Gas‐melt interactions and their bearing on chondrule formation

Abstract— Interactions between nebular gas and molten silicates or oxides could have played a major role in the formation and differentiation of the first solids formed in the solar system. In order to simulate such interactions, we set up a new experimental device in which isothermal condensation experiments have been conducted. Partially molten chondrule‐like samples have been exposed to high SiO(g) partial pressures, for intervals between 80 and 300 s and at temperatures ranging from 1600 to 1750 K. Results show that silica entering from the gas phase could be responsible for several textural and mineralogical features observed in natural chondrules. For instance, these experiments reproduce not only the mineralogical zonation of porphyritic olivine‐pyroxene chondrules with the peripheral location of pyroxenes, but also olivine resorption textures and the common poikilitical enclosure of olivines in pyroxenes. In the light of these similarities, we advocate that gas‐melt interactions through condensation are viable mechanisms for chondrule formation and hence may place severe constraints on the history of these primitive objects. In the nebula, high SiO(_g) partial pressures could have been established by the volatilization of regions with high dust/gas ratio. A possible scenario for this stochastic thermal activity is the intense activity of the protosun in its young stellar object phase.     

Landform classification from a digital elevation model and satellite imagery

The Iranian Soil and Water Research Institute has been involved in mapping the soils of Iran and classifying landforms for the last 60 years. However, the accuracy of traditional landform maps is very low (about 55%). To date, aerial photographs and topographic maps have been used for landform classification studies. The principal objective of this research is to propose a quantitative approach for landform classification based on a 10-m resolution digital elevation model (DEM) and some use of an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. In order to extract and identify the various landforms, slope, elevation range, and stream network pattern were used as basic identifying parameters. These are extractable from a DEM. Further, ASTER images were required to identify the general outline shape of a landform type and the presence or absence of gravel. This study encompassed a relatively large watershed of 451 183 ha with a total elevation difference of 2445 m and a variety of landforms from flat River Alluvial Plains to steep mountains. Classification accuracy ranged from 91.8 to 99.6% with an average of 96.7% based upon extensive ground-truthing. Since similar digital and ASTER image information is available for Iran, an accurate landform map can now be produced for the whole country. The main advantages of this approach are accuracy, lower demands on time and funds for field work and ready availability of required data for many regions of the world.     

Integrated modelling of population,employment and land-use change with a multiple activity-based variable grid cellular automaton

A constrained cellular automaton (CA) framework is used to model both land use and, at the same resolution, densities of population and economic activity. The multi-scale processes determining the location of population, economic activity and land use are captured in a variable grid CA, in which the neighbourhood of each cell includes the entire modelled area. The transition rules generating the spatial dynamics incorporate both the land use and the activities, and because they cover the entire modelled area, they represent interaction effects at all spatial scales; effectively, they are distance decay functions. In general, any particular cell hosts a number of activities (population, employment in various sectors) regardless of its land use, so in effect multiple land uses are modelled as multiple activities, although activity levels are normally highest on cells of the corresponding land use. The model is applied to both the urban-centred Greater Dublin Region and the country of Belgium, which consists of the entire polycentric urban system and its rural matrix. Results for both applications are good, as measured by the errors of both predicted populations and fractal dimensions, and the model outperforms the best existing models by these measures.     

打造过硬品牌以彰显地质公园在UNESCO世界级名录中的特殊地位——PPF理念(“过去—现在—将来”理念)

目前世界地质公园网络(GGN)共有90个成员,分布在27个国家和地区,尽管在这个网络建立过程中,联合国教科文组织起着关键作用,但在过去十多年里,其与地质公园的关系只能被定义为“特别支持”,眼下两者的关系应该在一个国际倡议或计划下被正式化,这将有利于进一步提高地质公园的管理、交流合作和资源利用.实现该目标,就要清晰地阐明地质公园核心的独有特色,使地质公园与联合国教科文组织已实施的计划形成互补,不会产生冲突或重叠.本文介绍的PPF理念将会是一个有效的方法,以此创建一个过硬的品牌,彰显地质公园在UNESCO世界级名录中的特殊地位.     

Between plate and salt tectonics—New stratigraphic constraints on the architecture and timing of the Dead Sea basin during the Late Quaternary

The Dead Sea is an extensional basin developing along a transform fault plate boundary. It is also a terminal salt basin. Without knowledge of precise stratigraphy, it is difficult to differentiate between the role of plate and salt tectonics on sedimentary accumulation and deformation patterns. While the environmental conditions responsible for sediment supply are reasonably constrained by previous studies on the lake margins, the current study focuses on deciphering the detailed stratigraphy across the entire northern Dead Sea basin as well as syn and post-depositional processes. The sedimentary architecture of the late Quaternary lacustrine succession was examined by integrating 851 km of seismic reflection data from three surveys with gamma ray and velocity logs and the stratigraphic division from an ICDP borehole cored in 2010. This allowed seismic interpretation to be anchored in time across the entire basin. Key surfaces were mapped based on borehole lithology and a newly constructed synthetic seismogram. Average interval velocities were used to calculate isopach maps and spatial and temporal sedimentation rates. Results show that the Amora Formation was deposited in a pre-existing graben bounded by two N-S trending longitudinal faults. Both faults remained active during deposition of the late Pleistocene Samra and Lisan Formations—the eastern fault continued to bound the basin while the western fault remained blind. On-going plate motion introduced a third longitudinal fault, increasing accommodation space westwards from the onset of deposition of the Samra Formation. During accumulation of these two formations, sedimentation rates were uniform over the lake and similar. High lake levels caused an increase in hydrostatic pressure. This led to salt withdrawal, which flowed to the south and southwest causing increased uplift of the Lisan and En Gedi diapirs and the formation of localized salt rim synclines. This induced local seismicity and slumping, resulting in an increased thickness of the Lisan succession within the lake relative to its margins. Sedimentation rates of the Holocene Ze'elim Fm were 4–5 times higher than before. The analysis presented here resolves central questions of spatial extent and timing of lithology, deposition rates and their variability across the basin, timing of faulting at and below the lake floor, and timing and extent of salt and plate tectonic phases and their effect on syn and post-depositional processes. Plate tectonics dictated the structure of the basin, while salt tectonics and sediment accumulation were primarily responsible for its fill architecture during the timeframe examined here.