壳内岩浆层演化的盆地效应:以中国东南部中生代盆地为例

中国东南部中生代发育有拗陷型、断裂型、断陷型3种不同类型的盆地,其中前者发育于晚三叠世-早侏罗世,其内多为含煤建造;次者发育于中侏罗世-早白垩世,主要为火山岩建造;后者发育于白垩纪-古近纪,主要为陆相红岩建造。研究结果表明,盆地构造类型的演化与该区中生代壳内岩浆层的演化密切相关。与联合古陆解体相伴随的古太平洋板块俯冲使得东亚陆缘岩石圈的内能逐渐升高,其结果是壳内岩浆层的形成和增厚以及其上盖层岩石的弯曲变形,导致中生代早期众多拗陷盆地的形成;燕山早期的构造运动使印支期已强烈变形的地壳进一步破裂,为壳内岩浆层的物质溢出或喷发提供了通道条件,从而在重熔界面(岩浆层上界面)埋深较浅的本区东部形成众多火山岩盆地;系统内能在晚侏罗世后逐渐下降,地壳冷却收缩使得断块的重力调整逐渐占主导位置,形成众多由正断层控制的断陷盆地。     

Land clearance and hydrological change in the Sahel: SW Niger

In the West African semiarid belt of the Sahel, for the second half of the XXth century, lasting droughts (1970s–1980s) and one of the World's highest population growths have resulted in major land cover and hydrological changes that can be quantified using aerial photographs. This paper aims to provide one of the longest combined observations of land cover and hydrological changes for semiarid areas using a time series of normalised mosaics of aerial photographs dating back from 1950, field inquiries, and updated groundwater data. The 500 km² study area in southwest Niger was chosen (i) for its rural environment representative of the rain-fed agriculture belt of the Sahel and (ii) to encompass the main hydrological study sites investigated in this region over the past two decades (Hapex-Sahel and AMMA experiments, 1990–2000s). Results have significant implications for future freshwater availability and food security in the Sahel.Between 1950 and 1992,  80% of the study area has been cleared, firstly to open new areas for agriculture and secondly for firewood supply (59% of the plateaux, 42% of the valley bottoms, and 87% of the hillslopes). Intermediate aerial photograph surveys (1960, 1975) attest an accelerated loss in the woody savannah that could not be recovered on the short term. A strong, indirect impact of land clearance is observed on the water resources. Land clearance has resulted in a modification of the soil properties and infiltration capacity and has led to an increase in Hortonian runoff collected in numerous gullies and ponds. Between 1950 and 1992, aerial photographs show a  2.5 fold increase of the drainage density with the development of large drainage systems and new ponds. Groundwater data also indicate a continuous rise in the water table, mostly noticeable since the 1980s with a mean groundwater level rise of  4 m for the 1963–2005 period (+ 15% in aquifer reserves). The relatively short  30 year time-lag between the onset of land clearance and the beginning of the water table rise is linked to the process of indirect groundwater recharge and is timed with the connectivity of the drainage network and the formation of new ponds. Finally, the sustained increase in surface runoff and groundwater recharge during the past four decades indicates that the indirect impact of land clearance on the terrestrial water balance has been stronger than that of the long-lasting Sahelian drought. As the rate of land clearance increased for the past century in semiarid Africa, its main hydrological effects may not yet be fully perceptible.     

Asymmetrical river valleys in response to tectonic tilting and strike‐slip faulting,northeast margin of Tibetan Plateau

The northeast margin of the Tibetan Plateau, a particularly important area to understand the mechanism of plateau formation, is characterized by large transpressional arcuate faults. There is debate on the amount of Quaternary sinistral displacement on the major Haiyuan Fault. Previously unrecognized systemic asymmetrical valleys have developed between the Haiyuan and Xiangshan faults. Southeast tilting and sinistral displacement on the northeast side of the Haiyuan Fault resulted in southeast migration of large rivers and asymmetrical widening of their valleys, leaving a systematic distribution of tilted strath terraces along their northwest sides. Where asymmetrical widening created by tilting kept pace with sinistral displacement, rivers have not been deflected, and the increase in valley width downstream from the fault should equate to total lateral displacement since river formation (e.g. Yuan River, a 7 km asymmetrical valley with a c. 2.2 Ma paleomagnetic age). Where river deflection and asymmetrical valley growth are coeval, valley width is less than total horizontal displacement (e.g. Hebao River, a c. 2.1 km asymmetrical valley with c. 2 km deflection). All rivers north of the Haiyuan Fault converge to cut across the Xiangshan Mountains as a gorge. Northeast thrusting of the upthrown side of the Xiangshan Fault has resulted in degradation and related strath terrace formation as the valleys asymmetrically widened. A probable earthquake‐induced landslide caused by movement on the Xiangshan Fault in latest Pleistocene blocked the gorge causing aggradation along all rivers and their tributaries. Deposition terraces were formed after the landslide dam was breached. Together with previous research on the Xiangshan Fault, it is concluded that there has been c. 7 km of Quaternary sinistral displacement on the Haiyuan and Xiangshan faults along the northeast margin of the Tibetan Plateau since the formation of rivers that intersect them. Copyright © 2014 John Wiley & Sons, Ltd.     

On the origin of the Kuiper belt

I review the work that has been done so far aiming at the understanding of the origin of the Kuiper belt. Three peculiar characteristics of the Kuiper belt are used as constraints for the formation models. These are the unexpected dynamical excitation of the orbits, the Kuiper belt outer edge near the 1:2 resonance with Neptune and the mass paucity of the belt. Among the various scenarios proposed, those based on a primordial planetary migration give the best results. In particular, the Nice model is analyzed with respect to its coherence with the present characteristics of the belt. Special attention is given to the controversy on the origin of the Kuiper belt cold population.     

