HOUSING INTEGRATION AND RENT SUPPLEMENTS TO EXISTING HOUSING*

This work examines the use of an annually updated metropolitan data system as a tool for evaluating benign racial location policies during the first year of the Section 8 Existing Rent Supplement program. Case-study evidence shows that the rent supplement program (with benign locational policies) is ineffective in reducing the isolation faced by minority groups, and that the information used to monitor compliance of the program with benign locational policies lags badly behind the true state of affairs. As a result, new areas of racial concentration have been encouraged and augmented.     

Comments on “The crustal structure of the Balearic Sea” — in light of deep-sea drilling in the Mediterranean

Supplementary to the paper by K. Hinz on The crustal structure of the Balearic Sea, some results are reported from the deep-sea drilling cruise of the “Glomar Challenger”.     

On the crystallinity,probability of occurrence,and rheology of lava and magma

Given a set of comagmatic lavas of similar composition but varying crystallinity, a diagram can be constructed using only the modes of the phenocrysts that quantitively shows the sequence of crystallization. This is done by plotting the amount of each phenocryst against the total crystallinity or percentage of melt of the lava itself. A histogram of the total phenocryst content measures the probability of the magma to be erupted as lava. This eruption probability (P _E ) is the product of the probability of finding the magma at any state of crystallinity (thermal probability, P _T ) and the rheological probability (P _R ) of the magma being physically able to erupt (i.e. P _E =P _T P _R ). It is shown that P _E is given by dX/dT, where X is the crystallinity of the magma as a function of temperature (T). Because crystal production is generally nonlinear—in most rocks it is step-like—P _E is a bellshaped curve stradling the temperature at which the magma is one half crystallized. Near the liquidus it is most favorable rheologically for the magma to erupt. But the probability is small of sampling a magma near its liquidus, because it cools quickly there. It is maximum when there are high rates of crystal production, because it then cools slowly. As the crystallinity increases, it reaches a critical point of maximum packing (i.e. lowest porosity) around 50–60% crystals where it becomes rheologically impossible to erupt. The magma looses its potential to become a lava and it becomes a pluton. From a histogram of crystallinity and P _T ,P _R can be found. This technique, as well as the construction of the mode-crystallization (M-C) diagram, is illustrated using a set of Aleutian lavas. These lavas also show that the point of critical crystallinity decreases with increasing silica content of the lava. Because this critical crystallinity is much lower for granitic magmas, they are much more probable than basaltic magmas to become plutons. Beyond this point, granitic magmas can only erupt as ash flows. This correlation of critical crystallinity and silica content is used to show a method by which the viscosity of the magma can be estimated as a function of crystallinity. This variation is found to compare favorably with Roscoe's equation of the dependence of viscosity on the concentration of suspended solids. These results show that differentiation probably can not normally take place beyond this critical crystallinity. The extraction of melt beyond this critical point by filter pressing is unlikely because the assemblage dilates upon stressing. Only if the phenocrysts deform viscously can additional melt be extracted, and this can probably only occur with large (–30km) bodies.     

Mesozoic tectonic evolution of the Southeast China Block: New insights from basin analysis

In order to better understand the Mesozoic tectonic evolution of Southeast China Block (SECB in short), this paper describes geological features of Mesozoic basins that are widely distributed in the SECB. The analyzed data are derived from a regional geological investigation on various Mesozoic basins and a recently compiled 1:1,500,000 geological map of Mesozoic–Cenozoic basins. Two types of basin are distinguished according to their tectonic settings, namely, the post-orogenic basin (Type I) and the intracontinental extensional basin (Type II); the latter includes the graben and the half-graben or faulted-depression basins. Our studies suggest that the formation of these basins connects with the evolution of geotectonics of the SECB. The post-orogenic basin (Type I) was formed in areas from the piedmont to the intraland during the interval from Late Triassic to Early Jurassic; and the formation of the intracontinental extensional basin (Type II) connects with an intracontinental crustal thinning setting in the Late Mesozoic. The graben basin was generated during the Middle Jurassic and is associated with a bimodal volcanic eruption; and the half-graben or faulted-depression basin, filled mainly by the rhyolite, tuff and sedimentary rocks during Early Cretaceous, is occupied by the Late Cretaceous–Paleogene red-colored terrestrial clastic rocks. We noticed that the modern outcrops of numerous granites and basins occur in a similar level, and the Mesozoic granitic bodies contact with the adjacent basins by large normal faults, suggesting that the modern landforms between granites and basins were yielded by the late crustal movement. The modern basin and range framework was settled down in the Cretaceous. Abundant sedimentary structures are found in the various basins, from that the deposited environments and paleo-currents are concluded; during the Late Triassic–Early Jurassic time, the source areas were situated to the north and northeast sides of the outcrop region. In this paper, we present the study results on one geological and geographical separating unit and two separating fault zones. The Wuyi orogenic belt is a Late Mesozoic paleo-geographically separating unit, the Ganjiang fault zone behaves as the western boundary of Early Cretaceous volcanic rocks, and the Zhenghe–Dapu fault zone separates the SE-China Coastal Late Mesozoic volcanic-sedimentary basins and the Wuyi orogenic belt. Finally, we discuss the geodynamic mechanisms forming various basins, proposing a three-stage model of the Mesozoic sedimentary evolution.     

