年1月26日高纬磁层顶通量管事件的观测研究--空间电流密度计算及分析

讨论了三种根据Cluster Ⅱ四颗卫星的磁场测量数据计算空间电流的方法及其误差,论证了这几种方法的内在一致性,并得到了完全相同的计算结果. 进而依据Cluster Ⅱ 磁场探测资料,计算了2001年1月26日多重磁通量管和FTE事件中高纬磁层顶边界层和磁鞘区的电流密度. 结果表明,磁通量管内电流密度较大,可达到约10-8A/m2;计算精度较高,结果可靠. 本文还应用最小方差分析法（MVA）,发现电流方向与通量管的轴向基本一致;论证了电流MVA分析在研究通量管性质时的作用,同时提出了电流管的概念.