Automated cleaning and uncertainty attribution of archival bathymetry based on a priori knowledge

Hydrographic offices hold large valuable historic bathymetric data sets, many of which were collected using older generation survey systems that contain little or no metadata and/or uncertainty estimates. These bathymetric data sets generally contain large outlier (errant) data points to clean, yet standard practice does not include rigorous automated procedures for systematic cleaning of these historical data sets and their subsequent conversion into reusable data formats. In this paper, we propose an automated method for this task. We utilize statistically diverse threshold tests, including a robust least trimmed squared method, to clean the data. We use LOESS weighted regression residuals together with a Student-t distribution to attribute uncertainty for each retained sounding; the resulting uncertainty values compare favorably with native estimates of uncertainty from co-located data sets which we use to estimate a point-wise goodness-of-fit measure. Storing a cleansed validated data set augmented with uncertainty in a re-usable format provides the details of this analysis for subsequent users. Our test results indicate that the method significantly improves the quality of the data set while concurrently providing confidence interval estimates and point-wise goodness-of-fit estimates as referenced to current hydrographic practices.     

Fauna of polyhaline subtidal marsh creeks in Southern New Jersey: Composition,abundance and biomass

Three polyhaline subtidal marsh creeks in southern New Jersey were sampled with weirs and seines to determine seasonal patterns of utilization by fishes and macroinvertebrates. Sixty-four species of fish, 13 invertebrates, and the diamondback terrapin were collected in 69 weir and 57 seine samples from April to November 1988 and April to October 1989. Average abundance, biomass, and faunal composition were strongly seasonal with greatest abundances during spring and summer, and peaks in May and August. Sixteen species were represented by all life-history stages, including the five most important species by combined ranks of percent frequency, mean abundance, and mean biomass. These five species were important during spring, summer, and fall and included the fishes Menidia menidia and Fundulus heteroclitus, the shrimps Palaemonetes vulgaris and Crangon septemspinosa, and the crab Callinectes sapidus. In addition, there were distinct seasonal assemblages of other species which utilized the creeks primarily as young-of-the-year. Importnat species in spring collections included the fishes Clupea harengus, Alosa aestivalis, Alosa pseudoharengus, Pollachius virens, and Urophysics regia, while Leiostomus xanthurus, Pomatomus saltatrix, Paralichthys dentatus, Mugil curema, and Strongylura marina were important in the summer. Fall samples were best characterized by declining abundances of summer species. Thus, subtidal marsh creeks in southern New Jersey appear to be valuable nurseries for a variety of species which spawn over the continental shelf, as well as one of the most important habitats for estuarine residents.     

Actinolite-hornblende pairs in metamorphosed gabbros,Hidaka mountains,Hokkaido

Actinolite-actinolitic hornblende and actinolitic hornblende-hornblende pairs are described from gabbroic amphibolites and epidote amphibolites formed by dynamic metamorphism during uplift of gabbroic rooks in the Hidaka Metamorphic Belt, Hokkaido. Electron microprobe analyses indicate that coupled substitutions involved in the transition from actinolite to hornblende are essentially those of edenite and tschermakite-ferritschermakite together with smaller amounts of glaucophane-riebeckite, i.e. Al^IV, Al^VI, Fe³⁺, A-site occupancy and Na^M4 increase with replacement of Mg by Fe²⁺+ Mn and Si by Al^IV. During metamorphism the amount of deformation due to shearing has affected the degree of compositional discontinuity in the actinolite-hornblende series and the compositional gap is most pronounced in the epidote amphibolite. The coexisting actinolite-hornblende do not represent an equilibrium pair as textural relations indicate that the actinolitic amphiboles are relics. It is suggested that shearing deformation during uplift has caused an overstepping of the changing physico-chemical conditions of metamorphism so that compositional readjustment of amphiboles was not achieved. Equilibrium-disequilibrium actinolite-hornblende pairs are discussed from other localities where rocks of basaltic composition have been metamorphosed.     

Alteration of metamict,rare-earth,AB2O6-type NbTaTi oxides

Primary and secondary alteration affect composition, physical properties and the results of annealing studies of metamict, rare-earth, AB₂O₆-type Nb-Ta-Ti oxides.Primary alteration (e.g. hydrothermal) causes a consistent increase in calcium content, generally a decrease in the uranium and thorium content, a decrease in the absolute rare earth concentrations, (with only one exception, the REE distributions remain constant), a slight decrease in B-site cations, and an increase in structural and absorbed water.Secondary alteration (e.g. weathering) is similar but produces a decrease in Ca content, an increased leaching of A-site cations and relative increase in B-site cations.R.I., S.G., and reflectance (546 nm) decrease with both types of alteration, but VHN₅₀ remains approximately constant in altered and unaltered areas of the same specimen. The deviation from stoichiometric proportions of A- and B-site cations with increased alteration results in complex recrystallization phase assemblages during annealing studies (500–1000°C at 1 bar). The effect of alteration on systems of nomenclature and identification procedures is discussed.     

Structure-configurational entropy and its effect on the thermodynamic stability of uranyl phases: With special application for geological disposal of nuclear waste

Uranyl phases are found as the alteration products of uraninite under oxidizing condi- tions[1—3]. They are also expected to be the dominant alteration products of spent UO2 fuel in an oxidizing environment, such as at nuclear waste repositories[4—8]. …