Tectonique transpressive en terre Adélie au Paléoprotérozoı̈que (Est Antarctique)Palaeoproterozoic transpression in Terre Adélie (East Antarctica)

The Palaeoproterozoic units of Terre Adélie show two types of structural domains associated with HT–LP metamorphic conditions: domes and NS–N340° striking vertical shear zones. Shear zones reflect dextral transpressive motions. Domes reflect sub-vertical shortening and principal stretching subparallel to shear zones. They could partly result from longitudinal flow coeval with transpression. Deformations are comparable to those described along the eastern and western boundaries of the Archean Gawler Craton (South-East Australia), which underlines the continuity between these two areas before opening of the Austral Ocean. To cite this article: A. Pelletier et al., C. R. Geoscience 334 (2002) 505–511.     

Fluxes of Sr into the headwaters of the Ganges

Himalayan weathering is recognized as an important agent in modifying sea water chemistry, but there are significant uncertainties in our understanding of Himalayan riverine fluxes. This paper examines causes of the variability, including that of the seasons, by analysis of downstream variations in Sr, ⁸⁷Sr, and major ions in the mainstream, in relation to the composition of tributary streams from subcatchments with differing geologic substrates.Water samples were collected over four periods spanning the premonsoon, monsoon, and postmonsoon seasons. Uncertainties in the relative fluxes have been estimated, using Monte Carlo techniques, from the short-term variability of mainstream chemistry and the scatter of tributary compositions. The results show marked seasonal variations in the relative inputs related to high monsoon rainfall in the High and Lesser Himalaya, contrasting with the major contribution from glacial melt waters from the Tibetan Sedimentary Series (TSS) at times of low rainfall. Much of the spread in previously published estimates of the sources of Sr in Himalayan rivers may result from these seasonal variations in Sr fluxes.The annual fluxes of Sr into the headwaters of the Ganges are derived from the three main tectonic units in the proportions 35 ± 1% from the TSS, 27 ± 3% from the High Himalayan Crystalline Series (HHCS), and 38 ± 8% from the Lesser Himalaya. The particularly elevated ⁸⁷Sr/⁸⁶Sr ratios characteristic of the HHCS and the Lesser Himalaya enhance their influence on seawater Sr-isotope composition. The TSS contributes 13 ± 1%, the HHCS 30 ± 3%, and the Lesser Himalaya 57 ± 11% of the ⁸⁷Sr flux in excess of the seawater ⁸⁷Sr/⁸⁶Sr ratio of 0.709.     

The interaction of matter and radiation in a hot-model universe

In this paper we continue the investigation initiated by Weymann as to the reason why the spectrum of the residual radiation deviates from a Planck curve. We shall consider the distortions of the spectrum resulting from radiation during the recombination of a primeval plasma. Analytical expressions are obtained for the deviation from an equilibrium spectrum due to Compton scattering by hot electrons. On the basis of the observational data it is concluded that a period of neutral hydrogen in the evolution of the universe is unavoidable. It is shown that any injection of energy att>10¹⁰ sec (red shiftz<10⁵) leads to deviation from an equilibrium spectrum.Translated by Peter Foukal.     

The evolution of the Dutch and Belgian coasts and the role of sand supply from the North Sea

During the Holocene, the Dutch and Belgian coasts evolved, controlled by post-glacial eustatic sea-level rise, spatially varying vertical subsurface motions (glacio-isostatic crustal rebound, compaction, tectonics) and spatially varying sediment supply (mainly marine sand). The marine sand supply changed as the tidal dynamics and the wave climate changed due to the changing geometry and depth of the North Sea during the Holocene transgression. These changes influenced the coastal evolution. This study compares the results of separate numerical model calculations of the large-scale Holocene tide- and wave-induced sand transport in the southern North Sea with existing geological data of the Dutch and Belgian large-scale coastal evolution, resulting in a qualitatively good correlation. The large-scale coastal evolution is interpreted in terms of the oceanographical forcing, and an integrated conceptual model of the Holocene evolution of the Dutch and Belgian coasts is proposed. The large-scale wave-driven bed-load transport was an order of magnitude smaller than the tidal transports. The modelled tidal transport direction changed from onshore before 6 ka BP to along shore at present for the Zeeland and Holland coasts; the influence that waves may have had on the tidal transport by suspending sand gradually decreased. This change in direction caused the modelled tidal sand supply to the coast to decrease for the Belgian, Zeeland and Holland coasts. While the offshore area of the Holland coast remained a zone of (small) deposition due to decreasing northward sand transports, the offshore area of the Zeeland coast became increasingly erosional after 6 ka BP due to the encroaching divergence of the tidal transports. Due to uncertainty in the magnitude of the modelled sand transports, but robustness in the transport patterns, the focus is on the qualitative rather than the quantitative model results. When compared with the trend of closure, expansion and later erosion and reopening of the coast, the above decrease in sand supply must have been slow enough compared with the decrease in sea-level rise to cause a temporary sand surplus which decayed to a slight deficit as the decrease in supply and the rise in sea level continued. The Wadden Sea coast exchanged little or no sand with the adjacent deeper North Sea throughout the Holocene.